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Great Island Feasibility Study for Road
and Bridge Resiliency Improvements
December 2024
PREPARED FOR:
Great Island Homeowners Association
1100 Great Island Road
Yarmouth, MA 02673
PREPARED BY:
Woods Hole Group, Inc.
A CLS Company
107 Waterhouse Rd
Bourne, MA 02532 USA
Great Island Feasibility Study for Road
and Bridge Resiliency Improvements
December 2024
Prepared for:
Great Island Homeowners Association
1100 Great Island Road
Yarmouth, MA 02673
Prepared by:
Woods Hole Group
A CLS Company
107 Waterhouse Road
Bourne, MA 02532 USA
(508) 540-8080
and
Fuss & O’Neill
317 Iron Horse Way
Suite 204
Providence, RI 02908
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association ESi December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
EXECUTIVE SUMMARY
The Great Island causeway and bridge face unique challenges, including "sunny day" tidal
flooding, rising sea levels, coastal erosion, and storm surge, which threaten the sole means of
vehicle access between developed properties on Great Island and the res t of Yarmouth. The
vulnerability of the causeway and bridge has been highlighted by recent winter storms that have
eroded protective coastal dunes and exposed the road to the damaging effects of elevated water
levels and high energy waves. In response to these threats, the Great Island Homeowners
Association (GIHA) initiated the Great Island Feasibility Study for Road and Bridge Resiliency
Improvements (Feasibility Study).
The purpose of this study is to determine a long-term resilience strategy aimed at reducing the
vulnerability of infrastructure and ensuring that Great Island remains accessible in the face of
changing environmental conditions. Woods Hole Group and Fuss & O’Neill worked over a period
of ten (10) months to identify adaptation strategies that will allow the transportation and utility
infrastructure to continue functioning during periods of high tide and low to moderate intensity
storms into the future. The team worked to find ways for Great Island to withstand and rapidly
recover from disruption due to coastal hazards, while preserving the character of the community.
The focus of the Feasibility Study is to enable GIHA to move beyond reactive temporary responses
toward a strategic approach for building near- mid- and long-term resilience.
The Feasibility Study includes the following primary components:
1. Review of Existing Conditions: Explores the existing physical and natural resources on
Great Island.
2. Assessment of Current Vulnerability: Evaluates the impacts of rising sea levels and storm
surges on roads throughout Great Island.
3. Adaptation Strategies: Develops a range of adaptation strategies to enhance the resiliency
of the roads and bridge infrastructure.
4. Long-Term Resilience Strategies: Develops a roadmap for maintaining access to the island
and mitigating climate-related risks over the next 50 years.
Review of Existing Conditions
The Feasibility Study provides a comprehensive overview of the historical, ecological, and
physical characteristics of Great Island. This section serves as a foundation for understanding
which adaptation strategies are best suited for the site based on existing environmental
conditions.
Critical takeaways from this section include:
• The topography of Great Island is generally very low, with elevations ranging from sea
level to 24 feet NAVD88. Elevations along Great Island Road vary between 2.6 and 8.4 ft
NAVD88, with the lowest elevations occurring in the vicinity of the bridge. White Cedar
Point Road is also very low, with an average elevation of 2.7 ft NAVD88.
Woods Hole Group, Inc. • A CLS Company
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• A comprehensive wetland delineation identified coastal resources on Great Island,
including coastal beaches, dunes, and salt marshes. This delineation informs the design
and evaluation of adaptation strategies, by using local, state, and federal regulations
associated with each wetland type as a guide for specific adaptations.
• Sediment samples collected indicate that the beach and dune systems primarily consist
of medium- to fine-grained sand. This information can be used to guide future
nourishment projects by ensuring that sources of nourishment material are compatible
with the naturally occurring beach and dune sand.
• A Hohonu tide sensor was installed on Great Island Road near the bridge in January 2024
to provide real-time monitoring of the frequency and duration of flooding over the road.
The sensor was set up to measure flood depths, particularly during non-storm conditions
such as sunny day or high tide flooding. These data can be accessed at
https://dashboard.hohonu.io/map-page/hohonu-25/GreatIsland,Yarmouth,MA. From
January to August 2024, the sensor recorded 29 flood events, with some events reaching
up to 4 feet above the road surface, highlighting present day risks to Great Island
accessibility
Assessment of Current Vulnerability
The Feasibility Study evaluates current vulnerabilities on Great Island to identify how "sunny day"
tidal flooding, rising sea levels, coastal erosion and storm surge affect the existing infrastructure.
The study uses the Massachusetts Coast Flood Risk Model (MC-FRM) to evaluate future sea level
rise and storm surge scenarios. While flooding is commonly observed on Great Island Road in the
present day, data from MC-FRM add another layer of insight into observed flooding, offering
perspective on how flood vulnerability may change over time.
Key findings include:
• Road vulnerability: As soon as 2030, the majority of the causeway will have a 20%
probability of flooding at least once per year. Parts of the causeway and all of White Cedar
Point Road are projected to flood at least once per year, and small segments within these
areas are projected to flood under "sunny day" high tide conditions. As soon as 2050, the
majority of the causeway and a significant portion of the internal roads are projected to
flood at least once per year. Increasing portions of the causeway a re also projected to
flood under "sunny day" high tide conditions as soon as 2050 and 2070.
• Bridge vulnerability: The bridge is at risk of structural failure due to rising water levels and
increased storm intensity. Immediate repairs are needed to extend its operational life.
• Utility risks: Erosion and flooding pose a significant threat to buried utility lines along
Great Island Road (electric and fiber optic). These utilities are highly susceptible to
erosional damage from waves and tidal action as the shoreline continues to retreat.
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Adaptation Strategies
The alternatives described in this section were developed with the intention of maximizing the
usable life of the roadway infrastructure on Great Island, while acknowledging that the roadway
infrastructure is not likely to be functional in perpetuity. Main taining access to Great Island
depends on mitigating flooding and erosion hazards from both Lewis Bay and Nantucket Sound,
the combination of which limit the number of feasible approaches. The proximity of the roadway
infrastructure to salt marsh resources, residential private properties, and an eroding coastal dune
present further physical constraints to the potential resiliency alternatives. An approach that
includes no modification to the Great Island roadway infrastructure would result in daily tidal
flooding as soon as 2030, as well as significant risk of erosional damage. Daily tidal flooding of
the Great Island roadway infrastructure would include flooding of large stretches of the current
roadway twice per day, up to one-foot deep.
The Feasibility Study presents ten (10) initial conceptual alternatives that were then further
refined into four (4) alternatives. Refinement of the alternatives was based on stakeholder
engagement, permitability, costs, and technical analysis. The alternatives aim to address both
the immediate risks posed by storms and “sunny day” flooding, as well as long-term sustainability
and access to the island.
The four refined alternatives area:
Refined Alternative 1: Maintain Existing Infrastructure with Minimal Investment
This alternative involves maintaining the current road alignment and bridge without significant
changes, aside from emergency repairs, erosion control for the road, and periodic beach and
dune nourishment to mitigate erosion. This approach offers the lowest upfront costs but does
not decrease flood risk. The roadway infrastructure will be exposed to daily tidal flooding as soon
as 2030; this alternative assumes that storms may destroy the dunes and road even when
the best available erosion control measures are taken.
Refined Alternative 2: Minor Road Raising and Bridge Replacement
This alternative proposes to raise vulnerable sections of Great Island Road and White Cedar Point
Road and replace the bridge to mitigate the impacts of sea level rise and moderate storms. Low -
lying sections of the road would be raised to approximately 4.5’ NAVD88, which is two feet higher
than the current low point east of the bridge. This alternative delays daily high tide flooding
beyond that of Refined Alternative 1 (delaying the onset of daily tidal flooding until after 2050
and eliminating all present-day tidal flooding), but still leaves the road vulnerable to flooding
during most storms. The roadway infrastructure will be exposed to daily tidal flooding as soon as
2050; this alternative assumes that storms may destroy the dunes and road even when best
available erosion control measures are taken.
Refined Alternative 3: Major Road Raising and Bridge Replacement
This alternative proposes to raise sections of Great Island Road and White Cedar Point Road to
approximately 7.5’ NAVD88, which is five feet higher than the current low point east of the
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bridge. Replacing the bridge with a new structure is also included with this alternative. This
alternative also includes shifting portions of the road landward to reduce the risk of erosion and
loss of the causeway. Refined Alternative 3 is the least likely to be impacted by coastal flooding
and erosion when compared to Refined Alternatives 1 and 2; however, it results in disruption to
residents during construction, the largest project footprint, the most significant cost, and work
on a Town-owned roadway. This alternative delays the onset of daily tidal flooding until after
2070 and eliminates all present-day tidal flooding. Flooding due to storm surge still occurs during
significant storms in the present day with increases in frequency and severity over time.
Refined Alternative 4: Transition to a Ferry-Based System
As a long-term solution, this alternative proposes phasing out use of the causeway and bridge
and replacing them with a private launch or ferry service. This approach would protect vehicle
access routes to the island from coastal flooding entirely, but it will require significant changes
to the community’s access and infrastructure, including the construction of ferry landings. There
are many aspects of Refined Alternative 4 that were not specified during the Feasibility Study,
such as ferry size, landing locations, and schedule. These will need to be evaluated during future
considerations of this alternative.
The refined alternatives range in cost from maintaining current infrastructure with minimal
investment, to the significant expense associated with raising roads, rebuilding the bridge, or
transitioning to a ferry system. Planning-level cost estimates are provided for each alternative:
• Refined Alternative 1: $100,000 to $1,000,000 annually, depending on the frequency of
storms and the extent of necessary emergency repairs.
• Refined Alternative 2: $5 million to $10 million for road raising and bridge replacement,
with ongoing maintenance costs.
• Refined Alternative 3: $15 million to $25 million for major road raising and bridge
construction, providing the highest level of protection.
• Refined Alternative 4: Costs for a ferry system could reach $30 million over several
decades, with annual operating costs of $500,000 to $1 million. Initial and annual costs
vary widely with factors such as ferry type and operating schedule.
The Feasibility Study emphasizes the importance of phasing these investments over time, starting
with near-term actions that can mitigate immediate risks. Construction of the more expensive
long-term projects may be deferred, but the planning, design, and permitting for the longer-term
projects should be completed now so that GIHA is ready to act when climatic conditions indicate
that action is needed. The selection of a major road raising and realignment in the near-term
(Refined Alternative 3), allows GIHA to monitor conditions as they develop, given the uncertainty
of the rate of sea level rise and the future policy landscape. In response to the level of uncertainty,
this study introduces the concept of dynamic adaptation pathways. This flexible decision-making
framework allows GIHA to implement different strategies over time based on the evolving risks.
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Key elements of this approach include:
• Critical decision points - These are points at which GIHA may choose to switch to a
different strategy based on updated climate data or changes in the Massachusetts
regulatory landscape.
• Tipping points – These occur when a particular adaptation measure will no longer be
effective, prompting the need for a new approach.
By utilizing a dynamic framework, GIHA can adjust its response to climate change as conditions
evolve.
Next Steps
The selection of refined alternative(s) ultimately depends on GIHA's financial capacity, risk
tolerance, willingness to endure disruptions during implementation, and long-term access goals.
Near-term actions to maintain existing conditions are critical, while planning for future
intervention. Near-term actions should focus on securing permits for emergency road protection,
bridge repairs and stockpiling materials needed for roadway protection. To mitigate current and
future flood risk beyond these near-term actions, the primary recommendation of the Feasibility
Study is to arrive at a consensus among the community around a preferred adaptation pathway
and begin implementation. Clarifying what long-term access means to GIHA is essential to
selecting an adaptation approach for Great Islands roadway inFfrastructure.
A no action approach to the roadway infrastructure (Refined Alternative 1) (with limited near-
term actions such as reactive road repair), accepts decreased functioning of the road over time,
resulting in loss of vehicle access in as few as ten (10) years. Refined Alternative 2 sustains daily
access for several decades. Both of these refined alternatives accept continued risk to erosion
and roadway damage, and emergency repairs will need to continue. Refined Alternative 3
mitigates the erosion threat, likely provides daily access for the next fifty (50) years and
potentially into the next century and provides limited near-term mitigation of risk from coastal
storm flooding. Elevation and/or relocation of the road with Refined Alternatives 2 or 3 can
extend daily vehicle access to Great Island, however, since it is not feasible to fully mitigate the
risk of flooding during all storm conditions, emergency response preparedness is an important
consideration in improving GIHA resilience. Community consensus around and immediate
implementation of one of these alternatives is essential to securing generational access to Great
Island.
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association i December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Table of Contents
EXECUTIVE SUMMARY ......................................................................................................... ESI
1.0 INTRODUCTION AND PROJECT NEED ............................................................................ 1
1.1 STUDY METHODS ............................................................................................................... 2
1.1.1 Meetings & Community Outreach .......................................................................... 2
1.1.2 Key Steps for Study Approach ................................................................................. 3
2.0 EXISTING CONDITIONS ................................................................................................. 5
2.1 SITE LOCATION ................................................................................................................... 5
2.2 HISTORY OF DEVELOPMENT AND SHORE PROTECTION .................................................... 7
2.2.1 Historic and Archaeological Resources ................................................................. 12
2.3 PROPERTY OWNERSHIP ................................................................................................... 12
2.4 TOPOGRAPHY AND NEARSHORE BATHYMETRY .............................................................. 15
2.5 TIDES ................................................................................................................................ 17
2.5.1 Tidal Datums ......................................................................................................... 17
2.5.2 Tidal Elevation Survey ........................................................................................... 18
2.5.3 Water Level Monitoring ........................................................................................ 20
2.6 SEDIMENT CHARACTERIZATION ...................................................................................... 23
2.7 WETLAND RESOURCES..................................................................................................... 24
2.7.1 Coastal Beach ........................................................................................................ 26
2.7.2 Coastal Dune ......................................................................................................... 28
2.7.3 Barrier Beach ......................................................................................................... 33
2.7.4 Coastal Bank .......................................................................................................... 35
2.7.5 Salt Marsh ............................................................................................................. 35
2.7.6 Land Containing Shellfish ...................................................................................... 39
2.7.7 Estimated Habitats of Rare Wildlife ...................................................................... 41
2.7.8 Land Subject to Coastal Storm Flowage ............................................................... 43
2.8 SHORELINE AND DUNE CHANGE ..................................................................................... 43
2.8.1 Shoreline Change Analysis .................................................................................... 43
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association ii December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
2.8.2 Toe of Dune Analysis ............................................................................................. 45
2.9 WIND AND WAVE CLIMATOLOGY ................................................................................... 47
3.0 VULNERABILITY ASSESSMENT - DATA AND METHODS ................................................. 49
3.1 SEA LEVEL RISE PROJECTIONS .......................................................................................... 49
3.2 MC-FRM COASTAL INUNDATION MODELING ................................................................. 51
3.3 MC-FRM OUTPUTS........................................................................................................... 52
3.4 MODEL DISCLAIMER ........................................................................................................ 56
3.5 DAILY TIDAL FLOODING .................................................................................................... 56
3.6 FLOOD PATHWAYS ASSESSMENT .................................................................................... 59
3.7 COASTAL EROSION ........................................................................................................... 59
4.0 VULNERABILITY ASSESSMENT RESULTS ....................................................................... 61
4.1 ROADWAY VULNERABILITY ASSESSMENT ....................................................................... 61
4.2 BRIDGE VULNERABILITY ASSESSMENT ............................................................................ 71
4.3 UTILITIES VULNERABILITY ASSESSMENT .......................................................................... 71
5.0 ALTERNATIVES ASSESSMENT ...................................................................................... 73
5.1 INTRODUCTION AND METHODS ...................................................................................... 73
5.2 CONCEPTUAL ALTERNATIVES .......................................................................................... 74
5.3 REFINED ALTERNATIVES .................................................................................................. 79
5.3.1 Refined Alternative 1: Maintain Road and Bridge ................................................ 79
5.3.2 Refined Alternative 2: Minor Road Raising and Bridge Replacement .................. 83
5.3.3 Refined Alternative 3: Major Road Raising and Bridge Replacement .................. 90
5.3.4 Refined Alternative 4: Community Ferry .............................................................. 97
5.3.8 Comparison Matrix ............................................................................................. 102
5.3.9 Dynamic Adaptation Pathways ........................................................................... 104
6.0 RECOMMENDED NEXT STEPS .................................................................................... 105
7.1 NEAR-TERM RECOMMENDATIONS (1 – 5 YEARS): ........................................................ 106
7.2 MID-TERM RECOMMENDATIONS (6 – 25 YEARS): ........................................................ 106
7.3 LONG-TERM RECOMMENDATIONS (26 – 50 YEARS): .................................................... 106
7.0 REFERENCES .............................................................................................................. 108
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association iii December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX A. COMMUNITY SURVEY RESPONSES .................................................................... 1
APPENDIX B. CONSERVATION RESTRICTION ........................................................................... 1
APPENDIX C. EXISTING CONDITIONS PLAN ............................................................................. 1
APPENDIX D. TIDAL ELEVATION SURVEY TECHNICAL MEMORANDUM .................................... 1
APPENDIX E. HOHONU MONTHLY DATA COLLECTION SUMMARIES ........................................ 1
APPENDIX F. LABORATORY GRAIN SIZE DATA ........................................................................ 1
APPENDIX G. WETLAND DELINEATION TECHNICAL MEMORANDUM ....................................... 1
APPENDIX H. VULNERABILITY ASSESSMENT ROADWAY SEGMENTS ........................................ 1
APPENDIX I. GREAT ISLAND BRIDGE INSPECTION MEMORANDUM ......................................... 1
APPENDIX J. APPROXIMATE LOCATION OF BURIED UTILITIES ................................................. 1
APPENDIX K. CONCEPTUAL ALTERNATIVES ............................................................................ 1
APPENDIX L. DYNAMIC ADAPTATION PATHWAYS .................................................................. 1
Table of Figures
Figure 1. Aerial photo of project site showing Great Island and barrier beach system. ............. 6
Figure 2. Aberdeen Hall c.1902-1924 (Historical Society of Old Yarmouth). .............................. 7
Figure 3. Plan of Yarmouth – 1830 (left) and Atlas of Barnstable County – 1910 (right), showing
early development on Great Island and alignment of the access road. ....................... 8
Figure 4. Aerial photo of Great Island from Dec. 11, 1938, showing White Cedar Point Rd. ..... 8
Figure 5. Aerial photograph showing the current location of Great Island Road as compared
with the pre-1973 road layout .................................................................................... 11
Figure 6. The subdivision plan of Great Island was completed in 1987 and filed with the Land
Registration Office on May 6, 1988. ........................................................................... 12
Figure 7. Property ownership and conservation restrictions on Great Island and in the
surrounding area. ........................................................................................................ 14
Figure 8. Topographic and bathymetric data for the Great Island area derived from a US Army
Corps of Engineers (USACE) digital elevation model from 2018. ............................... 17
Figure 9. Locations of tidal data logger stations GI-1 and GI-2. ................................................ 19
Figure 10. Time-series of water surface elevation at both stations (top) and daily precipitation at
Hyannis Airport (bottom) during the deployment period. ......................................... 20
Figure 11. Schematic showing Hohonu sensor elevation and data reading in relation to depth of
flooding over the road. ............................................................................................... 21
Figure 12. January 2024 Hohonu record for Great Island Road. ................................................. 22
Figure 13. Sediment grab sample locations for December 2023 sampling event. ...................... 23
Figure 14. Grain size distribution for beach and dune sediment samples collected from the south
side of Great Island Road. ........................................................................................... 24
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association iv December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Figure 15. Coastal resource areas delineated within the study area on January 17 th and 19th,
2024. ........................................................................................................................... 25
Figure 16. Coastal beach seaward of Great Island Road. Photo taken facing southwest. .......... 26
Figure 17. Cobble strewn coastal beach at western end of survey area. Photo taken facing
southwest.................................................................................................................... 27
Figure 18. Shell deposit within sandy coastal beach. .................................................................. 27
Figure 19. Groin structures along coastal beach. Photo taken facing northeast. ....................... 28
Figure 20. Primary frontal dune along Great Island Road. Photo taken facing northeast. ......... 29
Figure 21. Example of primary coastal dune bound by coastal beach and secondary dune. Photo
taken facing southwest. .............................................................................................. 29
Figure 22. Erosional scarping along the seaward face of the primary dune. .............................. 30
Figure 23. Stone rip rap armoring primary frontal dune. Photo taken facing southwest. .......... 30
Figure 24. Transition from coastal dune to salt marsh. Photo taken facing northeast. .............. 31
Figure 25. Evidence of storm overwash within coastal dune. Photo taken facing east. ............. 32
Figure 26. Typical coastal dune vegetation. Photo taken facing south. ...................................... 32
Figure 27. Maritime forest vegetation within coastal dune. Photo taken facing south. ............ 33
Figure 28. Massachusetts Office of Coastal Zone Management (CZM) Massachusetts Barrier
Beach Inventory (MassGIS). ........................................................................................ 34
Figure 29. Coastal bank near southwest extent of survey area. Photo taken facing north. ....... 35
Figure 30. Narrow salt marsh areas west of the Great Island Road bridge. ................................ 36
Figure 31. Salt marsh east of Great Island Road bridge. Photo taken facing east. ..................... 37
Figure 32. Salt marsh vegetation north of Great Island Road. Photo taken facing south. .......... 37
Figure 33. Salt marsh between open water (left) and coastal dune (right). Photo taken facing
east. ............................................................................................................................. 38
Figure 34. Fringing salt marsh patches between the remnant revetment and coastal engineering
structure. Photo taken facing northeast. ................................................................... 38
Figure 35. Shellfish suitability habitat within and adjacent to the project area. ........................ 40
Figure 36. Natural Heritage and Endangered Species Program Estimated and Priority Habitat
within and adjacent to the project area. .................................................................... 42
Figure 37. Short-term rates of shoreline change (1970 to 2018) for the south facing Great Island
shoreline. .................................................................................................................... 44
Figure 38. Erosion hot spots and toe of dune delineation for 2024. Background imagery was
taken March 21, 2024. ................................................................................................ 46
Figure 39. Wind rose of data from NOAA buoy 44020 for the period 2009 to 2023. ................. 48
Figure 40. Wave rose of data from NOAA buoy 44020 for the period 2009 to 2023. ................ 48
Figure 41. Sea level projections for the MC-FRM South Grid 2008 (1999-2017 epoch). Mean sea
level for the average between the Woods Hole and Nantucket tide gages was -0.17
feet (NAVD88). ............................................................................................................ 50
Figure 42. MC-FRM model mesh in vicinity of Great Island. ....................................................... 51
Figure 43. MC-FRM annual exceedance probability for Great Island as soon as 2030 (“High” Seal
Level Rise Scenario). ................................................................................................... 53
Figure 44. MC-FRM annual exceedance probability for Great Island as soon as 2050 (“High” Seal
Level Rise Scenario). ................................................................................................... 54
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association v December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Figure 45. MC-FRM annual exceedance probability for Great Island as soon as 2070 (“High” Seal
Level Rise Scenario). ................................................................................................... 55
Figure 46. Projected mean high water shorelines for present day, as soon as 2030, 2050, and
2070 (“High” Seal Level Rise Scenario). ...................................................................... 58
Figure 47. Great Island Road flood pathways. ............................................................................. 60
Figure 50. Map of projected 2030 coastal flooding on road centerline points, color coded by
Annual Exceedance Probability................................................................................... 63
Figure 51. Map of projected 2050 coastal flooding on road centerline points, color coded by
Annual Exceedance Probability................................................................................... 64
Figure 52. Map of projected 2070 coastal flooding on road centerline points, color coded by
Annual Exceedance Probability................................................................................... 65
Figure 53. Map of road centerline points within projected mean high-water shorelines for 2030,
2050, and 2070. .......................................................................................................... 67
Figure 54. Criticality scores assigned to road points in the Great Island road network. ............ 69
Figure 55. Risk scores for each point on the Great Island road network (2030), determined by
multiplying each point’s AEP by its criticality score. .................................................. 70
Figure 56. Overview of Refined Alternative 1. ............................................................................. 81
Figure 57. Typical cross-section of eastern roadway segment with Refined Alternative 1. ....... 81
Figure 58. Bridge segment of roadway with Refined Alternative 1. ........................................... 82
Figure 60. Overview of changes to the roadway with Refined Alternative 2. ............................. 86
Figure 61. Typical cross-section of western roadway segment with Refined Alternative 2. ...... 86
Figure 62. Typical cross-section of eastern roadway segment with Refined Alternative 2. ....... 87
Figure 63. Erosion control with Refined Alternative 2 – no road raising is necessary along this
section of roadway. ..................................................................................................... 88
Figure 64. Refined Alternative 2 bridge modifications. ............................................................... 89
Figure 65. Overview of changes to the roadway with Refined Alternative 3. ............................. 93
Figure 66. Typical cross-section of western roadway segment with Refined Alternative 3. ...... 93
Figure 67. Typical cross-section of middle roadway segment with Refined Alternative 3. ........ 94
Figure 68. Typical cross-section of eastern roadway segment with Refined Alternative 3. ....... 95
Figure 70. Overview of changes to the roadways with Refined Alternative 4. ........................... 99
Figure 71. Typical cross-section showing long-term road removal in areas of salt marsh with
Refined Alternative 4. ............................................................................................... 100
Figure 72. Typical cross-section showing long-term road removal in areas of barrier beach with
Refined Alternative 4. ............................................................................................... 101
List of Tables
Table 1. Tidal Datums for the Nantucket Sound Side of the Project Area. ............................ 18
Table 2. Length of Roadway Vulnerable to Flooding in 2030, 2050 and 2070. ...................... 62
Table 3. Top Vulnerable Road Segments. ............................................................................... 68
Table 4. Summary of Alternatives. ......................................................................................... 77
Table 5. Comparison of the Four Refined Alternatives. ....................................................... 103
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association vi December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Glossary of Acronyms and Terms
AE AE Flood Zone - 1% Annual Chance of Flooding
AEP Annual Exceedance Probability
CLS Collect Localisation Satellites
CR Conservation Restriction
CTDs Conductivity-Temperature-and Depth Sensors
CZM Coastal Zone Management
DMF Division of Marine Fisheries
DSAS Digital Shoreline Analysis System
EH Estimated Habitat
FEMA Federal Emergency Management Agency
FIRMs Flood Insurance Rate Maps
GIHA Great Island Homeowners Association
GIS Geographic Information System
GPS Global Positioning System
HYA Hyannis Airport
LSCSF Land Subject to Coastal Storm Flowage
MACRIS Massachusetts Cultural Resource Information System
MassDEP Mass Department of Environmental Protection
MassGIS Massachusetts Barrier Beach Inventory
MC-FRM Massachusetts Coast Flood Risk Model
MEPA Massachusetts Environmental Policy Act
MHHW Mean Higher High Water
MHW Mean High Water
MLLW Mean Lower Low Water
MLW Mean Low Water
NAVD88 North American Vertical Datum of 1988
NHESP Natural Heritage and Endangered Species Program
NDBC National Data Buoy Center
NOAA National Oceanic and Atmospheric Administration
PH Priority Habitat
RCP Representative Concentration Pathways
SLOSH Sea, Lake, and Overland Surges from Hurricanes
Trustees The Trustees of Reservations
USACE US Army Corps of Engineers
USGS United States Geological Survey
VE VE Flood Zone - 1% or Higher Annual Chance of Flooding Each Year
VHB Vanasse Hangen Brustlin, Inc.
WHOI Woods Hole Oceanographic Institute
WSE Water Surface Elevation
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association 1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
1.0 INTRODUCTION AND PROJECT NEED
Great Island, a roughly 550-acre peninsula nestled between the eastern shoreline of Lewis Bay
and Nantucket Sound, is uniquely vulnerable to extreme weather. Its location exposes it to
increased natural hazards from ocean-based storm events, such as flooding and coastal erosion.
Recognizing the recurring impacts of these coastal hazards, the Great Island Homeowners
Association (GIHA) is actively pursuing strategies to safeguard its critical roadway, bridge
infrastructure, and natural resources over the next 50-years. The escalating frequency and
intensity of coastal storms driven by climate change pose even more significant risks to areas of
Great Island's infrastructure that are already prone to flooding from Lewis Bay and storm induced
erosion along Nantucket Sound. GIHA is committed to addressing these vulnerabilities and
understanding the risks that flooded roadways pose to public safety. This includes the
community's ability to access their properties, secure assets as a storm approaches, evacuate
safely, and ensure the ability of emergency personnel and utility crews to respond in the event
of an emergency.
Initial steps taken in 2021-2023 by GIHA to build resiliency for the island included work with VHB,
Foth Engineering, and Sustainable Coastal Solutions to develop plans for dune and beach
nourishment along the Vineyard Sound side of the roadway, between Fox Point and White Cedar
Point Road. The project was designed, and two (2) of the six (6) required regulatory approvals
were obtained. Understanding that a more wholistic view of climate change related
vulnerabilities and possible adaptations was needed, GIHA made the decision to pause the
permitting for the dune and beach nourishment so that a more comprehensive assessment of
resiliency improvements could be conducted.
In the fall of 2023 GIHA engaged the expertise of Woods Hole Group and Fuss & O’Neill to conduct
the Great Island Feasibility Study for Road and Bridge Resiliency Improvements. The study
provides crucial data on the potential impact s of threats to vulnerable areas of Great Island and
assists in the development and prioritization of strategies to minimize risks to infrastructure and
the community. The specific climate-related hazards addressed in this vulnerability assessment
are sea level rise and storm surge inundation, as well as coastal erosion and loss of valuable
habitat. Working closely with the GIHA Board, Woods Hole Group has developed asset -specific
probabilistic risk assessments based on exposure to sea level rise and storm surge (using the
Massachusetts Coast Flood Risk Model ‘MC-FRM’) and the relative significance of each
roadway. This risk assessment data forms the basis for the development and prioritization of
adaptation strategies that enhance resiliency of the road and bridge, which serve as the only
means of vehicle access to Great Island and Cedar Point. The findings of this Feasibility Study
provide the GIHA with valuable knowledge and data needed to shape detailed coastal resilience
planning efforts. The study also prioritizes coastal adaptation projects that are essential for the
community to be more resilient to the impacts of climate change.
Woods Hole Group is an environmental consulting firm with roots in the Woods Hole scientific
community. An offshoot of the Woods Hole Oceanographic Institute (WHOI), Woods Hole Group
was formed to apply scientific principles in oceanography and coastal processes to solve on-the-
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ground problems. The company consists of four central business units – Environment & Climate
Consulting, Sustainable Fisheries, Energy & Mining, and Satellite Telemetry. Woods Hole Group’s
consulting group specializes in coastal planning, climate change vulnerability assessment and
adaptation planning, and modeling risks to coastal communities and infrastructure from sea level
rise and storm surge. Woods Hole Group partnered with Fuss & O’Neill on this project. Fuss &
O’Neill is a nearly 100-year-old engineering and science-based firm specializing in planning,
design, and construction work in the transportation, water, environmental, building, and energy
market sectors. Since 2015, Woods Hole Group and Fuss & O’Neill have completed multiple
projects on Cape Cod and the Islands where the teams have evaluated, permitted, and
implemented adaptation strategies for vulnerable public and private transportation
infrastructure.
The overall goal of this project was to develop a suite of strategies that will provide the
foundation for future discussion and planning by GIHA, ultimately resulting in a plan that will
improve the long-term resilience of Great Island and White Cedar Point Roads. Throughout the
project's process, the GIHA Board played a crucial role, meeting bi-weekly to review work
products and provide input on the selection of planning scenarios, identification of assets,
evaluation of asset impact consequences to GHIA, and prioritization of adaptation strategies.
The following primary goals were established for this project:
• Study and evaluate flood vulnerability and erosion risk to the roadway infrastructure
• Prioritize nature-based or hybrid solutions
• Develop cost-effective adaptive alternatives
• Develop a plan for long-term resiliency (~50 yr)
1.1 Study Methods
1.1.1 Meetings & Community Outreach
A key component of the Feasibility Study was to raise the community's awareness of both the
escalating flood risks posed by sea-level rise and storm surge, as well as the strategies available
to GIHA to adapt to these changes over time. Community outreach events were scheduled at
each project milestone to keep the GIHA abreast of the latest findings, gather input at crucial
junctures, and facilitate active engagement over the time horizon of the project. At these events,
Woods Hole Group presented information on climate change, flood modeling, the vulnerability
and risk of GIHA infrastructure and natural resources, and adaptation options and costs. The
following is a list of the community outreach events organized as part of the project:
• January 25, 2024 - Project Kick-Off Meeting
• April 25, 2024 - Review of Vulnerability Assessment
• May 2, 2024 - Examination of Conceptual Alternatives
• July 13, 2024 - Open House at Great Island's Beach Club
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In addition to these community outreach events, an online tool was developed to provide the
GIHA with information on key challenges, vulnerabilities, and alternatives for building increased
resiliency to flooding and erosion. That resource can be found here:
https://experience.arcgis.com/experience/f6e6e271fb4b48e0ad104dfcd602c6f2/
A community survey was initiated in February and continued through March. Community
members were asked to answer a series of questions including, “How often does flooding affect
your access to the island (including your contractors, landscapers, and delivery personnel)?”. A
total of 64 residents responded to the survey, and their responses can be found in Appendix A.
1.1.2 Key Steps for Study Approach
To assist GIHA in assessing risk and prioritizing investments in adaptation planning over time,
Woods Hole Group developed a phased management approach to reduce vulnerability to natural
hazards and enhance coastal resiliency along the Great Island causeway, White Cedar Point Road,
and bridge. This phased management approach resulted in conceptual-level designs and
priorities for implementation. The study consisted of three main phases:
• Phase 1: Evaluation of Existing Conditions: The first phase of the project involved
collection and review of existing data and studies previously completed for the GIHA study
area, as well as collection of additional data to help develop an improved understanding
of the site and coastal processes. Existing information on eel grass distributions,
nearshore bathymetry, sediments, shoreline change, waves, and longshore sediment
transport were reviewed and summarized. A field delineation of wetland resources wa s
conducted and a topographic survey of the site, including roadway, pull outs, beaches and
dunes was performed, allowing preparation of an updated existing conditions plan. Water
surface elevations were measured on both sides of the Great Island bridge to evaluate
tidal attenuation, and engineers conducted a structural assessment of the bridge to
identify structural deficiencies and vulnerabilities. Information gathered during Phase 1
was important for gaining a deeper understanding of the coastal processes acting to
shape Great Island and for the development of appropriate conceptual alternatives.
• Phase 2: Development of Conceptual Phased Management Approach: The next phase of
the project involved development of conceptual alternatives and a phased management
approach for increasing coastal resiliency of the Great Island causeway and bridge. Results
from Woods Hole Group’s MC-FRM were used to conduct a risk and vulnerability
assessment of the site. Inundation maps for different planning horizons over the next 50
years showing tidal and storm-induced flooding were developed and flood pathways were
identified. Conceptual designs for reducing vulnerability to flooding and erosion were
developed, which included infrastructure modifications, roadway elevation and
realignment, alternative modes of transportation, and nature-based features as
adaptation strategies. The project team then strategically analyzed and prioritized
potential short-, medium-, and long-term adaptation strategies that would result in the
most significant benefit to the GIHA using the dynamic adaptation pathways approach.
Respective timelines for implementation, permitting requirements and constraints,
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maintenance requirements, environmental impacts, and engineering cost estimates for
all alternatives were generated. Cost estimates included construction and maintenance
figures and considered both hard and soft costs for the respective alternatives.
• Task 3: Final Technical Report: The following final technical report summarizing the
various conceptual design imagery for the selected adaptation strategies is the final phase
of this project. The report aims to capture the results of the study and serve as a resource
for future planning and permitting.
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2.0 EXISTING CONDITIONS
2.1 Site Location
Great Island is in the Town of Yarmouth between the eastern shoreline of Lewis Bay and
Nantucket Sound. The site is made up of an approximate 315-acre upland area where most of
the development is located and a lower 235-acre barrier beach and salt marsh system that
connects the island to the rest of Yarmouth (Figure 1). Great Island Road and the bridge provide
the sole means of vehicle access to the island and are located on the Nantucket Sound side of
the barrier beach. Uncle Roberts Cove separates the island from the barrier beach system and
provides boat access to Lewis Bay and beyond.
The upland portion of the site is comprised of sediments deposited approximately 16,000 years
ago when glaciers advanced into New England. The barrier beach system was formed after the
glaciers retreated as winds, waves, and longshore sediment transport reshaped sediment
deposited by the glaciers.
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Figure 1. Aerial photo of project site showing Great Island and barrier beach system.
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2.2 History of Development and Shore Protection
Development on Great Island began in the early 1800s with the construction of a smallpox
hospital. The Gammon Point lighthouse and stone keeper’s house were built in 1816. The
lighthouse was decommissioned in 1858 and converted into a bird-watching observatory after
1882. Aberdeen Hall was built in 1902 on the northwest side of the island, serving as a high -end
hotel. The hotel was destroyed by a fire in 1924, and the time of Great Island being opened to
the public ended then as well (Figure 2).
Figure 2. Aberdeen Hall c.1902-1924 (Historical Society of Old Yarmouth).
Through the remainder of the century, development on the island grew, and in the present day,
there are 43 privately owned properties. Roadway access to the island along the Nantucket
Sound side of the barrier beach was established in the early 1800s. The road alignment essentially
followed the shoreline from greater Yarmouth to the area of the existing bridge and then
connected with the circular road system on the island (Figure 3). White Cedar Point Road was
built in the early 1900s to allow access to properties that were developed on Cedar Point starting
in 1930 (Figure 4).
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Figure 3. Plan of Yarmouth – 1830 (left) and Atlas of Barnstable County – 1910 (right), showing early development on Great
Island and alignment of the access road.
Figure 4. Aerial photo of Great Island from Dec. 11, 1938, showing White Cedar Point Rd.
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Subsequent changes to relocate a portion of the road north and south of White Cedar Point Road
further from the shoreline were made between 1969 and 1973 (Figure 5). A series of shore-
perpendicular groins, ranging in length between 60 and 145 feet, were also installed along the
shoreline east of the road between 1938 and 1969. Research conducted by VHB indicates that
licenses were obtained for all these structures. A small section of the road located mid-way
between White Cedar Road and the bridge was armored with a rip rap revetment sometime in
the late 1970s. The armoring extends along approximately 750 linear feet of the roadway.
During the winter of 1989-1990, a large-scale beach nourishment project was implemented along
the south end of Great Island between the Beach Club and Fox Point. Approximately 330,000
cubic yards of material was pumped from an offshore borrow site and used to nourish the beach
and dune resources. Permits for this project are no longer valid . Designs for another beach and
dune nourishment project between Fox Point and White Cedar Point Road were developed in
2021 by VHB, Foth Engineering, and Sustainable Coa stal Solutions. The project was intended to
provide near term resiliency for the southern end of Great Island Road until a longer-term project
could be designed and permitted. Regulatory reviews for the nourishment project have been
completed by the Massachusetts Environmental Policy Act (MEPA) Unit, the Natural Heritage and
Endangered Species Program (NHESP) and the Yarmouth Conservation Commission. Additional
reviews and permits are needed from the Massachusetts Department of Environmental
Protection Waterways Division (Chapter 91 Permit), Massachusetts Office of Coastal Zone
Management (Federal Consistency Determination), and the US Army Corps of Engineers. During
December 2022, GIHA also implemented a small dune restoration project east of White Cedar
Point Road to protect the road from storm damage.
The winter storms of December 2023 and January 2024 brought extreme weather conditions to
Great Island, resulting in significant coastal damage that prompted emergency intervention by
the Woods Hole Group and Crawford Land Management. This unusual storm se ason included
three severe coastal storms: on December 18, January 10, and January 13. These storms brought
high water levels, strong winds from uncommon southerly directions, and significant wave
energy that eroded the coastal dune, overwashed sand onto the road, and left Great Island Road
highly vulnerable. Due to the immediate threats posed to infrastructure and the access road, an
Emergency Certificate was issued on January 5, 2024, to enable rapid mitigation efforts.
Woods Hole Group, with Crawford Land Management as the general contractor, undertook
emergency measures to restore and protect the degraded dune system temporarily. The
emergency response involved placing approximately 237 bulk sandbags, each holding over a ton
of compatible sand, along the dune toe. This sandbag barrier was covered with additional clean
sand to shield the bags from UV degradation and simulate a natural dune structure. The work
commenced on January 8, 2024, with bulk bag filling and placement continuing through January
12. On January 10 and 13, during the construction, two more intense storms struck the area,
resulting in partial loss of the newly placed sand cover, but the bulk bags withstood the waves
with minimal displacement.
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The second phase of the emergency work involved reinforcing the initial sand cover to create a
natural slope over the bulk bags. Between February 6 and 8, 2024, Robert Childs, Inc., the
contractor for this phase, delivered and graded over 2,026 tons of sand over the bulk bags,
constructing a dune slope with a 4:1 grade. This reinforced sand layer was intended to mimic
natural dune functions by retaining sand in place and providing a temporary buffer against future
storm damage.
The completed temporary structure is expected to serve as an enhanced coastal buffer,
mimicking natural dune processes to mitigate wave energy during future storms. This emergency
intervention remains a provisional measure until a long-term resilience plan can be developed
and implemented for Great Island.
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Figure 5. Aerial photograph showing the current location of Great Island Road as compared with the pre-1973 road layout
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2.2.1 Historic and Archaeological Resources
A review of the Massachusetts Historical Commission’s Massachusetts Cultural Resource
Information System (MACRIS) indicated no historical or archaeological resources within the
project area.
2.3 Property Ownership
By 1988, Great Island was separated into 82 distinct parcels of land (Figure 6). In many cases,
properties have been passed down through multiple generations, and the current community
members take great pride in the rich and enduring heritage that comes with owning these
properties.
Figure 6. The subdivision plan of Great Island was completed in 1987 and filed with the
Land Registration Office on May 6, 1988.
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In addition to private ownership on Great Island, 7 of the parcels on Great Island contain
conservation restrictions. The intention of a conservation restriction (CR) is to allow landowners
to preserve their property as protected open space in perpetuity, defining permitted uses of the
land. The Trustees of Reservations (Trustees), a non-profit organization dedicated to preserving
natural and historical places, maintain the CRs on these 7 Great Island parcels, totaling 20,000
acres of land. The parcels with CRs along Great Island Road were gifted to the Trustees by Arnold
B. Chase, JR. and Malcolm G. Chace III (the Grantors) in 1986 (Figure 7).
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Figure 7. Property ownership and conservation restrictions on Great Island and in the surrounding area.
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The CR (found in Appendix B) describes that the following activities are permitted under the
conservation restriction:
(1) In the event the roads or ways shown on the Plan referred to in Exhibit A are destroyed
by Storms or other causes beyond the control of the Grantors, and can be restored if
relocated in part on the Premises, the installation, maintenance, repair, improvement and
replacement of said relocated roads and ways and use of such roads and ways for all
purposes for which ways are used in the Town of Yarmouth.
(2) Installation, maintenance, repair, improvement and replacement of utilities, above or
below grade.
The CR specifies that the Grantors, as well as their successors and assigns, must obtain all
necessary permits, licenses, and approvals from the relevant public authorities and comply with
the provisions. The provisions outlined in the CR prohibit the construction of buildings, or
dumping on the property, as well as the destruction of vegetation (except for limited activities
like selective clearing, agricultural operations, or trail maintenance that align with conservation
goals). Additionally. mining, excavating, dredging, or removal of sediment is prohibited, except
when related to the installation or maintenance of underground utilities, septic systems, or for
drainage and soil conservation practices. Any potential projects on this land require the Trustees
to be provided with a written plan for approval before commencement. Furthermore, the
proposed project must aim to avoid and minimize impacts that are not consistent with the
intention of the CR to the greatest extent possible.
2.4 Topography and Nearshore Bathymetry
Information on the topography and nearshore bathymetry in the vicinity of Great Island Road
were gathered to help with evaluation of flood vulnerability, assessment of nearshore coastal
processes and sediment transport, and development of potential resilie ncy alternatives.
Topographic survey data were collected by a Woods Hole Group Professional Engineer and Land
Surveyor on January 26, February 8, August 7, and August 14, 2024. Additional topographic data
were collected during the wetland delineation condu cted on January 19, 2024. A Real Time
Kinematic Global Positioning System was utilized during the surveys to capture the elevations
and locations of the roadway, coastal engineering structures, bridge infrastructure, vehicle turn-
outs, wetland resources, observed high water line, and other key features of the landform along
Great Island and White Cedar Point Roads. The survey data were used to prepare an Existing
Conditions Plan Set for the project area (Appendix C).
Additional elevation data covering the entire barrier beach, Great Island, and nearshore areas
surrounding the site were obtained from a US Army Corps of Engineers (USACE) LiDAR dataset
collected in 2018 (Figure 8). More recent surveys of nearshore bathymetry were conducted by
FOTH Infrastructure & Environment, LLC on June 8 and 30, 2020. These surveys extended from
Fox Point to the northern end of the barrier beach, capturing nearshore bathymetry over an area
approximately 1,000 feet seaward of the roadway.
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Collectively these data show that the highest elevations of 24 ft NAVD88 occur across the central
and southern portions of Great Island. The next highest areas with elevations between 6 and 15
ft NAVD88 occur along the peninsula to the north of Uncle Roberts Cove and along the north and
northeast sections of the barrier beach. The southwestern end of the barrier beach is lower,
ranging in elevation between 1 and 6 ft NAVD88. Elevations along Great Island Road vary
between 2.6 and 8.4 ft NAVD88, with the lowest elevations occurring in the vicinity of the bridge.
White Cedar Point Road is also very low with an average elevation of 2.7 ft NAVD88. Coastal dune
crest elevations on the south side of Great Island Road are highest along the northeastern end of
the barrier at 12 ft NAVD88, tapering down to 6 ft NAVD88 at the southwestern end of the
barrier. The toe of the coastal dune falls between 4 and 6 ft NAVD88. The width of the primary
coastal dune south of the road decreases from 90 ft at the northeast end to 5 ft at the southwest
end. The width of the high tide beach above the 0 ft NAVD88 datum ranges between 60 and 100
ft with an average slope of 1V:10H.
The nearshore bathymetry data show a series of shore parallel sand bars extending to the
northeast from Fox Point. Bar crest elevations range between -3 and -5 ft NAVD88 with
intervening troughs at -6 to -7 ft NAVD88. Average nearshore slopes within 1,000 ft from the
shoreline were identified by Foth and Sustainable Coastal Solutions, Inc. during the 2020 survey
to be considerably flatter than the beach, on the order of 1V:1000H.
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Figure 8. Topographic and bathymetric data for the Great Island area derived from a US
Army Corps of Engineers (USACE) digital elevation model from 2018.
2.5 Tides
2.5.1 Tidal Datums
The nearest long-term tide gauge for the Project area is the National Oceanic and Atmospheric
Administration (NOAA) historical datum station #8447605 in Hyannisport, MA. This tide station
was located in Hyannis Harbor near the Hyannisport Yacht Club. NOAA used data recorded at t his
station between 1983 to 1994 to calculate elevations for a range of tidal datums as shown in
Table 1. Due to the proximity of the NOAA tide gauge station to Great Island, the tidal datums
shown in Table 1 were applied to the project site.
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Table 1. Tidal Datums for the Nantucket Sound Side of the Project Area.
Tidal Datum Elevation (ft, NAVD88)
High Tide Line (highest astronomical tide) 2.34
Mean Higher High Water (MHHW) 1.34
Mean High Water (MHW) 0.99
NAVD88 0
Mean Low Water (MLW) -2.21
Mean Lower Low Water (MLLW) -2.46
Tidal Range (MHW to MLW) 3.20
2.5.2 Tidal Elevation Survey
Site specific water level elevations were measured in the vicinity of the Great Island bridge during
the course of this Feasibility Study. The purpose of the measurement program was to determine
whether the bridge infrastructure is restricting passage of the tidal signal to the salt marsh
located on the upstream (south) side of the bridge . Two (2) AquaTroll 200 conductivity-
temperature-and depth sensors (CTDs) were deployed on either side of the Great Island bridge
for a monthly lunar tidal cycle between March 13 and April 16, 2024 (Figure 9). The instruments
collected conductivity (salinity), temperature, and absolute pressure (water plus atmospheric
pressure) readings at 6-minute intervals over the 34-day deployment period. Elevations of the
sensors were surveyed and atmospheric pressure and precipitation data during the deployment
period were retrieved from Hyannis Airport (HYA), located approximately 3.3 miles northwest of
the site. A Technical Memo describing the tidal elevation survey and recorded data is included in
Appendix D.
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Figure 9. Locations of tidal data logger stations GI-1 and GI-2.
Water elevation data from the gauges show that the tidal signal moves largely unobstructed by
the bridge infrastructure, as the high-water elevations on both sides of the bridge are nearly
identical (Figure 10). Low water elevations at station GI-2 are slightly higher in comparison with
station GI-1, indicating that water levels are perched on the upstream side of the bridge.
The water surface elevations are slightly sensitive to precipitation at both stations. While the
March 23rd and 28th rain events had very little impact on the system, the April 3 rd rain event
increased water surface elevations at both stations. Water surface elevations remained high for
2 to 3 tidal cycles before returning to pre-event levels. The inconsistency of the systems response
to precipitation indicates that winds may play a role in water surface elevation. Alternatively,
Hyannis may have been impacted by a series of highly local rainstorms that did not impact Great
Island.
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Figure 10. Time-series of water surface elevation at both stations (top) and daily
precipitation at Hyannis Airport (bottom) during the deployment period.
2.5.3 Water Level Monitoring
To address concerns of the GIHA over the frequency and magnitude of flooding over Great Island
Road, particularly during non-storm conditions when sunny day or high tide flooding has the
potential to impact access to the Island, a real-time water level sensor was installed near the road
east of the bridge. A sensor from the company Hohonu was installed facing the ground on January
5, 2024, so that flood elevations, or water depths over the roadway, can be measured. The sensor
collects a data point every 6 minutes and results are available for review via an online dashboard
(https://dashboard.hohonu.io/map-page/hohonu-25/GreatIsland,Yarmouth,MA). Flood depths
displayed on the dashboard are from an area beneath the Hohonu sensor, which is 0.5 ft above
the elevation of the adjacent road. Consequently, 0.5 ft must be added to the displayed water
depths to arrive at the depth of flooding over the ro ad (Figure 11).
The Hohonu data were summarized to indicate the total number of hours per month that the
road was impassable, defined as water depths greater than 0.5 feet on the road surface. A graphic
for data collected in January shows that the road was impassable for a total of 32.7 hours,
resulting from a combination of coastal storms and astronomical high tide flooding (Figure 12).
Since installation, there have been a total of 29 flood events through the end of August 2024
showing flooding of up to 4 feet over Great Island Road northeast of the bridge. Appendix E
includes a summary of Hohonu data for the period January to June 2024.
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Figure 11. Schematic showing Hohonu sensor elevation and data reading in relation to depth of flooding over the road.
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Figure 12. January 2024 Hohonu record for Great Island Road.
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2.6 Sediment Characterization
Information describing sediment characteristics of the beach and dune were generated as part
of this Feasibility Study to help with future calculations of sediment transport and to develop
specifications for compatible nourishment material as part of the alternatives analysis. A total of
eight (8) grab samples were collected from the beach and dune in December 2023 at the locations
shown in Figure 13. The samples were sent to the laboratory and analyzed for grain size
characteristics. Results from the laboratory testing indicate that the beach and dune sediments
are primarily medium- to fine-grained sand with a median grain size between 0.238 and 0.355
mm (Figure 14). This is consistent with the earlier Foth and Sustainable Coastal Solutions, Inc.
(2022) study which identified a representative grain size of 0.30 mm, based on sediment sieve
analysis of twelve (12) samples collected from the beach in January 2022. Laboratory results for
the December 2023 samples are included in Appendix F.
Figure 13. Sediment grab sample locations for December 2023 sampling event.
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Figure 14. Grain size distribution for beach and dune sediment samples collected from the
south side of Great Island Road.
2.7 Wetland Resources
Development of conceptual alternatives for building resiliency at Great Island is in large part
dependent on the type and extent of wetland resources at the site. To get a better understanding
of the locations of wetland resources within the jurisdiction of the local and state permitting
agencies, a wetland delineation was conducted by Woods Hole Group wetland scientists. The
survey was conducted on January 17 and 19, 2024 and extended from the west end of Great
Island Road bridge, along the roadway to the northeast end of the causeway, including areas of
the site north of the road. The wetland delineations were conducted using the definitions
provided in the Massachusetts Wetland Protection Regulations 310 CMR 10.00.
Although the entirety of the survey area is considered barrier beach (310 CMR 10.29), individual
resource areas within the barrier system were delineated for this study. Resource areas surveyed
included coastal beach (310 CMR 10.27), coastal dune (310 CMR 10.28), salt marsh (310 CMR
10.32), and coastal bank (310 CMR 10.30). Wetland resource boundaries were surveyed in the
field using a real-time Kinematic GPS. Resource areas such as land subject to coastal storm
flowage and estimated and habitats of rare wildlife (310 CMR 10.37) were delineated using
publicly available mapping datasets. Wetland resources at the site are depicted in Figure 15. They
are also shown on the Existing Conditions Plan in Appendix C. A Technical Memo describing the
wetland delineation is included in Appendix G.
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Figure 15. Coastal resource areas delineated within the study area on January 17 th and 19th, 2024.
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2.7.1 Coastal Beach
The Massachusetts Wetland Regulations 310 CMR 10.27 define Coastal Beach as extending “from
the mean low water line landward to the dune line, coastal bank line or the seaward edge of
existing human-made structures, when these structures replace one of the above lines,
whichever is closest to the ocean.” The project area contains coastal beach along the south side
of Great Island Road, between the mean low water line in Nantucket Sound and the toe of the
dune (Figure 16). A coastal beach resource is present along the entire 8,000 linear foot of
shoreline surveyed. At the time of the survey, the beach was gradually sloping and contained
primarily medium to fine-grained sediments with some areas containing cobble (Figure 17) and
shell deposits (Figure 18). The coastal beach resource transitions landward to coastal dune for
the entirety of the project area, except for an approximate 500 linear foot stretch at the
southwestern survey extent where it transitions to coastal bank. Shore perpendicular groins are
present at varying intervals along the entirety of the survey area shoreline (Figure 19). These
groins were observed to be trapping sediment traveling in an eastward direction along the
shoreline.
Figure 16. Coastal beach seaward of Great Island Road. Photo taken facing southwest.
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Figure 17. Cobble strewn coastal beach at western end of survey area. Photo taken facing
southwest.
Figure 18. Shell deposit within sandy coastal beach.
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Figure 19. Groin structures along coastal beach. Photo taken facing northeast.
2.7.2 Coastal Dune
The Massachusetts Wetland Regulations 310 CMR 10.28 define Coastal Dune as “any natural hill,
mound, or ridge of sediment landward of a coastal beach deposited by wind action or storm
overwash. Coastal dune also means sediment deposited by artificial means and serving the
purpose of storm damage prevention or flood control.” The site contains extensive coastal dune
resources including a primary dune resource on the south side of Great Island Road. Primary
frontal dunes are defined in the Massachusetts Wetla nd Regulations as “a continuous mound or
ridge of sediment with relatively steep seaward and landward slopes immediately landward and
adjacent to the beach and subject to erosion and overtopping from high tides and waves during
coastal storms. The Primary Frontal Dune is the dune closest to the beach. The inland limit of the
Primary Frontal Dune occurs at the point where there is a distinct change from a relatively steep
slope to a relatively mild slope.” Primary dunes are important as they provide the first line of
defense against storm surge and increased wave energy.
Using this definition, primary frontal dune was delineated for a continuous stretch from the
eastern survey extent to a point 7,500 linear feet westward where a transition to coastal bank
occurred (Figure 20). For the entirety of its length, the primary frontal dune was bound on the
south by coastal beach and backed by either secondary coastal dune or Land Subject to Coastal
Storm Flowage (Figure 21). Vegetation within the primary dune included predominantly
American beachgrass (A. breviligulata), seaside goldenrod (S. sempervirens), and dusty miller (J.
maratima) with woody plant species including Northern bayberry (M. pensylvanica) Eastern red
cedar (J. virginiana) scrub oak (Q. ilicifolia), and pitch pine (P. rigida) interspersed. The seaward
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face of the primary frontal dune contained an erosional scarp for a significant portion of its full
length (Figure 22). A stone rip-rap coastal engineering structure was present along the face of
the primary dune in some areas (Figure 23).
Figure 20. Primary frontal dune along Great Island Road. Photo taken facing northeast.
Figure 21. Example of primary coastal dune bound by coastal beach and secondary dune.
Photo taken facing southwest.
Landward toe of Primary Dune
Toe of
Primary Dune
Landward peak of Primary Dune
Backslope
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Figure 22. Erosional scarping along the seaward face of the primary dune.
Figure 23. Stone rip rap armoring primary frontal dune. Photo taken facing southwest.
Secondary coastal dunes are also present at the project site in areas beyond (north) the landward
toe of the primary dune. The crest elevation of the secondary dune is generally higher than the
primary dune and the landward edge tapers down on the Lewis Ba y side of the barrier beach as
the resource transitions to salt marsh (Figure 24). Evidence of storm overwash over the coastal
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dune was observed in fans on the western side of the project site (Figure 25). The secondary dune
was well vegetated with perennial dune vegetation including American beachgrass, seaside
goldenrod, dusty miller, reindeer moss (C. rangiferina). Saltmeadow cordgrass (S. pumilus) and
sea blight (Sueda spp.) are present in the dune near where it transitions to salt marsh. Woody
vegetation was present intermittently in some areas, as well as in more dense maritime forest in
other areas (Figures 26-27). Overstory species included Eastern red cedar, Atlantic white cedar
(C. thyoides), white oak (Q. alba), scrub oak, and pitch pine, with an understory of high tide bush
(I. fruescens) and Northern bayberry.
Figure 24. Transition from coastal dune to salt marsh. Photo taken facing northeast.
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Figure 25. Evidence of storm overwash within coastal dune. Photo taken facing east.
Figure 26. Typical coastal dune vegetation. Photo taken facing south.
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Figure 27. Maritime forest vegetation within coastal dune. Photo taken facing south.
2.7.3 Barrier Beach
The Massachusetts Wetland Regulations 310 CMR 10.29 define Barrier Beach as a “narrow low-
lying strip of land generally consisting of coastal beaches and coastal dunes extending roughly
parallel to the trend of the coast. It is separated from the mainland by a narrow body of fresh,
brackish or saline water or a marsh system. A barrier beach may be joined to the mainland at one
or both ends.” Figure 28 shows the sections of Great Island which are included in the
Massachusetts Barrier Beach Inventory. These include the beaches and dunes along Great Island
Road from the entrance at the northeast to Fox Point.
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Figure 28. Massachusetts Office of Coastal Zone Management (CZM) Massachusetts Barrier Beach Inventory (MassGIS).
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2.7.4 Coastal Bank
The Massachusetts Wetland Regulations 310 CMR 10.30 define a coastal bank as “the seaward
face or side of any elevated landform, other than a coastal dune, which lies at the landward edge
of a coastal beach, land subject to tidal action, or other wetland.” Coastal bank slopes must be
equal to or steeper than 1V:10H. The wetland delineation identified a 500 linear foot stretch of
coastal bank at the southern extent of the barrier beach system near Fox Point. The eroded
seaward face of the bank revealed glacial sediments composed of cobble, gravel and fine-grained
sediments overlain by 2-3 inches of sand (Figure 29). Vegetation along the top of the coastal bank
included American beachgrass, Northern bayberry, pitch pine, and Eastern red cedar. The coastal
bank was fronted by transition to coastal beach and backed by transition to coastal dune. Cobble
and sediments were observed to be eroding from the bank and conveying seaward onto the
beach.
Figure 29. Coastal bank near southwest extent of survey area. Photo taken facing north.
2.7.5 Salt Marsh
The Massachusetts Wetland Regulations 310 CMR 10.32 define salt marsh as “a coastal wetland
that extends landward up to the highest high tide line, that is, the highest spring tide of the year,
and is characterized by plants that are well adapted to or prefer living in, saline soils”. Salt marsh
was present along the entire extent of the bayside shoreline of the Great Island barrier system.
West of the Great Island Road bridge, narrow swaths of salt marsh were also present along the
shoreline (Figure 30). Vegetation in this area included primarily smooth cordgrass (S.
alterniflorus) and saltmeadow cordgrass. East of the bridge, wide areas of continuous salt marsh
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continued on both the north and south sides of Great Island Road (Figure 31). Salt marsh south
of Great Island Road included upland hummocks scattered throughout that were backed by
transition to coastal dune. North of Great Island Road, salt marsh continued along the entirety of
the barrier system. Vegetation within the salt marsh included primarily smooth cordgrass,
saltmeadow cordgrass, sea pickle, with high tide bush clu stered in areas of slightly higher
elevation (Figure 32). Phragmites (P. australis) was present in a discrete area to the east. Toward
the eastern extent of the barrier system, salt marsh narrowed to approximately 30 -40 feet wide
between open water and the coastal dune (Figure 33). Salt marsh continued to narrow and
become more intermittent moving eastward until reaching the northeast extent of the survey
area, where it continued along the shore of the channel. Fringing patches of salt marsh were also
present on the south side of Great Island Road in the vicinity of the remnant revetment a nd
adjacent groins (Figure 34).
Figure 30. Narrow salt marsh areas west of the Great Island Road bridge.
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Figure 31. Salt marsh east of Great Island Road bridge. Photo taken facing east.
Figure 32. Salt marsh vegetation north of Great Island Road. Photo taken facing south.
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Figure 33. Salt marsh between open water (left) and coastal dune (right). Photo taken
facing east.
Figure 34. Fringing salt marsh patches between the remnant revetment and coastal
engineering structure. Photo taken facing northeast.
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2.7.6 Land Containing Shellfish
The Massachusetts Wetland Regulations 310 CMR 10.34 define land containing shellfish as “land
under the ocean, tidal flats, rocky intertidal shores, salt marshes and land under salt ponds when
any such land contains shellfish.” North of the Great Island study area, areas along the bayside
shoreline are identified by the Massachusetts Division of Marine Fisheries (DMF) as spawning
and settlement habitat for quahog (M. mercenaria), bay scallop (A. irridans), soft shell crab (S.
serrata) and American oyster (C. virginica) (Figure 35). No live shellfish were observed during the
delineation.
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Figure 35. Shellfish suitability habitat within and adjacent to the project area.
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2.7.7 Estimated Habitats of Rare Wildlife
The project area includes Priority and Estimated Habitats of Rare Species (PH 945, EH 756) as
published by the Natural Heritage and Endangered Species Program (Figure 36). As described in
the Massachusetts Wetland Regulations 310 CMR 10.37, Estimated Habitat Maps are “based on
the estimated geographical extent of the habitats of all state-listed vertebrate and invertebrate
animal species for which a reported occurrence within the last 25 years has been accepted by
the Program and incorporated into its official data base”. According to the Natural Heritage and
Endangered Species Program, the study area includes Priority habitat of Piping Plover (Charadrius
melodus – threatened), Least Tern (Sternula antillarum – Special Concern) and New England
Blazing Star (Liatris novae-angliae – Special Concern).
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Figure 36. Natural Heritage and Endangered Species Program Estimated and Priority Habitat within and adjacent to the
project area.
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2.7.8 Land Subject to Coastal Storm Flowage
Land subject to coastal storm flowage (LSCSF) is defined in the Massachusetts Wetland
Regulations 310 CMR 10.04 as land subject to any inundation caused by coastal storms up to and
including that caused by the 100-year storm, surge of record or storm of 100-year storm, surge
of record or storm of record, whichever is greater. LSCSF includes AE and VE zones designated by
the Federal Emergency Management Agency (FEMA) on the Flood Insurance Rate Maps (FIRMs)
and encompasses all resource areas documented on site including coastal beach, primary frontal
dune, coastal dune, salt marsh, and coastal bank.
2.8 Shoreline and Dune Change
2.8.1 Shoreline Change Analysis
The Massachusetts Office of Coastal Zone Management (CZM), in collaboration with the U.S.
Geological Survey (USGS), launched the Shoreline Change Project in 1989 and produced maps for
the entire coast with historical shoreline positions to provide scientific data supporting coastal
land-use decisions. Data from the project illustrates the shifting high-water shoreline from the
1800s to 2018 using historical Mean High Water (MHW) shoreline positions. The project helps to
demonstrate how the high-water shoreline has shifted between the mid-1800s and 2018 along
predominantly open-water-facing sections of the Massachusetts coast. It covers ten historic
shorelines at 50-meter intervals, providing data on shoreline movement, change rates, and
uncertainty values.
Woods Hole Group utilized data from CZM’s Shoreline Change Project to evaluate short -term
rates of change between 1970 and 2018 for the project area (Figure 37). Annual rates of change
were computed at shore perpendicular transects starting west of Fox Point and extending
northeast to the end of the barrier beach. Negative rates of shoreline change indicate shoreline
erosion and positive rates of change indicate accretion. Over the 48-year period between 1970
and 2018, both areas of erosion and accretion are indicated with rates of change varying between
-2.2 ft/yr to +1.0 ft/yr. Despite these variations, CZM notes that the change rates are within the
uncertainty bands for the analysis, and the data indicate no significant statistical change in
shoreline change.
Considering the impacts of climate change that have affected New England shorelines over the
past decade, including increases in sea level and more intense and frequent storms, it is likely
that inclusion of more recent shorelines through 2024 would indicate a statistical trend of
shoreline erosion. In fact, the Foth and Sustainable Coastal Solutions, Inc. (2022) study noted that
“recent maximum erosion rates between 2009 and 2022 are as much as five time greater than
what is shown in the CZM Shoreline Change Project.” Based on an understanding that the CZM
rates of change are not representative of more recent erosion conditions at the site, Woods Hole
Group focused on a more detailed analysis of recent rates of dune change along Great Island
Road. Coastal dune was selected as an important indicator of trends in erosion or accretion, as
the dune provides critical protection for the causeway during coastal storms.
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Figure 37. Short-term rates of shoreline change (1970 to 2018) for the south facing Great Island shoreline .
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2.8.2 Toe of Dune Analysis
A computer-based shoreline mapping methodology within a Geographic Information System
(GIS) framework was used to compile and analyze changes in the historical toe of dune line along
the seaward side of Great Island Road. This task aimed to quantify the spatial and temporal
changes in toe of dune position using the most accurate data sources and compilation procedures
available and to evaluate the rates of change. If the trends continue at the same rate into the
future, the information from the toe of dune analysis can also be used to predict patterns of dune
erosion over the next several decades.
Woods Hole Group compiled and analyzed five (5) aerial photographs available from MassGIS
(Bureau of Geographic Information) and one (1) photo obtained from Airbus Earth Observation
Satellite Imagery Services (Google Earth). Six (6) time periods were evaluated in total spanning
26 years from 2021 to 2024. The aerial photographs were geo-referenced, and all data sources
were brought to a common coordinate system. Toe of dune locations were then identified and
digitized from each of the 6 data sources. The vegetated/non-vegetated line was used as the
indicator of the toe of dune.
Once the data were compiled, spatial and temporal changes in the data were computed using
Digital Shoreline Analysis System (DSAS) software version 4.3. DSAS is a software developed by
the United States Geological Survey (USGS) to calculate shoreline change over time within a GIS
framework. Toe of dune change rates were calculated by first identifying a series of shore normal
transects along the coastline where discrete measurements of change could be made through
time and where rates of change could be determined. For the change analysis, 85 shore normal
transects were established at 100 foot evenly spaced intervals along the coastline. At each
transect, distances of dune movement were calculated, and annual rates of change were
determined using the various time intervals between the data sources. Rates of change were
calculated using the linear regression method. Each transect characterizes the rate of dune
change in feet per year, where negative values indicate erosion and positive values indicate
accretion.
Toe of dune change trends throughout the study area for the period 2021 to 2024 were found to
be erosional, with an average rate of -1.26 ft/yr. Based on these findings, two erosion hot spots
were identified where risks associated with future dune erosion over the next 25 years could
impact the road and utility infrastructure (Figure 38).
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Figure 38. Erosion hot spots and toe of dune delineation for 2024. Background imagery was taken March 21, 2024.
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2.9 Wind and Wave Climatology
Information on the wind and wave climatology affecting the shoreline adjacent to Great Island
Road is important in evaluating potential alternatives for building resiliency and maintaining
vehicle access to the Island. The directions and rates of longshore sediment transport are largely
controlled by the incident wave climatology, and thus alternatives involving the use of beach
and/or dune nourishment must consider the impacts that waves will have on redistribution of
sediment.
For this Feasibility Study wind and wave data were obtained from buoy (44020) which is owned
and operated by the National Oceanic and Atmospheric Administration (NOAA) National Data
Buoy Center (NDBC). The buoy is located in Nantucket Sound 8 miles south of Great Island. The
buoy has been in operation since 2009, collecting a continuous record of wind speed and
direction, as well as wave height, period, and direction. Locally generated waves recorded at the
buoy are related to wind speed and direction, while longer period waves recorded by the buoy
propagate into the Sound from the Atlantic Ocean. Although wave conditions between the NOAA
buoy and the shoreline of Great Island are modified by the nearshore bathymetry, the buoy data
provide a good indication of the incident wave climatology impacting coastal processes along the
Great Island shoreline.
Wind is defined based on the direction from which the wind originates. The prevailing wind
direction is a southwesterly direction, between 202.5° and 247.5° (a 45° spread). This wind
direction occurs approximately 20% of the time. Winds from the northwest to northeast,
between 315° and 45° (a 90° spread), occur up to 25% of the time. Due to the orientation of the
shoreline along Great Island Road, most of these winds were blowing in an offshore direction.
While southeasterly winds were the least frequent to occur, they are the most damaging to the
region when they do happen. It is becoming increasingly likely to get stuck in weather patterns
that result in high impact events, like what was experienced durin g the winter of 2023/24. With
limited ice coverage in the arctic, the jet stream (the track for storm systems) becomes wavy.
This allows for persistent patterns to remain in place for at least 4 days. Think of a garden hose –
when there is a kink in the hose, the flow of water slows down, the same happens in the
atmosphere.
Waves measured at the NOAA buoy during the period 2009 to 2023 most often approached from
the west-southwest and east-northeast (Figure 40). Waves approaching from the western sector
tend to cause sediment transport away from Fox Point towards the eastern end of the barrier
beach, while waves approaching from the eastern sector tend to cause sediment transport
towards Fox Point. The largest waves approach from the northeast sector, with wave heights
ranging between 6 and 8 ft.
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Figure 39. Wind rose of data from NOAA buoy 44020 for the period 2009 to 2023.
Figure 40. Wave rose of data from NOAA buoy 44020 for the period 2009 to 2023.
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3.0 VULNERABILITY ASSESSMENT - DATA AND METHODS
Understanding the periodic and episodic impacts of sea level rise and storm surge on
infrastructure and natural resources requires a variety of tools. Coastal inundation modeling,
based on probabilistic sea level rise projections, hydrodynamic storm surge and wave modeling
are critical tools that can be used to provide inundation projections for the combined effects of
sea level rise and storm surge. For this Feasibility Assessment a risk assessment framework was
implemented to evaluate the vulnerability of roads managed by Great Island Homeowners
Association. This vulnerability assessment provided the basis for the conceptual adaptation
alternatives developed later in the project.
The projections in this report are based on the Massachusetts Coast Flood Risk Model (MC-FRM)
which was developed by Woods Hole Group for the State of Massachusetts. The model
incorporates the most recent developments in the science of climate change. While results from
the MC-FRM are the Commonwealth’s recommended tool for resiliency planning, it should be
recognized that the current models and projections are not guaranteed predictions of future
events or conditions. Resiliency planning efforts for any coastal community should consider the
most up to date science, data, and modeling techniques, as well as rates of sea level rise as they
are experienced along the coast.
3.1 Sea Level Rise Projections
Massachusetts has developed projections of future mean sea level elevation for use in climate
change planning that are locally downscaled from global climate models and provide a
probabilistic crosswalk for a range of scenarios (DeConto & Kopp, 2017). These scenarios include
different greenhouse gas emission futures and additional contributions from global ice sheet
melt. The Commonwealth uses the “High” sea level rise scenario for climate change planning
purposes, which is deliberately conservative and ensures that planning measures are not under-
predicting future sea levels. Figure 41 shows how the “High” scenario compares to other
scenarios, as well as the probability that it is not underpredicting sea level rise under RCP 4.5,
RCP 8.5, and both of those scenarios with additional contributions from ice sheet melt. In the
near term, most of the projected relative sea level rise comes from thermal expansion and land
subsidence, and there is little uncertainty in projections. After 2050, contributions f rom ice sheet
melt are uncertain, and the scenarios diverge significantly. The choice to use the “High” scenario
for MC-FRM means that flood probabilities from the model may occur later than their
corresponding year. In interpreting model results, 2030, 2050, and 2070 are generally treated as
the soonest that corresponding flood probabilities could be projected, and a 20 -year range is
applied. In practice, 2030 projections are treated as occurring sometime between 2030 and 2050,
and the same applies to 2050 and 2070.
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Figure 41. Sea level projections for the MC-FRM South Grid 2008 (1999-2017 epoch). Mean sea level for the average between
the Woods Hole and Nantucket tide gages was -0.17 feet (NAVD88).
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3.2 MC-FRM Coastal Inundation Modeling
The Massachusetts Coast Flood Risk Model (MC-FRM) was utilized to assess vulnerability to
coastal storm surge flooding for the Great Island Feasibility Study. The MC-FRM is a probabilistic
hydrodynamic model that is used as the state standard for coastal climate change planning in
Massachusetts (MC-FRM FAQ, 2022). The MC-FRM is high-resolution model that offers more
accuracy than other storm surge models, such as the Sea, Lake, and Overland Surges from
Hurricanes (SLOSH) model developed by the U.S. Army Corps of Engineers (USACE) and the
National Oceanic and Atmospheric Administration (NOAA). The MC-FRM is also more accurate
than a more rudimentary “bathtub” approach, since the latter does not account for critical
physical processes that occur during a storm event, including waves and winds, nor can it
determine the limited volume of water that may be able to enter certain areas, particularly those
with narrow entry points. Figure 42. shows the MC-FRM model mesh, which has an average
spatial resolution of 20-25 meters.
Figure 42. MC-FRM model mesh in vicinity of Great Island.
The MC-FRM evaluates a statistically robust sample of storms, including hurricanes, tropical
storms, and nor’easters, based on the region’s existing and evolving climatology. Using this storm
set, the model then calculates water surface elevations across t he flooded area to estimate the
probability that land will be inundated at each nodal point within the model boundary. The model
results are expressed as an annual probability of flooding for an area under projected time
horizons. With coastal communities facing significant risks from rising sea levels and increasingly
intense storms due to climate change, MC-FRM is an essential tool for identifying areas that are
most vulnerable to flooding.
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3.3 MC-FRM Outputs
Results of the MC-FRM were used to generate coastal flooding maps for the Great Island study
area. Annual Exceedance Probability (AEP) maps depict the annual chance of inundation from
coastal storm surge across the landscape. Inundation probabilities are represented as follows:
MC-FRM Annual Exceedance Probabilities
The MC-FRM produced results for three specific time horizons: 2030, 2050, and 2070. The
selection of these planning horizons was based on their relevance and usefulness in informing
decision-making processes. For instance, the flood risks associated with 2030 are considered a
near-term concern that should be acted on immediately. On the other hand, flood risks projected
for 2050 and 2070 serve as valuable tools for mid- and long-range planning, especially in the
context of large capital projects, infrastructure design, and permitting regulations.
As discussed in the previous section, these future conditions are based on a “High” sea level rise
scenario (Figure 41). Since completion of the MC-FRM, over five years of sea level rise and climate
change have transpired, offering more insight into the sea level rise scenario that may be closest
to future conditions. Based on these insights, the team chose to crosswalk MC -FRM results and
interpret 2030, 2050, and 2070 results as likely corresponding to the early 2040s, mid 2060s, and
early 2090s, respectively. This is an interpretive and communicative choice that does not change
the model results themselves, but rather attempts to increase the alignment between a state -
level, long-term model and local, near-term realities. The team’s interpretive choices around MC-
FRM may evolve further as more up-to-date information becomes available.
Annual Exceedance Probability (AEP) maps for the project area are provided for 2030, 2050, and
2070 for the “High” seal level rise scenario are shown in Figures 43-45.
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Figure 43. MC-FRM annual exceedance probability for Great Island as soon as 2030 (“High” Seal Level Rise Scenario).
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Figure 44. MC-FRM annual exceedance probability for Great Island as soon as 2050 (“High” Seal Level Rise Scenario).
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Figure 45. MC-FRM annual exceedance probability for Great Island as soon as 2070 (“High” Seal Level Rise Scenario).
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3.4 Model Disclaimer
The flood maps and probabilistic data presented in this report are derived from output of MC -
FRM for sea level rise and coastal storm simulations. These maps and data are provided without
any guarantees or warranty. This information is not intended for use as a flood insurance
determination, nor should it be directly related to FEMA FIRM maps or data since these data and
FEMA data are for different purposes. This information cannot be used for the purpose of
boundary resolution or location.
This public information should be accepted and used by the recipient with the understanding
that the maps and data received were developed and collected for future flooding analys is
purposes only. No liability is assumed as to the accuracy, sufficiency or suitability of the
information contained herein for any other particular use. While every effort has been made to
assure the accuracy and correctness of the data presented, it is acknowledged that inherent
mapping inaccuracies are present due to interpolat ion between MC-FRM calculation nodes. Any
reliance upon the maps or data presented herein used to make decisions or conclusions is at the
sole discretion and risk of the user. This information is provided with the understanding that
these data are not guaranteed to be accurate, correct, or complete and assumes no responsibility
for errors or omissions. Data and documents may not be the most currently available data, and
the data is subject to constant change given the changing climate.
Assets located near boundaries of a probability zone may or may not be within the probability
zone due to interpolation between model nodes. MC-FRM nodal spacing varies throughout the
Yarmouth study area (20–25 meters). The GIS rasters interpolate the values between model
nodes and therefore create probabilities that may represent transition zones between model
nodes.
3.5 Daily Tidal Flooding
High tides occur twice each day (one higher than the other due to diurnal inequality) and can
pose a risk to low lying areas like Great Island. As sea level rises, so too will the elevation of the
high tides, becoming more of a nuisance to low lying areas and roadways. Inundated roads
cannot provide reliable transportation corridors for residents or emergency responders. Since
there is a single roadway that allows access to Great Island and Cedar Point, it was crucial for the
Feasibility Study to evaluate areas of the road that may experience this type of “nuisance
flooding” so that adaptations could be developed for maintaining vehicle access into the future.
To determine the impact of future water levels at the project site, tidal benchmark elevations for
Mean High Water (MHW) for the 2030, 2050, and 2070 planning horizons consistent with the sea
level rise projections described above in Section 3.1 were utilized. Based on the local MC-FRM
modeling and projected sea level rise, MHW elevations (for the “High” seal level rise scenario)
for the project site could be:
• as high as 3.0 to 3.3 ft NAVD88 as soon as 2030
• as high as 4.4 to 4.6 ft NAVD88 as soon as 2050
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• as high as 6.2 to 6.4 ft NAVD88 as soon as 2070
MHW shorelines corresponding to the high end of these local tidal benchmark elevations were
developed by Woods Hole Group and used to identify road segments that may be vulnerable to
daily inundation under non-storm (“sunny day”) conditions for the 2030, 2050, and 2070 time
horizons (Figure 46). Contours corresponding to the projected high end of the projected MHW
elevation ranges were isolated and processed into projected shorelines.
The results show sections of Great Island Road near the bridge, and portions of White Cedar Point
Road, to be flooded daily by the year 2030. By 2050 daily high tide flooding extends further east
along Great Island Road from the bridge, and by 2070 all but the northeastern one -third of the
roadway is flooded on a daily basis during high tide.
Figure 46 shows the Great Island roads that are impacted by “sunny day” flooding for the three
time horizons, 2030, 2050, and 2070. This provides a clear picture of the areas within each time
horizon’s 100% AEP extent that will be flooded daily by tides, rather tha n at least once per year
by storms. Figure 46 also highlights the two lowest-lying and most vulnerable stretches of
roadway: White Cedar Point Road and Great Island Road near the bridge.
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Figure 46. Projected mean high water shorelines for present day, as soon as 2030, 2050, and 2070 (“High” Seal Level Rise
Scenario).
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3.6 Flood Pathways Assessment
Coastal flood threats to Great Island and White Cedar Point Roads are complex and originate
both from Lewis Bay to the north, and Nantucket Sound to the south. To provide high-resolution
insight into the propagation of water across the landscape during flo od events, an elevation-
based flood pathway analysis was performed, the results of which are shown in Figure 4 7. This
analysis confirms that the primary flood threat to Great Island and White Cedar Point Roads,
during small storms and astronomical high water events, is from Lewis Bay. During storm events
and long-term future MHW conditions, additional water from Nantucket Sound may also flood
the roadways. Unchecked dune erosion could increase the influence of Nantucket Sound flood
pathways over time. It is important to note that this analysis was performed with high -resolution
elevation data from 2021 and does not incorporate erosion since then or in the future.
Nevertheless, it is clear that the primary flood threat comes from Lewis Bay. Figure 4 7 was used
to inform the development of alternatives and communicate with community members about
the limitations of alternatives that focus exclusively on mitigating dune erosion as a way of
reducing flood vulnerability.
3.7 Coastal Erosion
Threats from coastal erosion with the potential to adversely impact access to and from Great
Island are primarily located on the south side of Great Island Road along the Nantucket Sound
shoreline. As described above in Section 2.8.2., erosional hot spots are located immediately to
the north and south of the “S-curve” (Figure 38). These areas have an average rate of dune
erosion of -1.26 ft/yr. Continued erosion of the dunes in these two areas has the potential to
cause damage to the road and utility infrastructure in the near future.
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Figure 47. Great Island Road flood pathways.
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4.0 VULNERABILITY ASSESSMENT RESULTS
4.1 Roadway Vulnerability Assessment
This vulnerability assessment used a protocol developed for the Cape Cod Low Lying Roads
Project to evaluate future flood risk to Great Island’s roads on a site-specific basis. To assess the
vulnerability of Great Island’s roads, accurate road center lines were developed by referencing
high-resolution LiDAR terrain data collected in 2021 by the US Geological Survey. The accuracy of
the LiDAR data set was confirmed through comparison with surveyed elevation points gathered
during previous stages of this project. Once center lines were established, road surface elevations
were extracted at points every 20 feet along the center lines. The elevations of these points were
then compared to the Water Surface Elevations (WSEs) corresponding to various Annual
Exceedance Probabilities (AEPs) to identify the annual flood exceedance probability of each
point. The highest probability AEP WSE exceeding the road elevation was used to determine the
road vulnerability at each point. An example of this analysis is shown in Figure 49 from the Cape
Cod Low Lying Roads project.
Figure 48. Cape Cod Low Lying Roads Vulnerability Assessment methods.
Water Surface Elevations at the 0.1%, 0.2%, 0.5%, 1%, 2%, 5%, 10%, 20%, and 100% AEPs were
used to assess the roadway points for each of the 2030, 2050, and 2070 time horizons. Lengths
of roadway found to be vulnerable to flooding are shown in Figure 50 an d summarized in Table
2.
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Figure 49. Miles of roadway vulnerable to flooding.
Table 2. Length of Roadway Vulnerable to Flooding in 2030, 2050 and 2070.
Length of Roadway (Miles)
AEP 2030 2050 2070
0.1% 3.67 4.73 5.11
0.2% 3.63 4.48 4.90
0.5% 3.53 4.18 4.52
1% 3.44 3.92 4.29
2% 3.35 3.79 3.97
5% 3.13 3.67 3.82
10% 2.84 3.49 3.73
20% 2.44 3.35 3.63
100% 0.95 2.12 3.08
For the 2030-time horizon, the majority of the approach road has a 20% AEP, indicating there is
a 20% probability of flooding at least once per year (Figure 50). Parts of the approach road, as
well as all of White Cedar Point Road, are projected to flood at least once per year (100% AEP).
Internal roads on Great Island have a maximum AEP of 20%. In the 2050 and 2070 time horizons,
the majority of the approach road and significant internal roads have a 100% AEP and are
projected to flood at least once per year (Figures 51 and 52).
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Figure 50. Map of projected 2030 coastal flooding on road centerline points, color coded by Annual Exceedance Probability.
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Figure 51. Map of projected 2050 coastal flooding on road centerline points, color coded by Annual Exceedance Probability.
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Figure 52. Map of projected 2070 coastal flooding on road centerline points, color coded by Annual Exceedance Probability.
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Figure 53 shows the areas of Great Island’s roads that are within the mean high water shorelines
for the three time horizons. This provides a clear picture of the areas within each time horizon’s
100% AEP extent that will be flooded daily by tides rather than at least once per year by storms.
Figure 53 also highlights the two lowest-lying and most vulnerable stretches of roadway: Cedar
Point Road and Great Island Road near the bridge. These two segments of road were constructed
through salt marsh and low-lying dune systems to connect Cedar Point and Great Island to the
mainland.
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Figure 53. Map of road centerline points within projected mean high -water shorelines for 2030, 2050, and 2070.
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In roadway vulnerability assessments, flood probability data is multiplied by a criticality score to
determine a road segment’s risk. To adapt this framework to Great Island, each road point was
assigned a criticality score according to the number of residences that must pass through it for
access (Figure 54). Figure 55. shows the results of multiplying flood vulnerability by criticality for
each road point. The highest risk scores were assigned to points on Great Island and Cedar Point
Roads. These scores, in addition to the 2030 AEP data, were used to identify road segments to
prioritize for adaptation. The top five road segments are shown in Table 3.
Table 3. Top Vulnerable Road Segments.
Description Length
(ft)
AEP
2030
Criticalit
y Score
2030
Risk
Score
Tidal Flooding Length
(ft) Erosion
Concern
s 2030 205
0 2070
A
Easternmos
t section of
Great Island
Road
3160 100 53.5 5350 0 440 1960 None
B
Great Island
Road
directly East
of Great
Island
(Includes
Bridge)
2960 100 46.5 4650 520 124
0 2840 Current
C
Segment
Between
Cedar Point
Road and
Deer Island
Access
1280 20 53.5 1070 0 0 1160 Current
D
Short
Segment
between
Cedar Point
Road and S
Curve
360 20 46.5 930 0 0 160 Future
E
White
Cedar Point
Road
1340 100 7 700 220 900 1180 None
These road segments and the order in which they are prioritized served as a starting point for
identifying vulnerability and are not meant to express the extent of an adaptation design. A full
list of road segments is available in Appendix H.
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Figure 54. Criticality scores assigned to road points in the Great Island road network.
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Figure 55. Risk scores for each point on the Great Island road network (2030), determined by multiplying each point’s AEP by
its criticality score.
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4.2 Bridge Vulnerability Assessment
The bridge to Great Island is increasingly vulnerable to damage and deterioration as tidal - and
storm-induced water elevations inundate the bridge on an increasingly frequent basis. As sea
level rises, the bridge will be inundated on a more frequent basis, which will increase the rate of
corrosion and deterioration of the concrete/streel bridge deck elements, and increase the risk to
stone armor abutments, timber piles and the timber support beam. In addition to increased risks
to the bridge structure, the pavement roadway segments immediately adjacent to the bridge will
be more significantly at risk to accelerated deterioration by worsening of cracks and erosion of
shoulders and resulting undermining of the pavement surface. The stone armoring currently
protecting the roadway embankment on both the east and west approaches to the bridge will
become increasingly vulnerable to displacement, after which risk of erosion to the roadway will
be significantly increased.
While no signs of erosion around the piles and/or undermining of stone abutments were
observed during the most recent inspection in 2024, it is expected that more severe storm/flood
events will increase the risk of erosion at the bridge structure. Loss of channel bed armor and
underlying sediment substrates adjacent to the piles and abutments will significantly increase
the risk of damage to these structures, which are critically important to the structural integrity
of the bridge deck and immediately abutting roadway segments. Further details from the 2024
bridge inspection can be found in the Great Island Bridge Inspection Memorandum provided in
Appendix I.
4.3 Utilities Vulnerability Assessment
Existing underground electric and telecommunication utilities are understood to be located
under/adjacent to Great Island Road, based on mapping obtained by GIHA from Eversource. This
mapping, which was received as discrete figure panels of respective segments along the length
of Great Island Road, were aligned and digitized on parcel and aerial mapping (Approximate
Location of Buried Utilities is included in Appendix J). While neither the type/depth of conduits
utilities were installed in, nor the date of installation, was reported by GIHA, it was reported that
utilities were installed using open trenching equipment. If correct, it is estimated that respective
utilities were installed within PVC conduit joined with solvent-glued push-on joints at a depth of
up to 3-4 feet below the ground surface.
It is noted that mapping depicts utilities located within the alignment of Great Island Road, with
above-ground cabinets (transformers and switchgear) and belowground vaults located at
periodic intervals along its length from the most easterly mapped locat ion (approximately 500
feet from the intersection with Whale Road), to the intersection of Great Island Road and White
Cedar Point Road, to the western end of provided mapping near the intersection of Wood Duck
Pond Road and Great Island Road. Due to Great Island Road’s susceptibility to flood erosion,
underlying buried utilities are similarly susceptible if erosive effects extend to the depth and
lateral extent of buried utilities. Erosion of soils around existing conduits would result in buried
conduits being exposed to inundation and waves/currents, presenting an increased risk of
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damage of unsupported conduit segments becoming dislodged and enclosed conductors
breaking.
From review of the toe of dune analysis (depicted Figure 38), the greatest risk of erosion of the
Great Island Road extends from a point approximately 900 feet east of its intersection with White
Point Cedar Road to a point approximately 1,900 feet west of White Cedar Point Road. While
planned implementation of recommended shoreline protection measures and roadway
stabilization measures are expected to avoid damage to these utilities from erosion, if/when
GIHA decides to cease shoreline protection elements and develop roadway access alternatives
along a new alignment or implement ferry services to/from Great Island, it is expected that
erosion would proceed to an extent that existing utilities will need to be protected independently
of the road, or the utilities relocated to a new alignment with associated switch/transformer
infrastructure.
It is recommended that future adaptation strategies for transportation infrastructure be
expanded to include protection and/or relocation strategies to assure continued service to
respective properties. The type and extent of protective/relocation measures will be addressed
in future phases of the project, when roadway adaptation measures are determined. If roadway
reconstruction is selected, we recommend specifically evaluating the utilities in concert with the
roadway to determine potential improvements to increase resiliency (e.g. concrete encasement,
raising utility structures above future key flood elevations, anchoring utility components, etc.). If
the bridge is reconstructed, the utilities should be located under the decking at a suitable
elevation.
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5.0 ALTERNATIVES ASSESSMENT
5.1 Introduction and Methods
The adaptation alternatives developed in this section are a menu of strategies that the GIHA may
consider implementing to build coastal resilience to future sea level rise and storm surge hazards.
There are multiple ways to achieve resilience, depending on a project's goals, which for this
project included:
• Study and evaluate flood vulnerability and erosion risk to the roadway infrastructure
• Prioritize nature-based or hybrid solutions
• Develop cost-effective adaptive alternatives
• Develop a plan for long-term resiliency (~50 yr)
Coastal resilience can be framed as preparedness and risk reduction, and the National Oceanic
and Atmospheric Administration (NOAA) defines resilience as "the ability to adapt to changing
conditions and withstand—and rapidly recover from—disruption due to emergencies." Resiliency
planning and adaptation involves considering the natural and built environment and often
consists of a combination of infrastructure improvements, land use planning, ecosystem
restoration, and community emergency response improveme nts to reduce vulnerability to
coastal hazards.
Adaptation strategies can be used alone; in other situations, a combination of approaches may
be most appropriate. Four adaptations principles are:
• Avoid risk,
• Accommodate,
• Protect, and
• Retreat
Avoid: Risk avoidance strategies typically involve planning level activities to prohibit future
development in areas subject to coastal hazards, such as sea level rise and storm surge impacts,
or in areas where the current level of risk is low but will increase over time.
Accommodate: Accommodate strategies allow continued use of the land or assets within a
higher-risk area by implementing changes to human activities and infrastructure to improve
resiliency to occasional flooding. This strategy does not stop flood waters from reaching essential
infrastructure but takes action to minimize and control the damage that would be caused during
such an event. Accommodation strategies may include physical or operational changes, such as
raising roads above flood elevation. Operational measures may consist of improved evacuation
or emergency planning and additional training for first responders.
Protect: Protect strategies utilize hard engineered structures (e.g., revetments, seawalls, flood
barriers) and/or soft measures (e.g., beach nourishment, dune enhancement, living shorelines)
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to protect an area and its assets from exposure to flooding. Shoreline infrastructure may need to
be raised incrementally to continue providing adequate protection in the future, given projected
sea level rise and increased storm intensity.
Retreat: Retreat strategies involve withdrawing infrastructure and development from high -risk
areas and relocating them to low-risk areas. These strategies acknowledge that it may be too
costly or technically infeasible to accommodate or protect an area or asset against escalating
flood risks. As hard infrastructure is relocated, previously developed areas along the coast can be
restored to healthy ecosystems, which can provide valuable ecosystem services. Retreat
strategies also allow ecosystems, such as salt marshes, to migrate landward as sea level rises.
The adaptation recommendations in this section are a menu of strategies that Great Island may
consider for future implementation to build coastal resiliency. Two major themes emerged
throughout the development of the conceptual alternatives - raising roadway infrastructure to
mitigate flooding, and/or retreating the roadway to mitigate erosion. These strategies are
conceptual as implantation of the adaptation strategies will need further refinement in the
design phase. Monitoring for implementation thresholds, as well as adjusting risk and
vulnerability assessments over time, given evolving science, will be essential elements in the
GIHA coastal resilience planning process.
While some adaptation strategies have been successful in other states and countries, if they have
not been implemented in the Commonwealth at this time, they are often not permittable under
the current Commonwealth’s regulations and policy. Consequently, the following
recommendations consider only solutions which are potentially, but in no way guaranteed,
permittable.
These conceptual alternatives were not developed in a vacuum. They were the result of
collaborative efforts from a team of coastal scientists, designers, and engineers, as well as
feedback from the GIHA stakeholders. Ten (10) conceptual alternatives were presented to the
GIHA on May 2, 2024. These were further refined down to four (4) conceptual alternatives based
on feedback from the GIHA stakeholders which were presented during the community workshop
held on July 13, 2024. This community involvement is a crucial part of the adaptation process.
The coastal resilience alternatives presented in this section will require continued discussion by
the GIHA so that a path forward can be selected that meets the community’s acceptable level of
risk and financial resources necessary for implementation, as well as disruptions to the natural
and built environment, and ability to meet the GIHA goals for reducing flood exposure and
increasing resilience to coastal hazards.
5.2 Conceptual Alternatives
The initial ten (10) conceptual alternatives developed during this Feasibility Study are shown in
Table 4 and full drawings for each alternative are included in Appendix K . For each alternative a
series of evaluation criteria were developed to help assess the level of flood and erosion
protection provided, permitting feasibility, estimated time period for implementation, and cost.
A description of each evaluation criteria is provided below:
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• Road low elevation – Lowest roadway elevation associated with each alternative in feet
with respect to the NAVD88 datum. While higher portions of the road may exist, use of
the lowest elevation allows predictions of flooding along low sections of the road that
may impact vehicle access. The road low elevation is the threshold used to evaluate
annual flood probability.
• Annual Flood Probability – Annual probability of road flooding caused by high tides or
storms for future conditions projected for 2030, 2050, and 2070. For example, a 10% flood
probability in 2030 means there is a 10% chance in a year that has the model’s 2030
conditions that the road will be flooded by high tides or storm activity.
• Daily High Tide Flooding – Projected year during which high tide flooding will impact at
least a portion of Great Island or White Cedar Point Roads on a daily basis.
• Potential for Future Erosion – Likelihood for erosion to impact Great Island Road causing
loss of access and/or damage to the utility infrastructure.
o High potential indicates likely damage to the roadway due to proximity of the road
to Nantucket Sound and the lack of a protective dune.
o Moderate potential indicates possible damage to the roadway due to proximity of
the road to Nantucket Sound and a regularly maintained coastal dune.
o Low potential indicates low likelihood of road damage due to greater setback of
the road from Nantucket Sound and the presence of a protective coastal dune.
• Ease of Permitting – Criteria indicates the level of permitting required for each alternative
as well as the difficulties associated with permitting given the current environmental
regulations. The estimates provided are based on the experience of environmental
permitting specialists at Woods Hole Group.
o Easy indicates that some permits (3) have already been issued and significant
issues are not expected with obtaining the remaining permits (3), as the work is
commonly permitted in the Commonwealth of Massachusetts.
o Moderate indicates that up to seven (7) permits will be required from local, state,
and federal agencies. The alternative includes minor to moderate unavoidable
impacts to sensitive coastal resources that may require on-site
mitigation/restoration. The work included in the alternative has been permitted
in the Commonwealth of Massachusetts.
o Difficult indicates that up to eight (8) permits will be required from local, state,
and federal agencies. The alternative includes significant unavoidable impacts to
sensitive barrier beach and marine resources that will likely require preparation
of a Conservation Management Plan and mitigation in the form of a financial
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contribution to a habitat restoration fund. Some aspects of the work have been
permitted in the Commonwealth of Massachusetts and other aspects are just now
moving through the permitting process as projects involving resiliency adaptations
in the coastal zone are being proposed.
o Extremely difficult indicates eight (8) or more permits will be required from local,
state and federal agencies. The alternative includes significant unavoidable
impacts to marine resources that would be difficult to mitigate. Few permits have
been issued in the Commonwealth of Massachusetts for this type of project.
• Earliest Possible Implementation – Estimates of the earliest year that construction of the
alternative could be finished, factoring in the necessary time for additional field
investigations, engineering design and environmental permitting. The estimates assume
that the design process begins in the first quarter of 2025 and that GIHA has the funds
necessary to begin construction as soon as the final permit is issued.
• Planning Level Cost Estimate – Estimates of planning level cost ranges are inclusive of
additional field investigations, engineering design, environmental permitting, and
construction. The cost estimates are meant to offer a means of comparing the conceptual
alternatives and are a loose approximation of total project cost.
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Table 4. Summary of Alternatives.
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Conceptual Alternatives 1, 2, and 4 do not involve any work on the road, and aim to reduce the
erosion threat along the Nantucket Sound side of Great Island Road through beach and dune
nourishment or an offshore breakwater. All three of these alternatives maintain the existing
road’s vulnerability to both tidal and storm flooding but have the potential to reduce erosion.
Further modeling work would be required to determine the effectiveness of these alternatives in
reducing erosion. The permitting for beach and dune nourishment associated with Alternative 1
was advanced through the Massachusetts Environmental Policy Act (MEPA) Unit , the Yarmouth
Conservation Commission, and NHESP with VHB, Foth Engineering, and Sustainable Coastal
Solutions; however, additional permits are still required from the Mass Department of
Environmental Protection (MassDEP), Massachusetts Coastal Zone Management (CZM), and the
US Army Corps of Engineers (USACE) before construction could begin. Amendments to the
current permits would be required to expand the nourishment footprint included in Alternative
2. An offshore wave attenuation structure would be extremely difficult to permit due to the
presence of submerged aquatic vegetation and the strict regulations around structures built on
land under the ocean resources. Beach and dune nourishment could likely be implemented in
the next 1-2 years, while an offshore wave attenuation structure would require 3 -5 years of
design, permitting, and construction.
Conceptual Alternatives 3 and 5 involve raising the road to two different target elevations. Both
of these alternatives maintain the current footprint of the road. Alternative 3 aims to reduce
vulnerability to tidal flooding in the near- and mid- term and accepts that the road will be flooded
during storms. This would entail raising the road by approximately two feet at its lowest p oint
and would make the road higher in elevation than all astronomical high tide flood events
observed by the Hohonu sensor in January-June of 2024. Alternative 5 raises the road by
approximately five feet at its lowest point, enough to offer resilience to tidal flooding for the
foreseeable future and reduction from a 100% annual chance to a 10% annual chance of flooding
in the near term. This would bring the road elevation higher than all observed water levels
between January and June of 2024. Beach and dune nourishment are recommended to reduce
the road’s vulnerability to erosion but are not expected to completely eliminate the risk of
erosion damage. Both of these alternatives would have permitting challenges, but may be slightly
easier to permit than alternatives that propose relocating the road. These alternatives could be
completed in the late 2020s at the earliest.
Conceptual Alternatives 6, 7, 8, and 9 involve raising the road significantly and changing its
location to avoid the threat of erosion. Alternative 6 recommends shifting the road slightly to the
north in areas where it is threatened by erosion, and Alternatives 7, 8, and 9 reroute the road
completely through Cedar Point. The target elevations in these alternatives would require road
raisings to continue onto Town-owned sections of the road near the entrance to the GIHA
controlled properties. Alternatives 6, 7 and 8 would result in grade changes to privately-owned
yards and driveways just outside the entrance to Great Island to tie-in the elevated roadway. The
target elevation for Alternative 9 is not compatible with the existing privately developed
properties along Great Island Road in the Great Islands Associates neighborhood and would likely
require structures to be removed or modified before construction. Alternative 6 relocates Great
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Road landward away from the current shoreline, while Alternatives 8 and 9 relocate the road
further north through Cedar Point. A variety of layouts were explored with these Alternatives,
many of which involve constructing new bridges over salt marsh, which would be extremely
difficult to permit under current regulations. The new bridge stretches in these alternatives also
result in much higher costs than the other alternatives. However, these alternatives offer a
meaningful reduction in flood risk, including eliminating the risk of daily tidal flooding for the
foreseeable future.
Conceptual Alternative 10 recommends establishing a community ferry and phasing out road use
over time. This would require landing locations on both the mainland and Great Island but could
offer flexible resilience to high tides and small storm events.
5.3 Refined Alternatives
During the course of the Feasibility Study the ten (10) conceptual alternatives discussed above
were refined and consolidated into four (4) conceptual alternatives that provide near-term, mid-
term, and long-term options for enhancing resiliency and maintaining access to Great Island over
the next 50 years. These four refined alternatives are described in the following section.
Requirements for permitting and preliminary cost ranges are provided for each refined
alternative.
5.3.1 Refined Alternative 1: Maintain Road and Bridge
The first refined alternative is a variation of Conceptual Alternatives 1 and 2 (Figure 56). It aims
to maintain use of the roads and bridge for as long as possible with minimum investment. If this
alternative were carried out, the road’s resilience to flooding would not increase, but erosion
impacts would be minimized.
According to an inspection carried out by Fuss & O’Neill engineers, short -term repairs are
necessary, and a full bridge replacement should be completed within 5 years. The timeframe for
full bridge replacement may be extended with annual inspections and as-needed maintenance
and repairs on a timely basis. Beach nourishment, dune nourishment, and emergency erosion
control would continue as necessary along eroding areas of the dune with this alternative.
Refined Alternative 1 would require a Notice of Project Change (NPC) to be filed with MEPA and
the existing Yarmouth Conservation Commission Order of Conditions for beach nourishment
from Fox Point to White Cedar Point Road would need to be amended so that the nourishment
footprint could be extended further to the north. Additional permits from Mass DEP (Chapter 91
Permit), CZM (Federal Consistency Determination), and the USACE (General Permit) would also
be required. GIHA has currently contracted with Woods Hole Group to design and permit
emergency erosion control along the edge of Great Island Road that can be implemented on an
as needed basis. Permit applications will be filed with the Yarmouth Conservation Commission
and NHESP for this emergency erosion control by the end of December 2024. It is expected that
permits for the emergency erosion control will be issued in the Spring 2025. Permits for the
expanded beach nourishment would take approximately 1.5 years to obtain.
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The road low point would remain at approximately 2.5’ NAVD88, leaving both Cedar Point and
Great Island roads vulnerable to monthly high tide and storm flooding in the present and daily
tidal flooding as soon as 2030 (Figure 57 & 58). The total annual cost is estimated at $100,000-
1,000,000, which includes approximate bridge repair and erosion control costs. Costs are
expected to vary dramatically depending on the frequency and severity of storms. Catastrophic
failure of the road and/or bridge in a major storm is an ongoing risk, and the cost of repairs is not
included in the cost estimate for this alternative.
Refined Alternative 1 results in minimal disruption to residents day to day activities during
construction when compared to other alternatives. However, this alternative is the least resilient
to future sea level rise and storm events, which will result in increasing road shutdowns and
maintenance. Future high tide flood elevations will cause continued inundation of portions of the
roadway. This means that there will be periods of time every day that residents will not be able
to enter or exit Great Island by land. As a result of this daily flooding, portions of the roadway will
be more susceptible to erosion and will require routine maintenance. This Refined Alternative 1
will require dedicated maintenance personnel to monitor the roadway conditions, monitor
upcoming severe weather events, and coordinate repair work with contractors and authorities
having jurisdiction. It is recommended that a permanent upland laydown and staging area be
identified and utilized to avoid any delays to critical m aintenance operations. If there is no
dedicated maintenance staff or personnel to coordinate maintenance operations, there will likely
be repair delays which may result in residents being stranded or not able to access Great Island.
In summary, Refined Alternative 1 results in limited disruption to residents during
implementation of protective for the continued use of the road but will result in more disruption
to residents during future daily high tide and storm events. It is noted that implementation of
protective measures will require use of the roadway’s full width, during which use access by other
vehicles will not be feasible. While construction could be scheduled during off -hours (night) to
avoid impacts with normal use by residents, such a construction schedule would entail an
increased cost of construction.
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Figure 56. Overview of Refined Alternative 1.
Figure 57. Typical cross-section of eastern roadway segment with Refined Alternative 1.
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Figure 58. Bridge segment of roadway with Refined Alternative 1.
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5.3.2 Refined Alternative 2: Minor Road Raising and Bridge Replacement
The second refined alternative is a variation on Conceptual Alternative 3 (Figure 60). It proposes
a modest road raising to approximately 4.5’ NAVD88, which is two feet higher than the current
low point east of the bridge. This target elevation is not final and may be modified in subsequent
stages of design. Segments of Great Island Road near the bridge, White Cedar Point Road, and
Great Island Road in the Great Islands Associates neighborhood would need to be raised. Erosion
control efforts described in Refined Alternative 1 would also need to continue to minimize
erosion damage to the road. If this alternative were carried out, daily tidal flooding of Great Island
and Cedar Point roads could be delayed until after 2050, and resilience to small storms in the
near term would also increase. All non-storm flooding observed by the Hohonu sensor from
January-June of 2024 would not have occurred with this road elevation.
In raised segments of road passing through salt marsh, the road would stay within its current
layout and be raised with vertical sheet pile or on bridge pilings (Figure 59). In raised segments
passing through other habitat types or developed areas, side slopes would be used to connect
the raised road with the existing grade. The bridge would be reconstructed at a height that
matches the target elevation and a span length that ensures that tidal exchange continues.
Figure 59. An example of vertical steel sheet pile of a 1-foot road raising (with crushed
stone). The specific technology and application used to raise Great Island may
vary from this example which shows PVC sheet piling opposed to steel. Credit
ESP Group.
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In summary, Refined Alternative 2 includes raising all road segments lower than the target
elevation to approximately 4.5’ NAVD88, delaying the onset of daily tidal flooding until after
2050, and eliminating all present-day tidal flooding. The total project cost is estimated to be $10-
20 million, and the following costs are estimated for different project components:
• Western Segment: $7.6 million
• Erosion Control: $0.6 million, varies annually
• Cedar Point Road: $4.6 million
• Eastern Segment: $0.6 million
These segment cost estimates represent 2024 installed material costs, with 40% escalation
(through 2030) and 15% contingency. Segment costs exclude design, permitting, mobilization,
and site controls. Phasing may increase the total project cost. Design and permitting costs of 25%
were applied to the sum of segment costs to estimate the approximate total project cost of $10-
20 million. Catastrophic failure of the road and/or bridge in a major storm is an ongoing risk, and
the cost of repairs is not included in the cost estimate for this alternative.
Refined Alternative 2 would require the following seven (7) regulatory reviews/permits. MEPA
NPC or new Expanded Environmental Notification Form (EENF), Order of Conditions from the
Yarmouth Conservation Commission, NHESP MESA Determination, Chapter 91 Permit and
License from Mass DEP, Water Quality Certification from Mass DEP, Federal Consistency
Determination from CZM, and Individual Permit from the USACE. It is estimated that permitting
for this alternative would take approximately 3 years to complete.
Refined Alternative 2 results in a more sustainable long-term solution when compared to Refined
Alternative 1, but results in more disruption to residents during construction. This alternative
delays daily high tide flooding beyond that of Refined Alternative 1 but will not result in
permanent fix to long-term sea level rise.
During construction, residents will experience temporary impacts to daily life. Vehicular bypass
during construction may be challenging due to existing narrow travel lanes. Reconstruction of
the bridge and portions of low-lying roadway may result in temporary road shutdowns. Residents
may not be able to get to their homes during certain periods of construction. A temporary ferry
may be required for residents to access Great Island during bridge construction, unless a
temporary bridge is constructed on an adjacent alignment around the existing bridge structure.
This may result in limited non-essential services such as home improvements and landscaping.
Daily construction noise, specifically that of driving sheet piling, may be audible at nearby
residences. Where sheet piles are not implemented and earthen side slopes are proposed,
construction may occur on private residences. Specific consideration will need to be given to
changing drainage patterns to avoid directing stormwater runoff towards homes. Additionally,
protection, or replacement, of landscaping on private residences may be required and
supplemented with slope stabilization. Slope stabilization can vary but may include stone
armoring infilled with coastal plantings suitable for long-term stabilization. Driveway aprons may
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also need to be replaced to blend the roadway grade with the adjacent residences. Specialty
pavers may need to be procured to replace residents’ driveways in kind.
Existing utilities may be considered for modifications during this time to reduce their
susceptibility to erosion. Improvements such as concrete encasement, raised structures above
future flood elevations, or other means may be implemented but could result in a temporary
pause of the service. A geotechnical analysis of the suitability of existing roadway base material
is recommended prior to construction. If the material is not suitable for re -use, additional
construction costs and time will result for the additional material and hauling. Construction
staging and laydown areas will need to be identified in upland areas approved by local
jurisdiction. The selected location may impact construction time depending on the proximity to
the construction.
Post construction, there will still be roadway maintenance required following storm surge
flooding, but not at the frequency of that of Refined Alternative 1. It is still recommended to have
dedicated maintenance personnel to monitor weather events and inspect and coordinate repair
work with contractors and authorities having jurisdiction. Over time, sea level rise will result in
daily high tide flood elevations exceeding that of portions of the roadway, which will in turn
require routine maintenance similar to that of near-term maintenance requirements of
alternative 1.
In summary, Alternative 2 results in short-term construction related disruption to residents, but
improves the resiliency of the roadway over the coming years. This alternative does not remedy
long-term impacts of sea level rise but does extend the useful life of the roadway beyond that of
alternative 1 with less short-term maintenance needs (Figures 60 - 63).
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Figure 60. Overview of changes to the roadway with Refined Alternative 2.
Figure 61. Typical cross-section of western roadway segment with Refined Alternative 2.
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Figure 62. Typical cross-section of eastern roadway segment with Refined Alternative 2.
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Figure 63. Erosion control with Refined Alternative 2 – no road raising is necessary along this section of roadway.
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Figure 64. Refined Alternative 2 bridge modifications.
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5.3.3 Refined Alternative 3: Major Road Raising and Bridge Replacement
The third refined alternative is a variation on Conceptual Alternatives 6 and 7 (Figure 65). It
proposes a major road raising to approximately 7.5’ NAVD88, which is five feet higher than the
current low point east of the bridge. This target elevation is not final and can be modified in
subsequent stages of design. Nearly all of Great Island and Cedar Point roads would need to be
raised, including a short stretch of road owned by the Town of Yarmouth. To prevent work on
Town-owned roads, the target elevation would need to be lowered to 6.8’ NAVD88. Portions of
the road that are currently adjacent to the dune are shifted north to prevent erosion. If this
alternative were carried out, daily tidal flooding of Great Island and Cedar Point roads could be
delayed until late in the 21st century, and resilience to storms in the near- and mid- term would
also increase. No flood water levels higher than 7.5’ NAVD88 were observed by the Hohonu
sensor between January and June of 2024.
In raised segments of road passing through salt marsh, the road would stay within its current
layout and be raised with vertical sheet pile or on bridge pilings. In raised segments passing
through other habitat types or developed areas, side slopes would be used to connect the raised
road with existing grade. Careful design would be required in the Eastern Segment of raised road
to minimize the impact of side slopes to private property. The bridge is reconstructed at a height
that matches the target elevation and a span length that ensures that tidal exchange continues.
The road low point is raised to approximately 7.5’ NAVD88, delaying the onset of daily tidal
flooding until after 2070, and eliminating all present -day tidal flooding. Flooding due to storm
surge still occurs in major storms in the present day and increases in frequency and severity over
time. The total project cost is estimated to be $20-30 million, and the following costs are
estimated for different road segments:
• Western Segment: $11.3 million
• Middle Segment: $2.7 million
• Cedar Point Road: $5.1 million
• Eastern Segment: $3.1 million
These segment cost estimates represent 2024 installed material costs, with 40% escalation
(through 2030) and 15% contingency. Segment costs exclude design, permitting, mobilization,
and site controls. Phasing may increase the total project cost. Design and permitting costs of 25%
were applied to the sum of segment costs to estimate the approximate total project cost of $20-
30 million.
Refined Alternative 3 would require the following eight (8) regulatory reviews/permits. MEPA
NPC or new Expanded Environmental Notification Form (EENF), Order of Conditions from the
Yarmouth Conservation Commission, NHESP MESA Determination, NHESP Conservation
Management Permit, Chapter 91 Permit and License from Mass DEP, Water Quality Certification
from Mass DEP, Federal Consistency Determination from CZM, and Individual Permit from the
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USACE. It is estimated that permitting for this alternative would take approximately 4 years to
complete.
Refined Alternative 3 results in the most sustainable long-term solution when compared to
Alternatives 1 and 2, but results in disruption to residents during construction and the largest
limit of work when compared to other alternatives. During construction, resid ents will experience
temporary impacts to daily life. Vehicular bypass during construction may be challenging due to
existing narrow travel lanes. However, unlike Refined Alternative 2, a large portion of the
roadway will be relocated, and the existing roadway can be utilized for residents during
construction. Reconstruction of the bridge and portions of low -lying roadway may result in
temporary road shutdowns. Residents may not be able to get to their homes during certain
periods of construction. A temporary ferry may be required for residents to access Great Island
during bridge construction. This may result in limited non -essential services such as home
improvements and landscaping.
Daily construction noise, specifically that of driving sheet piling, may be audible at nearby
residences. Where sheet piles are not implemented and earthen side slopes are proposed,
construction may occur on private residences. Specific consideration will need to be given to
changing drainage patterns to avoid directing stormwater runoff towards homes. This alternative
results in an additional three feet of road raising when compared to Refined Alternative 2, and
as much as five feet relative to the existing low points of the road. This will have a significant
visual change to what residents are used to.
Additionally, protection, or replacement, of landscaping on private residences may be required
and supplemented with slope stabilization. Slope stabilization can vary but may include stone
armoring infilled with coastal plantings suitable for long-term stabilization. Driveway aprons may
also need to be replaced to blend the roadway grade with the adjacent residences. Specialty
pavers may need to be procured to replace residents’ driveways in kind. There will likely be more
work on private properties as compared to Refined Alternative 2 because of the increased road
elevation. Existing utilities may be considered for modifications during this time to improve their
susceptibility to erosion. Improvements such as concrete encasement, raised structures above
future flood elevations, or other means may be implemented but could result in a temporary
pause of the service.
A geotechnical analysis of the suitability of existing roadway base material is recommended prior
to construction. If the material is not suitable for re -use, additional construction costs and time
will result for the additional material and hauling. Construction staging and laydown areas will
need to be identified in upland areas approved by local jurisdiction. The selected location may
impact construction time depending on the proximity to the construction. Post construction,
there will still be roadway maintenance required following storm surge flooding, but at a far more
limited basis when compared to Refined Alternatives 1 & 2. This alternative, while most
expensive and likely the longest construction duration, will require the least amount of
maintenance and care once constructed.
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In summary, Refined Alternative 3 results in short-term construction related disruption to
residents but reduces the daily and yearly disruption of sea level rise and storm surge the most
when compared to the other alternatives (Figures 65 – 68).
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Figure 65. Overview of changes to the roadway with Refined Alternative 3.
Figure 66. Typical cross-section of western roadway segment with Refined Alternative 3.
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Figure 67. Typical cross-section of middle roadway segment with Refined Alternative 3.
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Figure 68. Typical cross-section of eastern roadway segment with Refined Alternative 3.
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Figure 69. Refined Alternative 3 bridge modifications.
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5.3.4 Refined Alternative 4: Community Ferry
The fourth refined alternative is a variation on Conceptual Alternative 10 (Figure 70). It proposes
establishing a community ferry service that eventually replaces the road as the primary means of
accessing Great Island. This would involve purchasing a vessel and establishing landing locations
on Great Island, Cedar Point, and the mainland. As shown in Figure 70, certain roads on Great
Island would also need to be adapted to maintain access to the ferry landing during storm and
future high tide conditions. If this alternative were implemented, resilience to flooding would
depend on the final landing elevations. A ferry would likely not run during storm conditions,
though keeping the route within sheltered Lewis Bay could minimize weather disruptions.
Landings could be established at the existing dock, on the beach east of the existing dock, and on
a currently undeveloped part of Cedar Point. If a ferry service provided consistent access to Great
Island and Cedar Point, the existing access roads could be removed and habitat could be restored
(Figures 70 and 71). Many island communities in New England are exclusively accessed by private
ferry and boat. Locally, the M/V Cormorant provides ferry service between Woods Hole and the
private island of Naushon. It runs 3-5 daily scheduled trips in the summer. It is primarily used by
the island’s summer residents and their staff, but also transports scientists to access Naushon
field sites with special permission.
The initial cost of a ferry service is estimated to be $5-20 million, and annual costs could range
from $100,000- $1,000,000 or more. Ferry costs are deeply uncertain and include purchase and
licensing of a vessel, construction or rental of landings, compensation of crew, and maintenance.
Options around vessel size, vessel type, and frequency of service determine the over all cost and
implementation timeline. If this alternative is being considered, we recommend contracting with
a firm with experience setting up private ferry services.
Refined Alternative 4 would require the following seven (7) regulatory reviews/permits. MEPA
Expanded Environmental Notification Form (EENF) and possible Environmental Impact Report
(EIR), Order of Conditions from the Yarmouth Conservation Commission, NHESP MESA
Determination, Chapter 91 Permit and License from Mass DEP, Water Quality Certifi cation from
Mass DEP, Federal Consistency Determination from CZM, and Individual Permit from the USACE.
It is estimated that permitting for this alternative would take approximately 6 years to complete.
Alternative 4 results in the fewest short-term impacts when compared to Refined Alternatives 2
& 3. However, residents would need to modify their daily life. Long -term impacts would include
limited access to the island by land. This would require residents to plan daily needs such as
getting groceries or visiting a convenience store based on ferry times or low tides. Emergency
response may also be delayed.
Transportation needs to be considered at all ferry landing locations. Parking would likely need to
be acquired at the mainland side. Parking lots or a shuttle service would need to be provided at
community landing locations. During construction, access to the island would continue to be
disrupted by high tide as well as storm surge flooding. Select roadways within the island would
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need to be raised to provide access from ferry landings to residences. Depending on the elevation
selected for these roadways, they may be impacted by storm surge or sea level rise similar to
those of Refined Alternatives 2 & 3 and require maintenance.
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Figure 70. Overview of changes to the roadways with Refined Alternative 4.
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Figure 71. Typical cross-section showing long-term road removal in areas of salt marsh with Refined Alternative 4.
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Figure 72. Typical cross-section showing long-term road removal in areas of barrier beach with Refined Alternative 4.
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5.3.8 Comparison Matrix
The four Refined Alternatives are summarized in Table 5. Planning-level cost ranges are included
in this table. These costs are meant to offer a means of comparing alternatives, and do not
represent final project costs. Section 6 of this report offers a mo re holistic perspective on phasing
and combination of these alternatives.
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Table 5. Comparison of the Four Refined Alternatives.
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5.3.9 Dynamic Adaptation Pathways
Following the development and evaluation of the range of adaptation options, Woods Hole
Group explored the planning and phasing of these alternatives using the Dynamic Adaptation
Pathways (DAP) framework. DAPs are a long-term planning tool for exploring and sequencing
adaptation options over time given uncertain future climate conditions, including adaptations
that are currently impractical due to feasibility, cost, permitability, etc. It allows a preferred
adaptation approach to evolve over time, enabling GIHA to establish a flexible plan that achieves
community goals while being responsive to changing conditions and projections. When
adaptation is phased over time, it ensures that actions are implemented when they are most
needed and effective.
The DAP provides a visual framework for understanding the sequence of potential adaptation
actions focused on the goal of maintaining access to Great Island during non-storm conditions
for as long as practicable. Actions are represented by lines that correspond to different strategic
themes (e.g., maintaining, elevating, and abandoning infrastructure). The framework highlights
when specific actions are effective, when their performance begins to decline, and when they
reach tipping points (i.e. when they can no longer achieve their in tended goals). Beyond a tipping
point, an adaptation option may either terminate or continue in a reduced capacity, prompting
GIHA consider adopting a different action if the reduced functionality is unacceptable. Typically,
during the DAP process, communities identify their preferred sequencing of actions (a pathway)
to achieve goals over time, but acknowledge that at any point a different pathway may be more
preferable if either goals or climate conditions change.
Appendix L Dynamic Adaptation Pathways describes two feasible pathways for providing long-
term access to Great Island that consider timelines for design, construction, and permitting. A
key takeaway from this exercise is the importance of acknowledging that there is planning time
associated with various actions. Complex projects, such as elevating infrastructure, or
implementing a ferry service, require significant time for detailed design, engineering,
permitting. GIHA's commitment to early planning and adaptive management ensures these
hurdles are addressed before conditions become untenable.
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6.0 RECOMMENDED NEXT STEPS
The Feasibility Study underscores that temporary solutions, such as emergency road protection
and dune reinforcements, are solutions that can be used to address immediate vulnerabilities
and provide a necessary buffer for the road, they are not sufficient to fully combat the increasing
impacts of sea level rise, storm surge, and coastal erosion. There is a need to shift to a proactive,
long-term strategy—such as road elevation, a landward shift of the roadway and/or transitioning
to alternative access methods. By prioritizing a forward -looking approach, GIHA can move
beyond perpetual crisis management and focus on building a resilient future for GIHA. The
selection of an adaptation strategy for Great Island's roadway and bridge infrastructure hinges
on several key factors, including the community's financial capacity, tolerance for risk, willingness
to accommodate disruptions during implementation, cost-effectiveness over time, and long-term
access goals.
The Feasibility Study highlights the varying impacts and benefits of the proposed Refined
Alternatives. Refined Alternative 1 will help to maintain vehicle access for the near term, but a
progressive loss of roadway functionality likely result, as it relies heavily on emergency repairs
and does not address the underlying roadway vulnerabilities. Conversely, Refined Alternative 2
offers a moderate extension of roadway access, sustaining daily functionality for several decades,
but still leaves the infrastructure exposed to long-term erosion and damage risks. For a more
robust solution, Refined Alternative 3 provides the highest degree of protection by addressing
erosion risks and raising or relocating the road, and is projected to maintain reliable access for
the next 50 years or more. However, it is important to note that even this alternative cannot
completely eliminate flooding risks during severe storm events. The Feasibility Study emphases
the importance of continuing to integrate emergency response preparedness into the
community's planning efforts.
The path forward requires establishing a consensus-driven, long-term resilience strategy and
implementation of a preferred adaptation strategy. The Feasibility Study confirms the
community’s concerns that coastal erosion, rising sea levels, and storm intensity pose significant
risks to the causeway, bridge, and associated utilities, which serve as lifelines for the Great Island
community. The path for GIHA moving forward must align with community values, adhere to
regulatory frameworks, and account for the dynamic and evolving nature of climate risks.
Immediate action, coupled with a clear, community-supported plan, will ensure the resilience of
Great Island’s infrastructure for generations to come.
To prepare for the work ahead, Woods Hole Group and Fuss and O'Neill have prepared a set of
near- and mid- to long-term recommendations based on the outcome of the alternatives
assessment and the development of Dynamic Adaptation Pathways. Categorizing act ions into
near-, mid-, and long-term recommendations allows for a more streamlined approach to building
resiliency. This strategy supports prioritizing actions based on their urgency and potential impact,
ensuring that immediate needs are addressed while a lso considering sustained efforts for long-
term resiliency. Furthermore, it facilitates effective resource allocation and timing of
interventions, leading to a more comprehensive and sustainable resiliency -building strategy.
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7.1 Near-Term Recommendations (1 – 5 Years):
• Proceed with Alternative 1 as a first step by preparing and filing a pro-active Notice of
Intent with the Yarmouth Conservation Commission for emergency road protection as
needed.
• To facilitate implementation of emergency road protection under Alternative 1, stockpile
materials such as fiber rolls, anchors, beach and dune compatible sand necessary for
emergency road protection.
• Gain consensus among GIHA stakeholders on proceeding with one of the following
conceptual Alternatives for improving the resiliency of Great Island and White Cedar Point
Roads:
o Alternative 2 – Minor road raising and bridge replacement
o Alternative 3 – Shift road back, major road raising, and bridge replacement
• Initiate work to design (30% to 100% design) and permit the selected alternative.
• Develop protocols and automated notification system for evacuation and shelter in place
in the event of a major storm event.
• Develop protocols in the event of delayed emergency response.
• Confirm location of utilities along Great Island and White Cedar Point Roads. Make plans
for protecting the utilities from damage caused by erosion and/or flooding, where
needed.
• Proceed with replacing existing timber bridge rails with compliant barrier railings and a
wing wall cap.
7.2 Mid-Term Recommendations (6 – 25 Years):
• Move forward with steps necessary to protect and/or relocate the existing utility lines.
o Possible improvements include installing concrete encasements, raising utility
structures above future key flood elevations, and/or anchoring utility components.
o If the bridge is reconstructed as part of Alternative 2 or 3, the utilities should be
located under the decking at a suitable elevation.
• Move forward with recommended bridge replacement as part of Alternative 2 or 3.
o Replacement alternatives for the bridge at its current location should evaluate the
required deck elevation to avoid/minimize the risk of inundation during the
structure’s service life, as well as the increased risk to scour erosion associated
with future storm/flood events. If an alternative roadway alignment or ferry
alternative is selected for future implementation, it is recommended that
repair/protection measures be selected and implemented considering the
remaining service life of the structure and adjacent roadway.
7.3 Long-Term Recommendations (26 – 50 Years):
• Work with ferry consultant to refine feasibility, costs, and impacts associated with
proceeding with Alternative 4 in the future, as necessary.
o ID type and size of ferry
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o Location of docking facilities in Hyannis Harbor, Great Island, and Cedar Point
o Annual operation and maintenance costs
o Staffing requirements
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7.0 REFERENCES
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erosion of coastal dune barriers in the southern North Sea. Geomorphology.
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Arkema, K. K., Guannel, G., Verutes, G., Wood, S. A., Guerry, A., Ruckelshaus, M., Kareiva, P.,
Lacayo, M., & Silver, J. M. 2013. Coastal habitats shield people and property from sea -
level rise and storms. Nature Climate Change. https://doi.org/10.1038/nclimate1944
Barbier, E., Hacker, S., Kennedy, C., Koch, E., Stier, A. and Silliman, B. 2011. The value of estuarine
and coastal ecosystem services. Ecological Monographs. https://doi.org/10.1890/10-
1510.1
Cooper, J. and Pilkey, O. 2012. Pitfalls of Shoreline Stabilization.
https://link.springer.com/book/10.1007/978-94-007-4123-2
Dean, R. 2002. Beach nourishment: theory and practice. World Scientific.
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Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association A-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX A. COMMUNITY SURVEY RESPONSES
Great Island Homeowner Resiliency Planning
How often does flooding affect your access to the island (including your contracto…
Answered: 61 Skipped: 3
Frequently - more than six times per year
Sometimes - 3 to 6 times per year
Occasionally - up to 3 times per year
Never
0 10 20 30
Never 5 7.81%
Occasionally - up to 3 times per year 25 39.06%
Sometimes - 3 to 6 times per year 23 35.94%
Frequently - more than six times per year 8 12.5%
In your opinion, which of the following coastal hazards is the greatest threat to Gre…
Other
Shoreline Erosion
Precipitation-based Flooding
Storm Surge Flooding / Storm Damage
High Tide Flooding
0 20 40 60
Answers Count Percentage
Answered: 64 Skipped: 0
High Tide Flooding 10 15.63%
Storm Surge Flooding / Storm Damage 44 68.75%
Precipitation-based Flooding 1 1.56%
Shoreline Erosion 5 7.81%
Other 4 6.25%
Which of the following best describes your expectations in terms of acceptable…
Answered: 64 Skipped: 0
Year-Round Access, 24-hours a
Year-Round Access, except during any major coastal storm
or high tide flooding (HAT)
Seasonal Access (Memorial Day through Labor Day) 24-
hours a day
Seasonal Access (Memorial Day through Labor Day), except
during any major coastal storm or high tide flooding (HAT)
0 20 40 60
Seasonal Access (Memorial Day through Labor Day), except durin
g any major coastal storm or high tide flooding (HAT)
4 6.25%
Seasonal Access (Memorial Day through Labor Day) 24-hours a d
ay
4 6.25%
Year-Round Access, except during any major coastal storm or hig
h tide flooding (HAT)
44 68.75%
Year-Round Access, 24-hours a day 12 18.75%
What concerns you most about the coastal risks faced by GIHA?
Answers Count Percentage
Answers Count Percentage
Answered: 64 Skipped: 0
Changes to the natural condition of Great Islands
beaches/marshes
Fear of long-term (generational) loss of access due to sea
level rise
Inconvenience and disruption from storm events
The cost of protecting access to Great Island
Risk to personal safety (limited access to help, risk of being
caught in flood waters)
0 20 40 60
Risk to personal safety (limited access to help, risk of being caugh
t in flood waters)
7 10.94%
The cost of protecting access to Great Island 10 15.63%
Inconvenience and disruption from storm events 3 4.69%
Fear of long-term (generational) loss of access due to sea level ris
e
42 65.63%
Changes to the natural condition of Great Islands beaches/marsh
es
2 3.13%
Please use this space to describe any additional concerns or questions regarding the…
access
islandCostroad
high
ooding Great
storm Causeway
-
tide time
protecting
concerned costs GI
questionIsland.
loss
surge
risk
bridge
property
access.
point
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make
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term
major
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thinking
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24
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events
ferry
generational
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charts
adapt
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data
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ultimately
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dredge
permit dunes
protection
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past
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10
35
50
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case
medical
emergency
re
emergency.
safely.
frequent
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summer
months
paramount
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year.
beauty
needed
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"off
island"
necessity
(food
gas
hospital
etc.)
lifeline.
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xes.
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ooding)impossible
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normal
(
start likelihood
roads
Test
Craig
WHG!
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stem
habits
etc.
put
work
mode
duck
sand
-The
fail
Craig.
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it.
Answers Count Percentage
For the last question, our primary concern is the risk of losing Great Island in general, but also the changes t
o the natural condition of the island and the cost of protecting access to the island. With respect to the cost
of the protecting the island, we are concerned about the initial cost as well as the future incurred costs over
time and the ability for every household to afford them.
2
We need full access not only to access our home but in case of medical emergency or fire emergency. I live
on GI all year and I need to access my home safely.
1
We are concerned that these frequent HAT and strengthening storm events will make access on and off Gre
at Island a safety concern. While the summer months are paramount, we often are in residence on GI at all t
imes of the year. The beauty of Great Island is that we've never needed to get on a ferry boat to come and g
o freely. We go "off island" for every necessity (food, gas, hospital,etc.) the causeway and the bridge are our
lifeline. Looking forward to 2050 we are concerned about the loss of property value and the generational los
s of access. We support a robust solution that will address these concerns
1
There is no point in short term fixes. Let's do what we have to do to assure 50 years of access. I think that
means elevating the road near the bridge first, then moving the causeway road away from the water.
1
The question about access seems a little imprecise. I would shoot for finding a solution which provides 24 h
our access to the island at all regular tides during non-storm conditions - year round. Occasional king-tide fl
ooding would be fine. I would not expect the have guaranteed access to the island during times of major cos
tal storms (which might also trigger high tide flooding) in any season. If this level of access is impossible, I w
ould like to have seasonal access at all normal tides and non-storm conditions ( although I gather that even
non-king high tides will start to be a problem "in-season"). The question about current frequency of flooding i
ssues is a little mis-leading. While my access to GI hasn't frequently been impacted yet, I believe that the lik
elihood that it will be will increase over time - with the roads flooding at each high tide within the next decad
e.
1
Test Only from Craig Fleming - Thanks WHG!1
Still thinking about the predictive charts with the maps of GI under water in 30-50 years. While we want to ta
ke measures to stem this as best we can, we also need to adapt our habits, whether it be by checking high t
ide charts to plan when we drive on or off the island, explore boat options etc. Thank you for all the time and
effort put into thinking about this issue and helping us plan for the future. Great Island is special place, and
while unsettling to see the data I appreciate the effort to plan for the future.
1
Many of these response choices seem to be intermingled. Perhaps that is the point to make us realize there
is no simple solution. While the high tide flooding seems to be “gentler” in nature and therefore worries me l
ess, shoreline erosion is an outcome of this as well as the storm surge flooding so evident this winter seaso
n. Similarly, I am most concerned about generational long term access to the island, and believe that the go
vernment will ultimately need to work more collaboratively with us in adapting to these new circumstances. I
do obviously also think about the inconvenience of no access and the risk if trapped out there. I believe thos
e risks are the responsibility of the community to acquire a reasonable mode of access- either a very large tr
uck, a duck boat or some such vehicle to make access plausible and possible on an ongoing basis and in e
mergencies. I don’t think general access should be a parameters of this WHO survey as there are far greate
r issues to consider.
1
Response Count
-Leslie helped achieve and implement the sand dredge and blow onto the coasts of GI which protected us f
or 35 years all around the island. Yes it has returned to the sea, but reactivating our permit to maintenace dr
edge and create new dunes for nesters and protection from erosion would be the most cost effective, long t
erm, beneficial and least disruptive option. I've been told that permit should and can be re-activated with the
help of a lawyer, despite the state's current objection to dredging and re-using spoils. other places own the
Cape are doing it now. -The idea that we will have no Great Island in 70 years should be considered an abs
olute fail by all of you. This is a third generation island and you are saying we lose it all this gen. The cost of
the loss of property The cost of the loss of property to us all would far exceed the costs of your studies and
stop-gaps. The same goes for loss of access to the island 24/7. The rest is in email to Craig.
1
It's too bad I couldn't click more than one answer for some of these questions. High tide flooding and storm
surge are the biggest threats to the road - storm surge on the causeway, high tide/storm tide at the bridge.
1
In the past we moved the road inland every time there was a major storm and the road appeared too close t
o the beech. When we negotiated the conservation easement on the causeway with The Trustees of Reserv
ations we retained the right to relocate the roadway inland to maintain the access.
1
I was on Island for the reconstruction of the dunes and for some of the epic high tides. Our property is a HU
GE investment and I fear that road access is in real jeopardy as is our lot.
1
I think the question about whether storm surge or flooding is a bigger issue is a bit disingenuous. While floo
ding is a temporary phenomena that has more real time impact on island access, it’s not permanent. Storm
surge destruction is permanent and has long standing repercussions unless adequately addressed. They ar
e 2 separate problems with equal but different impact and should not be played off against each other.
1
I suspect High Tide flooding will impact access with increasing frequency but that storms pose the most risk
to actual infrastructure damage. We hope that WHG can help us consider the pros and cons of multiple opti
ons weighed against financial commitment.
1
I hope we can do something to help save the causeway and the bridge, but I have to wonder if major mitigat
ion like building a big wall in or near the marsh will keep Mother Nature out in the end. I am not convinced th
at we can vanquish nature. We may need to see what happens and go from there. A ferry - a new bridge or
a new location for the causeway road.
1
I hope the road will be fortified so that if can be cleaned after a storm. Expect to eventually settle for low tide
access. Suspect that a breakthrough on either side of Fox Point could change the calculations dramatically.
I don’t think we are paying enough attention to that risk.
1
I believe that we need to be smart and proactive about protecting long-term access to Great Island. Howeve
r, I also think we need to be circumspect about high costs of solving for 100% access at all times, as well as
being so proactive that we are bearing the high costs of leading the charge to re-shape the regulatory lands
cape that will (in my opinion) ultimately be more accommodating.
1
I believe 24/7 access might turn out to be unrealistic - and too expensive - I would be comfortable with desig
ns that resulted in the road being closed for 24 hours while debris is removed. We need to adapt to the situa
tion - not try and conquer it. Terry
1
I am also deeply concerned about the cost of protecting access to GI and the impact on our community and
individual families. We do need to look at new ideas and options that might exist in other parts of the countr
y or world in order to shift our thinking about how we live on our planet and in particular how we view our liv
es on Great Island. Thanks for the survey
1
Answered: 25 Skipped: 39
Given the long-term nature of the sea level rise/coastal erosion effect on island access it will be helpful to un
derstand the variety of long-term solutions and the associated costs. This reporting might be easiest for ho
meowners to analyze against both a timeline (i.e. in 10 years the expected rate of sea level rise creates nee
d for 1 mile of road build-up which costs $xx) and circumstance (i.e. Nor'easter washes out 1/2 mile of caus
eway, road nourishment cost $xx).
1
Ensuring we clearly articulate the set of investments that need to be made over time in a SIMPLE way that
allows for a decision to be made.
1
Cost of protection might also be an issue for us.1
Causeway road needs to be relocated in certain places as soon as possible as has been done in the past 1
At some point, you can’t stop these natural dynamic processes and need to assess what is financially sustai
nable and what is not. I don’t believe it is unrealistic to have 24/7 access always. With higher tides and stor
m events there will be flooding and short periods of limited access which people have been living with. The
Woods Hole studies and the data being collected can help us take a targeted approach, find appropriate co
astal resiliency solutions, and anticipate any problems with access so that we can plan around them.
1
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association B-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX B. CONSERVATION RESTRICTION
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Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association C-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX C. EXISTING CONDITIONS PLAN
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E
GR
E
A
T
I
S
L
A
N
D
R
O
A
D
BRIDGE
2
2
4
4
4
4
UNCLE
R
O
B
E
R
T
'
S
COVE
EB
B
FL
O
O
D
LEWIS BAY
SMITHS
POINT
NANTUCKET SOUND
POINT
GAMMON
LIGHT
GREAT
ISLAND
CE
D
A
R
RO
A
D
WH
I
T
E
UNCL
E
R
O
B
E
R
T
S
C
O
V
E
GRE
A
T
ISL
A
N
D
ROAD
MATCHLINE VIEW 2
VIEW 1
VI
E
W
2
VI
E
W
5
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 4-4
NANT
U
C
K
E
T
S
O
U
N
D
E
B
B
F
L
O
O
D
FIR
M
Z
O
N
E
AE
(
E
L
.
1
3
)
FIR
M
Z
O
N
E
VE
(
E
L
.
1
3
)
NH
E
S
P
B
O
U
N
D
A
R
Y
NH
E
S
P
B
O
U
N
D
A
R
Y
FIR
M
Z
O
N
E
VE
(
E
L
.
1
3
)
FIR
M
Z
O
N
E
VE
(
E
L
.
1
4
)
FIRM ZONE
V
E
(
E
L
.
1
4
)
FIRM ZONE
V
E
(
E
L
.
1
3
)
-2
0
2
STONE
GROIN
COASTAL BEACH
HTL
MHW
STONE
GROIN
-2
0
2
4
-2
0
2
4
SALT
MARSH
SALT
MARSH
COASTAL BEACH
COASTAL
DUNE
LAND CONTAINING
SHELLFISH
4
MATCHLINE
VIEW 3
VIEW 2
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
COASTAL
BEACH
COASTAL
DUNE
HTL
Re
v
i
s
i
o
n
s
7.5.4.6.1.2.3.
Ti
t
l
e
:
Location Map Not to Scale
Da
t
e
Graphic Scale
0
1" = '
60 30 60 180
60
A
C
L
S
C
O
M
P
A
N
Y
GR
O
U
P
WO
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10
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M
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0
2
5
3
2
TE
L
E
P
H
O
N
E
:
(
5
0
8
)
5
4
0
-
8
0
8
0
F
A
X
:
(
5
0
8
)
5
4
0
-
1
0
0
1
Pl
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n
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s
A
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s
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c
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a
t
i
o
n
2 6
23-0169
23-0169_SP.dwg
1" = 60'
08/19/2024
23
-
0
1
6
9
_
S
P
.
D
W
G
Wo
o
d
s
H
o
l
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M
A
0
2
5
3
2
50
8
-
5
4
0
-
8
0
8
0
References:
1.Assessors Map 4, Parcel 4; Map 6, Parcels 6, 7 & 8; Map 7, Parcel 1; Map 9,
Parcels 1 & 5 and Map 10, Parcel 1
2.GIS parcel lines compiled from MassGIS shown are approximate and do not
represent an actual property boundary survey.
Survey Notes:
1.Coastal and Wetland Resource delineation conducted on 1/19/24 by Woods Hole
Group, Inc.
2.Field Data collected by Woods Hole Group between 1/26/24 and 2/08/24, and
between 8/7/24 and 8/14/24.
Flood Note:
1.Portions of areas depicted lie within Special Flood Hazard Zone X, AE (El=11),
AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA Firm Panel
#25001C0782J, effective 7/16/2014; AE (El=11), AE (El=13), VE (El=13) and
VE (El=14) as depicted on FEMA Firm Panel #25001C0569J, effective
7/16/2014; and AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA
Firm Panel #25001C0588J, effective 7/16/2014.
General Notes:
1.Priority Habitats of Rare and Estimated Habitats of Rare Wildlife shown on plan
are in accordance with the Massachusetts Natural Heritage Atlas, 15th Edition.
2.Entire site is within Barrier Beach and Land Subject to Coastal Storm Flowage.
3.Geotextile bags shown on Views #4 and #5 were installed under Emergency
Order issued by the Yarmouth Conservation Commission on January 5, 2024.
Datum Notes:
1.Coordinates are based on Massachusetts State Plane NAD83, Mainland Zone
(2001), in units of US Survey Feet.
2.Elevations are referenced to the North American Vertical Datum of 1988
(NAVD88) in US survey feet.
3.Tidal Datum Elevations are based on NOAA published Data & OPUS
Observation of Hyannisport Tidal Benchmark Station.
LEGEND
Su
r
v
e
y
e
d
B
y
:
Project Number:
Date:
Dwg File:
Page of
Drawn: RHV
Approved:
Scale:
VIEW #1
VIEW #2
VIEW #2
VIEW #1
GIS Parcel Line
Existing Contours (Ground Survey)
Existing Spot Elevation (Ground Survey)
High Tide Line (HTL)
Mean High Water (MHW)
Mean Low Water (MLW)
Existing Stone Groin, Riprap areas
Bulk Sand Bags installed in Dune
Landward Edge of Coastal Beach
Landward Edge of Primary Coastal Dune
Landward Edge of Salt Marsh
NHESP Boundary (PH-2156)
Soil Sample Location
X 8.4
10
2
LEGEND
TH-34756
Datum
HTL
MHW
NAVD88 ft
2.34
0.99
NAVD88 0
MLW -2.21
Based on NOAA
Hyannisport Station
GIS PARCEL LINE
LEWIS BAY
SMITHS
POINT
NANTUCKET SOUND
POINT
GAMMON
LIGHT
GREAT
ISLAND
CE
D
A
R
RO
A
D
WH
I
T
E
UNCL
E
R
O
B
E
R
T
S
C
O
V
E
GRE
A
T
ISL
A
N
D
ROAD
NANT
U
C
K
E
T
S
O
U
N
D
FIR
M
Z
O
N
E
VE
(
E
L
.
1
3
)
FIR
M
Z
O
N
E
VE
(
E
L
.
1
4
)
STONE
GROIN
-2
0
2
4SALT
MARSH
MATCHLINE
VIEW 3
VIEW 2
MATCHLINE
VIEW 4
VIEW 3
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 4-4
NANTUCKET SOUND
E
B
B
FL
O
O
D
NH
E
S
P
B
O
U
N
D
A
R
Y
COASTAL
BEACH
COASTAL
DUNE
LAND CONTAINING
SHELLFISH
NH
E
S
P
B
O
U
N
D
A
R
Y
F
I
R
M
Z
O
N
E
V
E
(
E
L
.
1
3
)
F
I
R
M
Z
O
N
E
V
E
(
E
L
.
1
4
)
FIRM
Z
O
N
E
AE (
E
L
.
1
3
)
FIRM
Z
O
N
E
VE (
E
L
.
1
3
)
GI
S
P
A
R
C
E
L
L
I
N
E
FI
R
M
Z
O
N
E
A
E
(
E
L
.
1
4
)
STONE
GROIN
HTL
MH
W
-2
-2
02
-2
MA
T
C
H
L
I
N
E
VIE
W
4
VIE
W
3
NH
E
S
P
B
O
U
N
D
A
R
Y
SALT
MARSH
COASTAL
DUNE
NANTUCKET SOUND
E
B
B
FL
O
O
D
COASTAL
BEACH
NH
E
S
P
B
O
U
N
D
A
R
Y
F
I
R
M
Z
O
N
E
V
E
(
E
L
.
1
3
)
F
I
R
M
Z
O
N
E
V
E
(
E
L
.
1
4
)
FIRM ZO
N
E
AE (EL.
1
3
)
FIRM ZO
N
E
VE (EL.
1
3
)
FIR
M
Z
O
N
E
AE
(
E
L
.
1
4
)
GI
S
P
A
R
C
E
L
L
I
N
E
GI
S
P
A
R
C
E
L
L
I
N
E
F
I
R
M
Z
O
N
E
A
E
(
E
L
.
1
4
)
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 4-4
STO
N
E
GR
O
I
N
S
T
O
N
E
G
R
O
I
N
HTL
MHW
HTL
MHW
0
2
4
6
-2
-2
0
2
Re
v
i
s
i
o
n
s
7.5.4.6.1.2.3.
Ti
t
l
e
:
Location Map Not to Scale
Da
t
e
Graphic Scale
0
1" = '
60 30 60 180
60
A
C
L
S
C
O
M
P
A
N
Y
GR
O
U
P
WO
O
D
S
H
O
L
E
10
7
W
A
T
E
R
H
O
U
S
E
R
O
A
D
,
B
O
U
R
N
E
,
M
A
0
2
5
3
2
TE
L
E
P
H
O
N
E
:
(
5
0
8
)
5
4
0
-
8
0
8
0
F
A
X
:
(
5
0
8
)
5
4
0
-
1
0
0
1
Pl
a
n
o
f
E
x
i
s
t
i
n
g
C
o
n
d
i
t
i
o
n
s
at
G
r
e
a
t
I
s
l
a
n
d
R
o
a
d
,
W
e
s
t
Y
a
r
m
o
u
t
h
,
M
A
Pr
e
p
a
r
e
d
f
o
r
:
Gr
e
a
t
I
s
l
a
n
d
H
o
m
e
o
w
n
e
r
s
A
s
s
o
c
i
a
t
i
o
n
3 6
23-0169
23-0169_SP.dwg
1" = 60'
08/19/2024
23
-
0
1
6
9
_
S
P
.
D
W
G
Wo
o
d
s
H
o
l
e
G
r
o
u
p
10
7
W
a
t
e
r
h
o
u
s
e
R
o
a
d
Bo
u
r
n
e
,
M
A
0
2
5
3
2
50
8
-
5
4
0
-
8
0
8
0
References:
1.Assessors Map 4, Parcel 4; Map 6, Parcels 6, 7 & 8; Map 7, Parcel 1; Map 9,
Parcels 1 & 5 and Map 10, Parcel 1
2.GIS parcel lines compiled from MassGIS shown are approximate and do not
represent an actual property boundary survey.
Survey Notes:
1.Coastal and Wetland Resource delineation conducted on 1/19/24 by Woods Hole
Group, Inc.
2.Field Data collected by Woods Hole Group between 1/26/24 and 2/08/24, and
between 8/7/24 and 8/14/24.
Flood Note:
1.Portions of areas depicted lie within Special Flood Hazard Zone X, AE (El=11),
AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA Firm Panel
#25001C0782J, effective 7/16/2014; AE (El=11), AE (El=13), VE (El=13) and
VE (El=14) as depicted on FEMA Firm Panel #25001C0569J, effective
7/16/2014; and AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA
Firm Panel #25001C0588J, effective 7/16/2014.
General Notes:
1.Priority Habitats of Rare and Estimated Habitats of Rare Wildlife shown on plan
are in accordance with the Massachusetts Natural Heritage Atlas, 15th Edition.
2.Entire site is within Barrier Beach and Land Subject to Coastal Storm Flowage.
3.Geotextile bags shown on Views #6 and #7 were installed under Emergency
Order issued by the Yarmouth Conservation Commission on January 5, 2024.
Datum Notes:
1.Coordinates are based on Massachusetts State Plane NAD83, Mainland Zone
(2001), in units of US Survey Feet.
2.Elevations are referenced to the North American Vertical Datum of 1988
(NAVD88) in US survey feet.
3.Tidal Datum Elevations are based on NOAA published Data & OPUS
Observation of Hyannisport Tidal Benchmark Station.
LEGEND
Su
r
v
e
y
e
d
B
y
:
Project Number:
Date:
Dwg File:
Page of
Drawn: RHV
Approved:
Scale:
VIEW #3
VIEW #4
GIS Parcel Line
Existing Contours (Ground Survey)
Existing Spot Elevation (Ground Survey)
High Tide Line (HTL)
Mean High Water (MHW)
Mean Low Water (MLW)
Existing Stone Groin, Riprap areas
Bulk Sand Bags installed in Dune
Landward Edge of Coastal Beach
Landward Edge of Coastal Dune
Landward Edge of Salt Marsh
NHESP Boundary (PH-2156)
Soil Sample Location
X 8.4
10
2
LEGEND
TH-34756
Datum
HTL
MHW
NAVD88 ft
2.34
0.99
NAVD88 0
MLW -2.21
Based on NOAA
Hyannisport Station
GIS PARCEL LINE
VIEW #3
VIEW #4
4.09
5.19
5.4
5.53
5.18
5.2
5.04
0
2
4
6
6
4
2
0
3.60
3.9
3.1
3.77
3.6
3.30
3.6
4.36
4.3
3.985.11
5.2
5.00
5.28
5.2
5.03
5.2
4.9
5.0
5.0
4.6
3.3
5.44
5.6
5.44
4.69
4.9
4.84
4.32
4.21
4.4
4.33
4.31
4.3
4.03
4.1
3.84
3.9
4.3
4.1
3.7
4.1 4.1 4.3 4.2
4.3
5.2
5.4
5.47
5.6
5.65
5.37
5.5
5.47
5.3
5.4 5.1
4.88
4.9
4.44
5.29
4.4
MA
T
C
H
L
I
N
E
VI
E
W
1
VI
E
W
5
VI
E
W
2
VI
E
W
5
M
A
T
C
H
L
I
N
E
V
I
E
W
5
V
I
E
W
6
Vehicle turn-around
(Dirt)
V
I
E
W
5
V
I
E
W
6
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-8
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-7
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-6
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
NANTUCKET SOUNDEB
B
FL
O
O
D
NHESP
B
O
U
N
D
A
R
Y
FIRM ZO
N
E
AE (EL.
1
3
)
NHESP BOUNDAR
Y
FIRM ZO
N
E
VE (EL.
1
3
)
FIRM ZONE
V
E
(
E
L
.
1
4
)
FIRM ZONE
V
E
(
E
L
.
1
3
)
ISLAND
Vehicle turn-out
(Dirt)
Vehicle turn-out
(Dirt)
Vehicle turn-out
(Dirt)Vehicle turn-out
(Dirt)
Vehicle turn-out
(Dirt)
Vehicle turn
-
o
u
t
(Dirt)
Vehicle turn
-
o
u
t
(Dirt)
Vehicle turn
-
o
u
t
(Dirt)
Vehicle turn
-
o
u
t
(Dirt)
Vehicle turn
-
o
u
t
(Dirt)
HTL
MHW
COASTAL B
E
A
C
H
COASTAL
DUNE
LAND CON
T
A
I
N
I
N
G
STONE
GROIN
SALT
MARSH
STONE
GROIN
STONE
GROIN
REVETM
E
N
T
-2
0
2
4
4
6
8 6
4
GIS PARCEL LINE
ROAD
GREAT
STONE
GROIN
STONE
GROIN
-2
0
2
4
LAND CONTAINING
SHELLFISH
COASTAL BEACH
COASTAL
DUNE
-2
0
4
4
4
4
Vehicle turn
-
o
u
t
(Dirt)
LEWIS BAY
SMITHS
POINT
NANTUCKET SOUND
POINT
GAMMON
LIGHT
GREAT
ISLAND
CE
D
A
R
RO
A
D
WH
I
T
E
UNCL
E
R
O
B
E
R
T
S
C
O
V
E
GRE
A
T
ISL
A
N
D
ROAD
4.09
5.19
5.4
5.53
5.18
5.2
5.04
0
2
4
6 6
4
2
0
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
3.60
3.9
3.1
3.77
3.6
3.30
3.6
4.36
4.3
3.98
5.11
5.2
5.00
5.0
4.6 3.3
5.47
5.6
5.65
5.37
5.5
5.47
5.3
5.4
5.1
4.88
4.9
4.44
5.905.8
5.29
7.627.8
7.63
6.90
7.06.88
7.0
5.1
4.4
8.09
8.2
8.01 7.13
7.
2
6.84
5.81 5.7
5.28
7.3
7.6
7.9
5.63
5.8
5.62
6.95
7.1
6.95
7.85
7.97.89
5.8
4.8
5.8
5.16
5.6
3.29
3.23.15
MA
T
C
H
L
I
N
E
VI
E
W
6
VI
E
W
7
VIEW 7
VIEW 8
MATCHL
I
N
E
MA
T
C
H
L
I
N
E
VI
E
W
5
VI
E
W
6
VI
E
W
5
VI
E
W
6
VI
E
W
6
VI
E
W
7
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-6
N/F: GREAT ISLAND REALTY TRUST
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
Address: GREAT ISLAND ROAD,
Assessors ID: 6-6
NANTU
C
K
E
T
S
O
U
N
D
EB
B
FL
O
O
D
NANTUCKET SOUNDEB
B
FL
O
O
D
NHESP BOUNDARY
FIRM ZONE
VE (EL. 13)
FIRM ZO
N
E
AE (EL. 1
3
)
FIRM ZO
N
E
VE (EL. 1
3
)
FIR
M
Z
O
N
E
V
E
(
E
L
.
1
4
)
FIR
M
Z
O
N
E
V
E
(
E
L
.
1
3
)
FIRM
Z
O
N
E
V
E
(
E
L
.
1
4
)
FIRM
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Vehicle turn-out
(Dirt)
Vehicle turn-out
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Vehicle turn-out
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Vehicle turn-out
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Vehicle turn-out
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23-0169
23-0169_SP.dwg
1" = 60'
08/19/2024
23
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Project Number:
Date:
Dwg File:
Page of
Drawn: RHV
Approved:
Scale:
VIEW #5
VIEW #6 Graphic Scale
0
1" = '
60 30 60 180
60
VIEW #6
VIEW #5
Datum
HTL
MHW
NAVD88 ft
2.34
0.99
NAVD88 0
MLW -2.21
Based on NOAA
Hyannisport Station
LEGEND
GIS Parcel Line
Existing Contours (Ground Survey)
Existing Spot Elevation (Ground Survey)
High Tide Line (HTL)
Mean High Water (MHW)
Mean Low Water (MLW)
Existing Stone Groin, Riprap areas
Bulk Sand Bags installed in Dune
Landward Edge of Coastal Beach
Landward Edge of Primary Coastal Dune
Landward Edge of Salt Marsh
NHESP Boundary (PH-2156)
Soil Sample Location
X 8.4
10
2
LEGEND
TH-34756
GIS PARCEL LINE
References:
1.Assessors Map 4, Parcel 4; Map 6, Parcels 6, 7 & 8; Map 7, Parcel 1; Map 9,
Parcels 1 & 5 and Map 10, Parcel 1
2.GIS parcel lines compiled from MassGIS shown are approximate and do not
represent an actual property boundary survey.
Survey Notes:
1.Coastal and Wetland Resource delineation conducted on 1/19/24 by Woods Hole
Group, Inc.
2.Field Data collected by Woods Hole Group between 1/26/24 and 2/08/24, and
between 8/7/24 and 8/14/24.
Flood Note:
1.Portions of areas depicted lie within Special Flood Hazard Zone X, AE (El=11),
AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA Firm Panel
#25001C0782J, effective 7/16/2014; AE (El=11), AE (El=13), VE (El=13) and
VE (El=14) as depicted on FEMA Firm Panel #25001C0569J, effective
7/16/2014; and AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA
Firm Panel #25001C0588J, effective 7/16/2014.
General Notes:
1.Priority Habitats of Rare and Estimated Habitats of Rare Wildlife shown on plan
are in accordance with the Massachusetts Natural Heritage Atlas, 15th Edition.
2.Entire site is within Barrier Beach and Land Subject to Coastal Storm Flowage.
3.Geotextile bags shown on Views #4 and #5 were installed under Emergency
Order issued by the Yarmouth Conservation Commission on January 5, 2024.
Datum Notes:
1.Coordinates are based on Massachusetts State Plane NAD83, Mainland Zone
(2001), in units of US Survey Feet.
2.Elevations are referenced to the North American Vertical Datum of 1988
(NAVD88) in US survey feet.
3.Tidal Datum Elevations are based on NOAA published Data & OPUS
Observation of Hyannisport Tidal Benchmark Station.
7.31
7.57.40
7.297.5
7.37
6.3
6.30
6.15
6.35.98
5.585.6
8 8 6 4
2
8 8 6
4
2
6
8
0
0
7.1
6.4
6.6
5.5
6.5
6.99
5.80
5.8
6.30
7.61 7.42
7.6
7.2
7.11
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
6
8 6 4
5.635.85.62
6.957.1
6.95
7.85
7.9
7.89
5.8
4.8
5.0
4.9
5.28
5.4
5.23
5.30
5.5
5.49
5.8
5.16
5.4
5.38
5.6
6.4
5.1
3.29
3.2
3.15
2.46
2.6
2.65
2.55
2.6
2.562.95
3.0
3.00
2.7
3.1
3.4
2.9
2.7
2.6
2.7
2.59
2.6
2.54
3.38
3.3
3.23
2.77
2.9
2.85
2.62
2.7
2.59
2.74
2.7
2.58
2.10
2.
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2.32
2.83 2
.
8
2.74
3.05
3.2
3.33
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N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 9-5
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 9-1
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-6
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Vehicle turn-around
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Vehicle turn-out
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5.6
5.20
5.4
5.29
5.6
5.46
5.5
5.08
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5.01 5.27
5.6
5.56 5.57
5.7
5.53
5.27
5.6
5.60
5.13
5.4
5.43
5.12
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6.6
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6.5
6.99
5.80
5.8
6.30
7.61
7.42
7.6
7.2
7.11
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD
Assessors ID: 10-1
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
5.59 5.44
0
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5.63
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4.9
5.28
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5.4
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N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 6-6
NANTUCKET SOUNDEB
B
FL
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Vehicle turn-out
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Vehicle turn-out
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V
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Vehicle turn-out
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Vehicle turn-out
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Vehicle turn-out
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Vehicle turn-out
(Sand)
66
6
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NHESP
B
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SALT
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5.36
COASTAL BEACH
LAND CONTAINING
SHELLFISH
COASTAL
DUNE
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COASTAL BEACH
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Location Map Not to Scale
Da
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23-0169
23-0169_SP.dwg
1" = 60'
08/19/2024
23
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:
Project Number:
Date:
Dwg File:
Page of
Drawn: RHV
Approved:
Scale:
VIEW #7
VIEW #8 Graphic Scale
0
1" = '
60 30 60 180
60
VIEW #7
VIEW #8
Datum
HTL
MHW
NAVD88 ft
2.34
0.99
NAVD88 0
MLW -2.21
Based on NOAA
Hyannisport Station
LEGEND
GIS Parcel Line
Existing Contours (Ground Survey)
Existing Spot Elevation (Ground Survey)
High Tide Line (HTL)
Mean High Water (MHW)
Mean Low Water (MLW)
Existing Stone Groin, Riprap areas
Bulk Sand Bags installed in Dune
Landward Edge of Coastal Beach
Landward Edge of Primary Coastal Dune
Landward Edge of Salt Marsh
NHESP Boundary (PH-2156)
Soil Sample Location
X 8.4
10
2
LEGEND
TH-34756
GIS PARCEL LINE
References:
1.Assessors Map 4, Parcel 4; Map 6, Parcels 6, 7 & 8; Map 7, Parcel 1; Map 9,
Parcels 1 & 5 and Map 10, Parcel 1
2.GIS parcel lines compiled from MassGIS shown are approximate and do not
represent an actual property boundary survey.
Survey Notes:
1.Coastal and Wetland Resource delineation conducted on 1/19/24 by Woods Hole
Group, Inc.
2.Field Data collected by Woods Hole Group between 1/26/24 and 2/08/24, and
between 8/7/24 and 8/14/24.
Flood Note:
1.Portions of areas depicted lie within Special Flood Hazard Zone X, AE (El=11),
AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA Firm Panel
#25001C0782J, effective 7/16/2014; AE (El=11), AE (El=13), VE (El=13) and
VE (El=14) as depicted on FEMA Firm Panel #25001C0569J, effective
7/16/2014; and AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA
Firm Panel #25001C0588J, effective 7/16/2014.
General Notes:
1.Priority Habitats of Rare and Estimated Habitats of Rare Wildlife shown on plan
are in accordance with the Massachusetts Natural Heritage Atlas, 15th Edition.
2.Entire site is within Barrier Beach and Land Subject to Coastal Storm Flowage.
3.Geotextile bags shown on Views #4 and #5 were installed under Emergency
Order issued by the Yarmouth Conservation Commission on January 5, 2024.
Datum Notes:
1.Coordinates are based on Massachusetts State Plane NAD83, Mainland Zone
(2001), in units of US Survey Feet.
2.Elevations are referenced to the North American Vertical Datum of 1988
(NAVD88) in US survey feet.
3.Tidal Datum Elevations are based on NOAA published Data & OPUS
Observation of Hyannisport Tidal Benchmark Station.
5.57
5.7
5.53 5.27
5.6
5.60
5.13
5.4
5.43 4.94
5.2
5.12
5.2
4.5 4.9
5.25
5.4
5.2
5.68
5.8
5.71
5.29
5.6
5.65
5.2
5.305.6
5.49
5.71
6.1
6.10
5.54 5.7
5.61 5.8 5.74
5.7
5.39
5.29
0
MA
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VI
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VI
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VI
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MA
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VI
E
W
7
VI
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W
9
VI
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W
9
VI
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W
1
0
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD
Assessors ID: 10-1
N/F: GREAT ISLAND REALTY TRUST
Address: GREAT ISLAND ROAD,
Assessors ID: 7-1
NANTUCKET SOUNDEB
B
FL
O
O
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FIRM ZONE
AE (EL. 13)
FIRM ZONE
VE (EL. 13)
FIRM ZONE V
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FIRM ZONE VE
(
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GREAT ISLAND ROAD
5.32
5.5
5.40
5.25
5.7
5.65
5.46
5.6
5.31
6.17
6.1
5.85
6.83
7.0
6.86
7.65
7.7
7.497.1
6.56.1
6.3
5.4
5.65.2
5.3
5.4
5.7 7.66
7.9
7.83
8.07
8.2
8.12 8.2Vehicle turn-out
(Sand)
Vehicle turn-out
(Sand)
Vehicle turn-out
(Sand)
Vehicle turn-out
(Sand)
Vehicle turn-out
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Drawn: RHV
Approved:
Scale:
VIEW #9
VIEW #10 Graphic Scale
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VIEW #10
Datum
HTL
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2.34
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NAVD88 0
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Based on NOAA
Hyannisport Station
LEGEND
GIS Parcel Line
Existing Contours (Ground Survey)
Existing Spot Elevation (Ground Survey)
High Tide Line (HTL)
Mean High Water (MHW)
Mean Low Water (MLW)
Existing Stone Groin, Riprap areas
Bulk Sand Bags installed in Dune
Landward Edge of Coastal Beach
Landward Edge of Primary Coastal Dune
Landward Edge of Salt Marsh
NHESP Boundary (PH-2156)
Soil Sample Location
X 8.4
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LEGEND
TH-34756
GIS PARCEL LINE
References:
1.Assessors Map 4, Parcel 4; Map 6, Parcels 6, 7 & 8; Map 7, Parcel 1; Map 9,
Parcels 1 & 5 and Map 10, Parcel 1
2.GIS parcel lines compiled from MassGIS shown are approximate and do not
represent an actual property boundary survey.
Survey Notes:
1.Coastal and Wetland Resource delineation conducted on 1/19/24 by Woods Hole
Group, Inc.
2.Field Data collected by Woods Hole Group between 1/26/24 and 2/08/24, and
between 8/7/24 and 8/14/24.
Flood Note:
1.Portions of areas depicted lie within Special Flood Hazard Zone X, AE (El=11),
AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA Firm Panel
#25001C0782J, effective 7/16/2014; AE (El=11), AE (El=13), VE (El=13) and
VE (El=14) as depicted on FEMA Firm Panel #25001C0569J, effective
7/16/2014; and AE (El=13), VE (El=13) and VE (El=14) as depicted on FEMA
Firm Panel #25001C0588J, effective 7/16/2014.
General Notes:
1.Priority Habitats of Rare and Estimated Habitats of Rare Wildlife shown on plan
are in accordance with the Massachusetts Natural Heritage Atlas, 15th Edition.
2.Entire site is within Barrier Beach and Land Subject to Coastal Storm Flowage.
3.Geotextile bags shown on Views #4 and #5 were installed under Emergency
Order issued by the Yarmouth Conservation Commission on January 5, 2024.
Datum Notes:
1.Coordinates are based on Massachusetts State Plane NAD83, Mainland Zone
(2001), in units of US Survey Feet.
2.Elevations are referenced to the North American Vertical Datum of 1988
(NAVD88) in US survey feet.
3.Tidal Datum Elevations are based on NOAA published Data & OPUS
Observation of Hyannisport Tidal Benchmark Station.
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association D-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX D. TIDAL ELEVATION SURVEY TECHNICAL MEMORANDUM
MEMORANDUM
DATE August 06, 2024 JOB NO. 2023-0169-00
TO Great Island Homeowners Association
1100 Great Island Road
West Yarmouth, MA, 02673
FROM Chris Gloniger
Woods Hole Group
Direct Phone: (508) 495-6217
cgloniger@woodsholegroup.com
Great Island Hydrologic Survey
Woods Hole Group (WHG) was contracted by the Great Island Homeowners Association to conduct a hydrologic study on
Great Island in Yarmouth, MA. The purpose of this work is to support a feasibility study for Great Island Road and bridge
resiliency. For the hydrologic study, two tide gauges were deployed on either side of the bridge on Great Island Road.
The purpose of this technical memorandum is to describe and summarize the tide gauge deployment and elevation
surveys.
Tide Gauge Data Collection
Two (2) In-Situ AquaTroll 200 conductivity-temperature-and depth sensors (CTDs) were deployed for 34 days (3/13/2024
– 4/16/2024) at the following station locations shown in Table 1 and Figure 1. All tide gauges were attached to a metal
pipe anchor and pushed into the bottom sediment (Figure 2). The instruments collected conductivity (salinity),
temperature, and absolute pressure (water plus atmospheric pressure) readings at 6-minute intervals over the 34-day
deployment period, which captured an entire monthly lunar tidal cycle (approximately 29.5 days). Each instrument was
surveyed with a real-time kinematic global positioning system (RTK GPS), which measures geodetic positioning data with
centimeter-level precision to the North American Vertical Datum of 1988 (NAVD88) in units of feet (ft) immediately after
deployment and before recovery. Atmospheric pressure and precipitation data during the deployment period were
retrieved from Hyannis Airport (HYA) located approximately 3.3 miles northwest of the site.
Table 1. Tide station locations.
Station Latitude Longitude Description
GI-1 41.620293 70.260254 North of Great Island Road Bridge
GI-2 41.619989 70.260092 South of Great Island Road Bridge
Page 2 of 5
Figure 1. Locations of tidal data logger stations GI-1 and GI-2.
Page 3 of 5
Figure 2. Tide gauge on a pipe anchor for deployment.
Data Processing
To calculate water surface elevation from the absolute pressure record measured by each tide gauge, barometric pressure
recorded at Hyannis Airport was subtracted from the instrument’s absolute pressure record. Upon removing barometric
pressure from the absolute pressure records and applying an equation of state for seawater, the remaining pressure
records are representative of the height of water (distance) above the sensor. The height of water was then converted to
water surface elevation using the surveyed elevation of each station. Once processed, data underwent QC procedures to
remove potential erroneous data including the following tests: gap tests, spike tests, out of water tests, and gross seasonal
range tests.
The time series of water surface elevation (NAVD88 ft) at each station was analyzed to produce the tidal datums for each
record. The tidal datums calculated include: mean higher high water (MHHW), mean high water (MHW), mean tide level
(MTL), mean low water (MLW), and mean lower low water (MLLW). Tidal range was calculated as the elevation between
datums MHHW and MLLW. These datums are calculated using the 34-day record and are not comparable to standard
NOAA tidal benchmarks, which are computed over a 19-year tidal epoch.
Results
Salinity in the Great Island system was largely saline (Figure 3, Table 2). Station GI-2, upstream of the Great Island Road
bridge was slightly fresher than GI-1, likely due to greater freshwater input in the confined system. Precipitation events
in March decreased the overall salinity in the system and increased salinity variability. The effects of precipitation events
were somewhat inconsistent, with each event decreasing salinity a variable amount. This indicates that there is another
factor influencing salinity in the system, such as wind vectors.
Page 4 of 5
Figure 3. Time-series of salinity (PSU) at all stations and daily precipitation recorded at Hyannis Airport
(bottom) during the deployment period.
Table 2. Salinity statistics for stations all stations.
Station
Minimum
Salinity
(PSU)
Maximum
Salinity
(PSU)
Average
Salinity
(PSU)
Standard
Deviation
(PSU)
GI-1 20.5 29.3 27.7 1.2
GI-2 18.9 28.9 27.4 1.4
The water surface elevations in the Great Island system were largely unobstructed (Figure 4, Table 3). MHHW and MHW
were roughly the same at GI-1 and GI-2, indicating unobstructed tidal flow to these stations. MLLW and MLW tides at
station GI-2 were slightly higher in comparison to GI-1, indicating upstream of the bridge is perched due to the culvert
invert. The higher MLLW and MLW also cause a higher MTL at BC-2 than BC-1 as well.
The water surface elevations are slightly sensitive to precipitation at both stations. While the March 23rd and 28th rain
events had very little impact on the system, the April 3rd rain event increased water surface elevations at both stations.
Water surface elevations remained high for 2-3 tidal cycles before returning to pre-event levels. The inconsistency of the
systems response to precipitation indicates that wind may play a role in water surface elevation. Alternatively, Hyannis
may have been impacted by a series of highly local rainstorms that did not impact Great Island.
Page 5 of 5
Figure 4. Time-series of water surface elevation (NAVD88, ft) at all stations (top) and daily
precipitation at Hyannis Airport (bottom) during the deployment period.
Table 3. Calculated tidal datums in feet, NAVD88 for all stations.
Tidal
Datum GI-1 GI-2
MHHW 2.3 2.4
MHW 2.0 2.0
MTL 0.5 0.6
MLW -1.1 -0.9
MLLW -1.3 -1.1
Range 3.1 2.9
Summary and Conclusions
The Great Island Road bridge does not significantly obstruct tidal flow into the south marsh system. The south marsh (GI-
2) is perched slightly due to the elevation of the upstream culvert invert. Salinity in the system indicates that it is impacted
by a combination of precipitation and wind-driven flooding. The south marsh is known to periodically flood from the east
due to over washing of the beaches from storms. Based on salinity and water surface elevations, that did not occur during
the deployment period.
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX E. HOHONU MONTHLY DATA COLLECTION SUMMARIES
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-2 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-3 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-4 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-5 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-6 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association E-7 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association F-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX F. LABORATORY GRAIN SIZE DATA
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association G-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX G. WETLAND DELINEATION TECHNICAL MEMORANDUM
MEMORANDUM
DATE March 20, 2024 JOB NO. 2023-0169
TO Mr. Craig Fleming
Great Island Homeowners Association
1100 Great Island Road
Yarmouth, MA 02673
FROM Alex Carbone
Direct Phone: (508)-495-6213
acarbone@woodsholegroup.com
Re: Coastal Resource Area Delineation
On January 17th and 19th 2024, two Woods Hole Group Coastal Scientists conducted a coastal resource area delineation
along a section of barrier beach connecting Great Island to the mainland in Yarmouth, Massachusetts. The study area
extended from the west end of Great Island Road bridge along Great Island Road to a point approximately 8,000 linear
feet northeast. Although barrier beach systems include both coastal beaches and coastal dunes, individual resource
areas within the barrier system were delineated for this study. Resource areas surveyed included coastal beach, primary
frontal dune, coastal dune, salt marsh, and coastal bank. Extents of paved surfaces associated with Great Island Road, as
well as certain coastal engineering structures were also surveyed. To delineate the extent of resource areas and capture
changes in topography, a survey-grade real-time Kinematic (RTK) GPS was used to collect data at sub-centimeter
accuracy in both horizontal and vertical datums. Horizontal data were recorded in Massachusetts State Plane 2001
(Mainland, US survey feet) and vertical data were collected in North American Vertical Datum of 1988 (NAVD88, US
survey feet). Land Subject to Coastal Storm Flowage (LSCSF) was also included in this study as mapped by FEMA flood
zones AE and VE. Descriptions of each resource area are included in the following sections.
Page 2 of 17
Figure 1. Coastal resource areas delineated within the study area on January 17th and 19th, 2024.
Coastal Beach
Coastal beach was present along the entirety of the 8,000 linear foot survey area shoreline (Figure 2). At the time of the
survey, the beach was gradually sloping and contained primarily medium to fine-grained sediments with some areas
containing more cobble (Figure 3) and shell (Figure 4) deposits. Coastal beach transitioned landward to primary frontal
dune for the entirety of the study area except for a ~500 linear foot stretch at the southwestern survey extent where the
beach transitioned to coastal bank. Shore perpendicular groin engineering structures were present at varying intervals
along the entirety of the survey area shoreline (Figure 5). Groins were observed to be trapping sediment traveling in an
eastward longshore transport direction. A narrow pocket of coastal beach was present landward of a remnant
revetment near the center of the survey area (Figure 6).
Page 3 of 17
Figure 2. Coastal beach seaward of Great Island Road. Photo taken facing southwest.
Figure 3. Cobble strewn coastal beach at western end of survey area. Photo taken facing southwest.
Page 4 of 17
Figure 4. Shell deposit within sandy coastal beach.
Figure 5. Groin engineering structures along coastal beach. Photo taken facing northeast.
Page 5 of 17
Figure 6. Pocket of coastal beach landward of remnant revetment. Photo taken facing northeast.
Primary Frontal Dune
The primary frontal dune is defined in the Wetlands Protection Act Regulations as “a continuous mound or ridge of
sediment with relatively steep seaward and landward slopes immediately landward and adjacent to the beach and
subject to erosion and overtopping from high tides and waves during coastal storms. The Primary Frontal Dune is the
dune closest to the beach. The inland limit of the Primary Frontal Dune occurs at the point where there is a distinct
change from a relatively steep slope to a relatively mild slope.” Using this definition (Figure 7), primary frontal dune was
delineated for a continuous stretch from the eastern survey extent to a point 7,500 linear feet westward where a
transition to coastal bank occurred. For the entirety of its length, the primary frontal dune was fronted by coastal beach,
and backed by either secondary coastal dune (Figure 8), or Land Subject to Coastal Storm Flowage. Vegetation within the
primary dune included primarily American beachgrass (A. breviligulata), seaside goldenrod (S. sempervirens), and dusty
miller (J. maratima) with woody plant species including Northern bayberry (M. pensylvanica) Eastern red cedar (J.
virginiana) scrub oak (Q. ilicifolia), and pitch pine (P. rigida) interspersed. The seaward face of the primary frontal dune
contained an erosional scarp for a significant portion of its full length (Figures 9 & 10). A stone rip-rap coastal
engineering structure was present on the seaward face of the primary dune in some areas where the length between
the dune and Great Island Road was narrow (Figure 11).
Page 6 of 17
Figure 7. Features of typical primary frontal dune. Photo taken facing northeast.
Figure 8. Representative example of transitions between resource areas. Photo taken facing
southwest.
Landward toe of Primary Dune Landward peak of Primary Dune
Backslope
Toe of
Primary Dune
Page 7 of 17
Figures 9 & 10. Erosional scarping along the seaward face of primary dune.
Figure 11. Stone rip-rap armoring primary frontal dune. Photo taken facing southwest.
Remnant Revetment Stones and Coastal Engineering Structure
As described in previous sections, remnants of a constructed stone revetment were observed seaward of Great Island
Road near the center of the survey area. (red area, Figure 1). It was composed of boulders between 4 -8 feet in their
largest dimension and extended approximately 300 linear feet parallel to the shore (Figure 12). Tides and waves appear
Page 8 of 17
to regularly bypass the remnant revetment stones, but they may still reduce incoming wave energy affecting the shore.
Landward of the remnant revetment was a narrow pocket of coastal beach with fringing salt marsh patches, which was
approximately 15 feet in width. A continuous ~750 linear foot coastal engineering structure was present landward, and
on either side of the remnant revetment, which armored the seaward edge of Great Island Road (Figure 13). Stones
placed in this area were between 1-4’ in their largest dimension.
Figure 12. Remnant stone revetment (left) and coastal engineering structure (right). Photo taken
facing west.
Figure 13. Coastal engineering structure armoring the seaward edge of Great Island Road.
Page 9 of 17
Coastal Dune
While primary frontal dune was included in the overall coastal dune delineation, Secondary dune(s) continued beyond
the landward extent of primary dune for the majority of the length of the barrier system. Crests of secondary dunes
typically reached a higher elevation than the primary dune (Figure 14), before tapering back down on the bayside of the
barrier system and transitioning to salt marsh (Figure 15). Evidence of storm overwash was observed in fans on the
western side of the study area (Figure 16). Great Island Road cuts through the coastal dune resource area and was
considered to be Land Subject to Coastal Storm Flowage. Perennial dune vegetation included American beachgrass,
seaside goldenrod, dusty miller, reindeer moss (C. rangiferina) (Figure 17), with saltmeadow cordgrass (S. pumilus) and
sea blight (Sueda spp.) present near transitions to salt marsh. Woody vegetation was present intermittently in some
areas (Figure 18), as well as in more dense maritime forest in other areas (Figure 19). Overstory species included Eastern
red cedar, Atlantic white cedar (C. thyoides), white oak (Q. alba), scrub oak, and pitch pine, with an understory of high
tide bush (I. fruescens) and Northern bayberry.
Figure 14. Secondary dune (right) higher in elevation than primary dune (left). Photo taken facing
southeast.
Page 10 of 17
Figure 15. Transition from coastal dune to salt marsh. Photo taken facing northeast.
Figure 16. Evidence of storm overwash within coastal dune. Photo taken facing east.
Page 11 of 17
Figure 17. Coastal dune ground cover vegetation.
Figure 18. Coastal dune vegetation. Photo taken facing south.
Page 12 of 17
Figure 19. Maritime forest vegetation within coastal dune. Photo taken facing south.
Salt Marsh
Salt marsh was present along the entire extent of the bayside shoreline of the Great Island barrier system. West of the
Great Island Road bridge, narrow swaths of salt marsh were present along the shoreline (Figures 20 & 21). Vegetation in
this area included primarily smooth cordgrass (S. alterniflorus) and saltmeadow cordgrass. East of the bridge, wide areas
of continuous salt marsh continued on both the north and south sides of Great Island Road (Figure 22). Salt marsh south
of Great Island Road included upland hummocks scattered throughout and was backed by transition to coastal dune.
North of Great Island Road, salt marsh continued along the entirety of the barrier system. Vegetation within the salt
marsh included primarily smooth cordgrass, saltmeadow cordgrass, sea pickle, with high tide bush clustered in areas of
slightly higher elevation (Figure 23). Phragmites (P. australis) was present in a discrete area to the east. Toward the
eastern extent of the barrier system, salt marsh narrowed to approximately 30-40 feet wide between open water and
the coastal dune (Figure 24). Salt marsh continued to narrow and become more intermittent moving eastward until
reaching the northeast extent of the survey area, where it continued along the shore of the channel. Fringing patches of
salt marsh were also present between the remnant revetment and the coastal engineering structure seaward of Great
Island Road (Figure 25).
Page 13 of 17
Figures 20 & 21. Narrow salt marsh areas west of the Great Island Road bridge.
Figure 22. Salt marsh east of Great Island Road bridge. Photo taken facing east.
Page 14 of 17
Figure 23. Salt marsh vegetation on the bayside of Great Island Road. Photo taken facing south.
Figure 24. Salt marsh between open water (left) and coastal dune (right). Photo taken facing east.
Page 15 of 17
Figure 25. Fringing salt marsh patches between the remnant revetment and coastal engineering
structure. Photo taken facing northeast.
Coastal Bank
An approximate 500 linear foot stretch of coastal bank was present at the southern extent of the barrier beach system.
The eroded seaward face of the bank revealed glacial subsurface sediments with cobble, with 1’-2’ of sand overlain
(Figures 26 & 27). Vegetation along the top of the coastal bank included American beachgrass, Northern bayberry, pitch
pine, and Eastern red cedar. The coastal bank was fronted by transition to coastal beach and backed by transition to
coastal dune. Cobble and sediments were observed to be eroding from the bank and conveying onto the seaward beach.
Figures 26 & 27. Coastal bank near southwest extent of survey area. Photo taken facing north.
Page 16 of 17
Land Subject to Coastal Storm Flowage
Land subject to coastal storm flowage (LSCSF) is land subject to any inundation caused by coastal storms up to and
including that caused by the 100-year storm, surge of record or storm of 100-year storm, surge of record or storm of
record, whichever is greater. LSCSF was inclusive of the AE and VE zones designated by FEMA and encompassed all
resource areas that were documented on site including coastal beach, primary frontal dune, coastal dune, salt marsh,
and coastal bank. Because LSCSF covered the entirety of the study area, areas that did not meet criteria for other
resource areas were delineated as LSCSF. This includes the entirety of Great Island Road (Figure 28).
Figure 28. Great Island Road, delineated as LSCSF. Photo taken facing northeast.
Natural Heritage Estimated & Priority Habitat and Massachusetts Division of Marine Fisheries Shellfish
Suitability Areas
Estimated and Priority Habitat for Rare or Endangered Species were identified adjacent to the study area by the
Massachusetts Natural Heritage and Endangered Species Program (Figure 29). North of the Great Island study area,
areas along the bayside shoreline were identified as spawning and settlement habitat for quahog (M. mercenaria), bay
scallop (A. irridans), and American oyster (C. virginica) (Figure 29). No live shellfish were observed during the
delineation.
Page 17 of 17
Figure 29. NHESP & Shellfish suitability habitat within and adjacent to the study area.
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association H-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX H. VULNERABILITY ASSESSMENT ROADWAY SEGMENTS
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association I-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX I. GREAT ISLAND BRIDGE INSPECTION MEMORANDUM
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M E M O R A N D U M
TO: Mr. Craig Fleming, Great Island Homeowners Association
CC: Chris Gloninger, Woods Hole Group, Senior Climate Scientist
FROM: Nils Wiberg PE, CFM, Chief Water Resources Engineer
Dan Whitmore PE, Structural Project Manager
DATE: June 28, 2024
RE: Great Island Bridge Inspection Memorandum
Great Island Homeowners Association - West Yarmouth, MA
Fuss & O'Neill Inc. Project No. 20230674.A10
On Monday April 15th, 2024 Fuss & O'Neill Inc. performed an inspection of the bridge along Great Island Road in
Yarmouth, Massachusetts for the Great Island Homeowners Association (GIHA), under a subconsultant agreement
to the Woods Hole Group, as an element of the larger climate vulnerability project. The bridge and abutting
roadway segment are owned by GIHA; while the bridge is not listed on the National Bridge Inventory (NBI) it is
licensed under MA Department of Environmental Protection Chapter 91 Waterways Regulation Program (License
15038 dated November 13, 2019).
Weather conditions at the time of the inspection were clear/sunny with a temperature of approximately 55
degrees F. The inspection included a hands-on assessment of superstructure and substructure elements above
the water line, including the railing, wearing surface, underdeck of the bridge, abutments, piles and bents.
Elements located below the water line, intrusive measurements and structural analysis were excluded from the
scope of this inspection. The purpose of the inspection was to document deficiencies and recommend action to
maintain safe access to respective properties on Great Island. The previous inspection, performed in August 2023
by GEI Inc. (inspection report included for reference as Attachment A), was reviewed prior to the inspection.
There was no evidence of a significant change from the last inspection or imminent danger of failure. It was noted,
in agreement with previous inspection, that previous repairs to the bridge are deteriorating at a rate that is
accelerated by overtopping and mean high water levels. Noted repair recommendations should be considered for
immediate implementation and normal maintenance activities should continue on a regular basis. It is understood
that replacement of the bridge and reconstruction/elevation of adjacent roadways is currently being evaluated along
with other resilience improvement alternatives. The timeline for implementation of these alternative elements
should be carefully evaluated in relation to the timeline for needed repairs and/or replacement of the bridge, or
abandonment/removal of the bridge if alternative means provide acceptable access to the island, to assure
continued safety and service until implementation of respective elements.
Inspection Performed by: Patrick Tierney PE, Fuss & O’Neill, Transportation Project Manager
Derek Newhall, Fuss & O’Neill, Water Resources Engineer
Inspection Report Reviewed by: Dan Whitmore PE, Fuss & O’Neill, Structural Project Manager
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
Page 2 of 6
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Site Description
The bridge is 18ft-8in long and consists of two spans that are supported by stone abutments and a single timber
bent (see Photos 1-4, included in Attachment B and Figures 1-3, included as Attachment C). The timber bent is
comprised of two 12in diameter timber piles and a single 12in x 12in timber pile cap. The deck is a concrete slab
comprised of fourteen (14) encased steel beams. The bridge spans over Uncle Roberts Cove, a salt marsh estuary
that connects to Lewis Bay to the north and occasionally receives water from Nantucket Sound to the south. The
cove is tidal, and water overtops the bridge approximately semi-annually during storm events and spring tides.
Vehicle travel over the bridge is restricted to one lane over a 12ft-3in wide roadway. The bridge is the only point of
access on and off Great Island. Traffic counts were not available and average daily traffic is estimated to be below
1,000 vehicles per day in the peak season. Commercial trucks were observed traveling over the bridge at the time
of inspection.
Inspection Methodology
The field inspection methodology was performed in accordance with the American Association of State Highway
Transportation Officials (AASHTO) Manual for Bridge Inspection Elements 2nd Edition, Federal Highway
Administration (FHWA) Record and Coding Guide for the Structure Inventory and Appraisal of the Nations Bridges
(FHWA-PD-96-001), and the MassDOT 2015 Bridge Inspection Handbook. Following the FHWA condition rating
guidelines, element conditions were classified on the following scale.
Description Code
NOT APPLICABLE N
EXCELLENT CONDITION 9
VERY GOOD CONDITION - No problems noted. 8
GOOD CONDITION - Some minor problems. 7
SATISFACTORY CONDITION - Structural elements show some minor deterioration. 6
FAIR CONDITION - All primary structural elements are sound but may have minor section loss,
cracking, spalling, or scour. 5
POOR CONDITION - Advanced section loss, deterioration, spalling or scour. 4
SERIOUS CONDITION - Loss of section, deterioration, spalling or scour have seriously affected
primary structural components. Local failures are possible. Fatigue cracks in steel or shear cracks in
concrete may be present.
3
CRITICAL CONDITION - Advanced deterioration of primary structural elements. Fatigue cracks in
steel or shear cracks in concrete may be present or scour may have removed substructure support.
Unless the bridge is closely monitored, it may be necessary to close the bridge until corrective action is
taken.
2
"IMMINENT" FAILURE CONDITION - Major deterioration or section loss present in critical structural
components or obvious vertical or horizontal movement affecting structure stability. Bridge is closed to
traffic but corrective action may put back in light service.
1
FAILED CONDITION - out of service - beyond corrective action. 0
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
Page 3 of 6
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Conditions Assessment
The following elements were inspected and assigned a condition.
Deck - Asphalt Wearing Surface
The asphalt wearing surface was observed to be in Satisfactory Condition. Transverse pavement cracks up to
1/16in were present at the limits of the bridge for the full length of the roadway (Photo 5, Attachment B).
Longitudinal cracks less than 1/16in and rutting up to 1/2in deep were present on the approach pavement. The
approach roadway changes direction at the crack which may indicate the loss of backfill behind the bridge.
Deck - Metal Bridge Railing
The metal railings on the bridge and the wood fence on the approaches are not in compliance or suitable as
vehicular barriers, therefore they are rated as Fair Condition and recommended to be replaced. On both
approaches to the bridge, the wood fence had been recently repaired (Photo 6, Attachment B).
Superstructure - Reinforced Concrete Slab
The underside of the concrete deck was observed to be in Poor Condition. All beams on the underside were
encapsulated in concrete, with several beams covered with patches from past exposure that was noted in previous
inspections.
The concrete encasing Beams Nos. 5 and 9 has deteriorated and were covered with patching for their full length. A
1/16in crack in the patching extends along the length of both beams. The patch on Beam No. 5 was wet and
exhibited signs of moderate deterioration with rust, cracks and efflorescence (Photo 7, Attachment B).
The concrete encasing the exterior beams (Beam Nos. 1 and 2) exhibited deterioration and had been patched over
a significant portion of its surface. 1/16in cracks in the patching extended along the length of beams with rust and
efflorescence (Photo 8, Attachment B). Beam No. 1 also had transverse cracks that extended to Beam No. 5 on
the east side of the bridge.
Approximately five (5) 2in diameter by 2in deep holes were observed on the underside of the bridge deck. Several
of the holes had been patched and several had cracks less than 1/16in wide extending through them.
Superstructure – Encased Beams
The beams were encased in concrete and were not visible during the inspection. Therefore, the beams did not
receive a condition rating. It is recommended that any concrete slab repairs temporarily expose the beams to
assess their condition and allow for repairs if required.
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
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Substructure – Stone Abutments
The stone abutments were observed to be in Satisfactory Condition. Stones were found to be intact and there was
no evidence of settlement in either abutment. Both abutments had moderate mortar loss between stones, with
most of the loss observed below the high-water mark. Mortar loss was observed in both bridge seats (locations
where bridge deck is supported by both abutments, Photo 9 in Attachment B).
The streambed was observed to consist of isolated cobbles and sand/gravel. Undermining and loss of material
was observed at the toe of both abutments and extended up to 6in in depth at the center of the abutments.
A void measuring 2ft-6in feet deep by 1ft long by 1ft wide in the east abutment was noted. The void was located
approximately 6.3ft from the north side of the east abutment and 2ft from the streambed (Photo 10, Attachment B).
An additional void in the east abutment was measured to be 1ft deep by 6in wide by 6in long at the south corner 1ft
above the streambed. A void measuring 1ft deep by 15in wide by 15in long was noted in the center of the west
abutment 1ft up from the streambed. It is assumed that the voids are present from stones that have been
displaced.
The abutments have concrete steps connected on all four corners, and some of those steps were either broken or
had large cracks greater than 6in wide (Photo 11, Attachment B). In some areas, the concrete steps act as
approach embankments and retain the bridge approaches. The slope embankment riprap has slumped and
exposed voids in the stones. It is noted that further deterioration will increase the risk of future undermining of the
road.
Substructure – Timber Pile and Cap
The two 10in diameter timber piles and 12inx12in pile cap were observed to be in Satisfactory Condition.
The concrete deck appeared to have full bearing on the timber pile cap provided by timber shims. Timber shims
were observed to be rotting (Photo 12, Attachment B).
The piles and pile cap had minor splintering, saturation and marine growth below the high-water mark. The piers
appear to be slightly out of plumb. The beam was saturated from the bottom up about 4in to 5in (Photos 13 and 14,
Attachment B). Based on review of prior inspection reports, it is unknown whether the pier has always been out of
plumb and when the shims were added.
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
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Maintenance and Repairs
The following maintenance/repair actions are recommended to keep the bridge and adjacent approaches safe and
in service. Estimated construction costs are provided based on published regional cost data and bid results for
comparable services in the region. The timeframes are recommended for the purposes of capital planning, and
estimated cost may be subject to escalation based on site/structure conditions and market conditions at the time
work is actually completed.
Immediate Maintenance/Repairs (completed within one year)
• The concrete deck defects need to be monitored and documented to track further changes in condition. An
annual or semiannual inspection schedule is recommended to document changes.
• It is recommended to replace the patching on the slab encasing Beam Nos. 5 and 9, repair cracks on the
slab encasing Beam Nos. 1 and 14 and document any section loss on the beams at that time.
o Deteriorated concrete shall be removed to properly bond patching material to the bridge deck;
embedded beams shall be exposed as directed during work to enable observation, assessment
and potential treatment of bridge beams exhibiting corrosion.
• Repairs to the abutment stones, undermining and mortar should be addressed by replacing missing stones
and repointing mortar.
• Shims placed between the timber pile cap and concrete deck should be removed and replaced. The angle
of the pile’s lean should be numerically measured and recorded for future comparison to determine if the
further displacement occurs, which may necessitate replacement of one or both piles.
• Timber piles and the pile cap should be treated with corrosion inhibitors formulated specifically for use in
marine environments.
The estimated cost to perform this work is $130,000 - $180,000.
Short Term Maintenance/Repairs (completed within 2-3 years)
• Replace the timber railings along both approaches to the bridge, and the barrier railing on the bridge with
compliant barrier railings and a wingwall cap (i.e., designed to withstand designated vehicle impacts at the
rated speed). Approximately 40 feet of bridge rail and 1,000 feet of timber or metal guardrail for the bridge
approaches would be installed.
The estimated cost to perform this work is $175,000 - $250,000.
Long Term Repairs (completed within 3-5 years)
For planning purposes, it is recommended that the bridge be considered for replacement in its entirety if the
evaluation of roadway resilience alternatives determines that access to Great Island will continue along the current
roadway and this waterway crossing. It is noted that the bridge was built prior to 1970 and has required substantial
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
Page 6 of 6
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repairs over the last 15 years. It is also noted that costs for maintenance after the periods noted above will
continue to increase.
The estimated construction cost to perform this work would range between $900,000 and $1,200,000 dependent on
the corresponding roadway reconstruction work required to elevate the bridge.
Summary and Recommendation
Overall, the bridge was found to be in Fair Condition. The concrete slab exhibited numerous cracks and patches,
many of which were observed to be in poor condition and will require significant ongoing maintenance. The
approach railings and railings on the bridge do not meet the definition for barrier rails and should be considered for
replacement.
As noted above, it is recommended that the bridge be considered for replacement if access to Great Island will
remain along the current roadway, to mitigate the cost related to the increase in frequency of inspections and
repairs that are caused by increased frequency and magnitude of high water and overtopping events. The future
bridge design should be designed and constructed with marine-compatible materials to withstand corrosion and
configured with protective elements for projected wave/scour conditions for its entire anticipated service life.
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Attachment A
August 2023 Inspection Report
Memo
To: Craig Fleming
From: Alan Pepin, P.E., Calvin Joseph, P.E.
c: Malcolm Kent
Date: September 20, 2023
Re: Great Island Bridge Inspection Memo
West Yarmouth, MA
GEI Project No. 2303506
Mr. Craig Fleming,
GEI Consultants, Inc. was retained by Great Island Homeowners Association to perform an inspection
of the Great Island Bridge located on Great Island Road in West Yarmouth, MA. Site Coordinates are
41°37'12.6"N, 70°15'36.8"W. This inspection included an above water inspection of the foundation
piles, stone abutment, topside wearing surface, underdeck of the bridge and soundings for mudline
elevations. The purpose of the inspection is to document any deficiencies found during the routine
bridge inspection. The previous inspection and report were dated July 2019, by Foth Infrastructure and
Environment, LLC, which is attached for reference.
SITE DESCRIPTION
The existing facility consists of a single lane two-span bridge, which bears on stone abutments at either
end and a timber bent at the approximate center. The bridge is approximately 18’-8” long, and 12’-4”
wide in-between curbs. The timber bent is comprised of two 12-inch diameter timber piles and a single
12-inch x 12-inch timber pile cap. The bridge spans over Uncle Roberts Cove in Cape Cod MA. The
cove is tidal, and experiences floods/ebb from the Atlantic Ocean.
INSPECTION METHODOLOGY
GEI personnel performed the inspection on August 11, 2023. The inspection was performed in
accordance with the American Society of Civil Engineers (ASCE) Manuals and Reports on Engineering
Practice No. 130 “Waterfront Facilities Inspection and Assessment” (MOP 130) and ASCE Manuals
and Reports on Engineering Practice No. 101 “Underwater Investigations” (MOP 101). Level I
inspection was performed for all elements within the inspection scope. The inspection level definitions
applicable to the project scope are summarized below:
• Level I Inspection: A visual and tactile inspection on 100% of the structure.
The concrete under deck, was reviewed for cracking and spalling, as well as the condition of the repair
work that had been performed since the previous Foth inspections. The abutment inspection included a
visual review of defects and measurements. No destructive testing was performed on any elements.
There was approximately 3 ft of water in the channel at the time of the inspection, and mudline visibility
was clear which correlated with low tide.
www.geiconsultants.com 124 Grove Street, Suite 300
Franklin, MA 02038-3156
774-277-6001
Craig Fleming -2- September 20, 2023
Conditions were documented for all members as defined in MOP 130 Element Level Damage Ratings (MOP
130 Tables 2-4 through 2-13) and Condition Assessment Ratings (MOP 130 Table 2-14). Refer to Tables 1-
2 and 1-3 on the following pages which are developed from the previously referenced MOP 130 tables.
Table 1-2. Damage Assessment Ratings
Damage Rating Damage Description
Not Inspected (NI) Not inspected, inaccessible, or passed by.
No Defects (ND) Sound surface material, light surface rust, no apparent loss of
section or material.
Minor (MN) Checks & splits, damage to protective coating, loss of thickness or
section up to 15%.
Moderate (MD) Loss of thickness or section 15% - 25%. More than 50% of surface
affected by corrosion. Damage to hardware, loose bolts, noticeable
hairline cracks, and splitting.
Major (MJ) Loss of thickness or section 25% - 50%. Heavily corroded
hardware, damaged coating or wrap, deteriorated edges, cracks up
to ¼” in width, significant pitting.
Severe (SV) Loss of thickness or section greater than 50%. Partial or complete
breakage, structural buckling, loss of bearing, broken hardware,
missing components.
*Damage Assessment Rating table shown is only meant to provide an understanding of the overall issues with the
elements rated. For an in-depth understanding of the damage ratings refer to ASCE Manual 130, Chapter 2, Tables 2-4
through 2-13.
Table 1-3. Condition Assessment Ratings
Member Rating* Member Rating Description
6 (A) Good No visible damage or only minor damage is noted. Structural elements
may show very minor deterioration, but no overstressing observed. No
repairs required.
5 (B) Satisfactory Limited minor to moderate defects or deterioration observed but no
overstressing observed. No repairs are required
4 (C) Fair All primary structural elements are sound but minor to moderate defects
or deterioration observed. Localized areas of moderate to advanced
deterioration may be present but do not significantly reduce the loading
capacity of the structure. Repairs are recommended, but the priority of
the recommended repairs are low.
3 (D) Poor Advanced deterioration or overstressing observed on widespread
portions of the structure but does not significantly reduce the load-
bearing capacity of the structure. Repairs may need to be carried out with
moderate urgency.
2 (E) Serious Advanced deterioration, overstressing, or breakage may have
significantly affected the load-bearing capacity of the primary structural
components. Local failures are possible, and loading restrictions may be
necessary. Repairs may need to be carried out on a high-priority basis
with urgency.
1 (F) Critical Very advanced deterioration, overstressing, or breakage has resulted in
localized failures(s) of primary structural components. More widespread
failures are possible or likely to occur, and load restrictions should be
implemented as necessary. Repairs may need to be carried out on a very
high-priority basis with strong urgency.
*The letter assigned to the rating was added to the MOP 130 table to assist with field operations.
Craig Fleming -3- September 20, 2023
CONDITIONS ASSESSMENT
Stone Abutments
The stone abutments were found to be in fair condition. There was little evidence of stone shifting or
settlement in the abutment. At both abutments, there was partial mortar loss in between individual stones,
below the high-water mark (HWM). There was complete mortar loss below the low water mark (up to 2
feet from the mudline). Undermining/loss of soil material was observed and extended up to 6 inches in depth
at the toe of the abutments. This was typical at both abutments.
There was a void observed in the east abutment. The void has dimensions of approximately 2.4 feet deep
by 1 foot high by 1 foot wide. The void was located approximately 6.3 feet from the north side of the east
abutment and 2 feet from the mudline (Photo 8).
The abutments has layers of concrete steps on all 4 corners, and some of those steps were either broken or
had cracks in the concrete (Photo 10).
Timber Bent
The two 10-in diameter timber piles and 12x12 pile cap were found to be in satisfactory condition.
The concrete deck appeared to have full bearing on the timber pile cap. Timber shims and grout was
observed which filled the voids in between the deck and pile cap. The piles had minor splintering and marine
growth below the high-water mark (Photos 11-14).
Superstructure
The underside of the concrete deck was found to be in fair condition. From Foth’s 2019 report, it was noted
that beam #5, which is designed to be encapsulated in the concrete, had lost its concrete cover. Foth’s report
had indicated that the beam was exposed, and repairs had been made to cover the beam. During the 2023
inspection performed by GEI, the repair patch appeared to be present (Photos16 &17). Hairline cracks with
apparent efflorescence leaking through were found at several locations on the deck underside, including
areas surrounding the previously installed deck patch. Several 2-inch diameter by 2 inch deep holes were
found in the deck underside. At least five (5) holes were observed, and it is unclear the cause (Photo 19).
The asphalt wearing surface was found to be in satisfactory condition. There were pavement cracks at both
approaches of the bridge, as well as several minor hairline cracks in between the bridge approaches. At the
time of the inspection, sink holes referenced in the Foth Report were not observed, and GEI did not observe
any steel plates on the topside of the deck. The metal railing appeared to be in satisfactory condition. On
both approaches to the bridge, the timber rails are in poor condition (Photo 21). It should be noted that the
railings on the approaches and the bridge are not in compliance for vehicular barriers and were only
reviewed for visual condition.
REGULTORY APPROVALS
GEI is recommending general maintenance repairs to be performed. Based on these maintenance
repairs, it is anticipated that the following regulatory approvals would be required.
• Yarmouth Conservation Commission Notice of Intent (NOI) → 2-3 months lead time
• Notification Letter of Maintenance: →2-3 weeks lead time
o Mass DEP Waterways Chapter 91*
Craig Fleming -4- September 20, 2023
o United Stated Army Corps of Engineers
*It is our understanding that there is a newly issued Chapter 91 license. Any repairs are
anticipated to be a “Letter Notification of Maintenance”.
• Massachusetts Environmental Policy Act (MEPA) → Not Required
• Water Quality Certification (WQC) → Not Required
CLIMATE CHANGE IMPACTS
The bridge is located on the south side of Cape Cod, connected to Lewis Bay. Lewis Bay is connected
to the Nantucket Sound / Atlantic Ocean. Where the bridge is located, it is only a short distance of
beach and salt marsh protecting the bridge from the Nantucket Sound. Below is a review of the
coastal elevations for the site.
• Datum elevations are based on Station 8447605, Hyannisport, MA, provided by NOAA
• Great Island Bridge is currently at Elevation +4.9’± Mean Lower Low Water (MLLW)
• According to USACE, high projected sea level rise by 2072 will be +2.68 feet.
• Current versions of FEMA Flood Insurance Rate Maps (FIRM) map the site within an AE
zone with 1% (1 in 100 chance) annual exceedance flood elevation of +12.3’ MLLW (FEMA
Firmette)
o With this flood elevation, the existing site would be approximately 7.4’ under water
in a FEMA 1% storm event.
o AE zone is an area with high risk of flooding where flood elevations are provided.
o Datum Conversion: NAVD88 +1.3ft = MLLW
• The bridge and upland elevations would be completely inundated under a current 1% annual
exceedance storm event with the current approaches and bridge elevations.
• Simplistic combination of this data would estimate a 1% annual exceedance event in 2072 to
have a flood elevation of at least +14.98’ MLLW. In practice the flood elevation is likely to
be higher due to larger waves at the site.
o The still water elevation does not account for waves in an AE Zone. This elevation
would be approximately the center of the wave resulting in an overall higher
observed water elevation.
Given the location and importance of the bridge to the community, climate change impacts should be
incorporated into any significant changes or upgrades to the bridge to increase the resiliency of the
site to flooding events.
SUMMARY AND RECOMMENDATIONS
Overall, the bridge was found to be in fair condition. The concrete superstructure has some cracks along the
underside, and there are minor deficiencies requiring maintenance. The approach railings and railings on
the bridge do not meet the definition for barrier rails and should be considered for replacement. The concrete
deck defects may need to be monitored and documented more frequently to track further changes in
condition. It should be noted that a load analysis has NOT been performed as part of this project.
Given the observations we believe the FOTH analysis is still valid, and no new analysis is required at this
time. Based on our inspection findings, it is recommended that the bridge elements be monitored with a
routine underwater inspection being performed on a recommended ASCE 5-year basis, or more frequent at
the client’s request.
Craig Fleming -5- September 20, 2023
Estimated Probable Costs
GEI has developed a schedule of recommended repairs in order of importance. Critical repairs are
recommended to be performed in the immediate timeframe (<12 months), less severe should be performed
in the short term (2-4 year) and capital improvement type repairs should be performed in the 5+ year plus
range. In the long-term plans for this structure, bridge replacement should be considered to be incorporated
with capital plans. Below is a summary of repairs for planning purposes. The concept level construction
costs outlined below do not include costs for design, permitting.
Immediate Repairs (Within the next 12 months):
The concrete deck defects may need to be monitored and documented more frequently to track further
changes in condition. It is recommended to patch any concrete voids on the deck underside using the
appropriate construction methodologies. Chinking stone / concrete repairs should also be placed in voids in
the abutments.
We estimate this work to be $20,000 in construction costs.
Short Term Repairs (2-4 yrs):
In the short term, it is recommended to repair the timber railings along the approach of the bridge,
along both north and south sides. We also recommend replacement of the barrier railing on the bridge
with compliant barrier railings.
We estimate this work to be $100,000 in construction costs.
Long Term Repairs (5yrs+):
For planning purposes, we recommend the bridge be considered for replacement in its entirety. The bridge
was built prior to 1970 and has required substantial repairs over the last 15 years. Replacement is
recommended to be budgeted as the costs for continued maintenance will continue to increase. GEI has
estimated the potential cost to replace the bridge including new abutments & wing walls, bridge deck,
approach slab, railings, and pavement. We have not accounted for sea level rise, temporary structures, design
or permitting.
We estimate this work to be in the range of $750,000 in construction costs.
B:\Working\GREAT ISLAND HOMEOWNERS ASSOC\2303506 Great Island Bridge Inspection\07_REPORT\2023 Report\2023.09.20 MEM Great Island Bridge Inspection RPT .docx
Project Photos - Great Island Bridge Inspection
i | P a ge
West Yarmouth, MA
Date: September 20, 2023
Photo No. 1 – Overall Site Photo ___________________________________________________________ 1
Photo No. 2 – Bridge Plan View ____________________________________________________________ 1
Photo No. 3 – Looking South ______________________________________________________________ 2
Photo No. 4 – Looking North ______________________________________________________________ 2
Photo No. 5 – Looking West ______________________________________________________________ 3
Photo No. 6 – Looking East _______________________________________________________________ 3
Photo No. 7 – Typical Abutment____________________________________________________________ 4
Photo No. 8 – Void in Abutment ____________________________________________________________ 4
Photo No. 9 – Typical Wing Wall ___________________________________________________________ 5
Photo No. 10 – Broken Concrete ___________________________________________________________ 5
Photo No. 11 – Timber Bent ______________________________________________________________ 6
Photo No. 12 – Timber Pile Cap ____________________________________________________________ 6
Photo No. 13 – Pile Cap/ Deck Shims ________________________________________________________ 7
Photo No. 14 – Typical Pile _______________________________________________________________ 7
Photo No. 15 – Typical Deck Underside ______________________________________________________ 8
Photo No. 16 – Concrete Patch ____________________________________________________________ 8
Photo No. 17 – Concrete Patch Size _________________________________________________________ 9
Photo No. 18 – Cracks in Deck Underside _____________________________________________________ 9
Photo No. 19 – Holes in Deck Underside _____________________________________________________ 10
Photo No. 20 – Cracks in Pavement ________________________________________________________ 10
Photo No. 21 – Dilapidated Timber Guard Rail ________________________________________________ 11
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
1 | P a ge
Photo No. 1 – Overall Site Photo
Photo No. 2 – Bridge Plan View
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
2 | P a ge
Photo No. 3 – Looking South
Photo No. 4 – Looking North
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
3 | P a ge
Photo No. 5 – Looking West
Photo No. 6 – Looking East
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
4 | P a ge
Photo No. 7 – Typical Abutment
Photo No. 8 – Void in Abutment
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
5 | P a ge
Photo No. 9 – Typical Wing Wall
Photo No. 10 – Broken Concrete
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
6 | P a ge
Photo No. 11 – Timber Bent
Photo No. 12 – Timber Pile Cap
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
7 | P a ge
Photo No. 13 – Pile Cap/ Deck Shims
Photo No. 14 – Typical Pile
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
8 | P a ge
Photo No. 15 – Typical Deck Underside
Photo No. 16 – Concrete Patch
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
9 | P a ge
Photo No. 17 – Concrete Patch Size
Photo No. 18 – Cracks in Deck Underside
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
10 | P a ge
Photo No. 19 – Holes in Deck Underside
Photo No. 20 – Cracks in Pavement
Project Photos - Great Island Bridge Inspection
West Yarmouth, MA
Date: September 20, 2023
11 | P a ge
Photo No. 21 – Dilapidated Timber Guard Rail
GREAT ISLAND HOMEOWNER’S ASSOCIATION
BRIDGE CONDITIONS ASSESSMENT REPORT
Foth Infrastructure and Environment, LLC
49 Bellevue Avenue
Newport, Rhode Island
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
1
1. Executive Summary
This General Condition Report for the Great Island Bridge was prepared by Foth Infrastructure
and Environment (Foth) for the Great Island Homeowner’s Association (GIHA). The report reviews
the areas of concern of the Great Island Bridge and provides a comprehensive summary of the
July 10, 2019 inspection.
The analysis utilized a HS 20 vehicle loading (two 32 kip rear axles/one 16 kip front axle), and a
local Yarmouth fire apparatus. The analysis indicated that the steel beams are 60% stressed and the
concrete deck is 12% stressed during those loading conditions. This is acceptable for this type of
structure. This also assumes that the heavily deteriorated Beam No. 5 was reecapsulated, but not
repaired following the 2007 inspection report. No major repairs are recommended as a
result of this inspection.
Several minor maintenance tasks are recommended to extend the service life of the bridge such
as concrete crack repair and installing additional shims between the timber pile cap and concrete
bridge deck.
2. Observed Conditions/Analysis
The primary focus of the investigation was the underside of the concrete bridge deck. The 2007
inspection report noted severe deterioration observed on the exposed steel beams, especially
Beam No. 5. That particular steel beam had lost its concrete cover and due to the deterioration
of the steel and had ceased to perform any structural role which could be calculated/predicted.
Since the 2007 inspection report findings, the exposed Beam No. 5 has been overlaid with
grout/concrete and is no longer exposed (except for a small area shown in Photograph 2).
Additional loss of concrete (spalls) were observed below deck and are shown in Photographs 4
and 5 below.
The timber piles and 12x12 timber pile cap were found to be in Good condition with no observed
signs of overstressing. Additional capacity could be activated by installing additional shims
between the timber cap and concrete deck underside. Photograph 3 provides a view of the
present shims and their condition.
The stone/rubble revetments do not show evidence of displacement when compared to the 2007
report. While highly irregular, the stone abutments and wing walls continue to serve their
structural function. Loss of fine material through the abutments is the cause of the subsidence at
either end of the bridge (below the asphalt surface). Steel plates have been placed at the
approach to the concrete deck to alleviate this erosion issue and appear to be functioning well.
The steel railing was not analyzed as there were no observed condition issues and there is no
modern code which would consider them a barrier to vehicular traffic.
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
2
Photograph 1: Deteriorated condition of Beam No. 5 in 2007.
Photograph 2: Concrete patch at Beam No. 5 in 2019.
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
3
Photograph 3: Gap between timber cap and concrete deck and shims
Photograph 4: Spalled concrete with exposed steel
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
4
Photograph 5: Spalled concrete with exposed steel
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
5
Photograph 6: Steel railing/timber connection (not analyzed)
Photograph 7: West stone abutment
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
6
Photograph 8: East stone abutment
3. Recommendations
The bridge analysis found that the calculated stress levels of both the steel and the concrete are
within acceptable levels for this type of structure. The recommendations therefore are focused
on extending the service life of the bridge. The following items are recommended through 2024;
Recommended Action 2019-2020 (Short Term):
• Remove loose concrete and clean out cracks on the concrete deck underside
and seal with appropriate repair grout (such as a Five Star Marine Grout) and
coat exposed steel with a rust inhibitor.
• Install composite shims between the timber pile cap and concrete deck
underside.
Recommended Action before 2024 (Long Term):
• Monitor approachway erosion, including removing and inspecting beneath the
steel plate to determine if a large void is continuing to expand. If so the void
beneath the plate should be filled with a flowable fill excavatable mix.
• Perform an updated bridge inspection in 2024 (assuming the short term repairs
are completed).
Foth Infrastructure and Environment
Scott R. Skuncik, P.E.
Client Team Leader – Ports & Harbors
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
7
Bridge Calculations
Client: Great Island HA
Project: Bridge Evaluation
Prepared by: Alex I. Mora
Checked by:
Project ID: 17G312.1
Date: 31 July 2019
Date:
Great Island Homeowners
Association
Evaluation of existing bridge.
1. Analysis Description
Evaluate existing bridge for vehicular loads.
2. Standards
1. AASHTO LRFD Bridge Design Specifications, Seventh Edition, 2014
3. Defined Units
Calculations in this document will use U.S customary units.
Page 1 of 5
4. Loads and Load Combinations
Loads and load combinations shall be in compliance with AASHTO LRFD Bridge Design Specifications,
Seventh Edition, 2014.
EI.OKIP 3'WKIP 52.0 KIP
I Q '¥:J'•o" I
Fi iJR 3.6.[ .2:.2:-1 ha111ct iistics o,' the Uesig E'1.'Ulc!k
Page 2 of 5
.......
..............................
............................
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---------------
Page 3 of 5
5. Materials
Concrete: f'c ≔ 3000 psi
Ec ≔ 57000 ⋅ (f'c ⋅ psi) 0.
5
= 3122018.578 psi
Steel: fy ≔ 36000 psi
Es ≔ 29000000 psi
6. Section Properties
Steel Beams: W8x21
A ≔ 6.16 in2
d ≔ 8.28 in
bf ≔ 5.27 in
I ≔ 75.3 in4
7. Soil Structure Interaction
No soil structure interaction will be considered for this evaluation.
8. Analytical Model
The analysis will be performed by STAAD.Pro.
Page 4 of 5
9. Analysis Results
The structure was modeled according to the description provided by the inspection report dated June 15,
2007, prepared by Ocean and Coastal Consultants, Inc.
Beam #5 was not included in the model to account for its corrosion condition (80% section loss on
bottom flange).
Two trucks were used, an HS 20 (two 32kip rear axles/one 16 kip front axle) and a fire truck (two 30kip
rear axles/one 24kip front axle). Axle loads were applied to maximize stress in concrete and steel beams.
Analysis results indicate steel beams are 60% stressed, which is acceptable for this type of structure.
The concrete deck show overstressing of 12% (assuming 3000psi concrete). This overstress is considered
acceptable, as the analysis is preliminary and there is information that was not known, such as concrete
deck reinforcement.
The steel beams are currently encapsulated in concrete. A corrosion rate was not determined. The
analysis considers the steel beams with the full section (conservative).
Page 5 of 5
10. Calculations
The bridge will be analyzed as recommended by AASHTO, using a refined method of
analysis for "Bridge-Slab Bridges". (S=1.0)
There is one design lane.
The model was fabricated with plate elements, representing the concrete deck, and
steel beams.
Two vehicles were used as loading:
HS20 and Fire Truck
10.1 STAAD.Pro Output
The structure was modeled according to the description provided by the inspection report dated June 15,
2007, prepared by Ocean and Coastal Consultants, Inc.
Beam #5 was not included in the model to account for its corrosion condition (80% section loss on
bottom flange).
Two trucks were used, an HS 20 (two 32kip rear axles/one 16 kip front axle) and a fire truck (two 30kip
rear axles/one 24kip front axle). Axle loads were applied to maximize stress in concrete and steel beams.
Analysis results indicate steel beams are 60% stressed, which is acceptable for this type of structure.
The concrete deck show overstressing of 12% (assuming 3000psi concrete). This overstress is considered
acceptable, as the analysis is preliminary and there is information that was not known, such as concrete
deck reinforcement.
The steel beams are currently encapsulated in concrete. A corrosion rate was not determined. The
analysis considers the steel beams with the full section (conservative).
CONSULTANTS, INC.
Ocean and Coastal Consultants, Inc.
a COWi North America Company
50 Resnik Road, Suite 201
Plymouth, MA 02360
PH 508-830-1110 FX 508-830-1202
www.ocean-coastal.com
June 15, 2007
Patricia Lawrence
General Manager
Great Island Homeowners Association
1100 Great Island Road
West Yarmouth, MA 02673
RE: OCC 205107.2 - Great Island Bridge Load Rating
Dear Ms. Lawrence:
Ocean and Coastal Consultants, Inc. (OCC) is pleased to provide you with this letter report of
our load rating analysis on the Great Island Bridge. The purpose of this work was to determine
the safe operating capacity for the structure; provide an estimate of remaining service life; and
present recommendations for repair and/or replacement of the bridge.
Introduction
The bridge is located in the gated community of Great I sland in West Yarmouth, and carries
Great Island Road over the salt marsh and shallow tributary of Uncle Roberts Cove. The
tributary is tidal and flows under the bridge from south (flood) to north (ebb).
OCC inspected the bridge in 2006, and recommended structural repairs be performed to prevent
further deterioration and prolong the service life of the structure. The recommended repair s
included patching areas of spalled concrete and exposed steel in the bridge under side of the
deck, as well as grouting the riprap that forms the abutments and approach embankments.
It is our understanding that the Great Island Homeowner's Association (GIRA) has approached
contractors to perform repairs, and have received prices for the work on the order of $70,000.
Given the magnitude of these cost estimates for the repairs, the GIRA requested information to
explore options for replacement of the bridge. As a first step, GIRA engaged OCC to perform a
load rating analysis of the bridge to evaluate the remaining service life.
A team of two registered professional engineers from OCC visited the bridge on May 23, 2007 to
collect detailed measurements for the load rating analysis and further evaluate the conditions of the
stone embankments.
June 15, 2007
Page 2
Great Island Homeowners Association
Great Island Bridge Load Rating
OCEAN AND COASTAL CONSULTANTS, INC.
occ 205107.2
Structure Description
The structure is a single lane bridge, originally constructed prior to 1970 as a single span with a
clear opening of 16 feet - 8 inches. A timber bent with two (2), 12-inch diameter timber piles
and a 12x12 timber cap was instalJed in 1986 creating two (2) spans, each measuring
approximately 8 feet - 4 inches long.
From first observation, the bridge superstructure appears to be a 16-inch thick reinforced
concrete slab with an asphalt overlay. Based on information provided by the GIHA caretaker
and observations made by OCC, the concrete superstructure contains steel beams spaced at 12
inches on center parallel to the roadway centerline. The beams are designated as Beams #1
through #14 from north to south. The approximate locations of wheels (i.e. live loads) from
passing vehicles would therefore be directly over Beams #5 and #10.
All but one of the steel beams is completely encased in concrete and not accessible for direct
visual observation. A spall on the underside of the concrete deck along the complete length
of Beam #5 has exposed this member. Based on measurements of the bottom flange size and the
concrete thickness, OCC assumed that the steel beams are comparable in size to W8x2 l.
The fascia to fascia width of the structure is 14 feet - 4 inches with 9-inch wide concrete curbs
cast integrally with the bridge deck on each side. Four (4) 2-inch diameter steel pipes are cast
directly into the concrete curb to form the bridge railing system. The approach railing consists of
aesthetic timber split rail fence. All of this railing is not AASHTO crash-tested or rated for
vehicle impact. The bridge and approach railings should therefore be upgraded to an appropriate
highway railing system.
Both abutments consist of short concrete pedestal seats cast integrally with the superstructure
deck and bearing on a stacked stone foundation. The widths of these seats are assumed to be 2
feet. The foundation stones range in size from 1 foot to greater than 4 feet in diameter. The
stones are not pinned or grouted together.
The bridge is currently posted for an 8-ton axle limit.
Load Rating Assumptions and Results
• The load rating analysis was performed in accordance with the (American
Association of State Highway Transportation Officials (AASHTO) Standard
Specification for Highway Bridges 16th Edition, 1996.
• OCC assumed the beam sections are W8x2 l for the load rating analysis. The strength
of the concrete deck and beam encasement was not considered in the structural
analysis, unless otherwise noted.
• Based in the age of the structure (greater than 30 years), OCC assumed the yield
strength of the steel to be 33.0 ksi.
June 15, 2007
Page 3
Great Island Homeowners Association
Great Island Bridge Load Rating
OCEAN AND COASTAL CONSULTANTS, INC.
ace 2os101.2
• Based on the approximate wheel positions with respect to the steel beam locations. OCC
assumed that wheel loads are transferred directly to a single beam underneath each
wheel.
• As noted above, Beam #5 was exposed and heavily deteriorated (Photograph #1).
The section loss of the bottom flange at the north abutment was greate r than 80%.
OCC assumed that Beam #5 does not provide any load bearing capacity, and
therefore distributed the live load capacity of Beam #5 to the adjacent beams (#4 and
#6).
• The underside of the deck beneath Beam #10 exhibits cracks with rust staining, which
indicate that the beam is experiencing some level of deterioration (Photograph #2).
For the purposes of this analysis, OCC assumed that the encased beams had less than
30% loss of section.
• The load rating analysis was performed based on a standard AASHTO H-20/HS-20
highway vehicle with a maximum axle load of 16-tons. The rating was then determined
as a percentage of that standard highway loading. It should be noted that the standard
H-20/HS-20 highway vehicle is comparable to any large single or double axle
commercial or municipal vehicle (e.g. moving trucks, delivery trucks, construction
vehicles, fire trucks, etc.)
• Photographs #3 and #4 show areas where the embankment is losing fill due to
displacement of the stone, resulting in voids and undermining of the roadway surface.
Typical practice for load rating analysis only considers the condition of the bridge span, and not
the bridge foundation units. By visual examination, however, OCC believes that with proper
maintenance, the existing stone embankments and stone abutments are adequate to support the rated
load.
For the existing conditions observed and the assumptions listed above, OCC's structural analysis of
the bridge span indicates that the 8-ton per axle load currently posted at the bridge is satisfactory as
long as the timber bent is in place. Without the timber bent, the maximum load rating would be 4-
tons per axle. OCC's calculations are provided as an attachment to this report.
Repair Options
A discussion of options for repair and replacement of the bridge follows:
No Repair Option - The first option to consider is the "do nothing" alternative. The analysis
indicates that the bridge is still performing to its currently rated capacity. If repairs to the bridge
span and embankments are not performed, OCC recommends that the bridge be re-inspected at least
every 2 years until the bridge is rehabilitated or replaced. If the GIHA selects this option, it should
anticipate and prepare for the need to replace the bridge in 5 to 10 years.
June 15, 2007
Page 4
Great Island Homeowners Association
Great Island Bridge Load Rating
OCEAN AND COASTAL CONSULTANTS, INC.
occ 205107.2
Repair Option - Timely repairs to the bridge deck and embankments can increase the service
life of the structure another lo+ years at its current load capacity. The recommended span repairs
include the installation of reinforcement "staples" to form a structural connection across the cracks
along deteriorated Beams #5 and #10. Alternatively, a 1-inch thick steel road plate can be laid
across the top of the deck. The purpose of these repairs is to distribute wheel loads more efficiently
to the less deteriorated beams in the deck. It is important to note that these repairs will only
maintain the bridge at its present Load capacity, and will not increase the allowable loads over the
bridge.
The embankments should be repaired by removing and re-setting stones as needed to fill large voids
and maintain a stable slope. OCC recommends that the repaired stone embankments be grouted by
a qualified mason to form a veneer of cementitious-bonded aggregate armor that will minimize
maintenance and prolong the life of the abutments and the approach embankments. Sub-drains
and weep holes should be installed prior to grouting the stone, in order to provide drainage and
prevent the build-up of hydrostatic pressures behind or beneath the structure.
The design strength of the grout should be 2,000 to 2,500 psi. The grout should consist of a sand
or concrete mixture, with a maximum aggregate size of ¾-inch. The design slump should be
between 5 and 7 inches to allow proper pumping and placement into the voids between stones. Anti-
washout admixtures should be added to grout placed underwater at the abutment walls and the toe
of the embankments.
While extensive, the embankment repairs would provide a more stable substructure for the
bridge and would enable the deck span to be replaced much quicker, easier, and more cost
effectively when the time comes. In effect, the embankment rehabilitation would be the first
phase of bridge replacement, and could be performed without taking the bridge out of service.
Replacement Option - Because the bridge provides the only land access to and from the island,
its replacement should be planned well in advance of its necessity. Total replacement of the
bridge span and abutments will likely take several weeks to complete, and will require
construction of a temporary embankment and span adjacent to the existing structure to re-route
traffic during demolition and reconstruction of the new bridge.
Obviously, this will greatly increase the cost of the project as well as complicate the permitting
process, since all temporary and permanent construction will occur within the salt marsh
resource area. Total replacement will also require modifications to the bridge to bring it up to
current standards, including the addition of properly sized guide rails along the span and
approach embankments.
If the embankments are grouted as suggested in the Repair Option above, a bridge replacement
project may become much simpler and less costly to construct. Because the embankments would
already have been stabilized and repaired, the bridge span could be replaced in kind without
requiring significant modification to the embankments. The span could be pre-fabricated off site
and construction to remove the old span and replace it with the new one would only require the
bridge to be out of service for several hours, rather than weeks. This operation would also have
June 15, 2007 Great Island Homeowners Association
Page 5 Great Island Bridge Load Rating occ 205107.2
OCEAN AND COASTAL CONSULTANTS, INC.
the benefit of not requiring construction of a temporary span in the salt marsh, which would then
have to be restored after construction.
Permittine,
All construction for bridge repairs and/or replacement falls entirely within resource areas under
the jurisdiction of the Massachusetts Wetlands Protection Act. (M.G.L.c.131, §40) and is subject
to 310 CMR 10.00: Wetlands Regulations. The work would therefore require the GIHA to file a
Notice of Intent with the Yarmouth Conservation Commission, in order to receive an Order of
Conditions to permit the project. The Order of Conditions typically expires after a period of
three (3) years, and can be extended by the Conservation Commission on a case by case basis.
Because the bridge is an unlicensed structure, the GIHA will also need to obtain approval from
the Massachusetts Department of Environmental Protection to comply with the Massachusetts
Public Waterfront Act (M.G.L.c.91), which is regulated by 310CMR 9.00: Waterways
Regulations. Under the current regulations, the Chapter-91 license would expire after 30-years.
Due to the age of the existing structure however, the GIHA may be able to apply for amnesty
from the DEP to authorize the bridge. A 401 Water Quality Certificate from Mass. DEP is not
required, because the proposed project would not require any dredging, and involves less than
100 cubic yards of fill.
In addition, any work on the bridge is subject to federal regulation under Section 10 of the Rivers
and Harbors Act of 1899 (33 U.S.C. 403), and will need to file for either a Programmatic
General Permit (PGP) or an Individual Permit, depending on the scope of work.
The GIHA should be aware that the local, state and federal permit process can take several months
to a few years to complete, and take this into account when planning for the repairs or replacement.
Bud2etary Costs for Construction
The table below provides budgetary costs for the recommended repairs to replace the bridge .
The costs presented are illustrative only, and do not include costs associated with engineering
design; permitting; contractor mobilization/demobilization; and other miscellaneous costs such
as topographic surveys, site restoration, or debris disposal.
Repair Item Typical Unit Cost
Estimated
Quantity
Extended
Cost
1. Embankment Repairs and Grout $1,000/CY 80CY $80,000
2. Pre-cast Concrete Bridoe Span $65/SF 280 SF $18,200
3. Timber Guide Rail $30/LF 400 LF $12,000
4. Timber Bridae Rail $75/LF 40 LF $3,000
Totals $102,400
Notes:
• Unit costs provided are typical for the item in-place, including contractor's labor,
materials, equipment, profit and overhead. Costs exclude contractor
mobilization and demobilization; demolition and disposal; and site restoration.
June 15, 2007 Great Island Homeowners Association
Page 6 Great Island Bridge Load Rating occ 205107.2
OCEAN AND COASTAL CONSULTANTS, INC.
Conclusions and Recommendations
At present, the Great Island Bridge is in fair to satisfactory condition for the posted load of 8-
tons/axle. Based on our observations of the existing conditions, we estimate that the bridge has a
.,,temaining service life of approximately 5 to 10 years unless major repairs are completed, as
discussed above.
Although OCC agrees that the bridge is adequate for its currently posted limits, we must
emphasize that the 8-ton per axle rating is less than that permitted by AASHTO design vehicle
designation H-20/HS-20, which typically has a maximum axle load of 16-tons. As such, these
heavy vehicles should not be allowed to cross the bridge.
OCC strongly recommends that the existing split rail fences along the bridge approaches and the
handrails across the bridge be replaced with properly designed timber or steel guide rails for
safety.
In addition, OCC recommends that the bridge be re-inspected at 2-year intervals (maximum)
until the recommended repairs to the deck and embankments are completed. The purpose of
these inspections is to monitor the deterioration and identify any additional repairs that may be
required to ensure the safety of the structure.
OCC further recommends that the GIHA plan to replace the bridge in 5 to 10 years. As
discussed above, the bridge reconstruction could take place in two phases including 1)
reconstruction and grouting of the embankments, and 2) replacement of the deteriorated bridge
span in-kind.
Very truly yours,
OCEAN AND COASTAL CONSULTANTS, INC.
Bryan N. Jones, P.E.
Project Manager/Office Manager
M:\PROJECTS\205107.2 Great Island Bridge Load Rating\Task 2 - Load Rating and Permit Analysis\20070615 Load Roting Report.doc
Great Island Homeowners Association June 15, 2007
Great Island Bridge Load Rating Page 7 occ 205107.2
OCEAN AND COASTAL CONSULTANTS, INC.
Photograph 1: View of spalled concrete under deck and deterioration of exposed Beam #5
Photograph 2: View of cracks and rust stains under Beam # l0, indicating some deterioration underneath.
Great Island Homeowners Association June 15, 2007
Great Island Bridge Load Rating Page 8 occ 205107.2
OCEAN AND COASTAL CONSULTANTS, INC.
Photograph 3: Typical undermining of the roadway surface above the bridge embankments.
Photograph 4: Small sinkhole at the west abutment, indicating a loss of fill through the stone embankment.
7
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I 96 00 8,00 \_5_00· AERIAL INLET ' NFPA M
ClJ HANNAY ELECTRIC REWIND CORO REEL \_ LJ LJ I STABILIZER CONTROLS
---2a.50----25.5□----2a.so----2s.so- 1518-17-18 WITH 200' OF 10/3 CABLE WITH SMOOTH ALUMINUM WITH CAPTIVE ROLLER ASSEMBLY
2o.o---- -- - 52. 00 ----1.50 J_ DOOR
70.00 123.50 104.50 FRAME CUTOFF 5 oo.=--
97.00 257. 00 WB ................................................................................................................ 152. 50
561.25 C46'-9.25WJ APPROX OAL
CHASSIS
VeLoe i ty Chass Is CBI g Block)
E N G I N E
505 HP Cummins X15
CAB
7010 Notched Velocity FR Cab
BUMPER
19w Extended Stainless Steel
A X L E , F R O N T , C U S T O M
24,000 Lb TAK-4 Axle
A X L E , R E A R
60,000 Lb Meritor Axle
T R A N S M I S S I O N
Allison 5th Gen, 4000 EVS P
PUMPHOUSE
52" Control Zone Side Mount
P UM P
1500 GPM Waterous CSU
CROSS LAYS, 1 o 50"
C2l 1,so" Standard Capac It
CROSS LAYS, 1 o 50"
2.50" Crossla Not Required
S P E E D L A Y S
Speedla s Not Required
G E N E R A T O R
Harrison 1Ok MAS-0 H drau Li c
SAFETY
Side Roll and
F r o n t a 1 I m p a c t P r o t e c t i o n
U T L
u TU JOB NOo 32594
APPROVED BY:
DATE
SCALE
I ,24 DATE
NOTE
DIMENSIONS SHOWN ARE APPROXIMATE
AND ARE SUBJECT TO MINOR DEVIATIONS
AS MAY OCCUR OR BE NECESSARY IN
CONSTRUCTION,
MINOR DETAILS NOT SHOWN,
1. ONE 1.50 OUTLET WITH 2.00 PIPING AND SWIVEL LOCATED IN CENTER BUMPER TRAY 11. AIR OUTLET WITH SHUT OFF VALVE LOCATED AT DRIVERS SIDE PUMP PANEL 21. ONE RECEPTACLE 120V WOODHEAD LOCATED TBD
2. SHORELINE RECEPTACLE WITH KUSSMAUL SUPER AUTO-EJECT LOCATED ON DRIVER SIDE OF THE CAB 12. S/STL DRIP PAN/GUARD FOR ROLL-UP DOOR LOCATEDPER SHOP ORDER 22. TWO CHECKERS ROADBLOCKS WHEEL CHOCKS LOCATED TBD
3. AIR INLET WITH DISCONNECT COUPLING IN THE DRIVER SIDE PUMP PANEL 13. TWO ALUMINUM SWING-OUT TOOLBOARD WITH PAC TRAC IN COMPARTMENTS PER SHOP ORDER
. BATTERY CHARGER LOCATED IN COMPARTMENT PER SHOP ORDER 14. PAC TRAC ON THE REAR WALL OF COMPARTMENTS PER SHOP ORDER
5. BATTERY CHARGE INDICATOR LOCATED NEAR DRIVER SEAT RISER WITH BRACKET 15. CIRCUIT BREAKERPANEL IN COMPARTMENTS PER SHOP ORDER MAXIMUM OVERALL HEIGHT= 143,00 Cll'-ll"l 6. NINE ADJUSTABLE SHELVES IN COMPARTMENTS PER SHOP ORDER 16. HOSE STORAGE BOX ON BOTH SIDE OF BASKET FOR 150' OF I .75' D.J. POLY HOSE
7. FOUR FLOOR MOUNTED SLIDE-OUT TRAY IN COMPARTMENT PER SHOP ORDER 17. L.E.D. LIGHTING ON AERIAL LADDER SECTIONS
8. 3.oo· RA!SED AERIAL PEDESTAL 18. 3-WAY INTERCOM SYSTEM BETWEEN PLATFORM,PUMP PANEL & TURNTABLE
9. 3-in-l LYFECOMBO BRACKETS AT AERIAL BASKET 19. BREATHING AIR TO AERIAL BASKET
10. 120V POWER TO AERl AL BASKET 20. NO LIMITED RETRACTION
CHASSIS
DATA TITLE 100 AERIAL PLATFORM & BODY ASSEMBLY DRAWN BY
LWE OIMAYIB
MAKE
PIERCE FOR CITY OF TUCSON
TUCSON, AZ
CHECKED BY
GRM IOMAYIB w
MODEL
VELOCITY
DWG
NO, 32694AD SHEET SIZE D SHEET NO.
1 OF 1 REV DATE BY CH
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 1 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
1
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Job Information
Structure Type SPACE FRAME
Included in this printout are data for:
All The Whole Structure
Included in this printout are results for load cases:
Reaction Summary
Engineer Checked Approved
Name: Alex I. Mora
Date: 7/31/2019
Project ID
Project Name
Number of Nodes 274 Highest Node 274
Number of Elements 242 Highest Beam 497
Number of Plates 238 Highest Plate 493
Number of Basic Load Cases 9
Number of Combination Load Cases 7
Type L/C Name
Combination 8 1.25(DC+DD)+1.75*IM*HS20 1
Combination 9 1.25(DC+DD)+1.75*IM*HS20 2
Combination 10 1.25(DC+DD)+1.75*IM*HS20 3
Combination 11 1.25(DC+DD)+1.75*IM*HS20 4
Combination 12 1.25(DC+DD)+1.75*IM*LIVE
Combination 15 1.25(DC+DD)+1.75*IM*FT 1
Combination 16 1.25(DC+DD)+1.75*IM*FT 2
Horizontal Vertical Horizontal Moment
Node L/C FX
(kip)
FY
(kip)
FZ
(kip)
MX
(kip-ft)
MY
(kip-ft)
MZ
(kip-ft)
Max FX 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Min FX 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Max FY 217 15:1.25(DC+D 0 52.196 0 0 0 0
Min FY 18 16:1.25(DC+D 0 -17.510 0 0 0 0
Max FZ 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Min FZ 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Max MX 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Min MX 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Max MY 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Min MY 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Max MZ 1 8:1.25(DC+DD 0 0.066 0 0 0 0
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 2 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
2
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
1 W8X21 W8X21 67562 1.000 0.067562 Cl.G1 16 6.160 75.300 9.770 0.2 82
2 W8X21 W8X21 0.134 1.000 0.134 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
3 W8X21 W8X21 0.220 1.000 0.220 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
4 W8X21 W8X21 0.288 1.000 0.288 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
5 W8X21 W8X21 0.344 1.000 0.344 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
6 W8X21 W8X21 0.388 1.000 0.388 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
7 W8X21 W8X21 0.419 1.000 0.419 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
8 W8X21 W8X21 0.437 1.000 0.437 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
9 W8X21 W8X21 0.441 1.000 0.441 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
10 W8X21 W8X21 0.437 1.000 0.437 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
11 W8X21 W8X21 0.419 1.000 0.419 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
12 W8X21 W8X21 0.388 1.000 0.388 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
13 W8X21 W8X21 0.344 1.000 0.344 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
14 W8X21 W8X21 0.288 1.000 0.288 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
15 W8X21 W8X21 0.220 1.000 0.220 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
16 W8X21 W8X21 0.134 1.000 0.134 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
17 W8X21 W8X21 0.068 1.000 0.068 Cl.G1 16 6.160 75.300 9.770 0.2 82
18 W8X21 W8X21 0.128 1.000 0.128 Cl.G1 12 6.160 75.300 9.770 0.2 82
19 W8X21 W8X21 0.178 1.000 0.178 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
20 W8X21 W8X21 0.253 1.000 0.253 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
21 W8X21 W8X21 0.317 1.000 0.317 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
22 W8X21 W8X21 0.368 1.000 0.368 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
23 W8X21 W8X21 0.407 1.000 0.407 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
24 W8X21 W8X21 0.433 1.000 0.433 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
25 W8X21 W8X21 0.445 1.000 0.445 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
26 W8X21 W8X21 0.444 1.000 0.444 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
27 W8X21 W8X21 0.445 1.000 0.445 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
28 W8X21 W8X21 0.433 1.000 0.433 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
29 W8X21 W8X21 0.407 1.000 0.407 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
30 W8X21 W8X21 0.368 1.000 0.368 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
31 W8X21 W8X21 0.317 1.000 0.317 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
32 W8X21 W8X21 0.253 1.000 0.253 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
33 W8X21 W8X21 0.178 1.000 0.178 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
34 W8X21 W8X21 0.128 1.000 0.128 Cl.G1 12 6.160 75.300 9.770 0.2 82
35 W8X21 W8X21 0.072 1.000 0.072 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
36 W8X21 W8X21 0.165 1.000 0.165 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
37 W8X21 W8X21 0.244 1.000 0.244 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
38 W8X21 W8X21 0.315 1.000 0.315 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
39 W8X21 W8X21 0.373 1.000 0.373 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
40 W8X21 W8X21 0.419 1.000 0.419 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
41 W8X21 W8X21 0.451 1.000 0.451 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
42 W8X21 W8X21 0.470 1.000 0.470 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
43 W8X21 W8X21 0.475 1.000 0.475 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
44 W8X21 W8X21 0.470 1.000 0.470 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
45 W8X21 W8X21 0.451 1.000 0.451 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 3 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
3
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio Cont...
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
46 W8X21 W8X21 0.419 1.000 0.419 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
47 W8X21 W8X21 0.373 1.000 0.373 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
48 W8X21 W8X21 0.315 1.000 0.315 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
49 W8X21 W8X21 0.244 1.000 0.244 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
50 W8X21 W8X21 0.165 1.000 0.165 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
51 W8X21 W8X21 72041 1.000 0.072041 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
52 W8X21 W8X21 0.089 1.000 0.089 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
53 W8X21 W8X21 0.197 1.000 0.197 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
54 W8X21 W8X21 0.288 1.000 0.288 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
55 W8X21 W8X21 0.361 1.000 0.361 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
56 W8X21 W8X21 0.420 1.000 0.420 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
57 W8X21 W8X21 0.465 1.000 0.465 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
58 W8X21 W8X21 0.496 1.000 0.496 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
59 W8X21 W8X21 0.513 1.000 0.513 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
60 W8X21 W8X21 0.517 1.000 0.517 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
61 W8X21 W8X21 0.513 1.000 0.513 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
62 W8X21 W8X21 0.496 1.000 0.496 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
63 W8X21 W8X21 0.465 1.000 0.465 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
64 W8X21 W8X21 0.420 1.000 0.420 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
65 W8X21 W8X21 0.361 1.000 0.361 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
66 W8X21 W8X21 0.288 1.000 0.288 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
67 W8X21 W8X21 0.197 1.000 0.197 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
68 W8X21 W8X21 0.089 1.000 0.089 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
69 W8X21 W8X21 0.082 1.000 0.082 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
70 W8X21 W8X21 0.185 1.000 0.185 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
71 W8X21 W8X21 0.270 1.000 0.270 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
72 W8X21 W8X21 0.341 1.000 0.341 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
73 W8X21 W8X21 0.398 1.000 0.398 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
74 W8X21 W8X21 0.443 1.000 0.443 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
75 W8X21 W8X21 0.474 1.000 0.474 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
76 W8X21 W8X21 0.492 1.000 0.492 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
77 W8X21 W8X21 0.496 1.000 0.496 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
78 W8X21 W8X21 0.492 1.000 0.492 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
79 W8X21 W8X21 0.474 1.000 0.474 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
80 W8X21 W8X21 0.443 1.000 0.443 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
81 W8X21 W8X21 0.398 1.000 0.398 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
82 W8X21 W8X21 0.341 1.000 0.341 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
83 W8X21 W8X21 0.270 1.000 0.270 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
84 W8X21 W8X21 0.185 1.000 0.185 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
85 W8X21 W8X21 0.082 1.000 0.082 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
86 W8X21 W8X21 0.094 1.000 0.094 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
87 W8X21 W8X21 0.207 1.000 0.207 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
88 W8X21 W8X21 0.301 1.000 0.301 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
89 W8X21 W8X21 0.378 1.000 0.378 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
90 W8X21 W8X21 0.438 1.000 0.438 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 4 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
4
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio Cont...
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
91 W8X21 W8X21 0.483 1.000 0.483 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
92 W8X21 W8X21 0.514 1.000 0.514 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
93 W8X21 W8X21 0.531 1.000 0.531 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
94 W8X21 W8X21 0.535 1.000 0.535 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
95 W8X21 W8X21 0.531 1.000 0.531 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
96 W8X21 W8X21 0.514 1.000 0.514 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
97 W8X21 W8X21 0.483 1.000 0.483 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
98 W8X21 W8X21 0.438 1.000 0.438 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
99 W8X21 W8X21 0.378 1.000 0.378 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
100 W8X21 W8X21 0.301 1.000 0.301 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
101 W8X21 W8X21 0.207 1.000 0.207 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
102 W8X21 W8X21 0.094 1.000 0.094 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
103 W8X21 W8X21 0.102 1.000 0.102 Cl.F2.1 11 6.160 75.300 9.770 0.2 82
104 W8X21 W8X21 0.567 1.000 0.567 Cl.G1 11 6.160 75.300 9.770 0.2 82
105 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
106 W8X21 W8X21 0.388 1.000 0.388 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
107 W8X21 W8X21 0.449 1.000 0.449 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
108 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
109 W8X21 W8X21 0.526 1.000 0.526 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
110 W8X21 W8X21 0.543 1.000 0.543 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
111 W8X21 W8X21 0.548 1.000 0.548 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
112 W8X21 W8X21 0.543 1.000 0.543 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
113 W8X21 W8X21 0.526 1.000 0.526 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
114 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
115 W8X21 W8X21 0.449 1.000 0.449 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
116 W8X21 W8X21 0.388 1.000 0.388 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
117 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
118 W8X21 W8X21 0.530 1.000 0.530 Cl.G1 11 6.160 75.300 9.770 0.2 82
119 W8X21 W8X21 0.102 1.000 0.102 Cl.F2.1 11 6.160 75.300 9.770 0.2 82
120 W8X21 W8X21 0.099 1.000 0.099 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
121 W8X21 W8X21 0.217 1.000 0.217 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
122 W8X21 W8X21 0.314 1.000 0.314 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
123 W8X21 W8X21 0.392 1.000 0.392 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
124 W8X21 W8X21 0.453 1.000 0.453 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
125 W8X21 W8X21 0.499 1.000 0.499 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
126 W8X21 W8X21 0.530 1.000 0.530 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
127 W8X21 W8X21 0.547 1.000 0.547 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
128 W8X21 W8X21 0.551 1.000 0.551 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
129 W8X21 W8X21 0.547 1.000 0.547 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
130 W8X21 W8X21 0.530 1.000 0.530 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
131 W8X21 W8X21 0.499 1.000 0.499 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
132 W8X21 W8X21 0.453 1.000 0.453 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
133 W8X21 W8X21 0.392 1.000 0.392 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
134 W8X21 W8X21 0.314 1.000 0.314 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
135 W8X21 W8X21 0.217 1.000 0.217 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 5 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
5
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio Cont...
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
136 W8X21 W8X21 0.099 1.000 0.099 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
137 W8X21 W8X21 0.099 1.000 0.099 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
138 W8X21 W8X21 0.217 1.000 0.217 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
139 W8X21 W8X21 0.315 1.000 0.315 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
140 W8X21 W8X21 0.393 1.000 0.393 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
141 W8X21 W8X21 0.455 1.000 0.455 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
142 W8X21 W8X21 0.501 1.000 0.501 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
143 W8X21 W8X21 0.532 1.000 0.532 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
144 W8X21 W8X21 0.549 1.000 0.549 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
145 W8X21 W8X21 0.553 1.000 0.553 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
146 W8X21 W8X21 0.549 1.000 0.549 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
147 W8X21 W8X21 0.532 1.000 0.532 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
148 W8X21 W8X21 0.501 1.000 0.501 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
149 W8X21 W8X21 0.455 1.000 0.455 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
150 W8X21 W8X21 0.394 1.000 0.394 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
151 W8X21 W8X21 0.315 1.000 0.315 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
152 W8X21 W8X21 0.217 1.000 0.217 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
153 W8X21 W8X21 0.099 1.000 0.099 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
154 W8X21 W8X21 0.100 1.000 0.100 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
155 W8X21 W8X21 0.215 1.000 0.215 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
156 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
157 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
158 W8X21 W8X21 0.445 1.000 0.445 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
159 W8X21 W8X21 0.490 1.000 0.490 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
160 W8X21 W8X21 0.521 1.000 0.521 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
161 W8X21 W8X21 0.538 1.000 0.538 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
162 W8X21 W8X21 0.542 1.000 0.542 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
163 W8X21 W8X21 0.538 1.000 0.538 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
164 W8X21 W8X21 0.521 1.000 0.521 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
165 W8X21 W8X21 0.490 1.000 0.490 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
166 W8X21 W8X21 0.445 1.000 0.445 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
167 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
168 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
169 W8X21 W8X21 0.215 1.000 0.215 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
170 W8X21 W8X21 0.100 1.000 0.100 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
188 W8X21 W8X21 88648 1.000 0.088648 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
189 W8X21 W8X21 0.195 1.000 0.195 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
190 W8X21 W8X21 0.281 1.000 0.281 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
191 W8X21 W8X21 0.353 1.000 0.353 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
192 W8X21 W8X21 0.411 1.000 0.411 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
193 W8X21 W8X21 0.463 1.000 0.463 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
194 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
195 W8X21 W8X21 0.504 1.000 0.504 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
196 W8X21 W8X21 0.508 1.000 0.508 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
197 W8X21 W8X21 0.504 1.000 0.504 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 6 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
6
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio Cont...
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
198 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
199 W8X21 W8X21 0.463 1.000 0.463 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
200 W8X21 W8X21 0.411 1.000 0.411 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
201 W8X21 W8X21 0.353 1.000 0.353 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
202 W8X21 W8X21 0.281 1.000 0.281 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
203 W8X21 W8X21 0.195 1.000 0.195 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
204 W8X21 W8X21 0.089 1.000 0.089 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
205 W8X21 W8X21 0.090 1.000 0.090 Cl.F2.1 11 6.160 75.300 9.770 0.2 82
206 W8X21 W8X21 0.565 1.000 0.565 Cl.G1 11 6.160 75.300 9.770 0.2 82
207 W8X21 W8X21 0.254 1.000 0.254 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
208 W8X21 W8X21 0.326 1.000 0.326 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
209 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
210 W8X21 W8X21 0.515 1.000 0.515 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
211 W8X21 W8X21 0.539 1.000 0.539 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
212 W8X21 W8X21 0.484 1.000 0.484 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
213 W8X21 W8X21 0.489 1.000 0.489 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
214 W8X21 W8X21 0.484 1.000 0.484 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
215 W8X21 W8X21 0.539 1.000 0.539 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
216 W8X21 W8X21 0.515 1.000 0.515 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
217 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
218 W8X21 W8X21 0.326 1.000 0.326 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
219 W8X21 W8X21 0.270 1.000 0.270 Cl.F2.1 10 6.160 75.300 9.770 0.2 82
220 W8X21 W8X21 0.531 1.000 0.531 Cl.G1 11 6.160 75.300 9.770 0.2 82
221 W8X21 W8X21 0.090 1.000 0.090 Cl.F2.1 11 6.160 75.300 9.770 0.2 82
222 W8X21 W8X21 0.128 1.000 0.128 Cl.G1 12 6.160 75.300 9.770 0.2 82
223 W8X21 W8X21 0.183 1.000 0.183 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
224 W8X21 W8X21 0.261 1.000 0.261 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
225 W8X21 W8X21 0.327 1.000 0.327 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
226 W8X21 W8X21 0.389 1.000 0.389 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
227 W8X21 W8X21 0.454 1.000 0.454 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
228 W8X21 W8X21 0.485 1.000 0.485 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
229 W8X21 W8X21 0.489 1.000 0.489 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
230 W8X21 W8X21 0.489 1.000 0.489 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
231 W8X21 W8X21 0.489 1.000 0.489 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
232 W8X21 W8X21 0.485 1.000 0.485 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
233 W8X21 W8X21 0.454 1.000 0.454 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
234 W8X21 W8X21 0.389 1.000 0.389 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
235 W8X21 W8X21 0.327 1.000 0.327 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
236 W8X21 W8X21 0.261 1.000 0.261 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
237 W8X21 W8X21 0.183 1.000 0.183 Cl.F2.1 12 6.160 75.300 9.770 0.2 82
238 W8X21 W8X21 0.128 1.000 0.128 Cl.G1 12 6.160 75.300 9.770 0.2 82
239 W8X21 W8X21 72472 1.000 0.072472 Cl.G1 16 6.160 75.300 9.770 0.2 82
240 W8X21 W8X21 0.152 1.000 0.152 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
241 W8X21 W8X21 0.233 1.000 0.233 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
242 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:51 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 7 of 7
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
7
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Utilization Ratio Cont...
Beam Analysis
Property
Design
Property
Actual Allowable Ratio Clause L/C Ax
(in2)
Iz
(in4)
Iy
(in4)
Ix
(in4)
Ratio Ratio (Act./Allow.)
243 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
244 W8X21 W8X21 0.448 1.000 0.448 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
245 W8X21 W8X21 0.484 1.000 0.484 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
246 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
247 W8X21 W8X21 0.491 1.000 0.491 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
248 W8X21 W8X21 0.495 1.000 0.495 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
249 W8X21 W8X21 0.484 1.000 0.484 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
250 W8X21 W8X21 0.448 1.000 0.448 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
251 W8X21 W8X21 0.386 1.000 0.386 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
252 W8X21 W8X21 0.310 1.000 0.310 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
253 W8X21 W8X21 0.233 1.000 0.233 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
254 W8X21 W8X21 0.152 1.000 0.152 Cl.F2.1 16 6.160 75.300 9.770 0.2 82
255 W8X21 W8X21 0.072 1.000 0.072 Cl.G1 16 6.160 75.300 9.770 0.2 82
494 W8X21 W8X21 0.531 1.000 0.531 Cl.G1 11 6.160 75.300 9.770 0.2 82
495 W8X21 W8X21 0.565 1.000 0.565 Cl.G1 11 6.160 75.300 9.770 0.2 82
496 W8X21 W8X21 0.530 1.000 0.530 Cl.G1 11 6.160 75.300 9.770 0.2 82
497 W8X21 W8X21 0.567 1.000 0.567 Cl.G1 11 6.160 75.300 9.770 0.2 82
Print Time/Date: 31/07/2019 13:58 STAAD.Pro CONNECT Edition 21.03.00.146 Print Run 1 of 1
Software licensed to Green Bay
CONNECTED User: Alex Mora
Job No
17G312.1
Sheet No
1
Rev
Part
Job Title Great Island HA Bridge Ref
By Alex I. Mora Date7/31/2019 Chd
Client Great Island HA File Bridge Deck 2.STD Date/Time 31-Jul-2019 13:38
Job Information
Structure Type SPACE FRAME
Included in this printout are data for:
All The Whole Structure
Included in this printout are results for load cases:
Plate Center Principal Stress Summary
Engineer Checked Approved
Name: Alex I. Mora
Date: 7/31/2019
Project ID
Project Name
Number of Nodes 274 Highest Node 274
Number of Elements 242 Highest Beam 497
Number of Plates 238 Highest Plate 493
Number of Basic Load Cases 9
Number of Combination Load Cases 7
Type L/C Name
Combination 8 1.25(DC+DD)+1.75*IM*HS20 1
Combination 9 1.25(DC+DD)+1.75*IM*HS20 2
Combination 10 1.25(DC+DD)+1.75*IM*HS20 3
Combination 11 1.25(DC+DD)+1.75*IM*HS20 4
Combination 12 1.25(DC+DD)+1.75*IM*LIVE
Combination 15 1.25(DC+DD)+1.75*IM*FT 1
Combination 16 1.25(DC+DD)+1.75*IM*FT 2
Principal Von Mis Tresca
Plate L/C Top
(ksi)
Bottom
(ksi)
Top
(ksi)
Bottom
(ksi)
Top
(ksi)
Bottom
(ksi)
Max (t) 485 16:1.25(DC+D 3.372 -0.055 3.345 3.345 3.372 3.372
Max (b) 383 12:1.25(DC+D 2.097 -1.187 1.821 1.821 2.097 2.097
Max VM (t) 485 16:1.25(DC+D 3.372 -0.055 3.345 3.345 3.372 3.372
Max VM (b) 485 16:1.25(DC+D 3.372 -0.055 3.345 3.345 3.372 3.372
Tresca (t) 485 16:1.25(DC+D 3.372 -0.055 3.345 3.345 3.372 3.372
Tresca (b) 485 16:1.25(DC+D 3.372 -0.055 3.345 3.345 3.372 3.372
Great Island Bridge
Inspection Summary
Foth Project No. 0017G312.10
Bridge Historic Plan Data
8
GREAT ISLAND HOMEOWNERS ASSOCIATION
2019 BRIDGE INSPECTION
WEST HYANNSPORT
WEST YARMOUTH
LEWIS BAY
SITE
GREAT ISLAND
NANTUCKET SOUND
LOCATION MAP VICINITY MAP
DRAWING INDEX
SHEET NUMBER TITLE
1 COVER SHEET AND DRAWING INDEX
2 SITE PLAN
3 SECTIONS (1 OF 2)
4 SECTIONS (2 OF 2)
GREAT ISLAND BRIDGE INSPECTION
GREAT ISLAND HOMEOWNERS ASSOCIATION
1100 GREAT ISLAND RD, WEST YARMOUTH, MA
SCALE: AS NOTED
Date: AUGUST 13, 2019
Revision Date:
UNCLE ROBERTS
COVE
SITE
GREAT ISLAND
Drawn By: MGB Checked By: TM/CF Project: 0017G312
GREAT ISLAND BRIDGE INSPECTION
GREAT ISLAND HOMEOWNERS ASSOCIATION
1100 GREAT ISLAND RD, WEST YARMOUTH, MA
0' 15' 30'
Date:
AUGUST 13, 2019
Revision Date:
BAR SCALE Drawn By: MGB Checked By: TM/CF Project: 0017G312
EXISTING BRIDGE CROSS SECTION A
SCALE: 1" = 4'
DETAIL A
GREAT ISLAND BRIDGE INSPECTION
GREAT ISLAND HOMEOWNERS ASSOCIATION
1100 GREAT ISLAND RD, WEST YARMOUTH, MA
SCALE: 1" = 4'
0' 4' 8'
Date:
AUGUST 13, 2019
Revision Date:
BAR SCALE
Drawn By: MGB Checked By: TM/CF Project: 0017G312
CROSS SECTION B
SCALE: 1" = 4'
STRUCTURAL BEAM LAYOUT
SCALE: 1" = 4'
0' 4' 8'
GREAT ISLAND BRIDGE INSPECTION
GREAT ISLAND HOMEOWNERS ASSOCIATION
1100 GREAT ISLAND RD, WEST YARMOUTH, MA
Revision Date: Date: AUGUST 13, 2019
BAR SCALE
Drawn By: MGB Checked By: TM/CF Project: 0017G312
Great Island Bridge Inspection Memorandum - Mr. Craig Flemmings
June 28, 2024
Page 8 of 6
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Attachment B
Bridge Inspection Photographs
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Bridge Inspection Photographs
Photo 1: Bridge Approach Looking East
Photo 2: Bridge Approach Looking West
Photo 3: Bridge Profile Looking South
Photo 4: Bridge Profile Looking North
Photo 5: Transverse Cracks at the Bridge Limits
Photo 6: Repaired Wood Fence Along Eastern Bridge Approach
Photo 7: Deteriorating Patch Encasing Beam No. 5
Photo 8: Cracks, Rust and Efflorescence on Patch Encasing Beam No. 1
Photo 9: Mortar Loss Between the Deck and East Abutment
Photo 10: Voids in East Stone Abutment
Photo 11: Damaged Steps Along Bridge Approach
Photo 12: Shims Exhibiting Rot
Photo 13: Saturation Line and Marine Growth on the Timber Piles and Pile Cap
Photo 14: Out of Plumb Timber Pile
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 1: Bridge Approach Looking East
Photo 2: Bridge Approach Looking West
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 3: Bridge Profile Looking South
Photo 4: Bridge Profile Looking North
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 5: Transverse Cracks at the Bridge Limits
Photo 6: Repaired Wood Fence Along Eastern Bridge Approach
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 7: Deteriorating Patch Encasing Beam No. 5
Photo 8: Cracks, Rust and Efflorescence on Patch Encasing Beam No. 1
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 9: Mortar Loss Between the Deck and East Abutment
Photo 10: Voids in East Stone Abutment
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 11: Damaged Steps Along Bridge Approach Embankment
Photo 12: Shims Exhibiting Rot
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Photo 13:Saturation Line and Marine Growth on the Timber Piles and Pile Cap
Photo 14: Out of Plumb Timber Pile
F:\P2023\0674\A10\Working\Inspection\20230674.A10 GIHA Bridge Inspection Memo_NW Rev 20240904.docx
Attachment C
Bridge Inspection Drawings
108 MYRTLE STREET, SUITE 502
QUINCY, MA 02171
617.282.4675
www.fando.com
SEAL SCALE:
DATUM:
VERT.:
HORZ.:
VERT.:
HORZ.:
PROJ. No.:
DATE:
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NOT TO SCALE
-
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DATENo. DESCRIPTION DESIGNER REVIEWER
FIG. 1
20230674.A10
JUNE 2024GREAT ISLAND HOMEOWNERS ASSOCIATION
BRIDGE AND APPROACH INSPECTION
GREAT ISLAND ROAD
YARMOUTH MASSACHUSETTS
108 MYRTLE STREET, SUITE 502
QUINCY, MA 02171
617.282.4675
www.fando.com
SEAL SCALE:
DATUM:
VERT.:
HORZ.:
VERT.:
HORZ.:
PROJ. No.:
DATE:
MS
V
I
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W
:
LA
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SBI-02
20230674.A10
JUNE 2024GREAT ISLAND HOMEOWNERS ASSOCIATION
LONGITUDINAL DECK AND HYDRAULIC SECTION
INSPECTION
GREAT ISLAND ROAD
YARMOUTH MASSACHUSETTS
NOT TO SCALE
108 MYRTLE STREET, SUITE 502
QUINCY, MA 02171
617.282.4675
www.fando.com
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SBI-03
20230674.A10
JUNE 2024GREAT ISLAND HOMEOWNERS ASSOCIATION
DECK SECTION AND UNDERSIDE INSPECTION
GREAT ISLAND ROAD
YARMOUTH MASSACHUSETTS
NOT TO SCALE
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association J-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX J. APPROXIMATE LOCATION OF BURIED UTILITIES
NORTH
Approximate Location of Buried Utilities
Great Island Homeowners Association
June 2024
Notes
1. Utility mapping (buried electrical and communication
conduits depicted in red) shown hereon was
provided by Eversource to GIHA as a series of
panels not georeferenced to a horizontal datum.
2. Mapping panels were aligned, digitized and overlain
on GIS parcel and aerial mapping.
Figure 1 of 3
Not to Scale
NORTH
Approximate Location of Buried Utilities
Great Island Homeowners Association
June 2024
Figure 2 of 3
Not to Scale
Notes
1. Utility mapping (buried electrical and communication
conduits depicted in red) shown hereon was
provided by Eversource to GIHA as a series of
panels not georeferenced to a horizontal datum.
2. Mapping panels were aligned, digitized and overlain
on GIS parcel and aerial mapping.
NO
R
T
H
Approximate Location of Buried Utilities
Great Island Homeowners Association
June 2024
Figure 3 of 3
Not to Scale
Notes
1. Utility mapping (buried electrical and communication
conduits depicted in red) shown hereon was
provided by Eversource to GIHA as a series of
panels not georeferenced to a horizontal datum.
2. Mapping panels were aligned, digitized and overlain
on GIS parcel and aerial mapping.
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association K-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX K. CONCEPTUAL ALTERNATIVES
Woods Hole Group, Inc. • A CLS Company
Great Island Homeowners Association L-1 December 2024
Feasibility Study for Road and Bridge Resiliency Improvements 2023-0169
APPENDIX L. DYNAMIC ADAPTATION PATHWAYS
May 24, 2024 2023-0169
Great Island Homeowners Association
1100 Great Island Road
Yarmouth, MA 02673
Re: Dynamic Adaptation Pathways
Introduction and Methods
Following development and evaluation of the range of adaptation options, the team began the
exploration of planning and phasing with dynamic adaptation pathways. Dynamic adaptation
pathways planning is an approach for exploring and sequencing adaptation options over time
that acknowledges deep uncertainty (deficiency of agreement on or knowledge of how likely
various future scenarios are) in climate projections and allows decision makers to establish a
flexible plan that achieves community goals while being responsive to changing conditions and
projections. This framework enables communities to prepare a range of responses to potential
future conditions, while preparing to implement solutions (or change approach) informed by
tipping points and knowledge of the capacity of each adaptation option. Dynamic adapta tion
pathways can provide a unique and powerful visualization of the potential adaptation actions
previously presented in this study, including the range of potential actions available to reduce
the flood vulnerability of a particular asset or group of ass ets, key water level and temporal
thresholds, and decision points. While these dynamic adaptation pathways figures appear
complex, once understood, they can be valuable decision tools.
A key to interpreting the dynamic adaptation pathways figures is presented in Figure 1. The
pathways associated with each action are color-coded by theme. There are four themes:
maintain road pathway (yellow), elevate road pathway (red), abandon road pathway (blue), and
Living with Water (blue). As you move left to right along a pathway for a particular action, at key
time steps you will encounter a “transfer station.” These transfer stations represent decision
points and opportunities to transition or shift to a different action (i.e., move up or down along
one of the vertical paths when a change in approach is decided upon due to variations in
community desires, climatic conditions, or overall municipal policies).
In many cases, the most beneficial and cost-effective approach to protecting an asset is to phase
in different actions over time or consider shifting the use of a specific asset over time. Rising
2
water levels prompt additional actions or an alteration in the way an asset may be used in the
future. Actions that are effective for addressing the projected 10% Annual Exceedance Probability
(AEP) Water Surface Elevation (WSE) are indicated by a thick so lid colored line. This is the water
elevation that has a projected 1 in 10 chance of occurring at least once in a given year in the
Massachusetts Coast Flood Risk Model. As sea level rises and strong storms become more
common over time, the 10% AEP water surface elevation gets higher. Adaptations that do not
increase in elevation over time may not provide the same amount of storm protection over time;
therefore, the diagram may transition to a thick dashed colored line (indicative of reduced storm
performance). Although these transitions to reduced levels of protectiveness indicate changes in
performance, they still represent choices for adaptation planning and are marked by transfer
stations on the diagram. If the community decides that a reduced state of p erformance is not
acceptable for a certain asset or group of assets, it can choose an alternate path (another
adaptation strategy) that satisfies community goals (if available).
Admittedly, adaptation actions cannot solve every flooding problem for all potential future storm
surge water levels. Tipping points, when an action can no longer function as intended, are
indicated by a black vertical bar. When this occurs, the thick solid or dashed colored line
representing an action will either end at that tipping point terminal (i.e., that action is no longer
effective), or the line will continue past the tipping point terminal as a dashed line. The dashed
line in this case indicates a change in function for that action – the action is able to provide a
solution for tidal inundation. Solid lines are functional up to a 10-year storm, thicker dashed lines
encompass alternatives that function during all non-storm tides or experience some monthly
tidal flooding, and the thinnest dashes encompass alternatives that function only during low
tides. The existing road falls into the middle dash category because it experiences non-storm tidal
flooding nearly every month, but it previously may have fallen into the thickest dash category
Figure 1. Key to interpreting Dynamic Adaptation Pathways
3
Finally, at the bottom of each figure are three threshold lines (Figure 2). The bottom two lines
provide a range of actionable timelines for when each action may be needed and effective. The
top line, indicating the total amount of sea level rise in feet, can be compared to actual measured
water levels over time to track whether climate change impacts are proceeding closer to the high
or intermediate scenario. Based on actual water level trends, planned timeframes for
implementation can be adjusted accordingly. For the purposes of the discussion below, however,
all timelines will be discussed related to the high sea level rise projections in terms of year.
Figure 2. Key for interpreting actionable timelines for each adaptation pathway.
Dynamic Adaptation Pathways for Great Island
The “long list” of alternatives, including the four refined alternatives, informs the dynamic
adaptation pathways graphic in Figure 3. Alternatives that have an identical profile have been
consolidated into the same line, and the additional non -car access options of helicopter and
private boat are included at the bottom of the graphic. The ferry service and private boat access
options will require dock and roadway elevation after a certain point and are included in both
the “Elevate” and “Abandon” themes after that point.
4
Figure 3. Dynamic adaptation pathways for Great Island.
5
Preferred Pathways
Based on community input and design and permitting experience, the project team identified
two preferred pathways that could provide long -term access to Great Island. Many options are
available, but the two preferred pathways allow access to be maintained while providing
flexibility to adapt to future conditions and changes. Both pathways consider timelines for design,
construction, and permitting.
Preferred Pathway 1 involves the continuation of erosion management on the existing dune, a
modest road raising, a ferry service, and emergency helicopter access. In this alternative, the
design process for roadway raising and ferry service start immediately. The road is raised only in
the most vulnerable areas, allowing it to stay operational during all tidal conditions until the ferry
service is fully operational. Erosion management on the existing road continues until the ferry is
fully operational and road use is phased out. Emergency services are provided by helicopter or
boat, which can respond more quickly and operate in a wider range of weather conditions than
a ferry. This approach deprioritizes investment in the road and aims to set up a ferry serv ice as
quickly as possible. It carries a lower road project cost and a shorter design, permitting, and
construction timeline, lowering the risk of daily tidal inundation impacting construction.
However, the position of the road remains unchanged, and even the elevated road is at risk of
damage and destruction from severe storms.
Preferred Pathway 2 involves the continuation of erosion management on the existing dune,
significant roadway raising, a ferry service, and emergency helicopter access. In this alternative,
the design process for roadway raising starts immediately. A ferry feasibility study is a prudent
near-term step, but implementation of a ferry service can be deferred until the mid -term. The
road is raised significantly and shifted back from the dune, allowing it to be used in near -term
small storms and mid-term high tides. Erosion management on the existing road continues until
construction on the raised and shifted road is complete. After road use is phased out, emergency
services are provided by helicopter or boat, which can respond more quickly and operate in a
wider range of weather conditions than a ferry. This approach aims to put off the transition to a
ferry service for as long as possible by investing heavily in the road. The corresponding road
project costs are higher, and the timeline for design, permitting, a nd construction is longer. If
construction starts after monthly tidal inundation begins to affect the road during work hours,
the construction timeline and corresponding costs could be affected by flooding -related work
stoppages and site controls. The finished road would have very low vulnerability to erosion.
A third pathway of continuing erosion management and transitioning to a ferry as quickly as
possible was considered but was ultimately abandoned due to its high risk of catastrophic road
failure and the uncertainty of the ferry timeline.
6
Figure 4. Preferred Pathway 1 for Great Island.
7
Figure 5. Preferred Pathway 2 for Great Island