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HomeMy WebLinkAboutPeer Review_Report_Coastal Processes_McCormack 1 | P a g e COASTAL PROCESSES AND HAZARDS SPECIALIST REPORT CAPE COD COOPERATIVE EXTENSION WOODS HOLE OCEANOGRAPHIC INSTITUTION SEA GRANT bryan.mccormack@capecod.gov | 774-994-3130 193 Oyster Pond Road, MS #2, Woods Hole, MA 02543-1525 9 July 2026 TO: Brittany DiRienzo, Yarmouth Conservation Agent CC: FROM: Bryan McCormack, Coastal Processes and Hazards Specialist (WHOISG & CCCE) RE: 166 Blue Rock Road, Yarmouth, MA Summary This report focuses on the property of, and land immediately surrounding, 166 Blue Rock Road in Yarmouth, MA. The Yarmouth Conservation Commission has requested a 3rd party review to examine a proposal to install a vertical bulkhead. The property contains coastal beach and a coastal bank that is likely to act as both a sediment source and vertical buffer. Soft stabilization measures such as fiber rolls may struggle to maintain stability due to frequent inundation, while a sloped revetment could require regrading of the bank and disturb existing vegetation. If approved, any coastal engineering structure shou ld be as low and as short as possible while protecting the pre-1978 structure, with attention given to minimizing end effects, maintaining vegetation, and preserving the function of the coastal bank. 2 | P a g e Site Details This report focuses on the property of, and land immediately surrounding, 166 Blue Rock Road in Yarmouth, MA. The Yarmouth Conservation Commission has requested a 3rd party review to examine a proposal to install a vertical bulkhead. No site visit took place as a part of this review. Figure 1: Location of 166 Blue Rock Road in Yarmouth, MA. According to the Massachusetts Department of Environmental Protection (DEP) Wetlands and Wetlands Change Area Map, the area includes coastal bank and borders open water (Figure 2). The Massachusetts Wetlands Protection Act (WPA) makes a distinction between sediment source banks and vertical buffer banks. Based on the site photos provided for this review, aerial imagery, and lidar elevation surveys of this location, it would appear that the coastal bank at this location shows signs of eroding and would supply sediment to the system, thus acting as a sediment source bank. Due to its height, the bank would also be a vertical buffer. These also show a coastal beach at the toe of the coastal bank. 3 | P a g e Figure 2: Massachusetts DEP Wetlands and Wetlands Change Area map delineations around 166 Blue Rock Road. The Buzzards Bay National Estuary Program (BBNEP) reports tidal datums for the Massachusetts coast through their Interactive Tidal Datum Viewer. The nearest location with reported datums is station #1674, which is about 900 feet from the property. Relevant datums for this station were last updated in 2025 and are listed below in Table 1. All datums are reported relative to NAVD88. Interested parties are encouraged to visit the BBNEP website for full documentation on datum calculations, uncertainties, and limitations of the data. Table 1: Buzzards Bay National Estuary Program Tidal Datums for Station #1674. Tidal Datum Elevation (ft, NAVD88) Mean Higher High Water (MHHW) 1.79 Mean High Water (MHW) 1.46 Mean Sea Level (MSL) -0.32 Mean Low Water (MLW) -2.24 Mean Lower Low Water (MLLW) -2.52 4 | P a g e Mean high water (MHW) and mean higher-high water (MHHW) tidal datum elevations were extracted from the 2021 United States Geological Survey (USGS) lidar data and displayed as contours (Figure 3). The Conservation Commission should consider these tidal elevations in their review of the proposed project. MHW and MHHW appear to be very close to the toe of the coastal bank, leaving only a small area of dry beach. Figure 3: Tidal datum elevation around 166 Blue Rock Road. Due to its location on the Bass River, this property is not likely to experience significant wave action due to the limited fetch. Despite this, the location would be subject to flow through the Bass River that is likely to mobilize sediment. There is also the potential for boat wake to reach the bank, especially at high tide. 5 | P a g e To examine the stability of the upper portion of the coastal bank, 2011 USGS and 2021 USGS lidar surveys were compared using a profile across the bank (Figure 4). Elevations from these two datasets were extracted every 3 feet along the profile (Figure 5). The upper portion of the bank exhibits a roughly 1.7:1 slope and has remained relatively stable when comparing between 2011 and 2021. The profiles do show some erosion at the toe of the coastal bank and any erosion that has occurred since 2021 would not be shown here. Figure 4: Location of profile used for lidar comparison on coastal bank. 6 | P a g e Figure 5: Elevation profiles extracted from lidar across the coastal bank at 166 Blue Rock Road. Based on the photos provided for this review, the existing bulkhead appears to be in severe disrepair and failing. Removal of the existing bulkhead would ensure that its continued degradation does not lead to debris that may cause hazards for boaters, or end up on neighboring properties or the marine environment. Project Review Since the project area contains coastal beach, and the coastal bank on this property is likely to act as a sediment source for adjacent beaches as well as a vertical buffer, 310 CMR 10.27 and 10.30 would apply. According to the Town of Yarmouth’s Vision Government Solutions Online Database, the structure on the property was built in 1970, which would predate the effective date of this portion of the WPA. Despite this, the project should still adhere to the performance standards as much as possible. The following section addresses the performance standards for these regulations. Considering the tidal datum elevation presented from BBNEP, a “soft solution” such as fiber rolls may struggle to maintain stability in this location due to frequent inundation. These solutions typically work best with a sand cover to help prevent degradation from ultraviolet (UV) light, which may be unsustainable due to limited access to the lower portion of the bank. Maintenance and repairs may be frequent and necessitate access from the water to be completed. 0 5 10 15 20 25 30 35 40 45 0 10 20 30 40 50 60 70 80Elevation (ft, NAVD88)Distance from onshore origin (ft) Profile 1 2021 2011 ~32 feet elev.change ~54 feet dist.change 7 | P a g e While a sloped revetment would help to minimize wave reflections when compared to a vertical bulkhead, there is unlikely to be significant wave action at this location. There may be some reflection during storm events or due to boat wake at high tide. A revetment may also necessitate regrading the bank if pulled as far landward as possible, which may disturb existing vegetation and potentially intercept the house based on its proximity to the top of the bank. If approved by the Conservation Commission, any coastal engineering structure should be as low in height and as short in length as possible while still adequately protecting the ‘pre-1978’ structure. It should also be pulled as far landward as possible, which will help to reduce the amount of fill that is needed. This will help to maintain as much of the function of the coastal bank and coastal beach as possible. The existing bulkhead on the property to the south could be examined for impacts to bank function and coastal beach at the locations will experience very similar processes. The site plans from Shorefront Consulting dated 5/15/2026 show a proposed 20-foot fiber roll return on the northern end. While this type of transition can be beneficial for mitigating end effects, these fiber rolls may encounter similar impacts described above and rapidly degrade. The Commission may wish to discuss a comprehensive maintenance plan for this fiber roll array including sand covering and replacement. Should these fiber rolls fail, the bulkhead is proposed to have a slight return and be about 5 feet from the property line. It is typically recommended to maintain about 15-20 feet from neighboring properties to ensure any end effects stay on the applicant’s property. This distance should be maximized to best ensure that there are no end effects on the neighboring property while maintaining protection for the ‘pre-1978’ structure. It is also common to taper the end so the reflective/refractive surface is reduced toward the end of the structure. On the southern side of the proposed structure, there is a “cosmetic,” non-structural connection to the adjacent bulkhead. It is unclear what a cosmetic connection entails. If the connection between the two bulkheads were to fail and leave a gap, this could channelize flow between the structures and lead to increased erosion from wave focusing or runoff. Ideally, these structures would be continuous in a manner that would not allow for any increase in the potential for failure. The addition of well-rooted vegetation will help to ensure that the bank remains stable. The current vegetation on the bank was not identified. If there are non-native or invasive species that are not suited to coastal banks, replacing them with appropriate species will help to ensure stability on the upper portion of the bank. Additional Resources Additional resources for the review of the project could include the Massachusetts Office of Coastal Zone Management’s (CZM) StormSmart Properties Fact Sheets which include information for bioengineering/fiber rolls and vertical bulkheads/seawalls. The Commission may also consider reviewing CZM’s Applying the Massachusetts Coastal Wetlands Regulations: A Practical Manual for Conservation Commissions to Protect the Strom Damage Prevention and Flood Control Functions of Coastal Resource 8 | P a g e Areas, or the ‘Coastal Manual’. The Coastal Manual, in section 3-38, reviews performance standards for the construction of coastal engineering structures on coastal banks. It is important to note that these materials often reference locations on more open, high-energy locations, so the local dynamics and processes for this project may differ from what is described in these materials. CZM StormSmart Properties: https://www.mass.gov/info-details/stormsmart-properties CZM Coastal Manual: https://www.mass.gov/doc/czm-coastal-manual-applying-the-massachusetts- coastal-wetlands-regulations/download 9 | P a g e GIS Analysis Information A GIS analysis of the property was performed using publicly available data to help inform the relevant coastal processes. All maps provided use the NAD83 Horizontal datum and NAVD88 Vertical Datum in feet. The map projection is State Plane 1983 Massachuset ts Mainland 2001. A GIS package of map data is available upon request. Links to the metadata for each dataset are listed below. The aerial imagery data set used in this analysis in the main frame is 2025 MassGIS Aerial Imagery unless otherwise noted. 2025 MassGIS Aerial Imagery: https://www.mass.gov/info-details/massgis-data-2025-aerial- imagery 2021 U.S. Geological Survey Lidar: https://www.fisheries.noaa.gov/inport/item/69417 2011 U.S. Geological Survey Lidar: https://www.fisheries.noaa.gov/inport/item/49844 Buzzards Bay National Estuary Program Interactive Tidal Datum Viewer: https://buzzardsbay.org/technical-data/tidal-datums-ma/interactive-tidal-datum-viewer/ Massachusetts Department of Environmental Protection Wetlands and Wetlands Change Area Map: https://maps.massgis.digital.mass.gov/images/dep/omv/wetviewer.htm Background Since the inception of the coastal processes position established within WHOISG & CCCE, on-site and remote technical assistance on coastal processes has been and continues to be an on-going, effective technical information communication and dissemination tool. Technical assistance relating to coastal processes, shoreline change, erosion control alternatives, coastal landform delineation, potential effects of various human activities on coastal landforms, coastal floodplains, coastal hazards and hazard mitigation analyses, and dune restoration techniques provided in the field and remotely will continue to be provided on an as-needed basis. Site visits generally address site-specific coastal processes or coastal hazards related issues. Follow-up unbiased, written technical alternatives analyses are generally provided.