Loading...
HomeMy WebLinkAboutYarmouth_140BlueRock_05_02_2023_gberman 1 | P a g e COASTAL PROCESSES SPECIALIST WOODS HOLE SEA GRANT | CAPE COD COOPERATIVE EXTENSION gberman@whoi.edu | gberman@barnstablecounty.org 508-289-3046 | 193 Oyster Pond Road, MS #2, Woods Hole, MA 02543-1525 May 08, 2023 TO: Yarmouth Conservation Commission CC: Mark Burgess (Shorefront Consulting) FROM: Greg Berman, Coastal Processes Specialist (WHSG & CCCE) RE: Site visit to 140 Blue Rock Road, Yarmouth, MA – 05/02/2023 Background: Since the inception of the coastal processes position established within WHSG & 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. 2 | P a g e Site Details: This report focuses on the property and land adjacent to the Bass River at 140 Blue Rock Road in Yarmouth (Figure 1). The applicant, via their consultant Shorefront Consulting, has submitted site plans (dated 01/26/2023), an NOI (dated 03/23/2023), as well as a revised Alternatives Analysis and Coastal Bank Performance Standards (undated). The proposal is for the installation of a bulkhead, with fiber roll returns, to reduce the erosion of the coastal bank at the site. The Yarmouth Conservation Commission requested a site visit and a follow-up report to examine the coastal bank and alternatives analysis for the proposed stabilization. During the site visit on May 2, 2023 a series of photographs were collected near high tide. Photograph 1 was taken looking south from the dock at the property. The beach at this site is likely a result of the coastal bank erosion. Within about 5’ of the toe of the bank the beach elevation drops off rapidly. Photograph 2 was taken looking north from the dock at the property. The bank shows evidence of recent slumping and appears to be comprised predominantly of sandy material. There is also extensive invasive vegetation (ivy, etc.), and much of the coastal bank is covered in species that are not beneficial for bank stabilization. Photograph 3 shows that much of the toe of the coastal bank is undercut, which the property owner indicated is used by wildlife. It should be noted that with the proposed vertical bulkhead this habitat space will cease to exist. The extent of root exposure on several trees makes it unlikely they will survive due to the banks’ current configuration. Photograph 4 was taken at a property to the south (184 Blue Rock Road), which had fiber rolls installed approximately 7 years ago in an attempt to reduce the erosion of the coastal bank. The coastal bank has experienced erosion (after installation of the fiber rolls) on the north side of the property, closest to the bulkhead that extends past the rest of the shoreline and into the river. This bulkhead is likely reducing the ability of the fiber rolls to protect the bank, however even further to the south (the bottom of Photograph 4) the fiber roll array is degraded. It appears unlikely that sand cover could be maintained on top of the fiber rolls, the lack of which greatly reduces the lifespan of coir products. Coastal Bank: There are two types of coastal banks under the Wetlands Protection Act (WPA), those that supply “sediment to coastal beaches” and those that only serve as a “vertical buffer to storm waters”. The coastal bank at this site supplies sediment to coastal beaches as there is a beach (see the 310CMR10.27(2) reference below) and is indicated in the site plans. 310CMR10.30(2+3) have been simplified as follows: “When a coastal bank…supplies sediment to coastal beaches…” then “no new bulkhead…shall be permitted on such a coastal bank except… when required to prevent storm damage to buildings constructed prior to… 1978, including reconstructions…” 310CMR10.27(2): “Coastal Beach means unconsolidated sediment subject to wave, tidal and coastal storm action which forms the gently sloping shore of a body of salt water and includes tidal flats. Coastal beaches extend from the mean low water line landward to the dune line, coastal bankline or the seaward edge of existing human-made structures, when these structures replace one of the above lines, whichever is closest to the ocean.” 3 | P a g e The Town of Orleans has a wetland regulation that does not allow CES construction if the house is more than 40’ from the top of the coastal bank. The town of Yarmouth is certainly not bound by the town of Orleans regulations and the regulation is provided here for informational purposes only, Town of Orleans Wetlands Regulations 196A-12H: “Where the applicant is unable to document the erosion rate, no CES shall be permitted where the building to be protected is more than 40 feet from the top of the bank or until monitoring the erosion shows an erosion rate that would expose the building foundation in 20 years or less.” It is the intention of the Orleans regulation to preserve the natural function of the landform, while still maintaining a minimum of 30’ between the top of bank and the building foundation. According to the site plans (01/23/2023), the house (not including the patio or deck) at 140 Blue Rock Road appears to be approximately 20’ from the top of the bank and the existing garage is only about 10’ from the top of the bank. The case can be made that the top of an eroding bank is “close enough” to the structure to warrant some kind of CES to prevent storm damage to the house (but not the stairs, patio, deck, lawn, etc.). The Alternatives Analysis allows the Conservation Commission to determine that the applicant’s preferred alternative will have the least negative impacts to the coastal resource areas, while still providing protection to the pre-1978 house. The Returns: The applicant’s proposal to include a transition zone of fiber rolls extending from the end of the proposed bulkhead is a well-designed way to reduce end effects of a bulkhead. However, the only reference to the fiber roll return was on the site plan Construction Note 16, “Provide a fiber roll “soft return” on both ends as shown. Utilize jute netting over and above the fiber rolls for slope stability and any plantings. Fiber rolls shall be 20” diameter, and anchored.” The “…as shown…” appears to reference an image from MassCZM’s SSPFS-4 Bioengineering - Coir Rolls on Coastal Banks. Also, the reference to being “anchored” is quite vague as there are many methods of anchoring, specific to the environment to which they’re being installed. As a transition and a buffer, these fiber rolls are an important aspect of the project and as they’re proposed up to the property line, improper installation may cause negative impacts on adjacent properties. MassCZM’s SSPFS-4 also indicates: “To ensure that essential design elements are appropriately implemented, construction should be conducted by a contractor with experience installing coir roll projects that have survived multiple storms and carefully supervised by a consultant with significant experience and demonstrated success with coastal coir roll projects. Monitoring and maintenance by a consultant with significant experience is also strongly recommended.” If the Conservation Commission is concerned about the experience of the installer they may wish to require an escrow account and/or daily site inspection. 4 | P a g e Alternatives Analysis (AA): The original AA listed four alternatives, however three of those were just varied construction methods of the preferred bulkhead, as opposed to different stabilization methods. The Revised AA covered two additional alternatives to supplement the minimum of “do nothing” and “preferred” alternatives. As indicated in the Revised AA, a rock revetment would be difficult to construct, and the main value of a sloped rock revetment (breaking up wave energy) is likely not relevant to this location with its limited fetch. The Revised AA indicated that there would be no high tide beach after the revetment was installed, however these CES should be conditioned to not extend further seaward. A revetment should start at the toe of the bank and not extend into the beach. With this limitation, existing steep angle of the bank, and minimal distance from the top of the bank to the house it is unlikely a revetment would be beneficial at this site. The Revised AA emphatically denies the viability of fiber rolls or other “soft solutions". It is reasonable to critically examine if these methods might be appropriate at this site, which is so close to MHW. If fiber rolls were installed at the toe of the coastal bank at this location they would likely lie within one vertical foot of MHW, and therefore have reduced longevity than if they were located further from the intertidal zone. According to CZM StormSmart Properties Fact Sheet 4: Bioengineering - Coir Rolls on Coastal Banks: “…coir rolls can be used on both sheltered sites and sites exposed to wave energy. However, they are most effective in areas with higher beach elevations with some dry beach at high tide, where the rolls are not constantly subject to erosion from tides and waves. If the dry beach is narrow, the beach elevation is relatively low, and/or the site is exposed to moderate wave energy, more than one row of coir rolls will likely be needed on the face of the bank, as well as at the base. In these exposed conditions, the rolls will have a shorter lifespan and will require more frequent maintenance such as resetting, anchoring, or replacement.” At this site frequent maintenance would be required due to almost constant daily inundation, and it would be highly difficult to maintain a sand cover on top of the fiber rolls at this elevation. This is similar to what was observed at 184 Blue Rock Road (Photograph 4). Fiber rolls and other “soft solutions”, by themselves, would most likely not be an effective stabilization strategy for this location. An Additional Alternative: Fiber rolls could likely be an effective component of a hybrid stabilization strategy. An additional alternative that the Conservation Commission might want examined is a combination of a low bulkhead at the toe of the bank with a fiber roll array above. This would likely include removal of the invasive vegetation and might require some regrade of the bank to a more stable angle. This type of strategy is a comprehensive method of dealing with coastal bank erosion while preserving as much function of an eroding coastal bank as possible. MassCZM’s StormSmart Properties Fact Sheet (SSPFS) 7 (Repair and Reconstruction of Seawalls and Revetments) recommends that “Rather than increasing the height of the structure efforts can be made to stabilize the upper bank using vegetation, natural fiber blankets, and/or coir rolls.” The current 5 | P a g e site plans (a portion of Section A-A shown below) indicate that the bulkhead will extend up to 8’ NAVD88. While a 5.5’ height is labeled on the section, the beach/bulkhead intersection appears to be at 2’ NAVD88 which would yield a 6’ bulkhead height. Regardless of starting point, the bulkhead would extend 6.4’ above MHW (1.6’ NAVD88). While the bulkhead is proposed below the flood zone (11’ NAVD88), it is likely that this area would experience relatively small waves due to the relatively short fetch. Fiber rolls may not be feasible for the first 1-2’ (accounting for waves and some sea level rise) above MHW. However, an additional alternative for the applicant to explore might be a low bulkhead (ex. MHW+2’ = ~3.6’ NAVD88) with fiber rolls above to further stabilize the coastal bank. This would still allow some erosion during larger storms (and preserve the function of a sediment source coastal bank) while at the same time preventing erosion from most smaller storms and boat wakes. 6 | P a g e Figure 1. Location of site. 7 | P a g e The red arrow on the image to the right indicates the location and direction of the photograph at the bottom of this page, and the other photographs in the series are indicated in yellow. Photograph 1. Looking south from the dock at the property near high tide. The beach at this site is likely a result of the coastal bank erosion. 8 | P a g e The red arrow on the image to the right indicates the location and direction of the photograph at the bottom of this page, and the other photographs in the series are indicated in yellow. Photograph 2. Looking north from the dock at the property. The bank shows evidence of recent slumping and appears to be comprised predominantly of sandy material. 9 | P a g e The red arrow on the image to the right indicates the location and direction of the photograph at the bottom of this page, and the other photographs in the series are indicated in yellow. Photograph 3. Much of the toe of the coastal bank is undercut, which the property owner indicated is used by wildlife. The extent of root exposure on several trees makes it unlikely they will survive due to the banks’ current configuration. 10 | P a g e The red arrow on the image to the right indicates the location and direction of the photograph at the bottom of this page, and the other photographs in the series are indicated in yellow. Photograph 4. This image is from a property to the south (184 Blue Rock Road), which had fiber rolls installed approximately 7 years ago in an attempt to reduce the erosion of the coastal bank.