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HomeMy WebLinkAboutProject Overview 6.8.202328 Lots Hollow Road | Orleans, MA 02653 WILKINSON ECOLOGICAL DESIGN Tel:(508)255-1113 | Fax:(508)255-9477 1 Work Protocols for Reinforced High Marsh and Fiber Rolls 4 Malfa Road, Yarmouth April 13, 2023 Revised 6/6/2023 Project Overview 4 Malfa Road exists at the northern edge of Lewis Bay, near the entrance of Hyannis Harbor. The property shoreline is low, relatively flat, and vulnerable to erosion by rising sea levels and increased wave and storm energy. The Massachusetts Shoreline Change Project has mapped and calculated erosion rates in Lewis Bay and lists the erosion rate of the property shoreline as 0.46’ per year. Page three of this document includes an image from the website. Further evidence shows more significant short-term episodic erosion of the beach and dune when comparing the recent survey data to 2018 aerial images from Google Earth. Based on aerial imagery, the dune was approximately 56 feet wide in 2018. According the to the survey data from early 2023 recorded the dune is now only 36 feet wide; a loss of 20 feet in a five-year period. This project proposes a coastal adaptation strategy that includes a fiber roll array combined with a reinforced high marsh to lessen the severity of erosion, preserve the existing plant community, and provide additional native plant species where none exists. The reinforced high marsh is a below-grade matrix of cobble, compatible sediment, coir fibers, and compost encased in a woven biodegradable material intended to serve as a reinforced rooting medium for transitional high marsh species such as salt marsh hay, spike grass, seaside goldenrod, switchgrass, and American beach grass. In addition, a modest fully-biodegradable fiber roll array will be installed along the landward edge of the reinforced high marsh to support the recovery of a coastal dune which has been eroding at a short-term rate of 4’ of loss per year since 2018. The proposed coastal adaptation strategy takes into account anticipated sea level rise. Refer to the Restoration plan by Wilkinson Ecological Design revised dated 6/6/2023 for more details. 00 20'40'MALFA ROAD MALFA ROAD EDGE OF DUNE - 2023EDGE OF DUNE - 2023WIDTH OF DUNE WIDTH OF DUNE 2023 - 36’2023 - 36’ WIDTH OF DUNE WIDTH OF DUNE 2018 - 56’2018 - 56’TOP OF SCTOP OF SCARP - 2023ARP - 2023#4 #4 DIAGRAM OF EXISTING DUNE COMPARED TO 2018 CONDITIONS 2018 aerial image from Google Earth. Edge of dune and top of scarp from Cape & Islands Engineering survey, 2023. 2 Access Access for all machines and materials will be via Malfa Road, along the existing footpath. This access route is across town-owned land. Approval from the Town of Yarmouth will be requested before installation. Ground protection mats will be laid along the access route, including any vegetation to protect the roots and soils from machinery and compaction. This will allow for full recovery of the vegetation following installation. The ground protection mats will be equivalent to AlturnaMats© at 4’x8’ or 3’x8’ made of recycled and rugged 0.5” HDPE material. The access route will be restored to pre-construction conditions following the installation. Additionally, all equipment will be removed from tidal and sandy access routes prior to any astronomic tidal or storm event. Installation of Reinforced High Marsh, Fiber Rolls, and Nourishment A reinforced high marsh is a below-grade matrix of cobble, compatible sediment, coir fibers, and compost encased in biodegradable material. The installation is a reinforced planting medium for transitional marsh species such as salt marsh hay, spike grass, seaside goldenrod, switchgrass, and American beach grass. This reinforced high marsh will be approximately 24” thick, composed of 50% 3”-6” rounded cobble, 25% coir fiber and compost, and 25% compatible sediment. The mixture of cobbles, coir fiber, compost, and compatible sediment will be encased in two layers of 700-gram coir fabric and one layer of 20 oz jute-burlap. Rounded cobbles will be placed in a staggered natural arrangement along the seaward edge of the reinforced high marsh to protect the installation and plantings from ice scour. Following construction, the specified native forbs and grasses shall be planted through the coir fabric into the reinforced high marsh. An 18” fence will be installed along the seaward edge of the reinforced marsh during the growing season to protect the plantings from smothering due to wrack accumulation. Fiber rolls will then be installed on the landward side of the reinforced high marsh. The array will be installed at a 2:1 slope angle, beginning with the lowest course of fiber rolls and continuing up gradient. A layer of 900- gram coir blanket will encapsulate the fiber rolls to provide protection from ultra-violet degradation. The fiber rolls will be secured with earth anchors attached to 42” steel cables, spaced 2.5’ +/- across the face of the fiber rolls into undisturbed soils as the array is constructed. All fiber rolls will be identified with stainless steel tags noting the name and phone number of the installer and the address of the installation location. Following installation and plantings, the fiber rolls will be nourished using compatible sediment. Ongoing sediment nourishment will supply the adjacent coastal resource areas with a sediment source. This nourishment will also help to extend the life of the fiber rolls. Nourishment of the dune with compatible sediment is also proposed as shown on the accompanying Restoration Plan. 215 cubic yards of compatible sediment will be placed over the dune. The existing American beachgrass has evolved to grow and thrive when covered by wind blown and overwash sand. To speed the process of re-establishing vegetation, the nourishment will be planted with American beachgrass at 18” on center. An annual dune nourishment is also being proposed and is detailed in the Ongoing Management section. A temporary irrigation system will be installed to provide supplemental water for the establishment period of the reinforced high marsh. This will encourage rapid colonization of the transitional high marsh within the first three years after planting. The irrigation system will be disconnected and removed from the project area following establishment of the plantings. Ongoing Maintenance Maintenance of the fiber rolls, associated plants, and bioengineering materials is critical to ensure a longer lifespan of the erosion management strategy. The project includes annual maintenance, as well as regular monitoring throughout the storm season to ensure extra maintenance and repairs will be undertaken when needed. The project will be monitored after significant winter storms to assess the need for minor maintenance activities. The maintenance may include the tightening of anchor cables and repositioning of fiber rolls. After maintenance work is complete, work areas will be restored to their previous condition, and any debris generated from maintenance work will be removed from the site. 3 Annual nourishment of the Coastal Dune is proposed to build the dunes elevation which will conserve the remaining dune. This nourishment will also be used to keep a sediment cover over the fiber roll array protect it from UV degradation and provide the adjacent coastal resource areas with a sediment source. 50 cubic yards of compatible sediment will be placed over the Coastal Dune between late March and early May for three seasons, to reach the targeted elevations listed on the Restoration Plan. This volume of sediment will cover the existing and previously planted beach grass with approximately five inches of sand. This depth of sand will have no negative affect on the American beachgrass as this plant species is capable of surviving when buried to a depth of 0.3 meter (11.8 inches) by wash over deposits (Knutson). Knutson, P. L. (1980). Experimental dune restoration and stabilization, Nauset beach, Cape Cod, Massachusetts. https://erdc-library.erdc.dren.mil/jspui/handle/11681/22208 Malfa Road Malfa Road #4 #4 This photo from the summer of 2022 shows a fiber roll array and reinforced high marsh that was installed in 2018. The fiber roll array and transitional high marsh installation have been outlined to show their respective locations under the dense native vegetation. Image from the Massachusetts Shoreline Change Project showing the transect and erosion rate at 4 Malfa Road. CCS-0684 (-0.46ft/yr) Reinforced High Marsh Fiber Roll Array