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Setbacks/Critical Erosion Subsection A. Significance: “Building close to the shoreline is a <br />common, but possibly poor, siting practice; it may render a building more vulnerable to wave, <br />flood, and erosion effects; may remove any margin of safety against multiple storms or erosion <br />events; and it may require moving, protecting, or demolishing the building if flood hazards <br />increase over time.” Subsection B. “1) A setback is the minimum distance from the inland <br />boundary of coastal feature at which an approved activity or alteration may take place. 2) <br />Critical erosion areas are areas, as shown on the maps prepared by the Massachusetts CZM <br />Shoreline Change Analysis project where average erosion rates are greater than 2 feet per year. <br /> <br /> <br />South Cape Cod <br /> The South Cape Cod region extends along the southern coast of Cape Cod in Nantucket Sound and <br />Vineyard Sound from Stage Harbor Light in Chatham to Nobska Point in Woods Hole (fig. 10). The region is <br />moderately to highly developed (Hapke and others, 2011). Jetties, bulkheads, seawalls, revetments, and extensive <br />groin fields are present throughout much of the region. The geomorphology of this region is predominantly sandy <br />headland beaches and small barrier systems fronting lagoons or ponds and well developed wetlands. <br /> Long-term rates of shoreline change were measured at 1,558 transects along approximately 91 km (57 <br />miles) of coastline. The highest erosion rate (-4.3 ±3.3 m/yr) was measured at Cockle Cove Beach in Chatham, east <br />of the entrance to Mill Creek. The beach at this location is backed by seawalls and is adjacent to a jetty system that <br />impedes the transport of sediment to the beach. The maximum long-term accretion rate is 3.3 ±2.1 m/yr at Davis <br />Beach on the updrift side of a jetty located at the mouth of Bass River. <br /> Short-term linear regression rates of shoreline change were calculated for 1,459 transects along 91 km (57 <br />miles) of coastline. The highest erosion rate of -2.6 ±2.5 m/yr was recorded at Cockle Cove Beach, approximately <br />300 m east of the location of the maximum long-term erosion rate. The highest accretion rate of 2.3 ±1.4 m/yr was <br />measured at Sampsons Island near the end of a westward-accreting spit at the entrance to Cotuit Bay. <br /> Long-term and short-term rates of shoreline change in the Cape Cod South region show erosion and <br />accretion trends that appear to be influenced by shoreline stabilization structures such as jetties and groin fields. <br />Relatively small beach nourishment projects are also common on the southern shore of Cape Cod and may have also <br />affected the rates of shoreline change. <br /> <br />Figure 10. Map and graphs showing long-term linear regression and short-term end-point rates of shoreline change <br />in Massachusetts for the South Cape Cod region. End-point shoreline change rates were calculated for 1994 to 2008. <br />Numbers on the map indicate distance alongshore in the graphs. <br /> <br />Map can be found on page 28 of the report hyperlink noted below. <br />https://pubs.usgs.gov/of/2012/1189/pdf/ofr2012-1189_report_508.pdf <br /> <br />Citation: Thieler, E.R., Smith, T.L., Knisel, J.M., and Sampson, D.W., 2013, Massachusetts Shoreline Change <br />Mapping and Analysis Project, 2013 Update: U.S. Geological Survey Open-File Report 2012–1189, 42 p., <br />http://pubs.usgs.gov/of/2012/1189/. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />19 <br /> <br /> <br />