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Modeling shows limited longshore transport but storms drive most beach loss at Easton’s Beach
Summary
Consultants presented numerical modeling and six months of ADCP data showing low average longshore sediment transport (hundreds of cubic yards/year) but significant cross‑shore sediment movement during storms; a December storm produced peak nearshore waves of about 12.7 feet.
Woods Hole Group and modelers told the Beach Commission their nested numerical models—validated against a six‑month ADCP record and an offshore buoy—show Easton’s Beach has low average longshore transport but is highly vulnerable to cross‑shore storm losses.
"Easton's Beach now is as uniformly flat, gentle sloping, and low in elevation," said Britney Hoffnagle, summarizing topographic and bathymetric survey results. Shoreline digitization over 13 historical shorelines produced a long‑term erosion rate under 0.25 feet per year and a short‑term rate just above 0.25 feet per year, indicating recent acceleration.
Kirk Bosma explained the models: longshore transport is limited because waves tend to align shore‑perpendicular in Easton Bay, so "on average... you're talking hundreds of cubic yards per year" rather than the hundreds of thousands seen on some open ocean beaches. But storm events increase longshore movement and, crucially, cause large cross‑shore sediment shifts that can form offshore bars and pull material away from the shoreline. "The peak wave height in the December 12–24 event was... 12.7 feet," Bosma said, and the team noted storm scenarios can produce splashover at Memorial Boulevard and threaten parking and built elements.
