Effect of Barrier Beach Breaching on Harbor Dynamics and Storm Surges

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by Y. J. Tsai, Stone & Webster Engineering Corp, Houston, United States,
Michael Goetz, Stone & Webster Engineering Corp, Houston, United States,

Document Type: Proceeding Paper

Part of: Hydraulic Engineering:

Abstract: This paper presents a summary of the flood insurance study, commissioned by the Federal Emergency Management Agency, to determine the 100-year flood elevation for Chatham, a seacoast town on Cape Cod, Massachusetts, that recently experienced severe coastal erosion. In 1987, the ocean severely damaged a barrier beach in Chatham Harbor. As a result, homes along the shoreline are subject to surges and wave activities from ocean storms. Several homes were damaged and one was eventually washed away. With the barrier beach opening, not only would the tidal hydrodynamic of the exposed harbor water be different but also the 100-year flood level would be changed from that of prior to breaching. Major emphases of the study were in three areas: (1) development of a site-specific tidal dynamic model including wind stresses; (2) verification of the model with recorded tide and current data obtained by the Woods Hole Oceanographic Institution; and (3) application of the model to the determination of the 100-year storm tide elevation. Several interesting phenomena have been observed from the model results and confirmed by the field measurements. The tidal ranges in some locations have increased by as much as three feet during the spring tidal cycle due to the opening of the barrier beach. At the new inlet, the currents are lagging behind the tides by about two hours. Finally, a statistically determined 100-year storm wind of 120 km/hr from southerly direction was used in determination of the 100-year storm tide elevation.

Subject Headings: Beaches | Storm surges | Tides | Gates (hydraulic) | Barrier islands | Ports and harbors | Model analysis | Dynamic models | North America | Massachusetts | United States

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