Shoreline Protection: Design Guidelines for Pocket Beaches in Chesapeake Bay, USA

The Chesapeake Bay Estuarine System consists of a variety of shorelines that vary from low upland banks and marshes to beaches and dunes to high bluffs. Erosion of these shorelines becomes significant when fetch exposures exceed a few miles and becomes severe when shorelines are exposed to fetches exceeding 16 kilometers or more. Critical erosion has been defined as that erosion that immediately threatens upland improvements and infrastructure no matter what the fetch exposure. The use of headland breakwaters coupled with beach fill to create stable pocket beaches for shoreline management has become somewhat common place. Over the last 15 years research and project installations respectively by the authors have paved the way for widespread usage. Utilizing the empirical database of 14 representative installations, design parameter relationships are derived for headland breakwater/pocket beach systems. Breakwater systems with a bimodal wave exposure have a breakwater length to breakwater gap ratio (Lb:Gb) of about 1:1.0 to 1:1.5. When headland breakwater systems are sited in more unidirectional settings, the Lb:Gb ratio can approach 1:1.7 to 1:2.0 particularly within embayed coastal settings that usually have an appreciable amount of natural littoral sands. Previous research by the authors have shown a relationship between the breakwater gap to pocket beach depth or indentation (Gb:Mb) ratio to be about 1:1.65. Further analysis shows us that for a unidirectional project setting that the Gb:Mb ratio can average 1:1.9. For a bimodal wave climate the Gb:Mb ratio reduces to 1:1.5.