Depth of Closure in Beach-Fill Design

This Technical Note presents guidance on use of the depth of closure for beach fills placed on the open coast. An operational definition of the depth of closure and the associated conceptual background are presented. Procedures for estimating the depth of closure are given and illustrated with calculation examples. The depth of closure (DoC) affects numerous coastal engineering operations such as beach-fill design, planning of beach-profile surveys, siting and functioning of structures (including jetties,groins, breakwaters, pipelines, and wastewater outfalls), sediment-budget analysis, sand borrow-site identification, dredged-material placement in the offshore, and deployment of marine instrumentation. This note concerns the DoC for beach-fill design. It is assumed that the engineer or planner is involved in developing the design of a sand beach fill for the open coast. The fill project will have an expected number of years between renourishments, such as 3 to 10 years, or have a certain lifetime without renourishment, as might be the situation in a Section-933 project (one-time placement of fill as a beneficial use of dredged material to achieve a specified level of protection). Some of the fill placed on the beach berm and inshore in a construction cross section will gradually move offshore to the DoC as the nourished profile adjusts to changes in water level and to wave action by shifting seaward to form the design cross section. Therefore,an accurate estimate of the DoC helps form an accurate estimate of the required fill volume.