Empirical depths of closure along the US East coast

Abstract

Depth of closure (DOC) is a commonly-used parameterization of the seaward limit in significant elevation change along a beach profile. Engineers, scientists, and resource managers use this parameter to make decisions and formulate designs for activities ranging from ecological restorations to beach nourishment and harbor construction. We present empirically measured DOC values from eight sites along the U.S. East Coast from Long Island NY to Georgia. The sites represent a spectrum of settings between fully wave-dominant and mixed-energy barriers and beaches, and five of the eight surveys extend back at least one decade. There are multiple DOC formulations based on wave conditions that tend to over-estimate DOC values compared to empirical observations. Our results show a similar pattern, with modeled DOC averaging 2.5 m (m) deeper than surveyed values but yielding reasonable results in wave-dominant environments. Along mixed-energy sites, modeled DOC values range from 1.0 to 5.7 m deeper than empirical observations. Alongshore comparison of observed DOC values within individual sites also suggests the movement of shoals on the lower shoreface near inlets may further complicate DOC estimates compared to strand-type shorelines with relatively featureless nearshore slopes.