Assessment of Depth of Closure on a Nourished Beach: Terschelling, The Netherlands

Abstract

Depth ofclosure is studied on a nourished beach in the light ofits autonomous behaviour over long temporal and large spatial scales. Long term data show that depth ofclosure is variable alongshore, being shallower to the west and deeper to the east. Following placement of a shore nourishment along the middle section of the coast, the spatial variation ofdepth ofclosure changes. Initially the depth ofclosure is shallowest where the fill was placed. With time after the placement of the fill, this effect diminishes. Depth of closure observed in this study is influenced by bar behaviour. The fill material affects the observed depths of closure by reducing offshore bar migration. Maximum depths of closure for any particular timescale observed in this study are well predicted by the Hallermeier (1981) formulation for the depth limit to the active profile. In conclusion, pre-flll observations and Hallermeier (1981) provide a useful limit to the observed post-fill depth of closure. Similar analysis ofother beach nourishmentprojects would be useful.