Morphologic Change by Overwash: Establishing and Evaluating Predictors

Abstract

The ability to predict cross-shore profile response to coastal overwash is important for both understanding how barrier islands respond to overwash and for disaster management on developed coastlines. This study establishes morphologic and hydrodynamic parameters for predicting the type of cross-shore profile response following overwash for given pre-storm profile and storm conditions. More than 50 data sets were categorised into 7 different types of cross-shore profile response to overwash. These responses are: 1) crest accumulation 2) landward translation of dunes/berms 3) dune lowering 4) dune destruction 5) barrier accretion 6) barrier rollover (short-term),and 7) barrier disintegration. Dimensionless parameters describing the pre-storm morphology and storm characteristics for these data sets were then plotted in two-dimensional space and trends for the different response types identified. For some responses it was possible to define criteria for their occurrence and for the others an approximate trend could be identified. Maximum surge level, maximum run-up level, storm overtopping duration, beach crest height, dune width and dune volume proved some of the most important parameters to distinguish responses. The criteria that are established and trends identified should allow the user to qualitatively predict the overwash response of a given cross-shore beach profile to a given set of storm conditions, using readily available data.