THE EFFECT OF LONGSHORE TOPOGRAPHIC VARIATION ON OVERWASH MODELLING

Abstract

This paper describes an application of the XBeach model to investigate the effect of longshore topographic variance on overwash. The model is used to simulate the morphological response of an eight- kilometer section of Santa Rosa Island, Florida, due to Hurricane Ivan (2004). The influence of longshore scales in the bed elevation is investigated by comparing the morphological response of the reference simulation to the morphological response of six sensitivity simulations in which the initial bed elevation was modified to remove longshore topographic variance. It is shown that the morphological response of the foreshore-foredune area to Hurricane Ivan is not influenced strongly by the initial longshore bed variance. The morphological response of the back barrier and the back barrier bay to Hurricane Ivan is influenced by features on the back barrier with longshore length scales of 100 - 500 meters, which hamper the flow across the island during inundation overwash. It is noted that these results may vary for other overwash regimes.