A behavioral template beach profile model for predicting seasonal to interannual shoreline evolution

Abstract

This contribution presents a simple behavioral template model for beach profile evolution which is calibrated and tested against a 6-year time series of shoreline position, derived from a coastal imaging system at the Gold Coast, Australia. From a coastal management perspective, the position of the shoreline is arguably one of the most important morphodynamic parameters to be monitored and predicted and therefore forms the focus of this paper. The template model attempts to encapsulate some of the current understanding of coastal dynamics deduced from both scientific investigations and observations. The model framework is based on a simple relaxation model, whereby the profile approaches a template exponentially with time under conditions of constant forcing. The template evolves dynamically in response to incident wave forcing such that when a threshold value of the dimensionless fall velocity (Ω = H s /wT p, where H s = offshore significant wave height, T p = peak wave period, and w = sediment fall velocity) is exceeded, the beach face erodes and flattens, and the shoreline retreats landward, forming an erosional scarp and a breakpoint bar. Conversely, when the Q falls below threshold, progradation and steepening of the shoreface ensues, accompanied by the evolution of a swash bar and breakpoint step. The Gold Coast data are used to calibrate the threshold value of Ω (≈4.0) which is close to the time series mean (3.8). Testing the calibrated model on unseen data shows that it is able to reproduce the dominant seasonal/interannual shoreline succession observed at this site and up to 77% of the detrended shoreline variability. Copyright 2009 by the American Geophysical Union.