Drivers of Alongshore Variable Dune Erosion During a Storm Event: Observations and Modelling

Abstract:

A key limitation to further understand storm induced beach erosion and the development of simple, yet accurate predictive coastal erosion models is the paucity of field scale data collected within a short period of time of an erosion event. Here we will discuss results from a new rapid-response airborne lidar that was tested and flown to collect topographic data of the active dry beach and dune and the subsequent analysis and modeling of the erosion event. Flights were flown daily (weather permitting) pre, during, and post storm over a 6 day period to assess the temporal and spatial evolution of the upper beach during this event.

Observations of dune erosion were compared against offshore buoy data, as well as calibrated inshore spectral wave model results to further understand the alongshore variation in beach response. Comparison of extreme runup (R_2%) with the 5 daily beach surveys indicates that the most severe erosion occurred at alongshore locations where the dune toe (z_dune) elevation was the lowest and where R_2% > z_dune during the peak of the storm.

Three simple dune erosion models were tested on the data. The Palmsten and Holman (2012) model and a modified version of this model reproduced approximately 60% of the observed alongshore variable dune erosion during the storm. Sensitivity analysis on the impact of alongshore averaging of the topographic input data and the wave forcing as well as the effect of altering the temporal resolution of both the wave and topography updating schemes will be discussed.