Beach Slope and Sediment-Grain-Size Trends as a Basis for Input Parameters for the SBEACH Erosion Model

Results from Storm-induced BEAch CHange (SBEACH) model calibration studies have provided new techniques and support for selection of model input parameters and interpretation of model output results. Beach and dune erosion analyses using the SBEACH erosion model in St. Johns County, Florida, demonstrated sensitivity of simulated erosion to changes of two model input parameters: sediment grain size and maximum slope prior to avalanching (MSPA). The MSPA parameter corresponds with the seaward slope of the dune or beach-berm erosion escarpment at the landward limit of the storm-induced erosion. Model calibration work demonstrated trends of these two model input parameters and of the sediment-transport rate coefficient K in relation to changes in beach slope. Evaluation of beach-slope values computed from county-wide topographic survey data in relation to the available mean sediment-grain-size data has shown clear correlation between these two parameters. This analysis provided a method for estimating mean sediment-grain-size values needed for SBEACH model input throughout St. Johns County. Results of SBEACH calibration work performed throughout St. Johns County demonstrated trends in the K and MSPA model input parameters relative to mean sediment-grain-size variations. Results of SBEACH model calibration studies in Panama City Beach, Florida; Brevard County, Florida; and on barrier islands within the Barataria Basin along the Louisiana coast demonstrated consistency with these identified trends.