DUNE MORPHOLOGICAL EVOLUTION FOR NOURISHED AND NON-NOURISHED BEACHES, SOUTH PADRE ISLAND, TEXAS

Beaches and dunes are a valuable part of coastal communities not only because of their buffering effect against storm surge but also for recreation and tourism. This study compares the volumetric and morphological evolution of beaches and dunes for developed, nourished areas and non-developed areas in South Padre Island, Texas. South Padre Island is a transgressive barrier that has experienced high rates of shoreline erosion ranging from 2.5- 4 meters per year. Beach nourishment is practiced as way to ameliorate erosion; every two years approximately 200,000 cubic meters of sand are placed on the beach. Beach nourishment contributes to the sediment budget which in turn contributes to the development and growth of dunes. The goal of this study is to gain insight into the processes and pattern of sand distribution and obtain a better understanding of the subaerial evolution of the beachfill.

Since dune morphology is considered to be a result of the relationship between beach and dune sediment budgets, volumetric evolution of the beach and dune environments is analyzed using a sediment budget approach. Steps in constructing a sediment budget include identifying sediment budget pathways, estimating volume change and estimating sediment flux. The change in volume of these environments is calculated from lidar derived Digital Elevation Models (DEM’s) from the years 2000, 2005, and 2009. The potential sediment flux is estimated using wind speed and direction data from a weather station located on the south end of South Padre Island. The comparison of the morphological evolution of dunes from nourished/developed beaches and non-nourished/non-developed beaches is done from shore-perpendicular profiles extracted from the various DEM’s. Since the sediment transport from the beach to the dune environment is controlled by a variety of factors including beach width, beach height, vegetation cover, erosion/accretion rates, and topography, the relationship between these factors and dune accretion is analyzed with the use of linear regression.