Overwash induced by storm conditions

Erosion problems are not only in the Texas area, but exist also along the coastline all over the world. Even though many researchers have studied coastal processes related with beach erosion and deposition over the decades, these processes are too complex to understand completely and field measurements are difficult to obtain during landfall of storms which cause fatal damages. Overwash is strongly suspected to cause extreme erosion as seen from long-term field measurements in the upper Texas coast. Overwash and washover are the source of cross-shore erosion and deposition of beach material along the coast, respectively. Waves superimposed on increased storm surges overtop and generate serious erosion of the berm. However, the data for these processes do not completely describe the shoreline erosion problems. Providing better descriptions requires field measurements and laboratory experiments with careful calibration. This study was conducted in two major sections. First was a field measurement and second was a laboratory experiment. This study used the RTK-DGPS to measure the change in the beach profile over multi year period. The GPS system is one of the ways to have the best resolution. The laboratory experiment was done in a 2D wave tank on mid-scale based on similitude law at Texas A&M University. The experiment was necessary to obtain better empirical formulas. The erosion rate of the sand was measured at different wave conditions and slopes of the berm or upper beach face in regular and irregular waves respectively. The erosion rate is much bigger at higher wave height, longer wave period and steeper beach face. The erosion rate is increased proportional to speed of bore and it is decreased with time. The empirical formulas were the first approach to simulate the impact of overwash. The laboratory results represented good agreement with the field data and might be applicable to predict the shoreline recession by overwash induced by storms. Further improvements can be expected by adding these empirical formulas to a numerical model to predict sediment transport in the swash zone.