Hyrdrodynamic and Sedimentary Response to Tropical Storm Bill in the Gulf of Mexico and Christmas Bay

Abstract

Follet’s Island is a sand starved barrier island along the Northern coast of Texas. Human interaction has provided this island with an extended history of erosion, with some estimates having the island be completely eroded in 100 years. Compounding the issue of erosion is the vulnerability to hurricanes, tropical storms, and cold fronts around Follet’s Island. These large storms cause major morphologic changes and erosion to the areas directly hit and surrounding the storm, and Follet’s Island has one of the shortest return periods in the country for Hurricanes and Tropical Storms. Two instrumentation pods were deployed in the Gulf of Mexico and Christmas Bay along a transect which bisected Follet’s Island, with each pod located approximately 800 m from the island. Each pod was equipped with an acoustic Doppler current profiler and optical backscatter sensor. During the deployment Tropical Storm Bill made landfall approximately 160 km southwest of the deployment allowing the pods to measure the hydrodynamics and suspended sediment concentrations in response to the storm. Maximum storm surge from the Gulf of Mexico and Christmas Bay pods were measured to be 0.81 m and 0.52 m, respectively. The maximum significant wave height recorded was 1.93 m in the Gulf of Mexico and 0.23 m in Christmas Bay compared to 0.15 and 0.03 m during calm conditions respectively. Maximum suspended sediment concentrations for both pods occurred after the storm had made landfall during the ebb of the storm surge. Suspended sediment concentration loads reached peaks of 8.59 g/L and 3.09 g/L for the offshore and back bay measurements, respectively. The time averaged cross shore and longshore sediment transports were calculated using the current velocity components and the suspended sediment concentration. The long shore transport showed a net drift to the west corresponding with the ebb of the storm surge. The cross shore transport displayed a net drift towards the ocean side of the island for both pods.