Hurricane, Cold-Front, and Vessel-Wake Hydrodynamic Impacts on Wetland Edges in Galveston Bay, Texas

Wetlands are an important ecological resource, enhance coastal flood resilience of nearby communities, and act as carbon sinks. Limited sediment supply, sea level rise, and hydrodynamic forcing from waves and vessel wakes act as continual stressors, leading to increased wetland erosion. A 1.5-year study on wetland edge erosion in Galveston Bay, Texas, was carried out in 2021/22. The overall objective of the project was to predict short (several-year) and long-term (200-year) wetland edge evolution by combining analysis of satellite imagery, unmanned aerial vehicle (UAV) imagery, and Delft3D numerical modeling. The focus here is on the hydrodynamic measurements in support of the modeling efforts and the importance of ship wakes as a cause of wetland erosion. Wetland edge erosion of up to 1 m per year has been observed. Four 2-week measuring campaigns were conducted at four field sites. Data include impacts from Hurricane Nicholas (Category 1), several cold fronts, as well as vessel-wakes at two of the sites stemming from barge traffic in the adjacent Gulf Intracoastal Waterway. Each site was equipped with three pressure transducers and either an acoustic Doppler velocimeter (ADV) or an acoustic Doppler current profiler (ADCP) along transects perpendicular to the respective wetland edge. Water level fluctuations and velocities were recorded with sampling rates up to 16 Hz in water depths ranging from 0.3 to 1.5 m near the wetland edges. The data were analyzed to produce spectral wave information and directional spectra as well as energy dissipation approaching the wetland and results show a significant impact of ship wakes on the overall hydrodynamic energy impacting wetland edges. The information is used for quantification of the relative importance of cold front and hurricane forcing to the four sites based on relative positioning in regards to prevailing wind fields.