Galveston Island, Texas has been experiencing high rates of erosion in recent years, spawning an interest in developing complex beach management programs. However, before any effective management project can be implemented we must understand all of the processes that control the shoreface. It is only recently that scientists have begun to recognize the importance of the role that the geologic framework plays on the coastal evolution of the shoreline. In this region, it is the antecedent geology as well as the anthropogenic obstructions which are the key factors controlling the formation of the modern shoreface. This study defines the extents to which these antecedent and anthropogenic factors influence the shoreface as well as refines the geologic interpretations offshore of Galveston Island. Using sidescan sonar, CHIRP seismic sonar, multibeam bathymetry data and sediment cores, the shoreface and subsurface geology were modeled. It was determined that the thickness, extent and slope of the modern sediment in the nearshore environment is controlled by the topography of the Beaumont Clay, a consolidated clay deposited during the Pleistocene. Anthropogenic obstructions, including the Galveston Seawall, groin and jetty system, have changed the sediment transport patterns in the region and have created a system of erosion and accretion not only along the shoreline, but for the entire length of the shoreface.

The purpose of this study was to compare vegetation systems among three artificially isolated wetlands on the west end of Galveston Island. Sample sites were identified as isolated wetlands and anthropogenic impact was observed. Wetland plant communities were identified through representative field studies using a modified quadrat method. Species composition, species diversity, evenness, cover and frequency were compared among the three sample sites. Salinity at all three sample sites remained at 0 ppt through June, July and August. Salinity increased to 10 ppt in both Lafitte’s Cove Nature Preserve and Dos Vacas Muertas Bird Sanctuary in September. No change in salinity was recorded at Isla Del Sol. At Lafitte’s Cove Nature Preserve the majority of the soil composition included Mustang-Nass. Dos Vacas Muertas Bird Sanctuary consisted of a Mustang fine sand complex while Isla Del Sol consisted of Mustang fine sand and Nass very fine sandy loam. Sampling at Lafitte’s Cove Nature Preserve produced 15 species. Dos Vacas Muertas Bird Sanctuary added 7 new species while Isla Del sol added 6 new species for a total of 28 species within the three sites. The overall plant species’ richness of Lafitte’s Cove Nature Preserve and Dos Vacas Muertas Bird Sanctuary remained low. A high frequency was observed in Sesbania drummondii and Cyperus odoratus at Lafitte’s Cove Nature Preserve. Sesbania drummondii retained the highest percent cover for the site. At Dos Vacas Muertas Bird Sanctuary, Phragmites australis and Spartina patens demonstrated a high frequency as well as percent cover. Frequency was highest in Juncus roemerianus and Eleocharis geniculata at Isla Del Sol. Several plant species exhibited a high frequency while overall frequency was more evenly distributed in Isla Del Sol than the other sample sites. Percent cover was highest in Juncus roemerianus and Borrichia frutescens. Isla Del Sol had the highest species diversity and evenness of all three sample sites. Similarity in species composition was high with the coefficient for pair-wise comparisons in Isla Del Sol and Lafitte’s Cove Nature Preserve being the highest. The three sample sites shared 53% to 73% of their species. Isla Del Sol possessed 6 species that were absent from the other sample sites. Dos Vacas Muertas Bird Sanctuary contained 4 unique species while Lafitte’s Cove Nature Preserve had only 3 unique species. Dos Vacas Muertas Bird Sanctuary had the lowest index score at 10. Lafitte’s Cove Nature Preserve had the highest index score at 24 while Isla Del Sol followed close behind at 22. For the Anthropogenic Activity Index, Lafitte’s Cove Nature Preserve still retained the highest score at 14. Results for Isla Del Sol showed an index score of 13 while Dos Vacas Muertas Bird Sanctuary scored only 7. The results of this study show that although Dos Vacas Muertas Bird Sanctuary had lower levels of disturbance when compared to the other sample sites, it still experienced a lower species diversity. Isla Del Sol had the highest species diversity and evenness of the sites. Lafitte’s Cove Nature Preserve had the highest level of disturbance and maintained a low level of diversity as well. When comparing the results to historical data, a reduction in salt marsh plant species was observed. Species that are often associated with freshwater to brackish marsh wetlands have become more dominant in the sample sites.

Vegetative health was measured both before and after Hurricane Harvey using remotely sensed vegetation indices on the coastal marshland surrounding Galveston Island's West Bay. Data were recorded on a monthly basis following the hurricane from September of 2005 until September of 2019 in order to document the vegetation response to this significant disturbance event. Both initial impact and recovery were found to be dependent on a variety of factors, including elevation zone, spatial proximity to the bay, the season during which recovery took place, as well as the amount of time since the hurricane. Slope was also tested as a potential variable using a LiDAR-derived slope raster, and while unable to significantly explain variations in vegetative health immediately following the hurricane, it was able to explain some degree of variability among spatially close data points. Among environmental factors, elevation zone appeared to be the most key in determining the degree of vegetation impact, suggesting that the different plant assemblages that make up different portions of the marsh react differently to the severe flooding that took place during Harvey.