SEDIMENT DISTRUBUTION IN THE BAHIA GRANDE WETLANDS, SOUTH TEXAS

We monitored and analyzed the distribution of sediment throughout Bahia Grande wetlands, South Texas. Bahia Grande wetlands were once wind-driven tidal flats. Due to the completion of the Brownsville ship channel in the 1934, the natural water flow connecting Bahia Grande wetlands to the Lower Laguna Madre were blocked. This transformed the system from a wind-driven tidal flat to a series of ephemeral ponds. Many different local and environmental organizations, government agencies and universities are involved in one of the United States largest wetland restoration projects ever attempted.

Sediment grain-size analysis (Folk, 1980) was done on pre-restoration sediments collected throughout the low-lying areas of Bahia Grande. These data were compared to those of post-reflood sediments to determine the changes sediment transportation and deposition resulting from the initial restoration efforts. Using randomized points on a grid, 24 shallow sediment cores were collected before initial flooding. After the pilot channel was opened in July 2005, additional cores were collected to monitor the impact during the early part of the restoration. The data was plotted in GIS (geographic information system) for spatial analysis of the distribution of sediment before and after the initial reflooding. The preliminary data suggest that water flow is uneven in the wetlands. The prevailing southeasterly winds drive most of the sediment and water movement throughout the system.