Monitoring Sediment Distribution in the Bahia Grande Wetlands Restoration Project

The Bahia Grande Unit of Laguna Atascosa National Wildlife Refuge is located north east of the Port of Brownsville in South Texas. This project is part of one of the largest wetlands restoration projects in the United States with more than 23,000 acres, of which 10,000 acres is below mean sea level. The dredging of the Brownsville Ship Channel in the 1930's isolated the Bahia Grande wetlands and it became an arid dustbowl. The U.S. Fish and Wildlife Service obtained the land from ranchers in 1998 and 1999. In July 2005 water flow was restored to the Bahia Grande through a small pilot channel connecting the Brownsville Ship Channel to the wetlands. The initial goal of the restoration is to reduce the source of windblown dust, additionally this project will provide habitat for migrating waterfowl, shrimp, crabs, clams, oysters and other gulf coast aquatic organisms.

The results indicate that the pilot channel used to re-flood the Bahia Grande, and the smaller communication channels within the Bahia complex are transporting sediment throughout the system. The remnants of the 1800's railroad trestle impair circulation and distribution of sediments. Pre-1930's distribution of sediment shows concentration of fine-grained fractions north of the railroad. Post-restoration distribution of sediment shows the concentration of fines south of the railroad.

The expanded pilot channel will supply the Bahia Grande Complex with higher flow rates increasing the relative speed and carrying capacity of the water incoming and outgoing from the wetlands. When the flow is increased it is expected to transport more of the finer grained sediment out of the Bahia Grande complex and further restoring the natural ecosystem.