Barataria Basin Dynamics
Located south and west of New Orleans, the Barataria Basin is bounded on the north and east by the Mississippi River, on the west by Bayou Lafourche, and on the south by the Gulf of Mexico (figure 21). The basin is approximately 120 miles long, with a width ranging from 24 to 35 miles. The basin contains approximately 1,565,000 acres, of which 341,500 acres (22%) are leveed or developed areas. The region contains major corridors of developed areas along the Mississippi River and Bayou Lafourche. While most of the land is privately owned, two wildlife management areas and one national park with a total of 65,000 acres are located within the basin.
Several natural and constructed physiographic features in Barataria Basin influence habitat distribution, hydrology, land use, and wetland restoration opportunities. Major features include natural and artificial levees of the Mississippi River and Bayou Lafourche, the GIWW, U.S. Highway 90, the central marsh landmass, the chenier complex, and a chain of barrier islands. The island chain is eroding and will continue to deteriorate unless restorative measures are implemented. The USACE maintains major navigation channels in the basin. These include the Barataria Bay Waterway, which runs from Barataria Pass at Grand Isle to the GIWW south of Lake Salvador; the GIWW, which runs east-west through the central reaches of the basin; and the Empire-Gulf Waterway, which runs from the gulf to the Mississippi River in southeast Barataria. All are major navigation routes for the oil and gas industry, the sulphur industry, and commercial and recreational fishing. Sediment deposited by the Mississippi River in the former St. Bernard and Lafourche deltas filled the margins of the Gulf of Mexico and built these marshes over the last several thousand years (Frazier 1967). These marshes received periodic inputs of sediment and fresh water from the Mississippi River until the early 1900s but are now isolated from the river. Although there is currently no river discharge into these marshes, extensive non-saline marshes exist where water exchange with the gulf is restricted, primarily because average rainfall (162 centimeters/year) exceeds average evapotranspiration (102 centimeters/year) in southeast Louisiana (Newton 1972).
Water volumes and water levels in the basin are strongly influenced by tides, winds, and precipitation. Tides of the northern gulf have a relatively small range between high and low, measuring 1 foot in the gulf and 0.1 foot in the upper basin (LCWCRTF 1993). Storm tides can account for more than half of the daily water level fluctuations in the basin (Jarrett 1976, Levin 1990). Water exchange within the basin is highly variable (Richie 1985, Richie and Penland 1989). The dominant water exchange route between the upper and lower basin is through Little Lake, Bayou Perot, and Lake Salvador.
Since 1932, Bararataria Basin has lost almost 17% of its land area (Dunbar et al. 1992). Recent annual wetland loss estimates in Barataria Basin range between 5,200 (Dunbar et al. 1992) and 7,100 (Barras et al. 1994) acres per year (figure 21). At this rate, Barataria Basin will lose up to 142,340 acres of land during the next 20 years-a loss greater than that in any other basin in Louisiana's coastal zone. The subsidence rate in the Barataria Basin, based on USACE tide gage readings (1947-78) at Bayou Rigaud, Grand Isle, Louisiana, is 0.80 centimeters (0.03 inches)/year (Penland et al. 1989).
Without actions to correct the land loss and habitat degradation in the Barataria Basin, another fifth of the basin's wetlands may be converted to open water by the year 2045. Approximately 65% of wetland loss would be concentrated in the southern half of the basin. The Barataria Bay would enlarge, absorbing adjacent water bodies, and its connection with the Gulf would become substantially larger as barrier islands disappear. As a result of continued erosion of the barrier island chain, the tidal passes will enlarge and deepen, reducing the potential hydrologic benefits of the islands to the basin.