Pontchartrain Basin Dynamics
The Pontchartrain Basin contains approximately 1.7 million acres and is bounded by the Pleistocene Terraces on the north and west, by Chandeleur Sound on the east, and by the Mississippi River and the disposal area of the Mississippi River Gulf Outlet (MRGO) on the south (figure 17). The marshes are primarily privately owned (625,000 acres); however, some extensive areas are managed as a federal wildlife refuge (25,400 acres) or as state wildlife management areas (100,000 acres). The basin is part of the abandoned St. Bernard delta and has approximately 935,000 acres (56%) of open water within its boundary. The remaining 44% of the Pontchartrain Basin is composed of 13% cypress/tupelo swamp, 2% fresh marsh, 2% intermediate marsh, 7% brackish marsh, 5% saline marsh, and 15% other land.
The major hydrologic features of the basin are Lakes Maurepas, Pontchartrain, and Borgne, and Chandeleur Sound. Lake Pontchartrain is connected to Lake Maurepas to the west and Lake Borgne to the east by passes through interlying land bridges (i.e., a land area separating two hydrologic features). The Inner Harbor Navigation Canal (IHNC) and the MRGO provide a direct link between Lake Pontchartrain and the Gulf of Mexico. Historically, fresh water entered the Pontchartrain Basin through Bayou Manchac (until its closure in 1812) and from natural crevasses
from the Mississippi River (until construction of the Mississippi River levees in the 1930s). Fresh water now enters the basin through leaks in the Bonnet Carr Spillway, through the IHNC Lock, the Violet Siphon, numerous small rivers and bayous (totaling approximately 9,500 cfs), and from direct rainfall. Urban storm water discharges from the New Orleans metropolitan area also enter Lake Pontchartrain.
Since 1932, over 76,000 acres of marsh (almost 8% of the basin's land area) have converted to open water in the Pontchartrain Basin (Dunbar et al. 1992, figure 17). Based on current loss rates, approximately 1,250 acres of marsh will continue to be lost each year without restorative action (Dunbar et al. 1992, Barras et al. 1994) . This loss amounts to approximately 25,000 acres during the next 20 years. If no action is taken to restore and protect the remaining wetlands, it is projected that an additional 23% will be lost by the year 2040 (LCWCRTF 1993).