Lake Pontchartrain Basin
The three large lakes, Maurepas,
Pontchartrain, and Borgne cover 55 percent of the basin. Lakes Maurepas and
Pontchartrain are separated by land bridges of cypress swamp and
fresh/intermediate marsh. A brackish marsh land bridge separates Lake
Pontchartrain from Lake Borgne.
The basin contains 483,390 acres of wetlands, consisting of nearly 38,500 acres of fresh marsh, 28,600 acres of intermediate marsh, 116,800 acres of brackish marsh, 83,900 acres of saline marsh, and 215,600 acres of cypress swamp. Since 1932, more than 66,000 acres of marsh have converted to water in the Pontchartrain Basin--over 22 percent of the marsh that existed in 1932. The primary causes of wetland loss in the basin are the interrelated effects of human activities and the estuarine processes that began to predominate many hundreds of years ago, as the delta was abandoned.
The Mississippi River levees significantly limit the input of fresh water, sediment, and nutrients into the basin. This reduction in riverine input plays a part in the major critical problem in the Pontchartrain Basin--increased salinity. Construction of the MRGO, which breaches the natural barrier of the Bayou La Loutre ridge and the Borgne land bridge, allowed saline waters to push farther into the basin. Relative sea level rise of up to 0.96 feet per century gives saltier waters greater access to basin wetlands. Mean monthly salinities have increased since the construction of the MRGO and other canals. However, these mean increases are less than the overall variability in salinity. In recent years, salinities have stabilized. The heightened salinity, caused mainly by subsidence, stresses wetlands, especially fresh marsh and swamp.
A second critical problem, occurring in the lower basin, is the erosion along the MRGO caused by ship-induced waves. The channel's north bank continues to eroding at a rate of 15 feet per year. This mechanism has resulted in the direct loss of over 1,700 acres of marsh since 1968.
The third critical problem is the potential loss of the Borgne and the Maurepas land bridges where wetland soils are especially vulnerable to erosion. Since 1932, approximately 24 percent of the Borgne Land Bridge has been lost to estuarine processes such as severe shoreline retreat and rapid tidal fluctuations, and the loss rate is increasing. During the same time, 17 percent of the Maurepas Land Bridge marshes disappeared due to subsidence and spikes in lake salinity. In addition, from 1968 to 1988, 32 percent of the cypress swamp on this land bridge either converted to marsh or became open water. These land bridges prevent estuarine processes, such as increased salinities and tidal scour, from pushing further into the middle and upper basins. If these buffers are not preserved, the land loss rates around Lakes Pontchartrain and Maurepas will increase dramatically.
The fourth critical problem is that several marshes in the basin are vulnerable to rapid loss if adequate protection is not provided soon. Examples of theses areas are: marshes adjacent to lakes and bays where if the narrow rim of shore is lost, interior erosion will increase dramatically; the perched fresh marsh on the MRGO disposal area which will drain and revegetate with shrub unless the back levee dikes are repaired; and near Bayou St. Malo, where unless canals are plugged, rapid water level fluctuations and salinity intrusion into adjacent marshes will continue.
Site specific problems of shoreline erosion, poor drainage, salinity stress, and herbivory are apparent throughout the basin. Solving these problems is important, but less urgent than solving the four critical problems described above.
Pontchartrain Basin Discussion
Basin-Wide Land Loss Map for Lake Pontchartrain Basin. |
Basin-Wide Habitats Maps for Lake
Pontchartrain Basin. |
(Time lapsed animation of basin from 1956 to 1993.)
CWPPRA Restoration Sites for the Lake Pontchartrain Basin
| PPL | Number | Agency | Project Name |
| 3 | PO-09a | NRCS | Violet Freshwater Distribution (Deauthorized) |
| 11 | PO-29 | EPA | River Reintroduction into Maurepas Swamp |
| 3 | PO-20 | EPA | Red Mud Demonstration (Deauthorized) |
| 9 | PO-26 | COE | Opportunistic Use of the Bonnet Carre Spillway |
| 3 | PO-19 | COE | Mississippi River Gulf Outlet (MRGO) Disposal Area Marsh Protection |
| 10 | PO-30 | EPA | Lake Borgne Shoreline Protection |
| 12 | PO-32 | COE | Lake Borgne and MRGO Shoreline Protection |
| 9 | PO-28 | NMFS | LaBranche Wetlands Terracing, Planting, and Shoreline Protection |
| 8 | PO-24 | NMFS | Hopedale Hydrologic Restoration |
| 13 | PO-33 | USFWS | Goose Point/Point Platte Marsh Creation |
| 2 | PO-06 | NRCS | Fritchie Marsh Restoration |
| 4 | PO-21 | NMFS | Eden Isles East Marsh Restoration (Deauthorized) |
| 9 | PO-27 | NMFS | Chandeleur Islands Marsh Restoration |
| 2 | PO-18 | USFWS | Bayou Sauvage National Wildlife Refuge Hydrologic Restoration, Phase 2 |
| 1 | PO-16 | USFWS | Bayou Sauvage National Wildlife Refuge Hydrologic Restoration, Phase 1 |
| 1 | PO-17 | COE | Bayou LaBranche Wetland Creation |
| 5 | PO-22 | COE | Bayou Chevee Shoreline Protection |
| 8 | PO-25 | NMFS | Bayou Bienvenue Pump Station Diversion and Terracing (Deauthorized) |
| 16 | PO-34 | COE | Alligator Bend Marsh Restoration and Shoreline Protection |
19 projects listed
PPL stands for "Priority Project List"