Atchafalaya Basin
Major features in the basin include the Lower Atchafalaya River, Wax Lake Outlet,
Atchafalaya Bay, and the Atchafalaya River and Bayous Chene, Boeuf, and Black
navigation channel. Features of the Mississippi River and Tributaries (MR&T)
flood control system, including the Old River complex and the Atchafalaya Basin
Floodway system, define the flow and sediment resources entering the basin and
influence the basin's evolution.
Previous Mississippi River delta complexes, including the Sale-Cypremort and the Teche deltas, formed the majority of the land within the Atchafalaya Basin. Delta growth in Atchafalaya Bay is a recent occurrence, with subaqueous delta, or land underwater, forming in the decade from 1952 to 1962 and subaerial delta, or land above the water, forming during the 1973 flood. About 16,000 acres of subaerial land exist today in the Lower Atchafalaya River and Wax Lake Outlet deltas in Atchafalaya Bay.
The Atchafalaya Basin is unique among the basins because it has a growing delta system with nearly stable wetlands. Wetland loss is minor in the areas north of Atchafalaya Bay when compared to the other basins. The total wetland loss in the area is approximately 3,760 acres between 1932 and 1990. The average loss from 1974 through 1990 is 87 acres per year. Wetland loss in this area is site dependent; loss is primarily due to erosion, human activities, and natural conversion. Storms and hurricanes cause shoreline erosion between Wax Lake Outlet and Point Chevreuil. Oil and gas pipelines disrupt the natural movement of flow and sediment within the wetlands. The development of the Lower Atchafalaya River, from a tidal to a riverine system, has created natural levees along the banks of the river, disrupting the movement of flow and sediment into the wetlands.
In Atchafalaya Bay, wetland gain, rather than loss, is taking place. However, natural processes and human activity are limiting the effectiveness of flow and sediment resources in creating new wetlands by affecting sediment delivery, deposition, and retention. Winter storm fronts, waves, and currents refine and reshape the deltas in the bay by eroding and reworking sediments. MR&T project features such as the Wax Lake Outlet Control Structure affect the location and quantity of flow and sediment entering the bay. Sediments available for delta building in the Lower Atchafalaya River delta deposit in the channel above Atchafalaya Bay. These sediments reach the delta only during significant high water events. The Chene, Boeuf, and Black navigation channel affects deposition and retention of sediments within the Lower Atchafalaya River delta. The majority of sediments conveyed by the Lower Atchafalaya River do not reach the delta; sands fall out in the navigation channel where they are dredged to maintain navigation; silts and clays are conveyed out of the bay. The lack of sediments available for delta growth in the Lower Atchafalaya River delta is evident when the growth rate of this delta is compared to that of the Wax Lake Outlet delta. The Wax Lake Outlet delta receives approximately one-third the amount of flow and sediment of the Lower Atchafalaya River delta, and yet grows at a rate three times as great.
Basin-Wide Land Loss Map for
Atchafalaya Basin. |
Basin-Wide Habitats Maps for
Atchafalaya Basin. |
(Time lapsed animation of basin from 1956 to 1993.)
CWPPRA Restoration Sites for the Atchafalaya Basin
| PPL | Number | Agency | Project Name |
| 2 | AT-02 | NMFS | Atchafalaya Sediment Delivery |
| 2 | AT-03 | NMFS | Big Island Mining |
| 9 | AT-04 | NMFS | Castille Pass Channel Sediment Delivery |
3 projects listed
PPL stands for "Priority Project List"
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