Terrebonne Basin
The Terrebonne Basin is an abandoned delta
complex, characterized by a thick section of unconsolidated sediments that are
undergoing dewatering and compaction, contributing to high subsidence, and a
network of old distributary ridges extending southward from Houma. The southern
end of the basin is defined by a series of narrow, low-lying barrier islands
(the Isles Dernieres and Timbalier chains), separated from the mainland marshes
by a series of wide, shallow lakes and bays (e.g., Lake Pelto, Terrebonne Bay,
Timbalier Bay).
The Verret and Penchant Subbasins receive fresh water from the Atchafalaya River and Bay, while the Fields Subbasin gets fresh water primarily from rainfall. The Timbalier Subbasin gets fresh water from rainfall and from Atchafalaya River inflow to the GIWW via the Houma Navigation Canal (HNC) and Grand Bayou Canal; it has the most limited fresh water resources in the entire Deltaic Plain.
The Terrebonne Basin supports about 155,000 acres of swamp and almost 574,000 acres of marsh, grading from fresh marsh inland to brackish and saline marsh near the bays and the gulf. The Verret Subbasin contains most of the cypress swamp (118,000 acres) in the Terrebonne Basin. The northern Penchant Subbasin supports extensive fresh marsh (about 166,000 acres), including a predominance of flotant marsh, with 98,000 acres of intermediate and brackish marsh in the Lost Lake-Jug Lake area and about 17,000 acres of saline marsh to the south. Fresh marsh is also dominant in the Fields Subbasin (approximately 23,000 acres). The Timbalier Subbasin grades from fresh marsh in the northern part of the subbasin to saline marsh near the bays, but is dominated by brackish (71,000 acres) and saline (153,000 acres) marsh types.
Of the four subbasins, only the Fields Subbasin experiences problems which are local and relatively minor. The Timbalier Subbasin experiences substantial subsidence and is essentially isolated from major freshwater and sediment inputs. Marsh loss rates are high due to the resulting sediment deficit, saltwater intrusion along the Houma Navigation Canal and other canals, historic oil and gas activity, and natural deterioration of barrier islands, which contributes to the inland invasion of marine tidal processes (including erosion, scour, and saltwater intrusion). The subbasin is rapidly converting to an open estuary.
In recent years, the Penchant and Verret Subbasins have experienced significant freshwater impacts from the Atchafalaya River. Historic wetlands loss resulting from subsidence, saltwater intrusion, and oil and gas activity appears to have moderated, but areas of cypress swamp (Verret) and flotant marsh (Penchant) are experiencing stress from high water levels in the Penchant Subbasin, the use of freshwater and sediment resources is not being maximized.
Basin-Wide Land Loss Map for
Terrebonne Basin. |
Basin-Wide Habitats Maps for
Terrebonne Basin. |
(Time lapsed animation of basin
from 1956 to 1993.)
CWPPRA Restoration Sites for the Terrebonne Basin
| PPL | Number | Agency | Project Name |
| 11 | TE-48 | NRCS | Raccoon Island Shoreline Protection/Marsh Creation |
| 10 | TE-43 | NRCS | GIWW Bank Restoration of Critical Areas in Terrebonne |
| 9 | TE-39 | NRCS | South Lake De Cade Freshwater Introduction |
| 6 | TE-34 | NRCS | Penchant Basin Natural Resources Plan, Increment 1 |
| 3 | TE-28 | NRCS | Brady Canal Hydrologic Restoration |
| 5 | TE-29 | NRCS | Raccoon Island Breakwaters Demonstration |
| 7 | TE-36 | NRCS | Thin Mat Floating Marsh Enhancement Demonstration |
| 1 | TE-18 | NRCS | Vegetative Plantings, Timbalier Island Demonstration |
| 1 | TE-17 | NRCS | Vegetative Plantings, Falgout Canal Demonstration |
| 4 | TE-31 | NRCS | Flotant Marsh Fencing Demonstration (Deauthorized) |
| 18 | TE-66 | NRCS | Central Terrebonne Freshwater Enhancement |
| 2 | TE-23 | COE | West Belle Pass Headland Restoration |
| 6 | TE-35 | COE | Marsh Creation East of the Atchafalaya River - Avoca Island (Deauthorized) |
| 12 | TE-49 | COE | Avoca Island Diversion and Land Building |
| 11 | TE-46 | USFWS | West Lake Boudreaux Shoreline Protection and Marsh Creation |
| 10 | TE-44 | USFWS | North Lake Mechant Landbridge Restoration |
| 6 | TE-32a | USFWS | North Lake Boudreaux Basin Freshwater Introduction and Hydrologic Management |
| 5 | TE-10 | USFWS | Grand Bayou/GIWW Freshwater Diversion (Deauthorized) |
| 9 | TE-41 | USFWS | Mandalay Bank Protection Demonstration |
| 10 | TE-45 | USFWS | Terrebonne Bay Shore Protection Demonstration |
| 19 | TE-72 | USFWS | Lost Lake Marsh Creation and Hydrologic Restoration |
| 4 | TE-30 | NMFS | East Timbalier Island Sediment Restoration, Phase 2 |
| 3 | TE-25 | NMFS | East Timbalier Island Sediment Restoration, Phase 1 |
| 3 | TE-26 | NMFS | Lake Chapeau Sediment Input and Hydrologic Restoration, Point Au Fer Island |
| 2 | TE-22 | NMFS | Point Au Fer Canal Plugs |
| 1 | TE-19 | NMFS | Lower Bayou LaCache Hydrologic Restoration (Deauthorized) |
| 16 | TE-51 | NMFS | Madison Bay Marsh Creation and Terracing |
| 16 | TE-52 | NMFS | West Belle Pass Barrier Headland Restoration |
| 11 | TE-47 | EPA | Ship Shoal: Whiskey West Flank Restoration |
| 9 | TE-40 | EPA | Timbalier Island Dune and Marsh Creation |
| 9 | TE-37 | EPA | New Cut Dune and Marsh Restoration |
| 3 | TE-27 | EPA | Whiskey Island Restoration |
| 2 | TE-24 | EPA | Isles Dernieres Restoration Trinity Island |
| 1 | TE-20 | EPA | Isles Dernieres Restoration East Island |
| 6 | TE-33 | EPA | Bayou Boeuf Pump Station (Deauthorized) |
| 13 | TE-50 | EPA | Whiskey Island Back Barrier Marsh Creation |
| 16 | TE-53 | EPA | Enhancement of Barrier Island Vegetation Demonstration |
37 projects listed
PPL stands for "Priority Project List"