Teche / Vermilion Basin

Location Map Much of the basin is occupied by three large bays: East Cote Blanche Bay, West Cote Blanche Bay, and Vermilion Bay. Marsh Island is an important hydrologic feature because it separates these bays from saltier water in the Gulf of Mexico. Therefore, marshes in this basin are primarily fresh, intermediate, and brackish with relatively few salt marshes. The Vermilion Basin lost 42,293 acres (14.8 percent) of marsh since 1932, nearly half of which was lost between 1951 and 1974, which is a relatively low rate compared to rates in other basins. Marsh loss is relatively slow because the basin is in the later stages of the delta lobe cycle; the more delicate wetlands deteriorated centuries ago. In fact, the delta lobe cycle has proceeded to the point that the basin should be experiencing rapid wetland creation in association with the emerging Atchafalaya River delta, but wetlands are not being built at maximum rates because the flow of fresh water and sediments down the Atchafalaya River is controlled at the Old River Control Structure. Fresh water and sediments from the Atchafalaya River benefit the basin nonetheless. Furthermore, numerous live and relic oyster reefs southeast of Marsh Island buffer water exchange between the big bays and the Gulf of Mexico, which also contributes stability.

Although the basin is geologically stable and benefits from the emerging Atchafalaya River delta, geomorphologic and hydrologic conditions have been altered by the dredging of navigation and petroleum access canals and the construction of spoil banks and levees. The effects of these alterations vary greatly from place to place, but generally they have created artificial barriers between wetlands and wetland maintenance processes, or removed natural barriers between wetlands and wetland decay processes. Interior marshes, traditionally maintained by annual flooding with fresh water in the spring, may deteriorate when exposed to increasing marine conditions, particularly in marshes where the soils have low mineral content. However, marshes near the Gulf of Mexico benefit from linkage with the gulf because winter storms deliver sediments to those marshes. Many landowners have responded to changing conditions caused by large-scale alterations by managing hydrologic conditions on a small scale using marsh management techniques. It is possible that some of these management efforts may not preserve marsh, particularly older ones. However, marsh management is an actively evolving field.

Some wetland loss might also be related to herbivory. Moderate herbivory alone is not believed to cause wetland loss, but it may be the "final straw" in marshes experiencing additional stresses such as flooding or saltwater intrusion.

Most wetland loss in the basin occurs either as shoreline erosion or in isolated hot spots. Areas are classified as hot spots when they experience rapid loss relative to other marshes within this basin. Hot spots in this basin are smaller than in other basins; they presumably originate from hydrologic changes that alter the balance between the marsh maintenance and deterioration processes, but the specific causes vary from place to place. Canals and spoil banks have impounded some areas and increased tidal energy in other areas. Thus, some areas have become isolated from sediment input, whereas water exchange removes more sediments than are introduced in other areas. Inadvertent impoundment also causes some areas to flood excessively.

Shoreline erosion on the large bays is caused primarily by natural wave energy. Wave energy has gradually increased over the centuries because the bays are naturally getting deeper due to the very slight but constant subsidence and global sea-level rise. Wave energy is also believed to have been increased because humans reduced the size of the oyster reefs between Marsh Island and Point Au Fer that shielded the large bays from wave and tidal energy in the Gulf of Mexico. Severe shoreline erosion occurs on Marone and Redfish Points, Shark Island, and the shore of Weeks Bay.

Shoreline erosion can dramatically affect wetland loss when it causes relatively isolated marsh drainage systems to become hydraulically connected with dynamic water bodies such as navigation canals and the large bays. In other areas, shoreline erosion is particularly rapid and causes the direct loss of significant wetland acreage. These may be classified as hot spots of erosion. Erosion caused by boat wakes and water surges associated with the passage of large vessels also causes wetland loss along the GIWW and other navigation canals.

Teche / Vermilion Basin Summary

Teche / Vermilion Basin Dynamics

Teche / Vermilion Basin Discussion

Basin-Wide Land Loss Map for Teche / Vermilion Basin.

Basin-Wide Habitats Maps for Teche / Vermilion Basin.

(Time lapsed animation of basin from 1956 to 1993.)

CWPPRA Restoration Sites for the Teche / Vermilion Basin

PPL	Number	Agency	Project Name
13	TV-20	NRCS	Bayou Sale Shoreline Protection
2	TV-09	NRCS	Boston Canal/Vermilion Bay Bank Protection
6	TV-16	NRCS	Cheniere Au Tigre Sediment Trapping Demonstration
3	TV-04	NRCS	Cote Blanche Hydrologic Restoration
14	TV-21	EPA	East Marsh Island Marsh Creation
9	TV-18	NMFS	Four Mile Canal Terracing and Sediment Trapping
9	TV-11b	COE	Freshwater Bayou Bank Stabilization - Belle Isle Canal to Lock
8	TV-17	NRCS	Lake Portage Land Bridge
5	TV-12	NMFS	Little Vermilion Bay Sediment Trapping
6	TV-14	COE	Marsh Island Hydrologic Restoration
6	TV-13a	NRCS	Oaks/Avery Canal Hydrologic Restoration, Increment 1
6	TV-15	NMFS	Sediment Trapping at "The Jaws"
1	TV-03	COE	Vermilion River Cutoff Bank Protection
9	TV-19	COE	Weeks Bay Marsh Creation and Shore Protection/Commercial Canal Freshwater Redirection

14 projects listed

PPL stands for "Priority Project List"