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Louisiana Wetland Restoration

John Foret and Joy Merino

Little Vermilion Bay Sediment Trapping

Location

This project is located in the northwestern corner of Little Vermilion Bay at its intersection with the Gulf Intracoastal Waterway (GIWW) in Vermilion Parish, Louisiana.  The project area encompasses 964 acres of shallow bay bottom

Problems

High winds and waves prevent GIWW sediments transported down the Freshwater and Schooner bayous from settling and forming the basis of vegetated marsh.  This same wind and wave energy also increases shoreline erosion rates.

Restoration Strategy

This project involved the construction of a series of vegetated terraces to diminish waves in Little Vermilion Bay, helping to increase sediment deposition and reduce the rate of shoreline erosion.  A pattern of channels was dredged 100-feet wide and 6-feet deep to beneficially distribute sediment from the GIWW through the Freshwater and Schooner bayous.  Dredged sediments were used to construct 23 earthen terraces with a combined length of 23,300 feet.  After settling, the average height of the terraces was 3.5 feet above mean sea level.

The bases of the terraces were planted with 20,450 gallons containers of smooth cordgrass (Spartina alterniflora).

The design allows commercial and recreational fisherman to access the project area and stimulates fishery production by creating new habitat.

Cost: $1.46 million

Constructed: 5/15/99 to 8/20/99

 

Black Bayou Hydrologic Restoration

Location

This project is located in Cameron and Calcasieu Parishes, Louisiana.  The project area encompasses 25,529 acres of intermediate to brackish marsh interspersed with shallow open ponds and lakes 

Problems

The area has suffered wetland loss because of hydrologic changes, including reduced freshwater flow, increased tidal fluctuations, increased salinities, high water levels, excessive water exchange, and artificial water circulation patterns caused by the construction of the Calcasieu and Sabine River ship channels, the GIWW and other navigation channels.  The purposes of Black Bayou Hydrologic Restoration project are to (1) restore coastal marsh habitat, and (2) slow the conversion of wetlands to shallow, open water in the project area.  The project limits the amount of saltwater intrusion into the surrounding marsh and canals from the GIWW and reduces erosion caused by wave action from nearby boats and tides.

Restoration Strategy

A 22,600-foot rock dike was placed on the southern spoil bank of the GIWW. A barge bay weir (70-foot bottom width) was constructed in a man-made canal.  Weirs with boat bays (10-foot bottom widths) were constructed in two additional man-made canals.  A collapsed weir was plugged and replaced by a fixed crest steel sheet-pile weir with a state-of-the-art self-regulating tide gate.  Spoil material from weir installation and the dredging of access routes was deposited in nearby open water areas to the height of existing marsh elevations.  A contract was recently awarded to install 55,000 wetland plants over the next two planting seasons 

Cost: $6.4 million

 Constructed: 2/15/01 to 11/19/01
 

 

Pecan Island Terracing

Location

This project is located in Vermilion Parish approximately 5 miles north of the Gulf of Mexico just south of Pecan Island and Hwy 82. The total project area is approximately 1,950 acres (5 acres brackish marsh and 1,945 acres water).

Problems

The marshland was transformed into dry pastureland in the mid 1950's by constructing continuous dikes and pumping out the water. Deterioration and loss of the perimeter levees in recent years has converted the entire area into a shallow, open water lake with a few small marsh islands. This project will convert areas of open water back to vegetated marsh through the construction of earthen terraces.

Restoration Strategy

Project features include construction of earthen terraces over a substantial portion of the project area. The 199,800-feet of earthen terraces consist of dredged bottom material deposited in 500 ft long berms with a 10 ft crown, 30 ft base, and a height of 2.5 ft above MSL, creating approximately 150 acres of marsh.  Breaks or voids were constructed in terrace alignment permitting sediment-laden water to move around the terraces to facilitate sediment settling. Submerged aquatic vegetation growth will be promoted in the terraced area due to reduced turbidity and wave action. Emergent vegetation growth will be stimulated by the planting of wetland vegetation on emergent soils produced by terrace construction.

 cost: $2.2 million

 Constructed: 12/20/02 to 8/19/03


Pecan Island terracing after two growing seasons



 

Four-Mile Canal Terracing and Sediment Trapping

Location

The project area is 2,500 acres and located approximately four miles south of Intracoastal City in the northwestern corner of Vermilion Bay, Vermilion Parish Louisiana.  There are approximately 219 acres of vegetated, intermediate (97 acres) to brackish (122) marsh and 2,390 acres of shallow open water within the project area.

Problem

The main cause of current marsh loss in this area is shoreline erosion, which occurs at approximately 8 ft per year.  A combination of wave and wake erosion continues to deteriorate this area, which is relatively unprotected and affected by storm events emerging from Vermilion Bay.  This erosion prevents sub-aerial marsh development from sediments introduced to the area by the GIWW through the Vermilion River and Four-Mile Canal.

Restoration Strategy

Project components include dredging approximately 54,000 linear feet of sediment/freshwater distributary channels and using the dredge material to build 42,000 linear feet of earthen terraces.  The channels are approximately 50 feet wide and 5 feet below the current bay bottom.  Terraces have a 25 foot crown, a height of 4 feet MSL, creating approximately 57 acres of marsh, and were vegetated with Smooth cordgrass (S. alterniflora).

Cost: $3.1 million

Constructed: 8/15/03 to 3/23/04
 
Four-Mile Canal terracing and sediment trapping, growth along terrace berms after several growing seasons
 

 

Sediment Trapping at The Jaws

Location

This project is located in St. Mary Parish near "The Jaws" in the northeast portion of West Cote Blanche Bay. The project area is 2,782 acres and contains 182 acres of fresh marsh and 2,600 acres of open water.

Problems

High winds and waves prevent GIWW sediments from settling and forming the basis of vegetated marsh.  The area is experiencing shoreline erosion at a rate of 15 ft/yr 

Restoration Strategy

This project will induce sedimentation to create emergent vegetated wetlands by reducing wave fetch. Project components include the dredging of 63,000 ft of distributary channels 60 ft wide and 6 ft deep.  The spoil material from the distributary channels will be used to construct 145 terraces approximately 60 ft wide at an elevation of 2 ft above (+) MSL, creating approximately 90 acres of emergent marsh.  In addition, wetland vegetation will be planted along the perimeter of each terrace 

Cost: $3.4 million 

Castille Pass Sediment Delivery

Location

This project is located off of East Pass in the Atchafalaya River Delta, in St. Mary Parish, Louisiana.  The project area encompasses 5,367 acres of open water areas of variable depth in Atchafalaya Bay.

Problem

Spoil dredged from the Atchafalaya River Channel has been placed east of the channel, thus restricting riverine flow into shallow water areas each of the channel, which has substantially reduced natural marsh creation.  Without riverine replenishment, subsidence and wave erosion will increase deltaic marsh loss.

Restoration Strategy

The majority of the area consists of dredge spoil islands containing fresh marsh on the east side of the Atchafalaya River delta.  The project consists of improving four areas of the East Pass Delta Channel.  The entrance to East Pass will be widened and the bottom ramped up to enhance diversion of fresh water and sediments from the Atchafalaya River into East Pass.  The existing East Pass channel will be widened and deepened from the entrance to the Castille Pass bifurcation.  The dredged material will be placed to create new emergent marsh.  The existing Natal Channel branch channel will be re-dredged, extended, and diked to direct the channel flows toward the southeast into deeper bay bottoms to extend the Delta Lobe building process.  The existing Castille Pass branch channel will be extended southeastward into the bay with diking placed to extend the Delta Lobe and build new marsh acreage.   A complete dike will be placed along the southwestern channel bank to redirect flows into the shallow bay bottom to create a still-water cove area enhancing sediment deposition, eventually leading to the creation of emergent marsh in the newly created bay between Castille Pass and the East Pass extension.  As presented, the proposed project is expected to create 520 acres of marsh initially, and 853 acres created from maintenance dredging at 5 yr intervals over the 20 year project life.

Cost: $31.2 million


 

Waves erode shoreline

Pieces of shore vegetation being eroded

Edge of vegetation, erosion bank

Rockefeller Refuge Gulf Shoreline Stabilization

Location

This project is located along the Rockefeller Refuge Gulf shoreline from Beach Prong to Joseph Harbor in Cameron Parish, Louisiana.  The project area encompasses 1,373 acres of saline marsh (908 acres) and open water (465 acres) in the Gulf of Mexico.

Problem

The project will be designed to address Rockefeller Refuge Gulf Shoreline retreat averaging approximately 39 feet per year with subsequent direct loss of saline emergent marsh.  Research has documented long-term 1883-1994 Gulf shoreline retreat rates ranging from 30-to-40 feet per year for this project area.  In addition, Tropical Storm Francis in September 1998 caused 60 feet of shoreline loss along this stretch over a four-day period.

Restoration Strategy

The project would entail construction of a continuous near-shore breakwater along the Gulf of Mexico shoreline, extending approximately 50,691 feet, along the –5 foot contour, from Beach Prong to Joseph Harbor.  It would be designed to attenuate shoreline retreat along this stretch of the Gulf shoreline, as well as promote shallowing, settling out, and natural vegetative colonization of over-wash material landward of the proposed structure.

 Cost: $95.9 million

A new project South Pecan Island Fresh Water Introduction currently under design

Location
North of the Pecan Island Terracing Project west of the town of Pecan Island.

Problem
From 1932 to 1990, the South Pecan Island Mapping Unit lost 25% of its marsh. Through 2050, 20% of the 1990 marsh acreage is expected to be lost. Future land loss will most likely occur in areas of existing loss and may become more apparent along Louisiana Highway 82. Highway (Hwy) 82 acts as a hydrologic barrier. The Chenier Subbasin south of Hwy 82 has been experiencing saltwater intrusion due to lack of freshwater and sediment input from the Lakes Subbasin north of Hwy 82, while north of the highway water is retained. As recommended in the Coast 2050, the Lakes Subbasin needs drainage to maintain a 2 ft MLG water level target. Although culverts were installed in some areas along the highway during construction, those have filled in over the years. Recent attempts to restore hydrology have been isolated and have included two projects with similar goals.

Restoration Strategy
The proposed project area is approximately 7,006 acres. The project would include the deepening of a 7,366 linear ft conveyance channel from White Lake to an existing drainage culvert going under Hwy 82. At Hwy 82, four 48” pipes would be installed to allow freshwater and sediment introduction from White Lake into an existing conveyance channel south of Hwy 82. The existing channel both north and south of Hwy 82 would be armored with rock for approximately 200’ on each side of the new structure to prevent erosion. The existing channel would be excavated approximately 4 ft in a channel with a 25 ft bottom width (40 ft top width). The excavated material would be used to build a 1,264 ft section of bank needed along the northeast portion of the channel, and to refurbish existing banks. An existing plug would be removed. at White Lake. The foreshore rock dike to be constructed by the Corps of Engineers ((ME-22) would be tied into the shoreline with this proposed project. The project would be constructed to allow excess freshwater to drain, while preventing saltwater intrusion into the Lakes Subbasin, by installing flap gates south of Hwy 82.

The project would provide freshwater flow over 200cfs to >7,000 acres for at least 3 months/year.
About 76 acres of marsh would be protected over the project life. An estimated 2,160 acres of marsh exist in the project area, which includes the 100 acres of terraces constructed for ME-14 (an additional 300 acres are expected in the next 20 years as a result of that project).
 
Additional information about these and other CWPPRA projects is available at http://www.lacoast.gov
and for photos of projects, at: http://www.photolib.noaa.gov/habrest/cwppra.html