Mississippi Delta Region, LA

Davis Pond Freshwater Diversion Project

AUTHORITY: The project was authorized by the Flood Control Act of 1928, (PL 70-391) and the Flood Control Act of 1965, (PL 89-298). The project was further amended by the Water Resources Development Acts (WDRA) of 1986 (PL 99-622), and of 1996 (PL 104-303).

PROJECT JUSTIFICATION: Deterioration of the marshes surrounding New Orleans is caused by several factors including subsidence, erosion, and saltwater intrusion. Introduction of fresh water, nutrients and sediments from the Mississippi River via the Davis Pond diversion structure will serve to reduce this degenerating trend in the project area. The project will improve existing commercial and recreational fisheries by enhancing existing marsh conditions, improving the project area's fish and wildlife habitat and resources. Estimated annual benefits: $14,997,000 for commercial fish and wildlife, plus $298,000 for recreation, or $15,295,000.

EXPECTED PROJECT OUTPUTS: The project will divert fresh water, with its accompanying nutrients and sediments, from the Mississippi River into the Barataria Basin - - reducing saltwater intrusion and establishing favorable salinity conditions in the area, thus combating land loss. These diversions will also increase commercial and recreational fish and wildlife productivity, and enhance vegetated growth for a healthier estuarine ecosystem in the Barataria Basin. The shallow embayments support oyster and crab production and shrimp and food fish reproduction, while the marsh areas produce food for fur-bearing animals and migratory waterfowl. Approximately 33,000 acres of wetlands will be preserved and 777,000 acres of marshes and bays will be benefited during the 50-year life of project. Fresh water diversions will occur under regulated conditions developed by monitoring basin salinities, and the fish and wildlife resources. The project area is 10,084 acres; 9,311 of these acres are in the ponding area.

PROJECT DEVELOPMENTAL HISTORY: Mississippi Delta Region studies were suspended in 1973 at the request of local interests who were restudying freshwater needs in the area. The project remained inactive until January 1982, when the State of Louisiana became interested in implementing the Caernarvon Freshwater Diversion structure. A Post-Authorization Change (PAC) report was approved in June 1987, authorizing relocating the Myrtle Grove site to the present Davis Pond site. The PAC increased the benefited marsh area and maximized the total benefits. Design Memorandum studies began in FY 1988, were submitted to higher authority in August 1991, and approved by the Assistant Secretary of the Army (Civil Works) in September 1992. The Project Cooperation Agreement between the Corps and the Louisiana Department of Natural Resources was signed on April 17, 1993. Construction began in Nov. 1996, and was substantially complete in Feb. 2002.

PROJECT COST:

Total Estimated Project Cost $119,600,000

Estimated Federal Cost $89,650,000

Estimated Non-Federal Cost 29,950,000

OYSTER LEASE RELOCATION: The State of Louisiana obtained Congressional authorization in Section 365 of WRDA 1996 (PL 104-303) for a $7,500,000 credit to the State for costs incurred in developing and relocating the active and productive leased oyster beds that will be adversely impacted by the project. This cost is included in the current project cost estimate, although an amendment to the PCA is required to incorporate this cost into the project. The Louisiana Department of Natural Resources has successfully relocated or purchased all of the oyster leases that will be adversely impacted by the project.

DIVERSION OF WATER: Freshwater diversions began in 2002. Hydrologic conditions and basin salinities dictate how much of a volume of fresh water will be diverted.

PROJECT INFORMATION:

Remaining Benefit/Cost Ratio 10.9 to 1 at 8 7/8%

Maximum Design Discharge 10,650 cfs

Dimensions: Structure - 4 – 14-ft x 14-ft box culverts

Sill Elevation: -12.0 NGVD

Inflow Channel - Length 535 ft.

Bottom width 85 ft.

Bottom elevation -11.0 NGVD

Outflow Channel - Length 11,043 ft.

Bottom width 120 ft.

Bottom elevation -15.5 to -16.6 NGVD