FINAL ENVIRONMENTAL STATEMENT MERMENTAU RIVER, BAYOUS NEZPIQUE AND DES CANNES, LOUISIANA ASSOCIATED WATER FEATURES GULF INTRACOASTAL WATERWAY, MERMENTAU RIVER, BAYOUS NEZPIQUE AND DES CANNES, AND LAKE ARTHUR Prepared by U. S. Army Engineer District, New Orleans New Orleans, La. August 1971 August 1971 MERMENTAU RIVER, BAYOUS NEZPIQUE AND DES CANNES, LOUISIANA ( ) Draft (X) Final Environmental Statement Responsible Office: U. S. Army Engineer District, New Orleans, Louisiana 1. Name of Action: (X) Administrative ( ) Legislative 2. Description of Action: The action consists of the enlargement and realignment of existing navigation channels with an accumulative length of some 43 miles, in Bayous Nezpique and des Cannes below Interstate 10 and also in the Mermentau River above the Gulf Intracoastal Waterway and in Lake Arthur to provide depths of 12 feet. It also provides for Federal participation in the cost of replacing the existing Louisiana State Highway 14 bridge at Lake Arthur, Louisiana. Located in Cameron, Vermilion, Jefferson Davis, and Acadia Parishes, Louisiana. 3. a. Environmental Impacts: The enlargement and realignment of the navigation channels will improve navigation conditions for commercial navigation and result in an increase in industrial and agricultural development of the area. The navigation project will result in changes in land use occasioned by construction including the reduction of bottom­ land hardwood, increase in water areas, and formation of oxbow lakes. b. Adverse Environmental Effects; A loss or change in approximately 2,000 acres of wildlife habitat will occur. Temporary turbidity and siltation will occur during construction and maintenance dredging operations. 4. Alternatives: Alternative construction methods and foregoing the channel realignment and improvements. 5. Comments Received; Water Quality Office, Environmental Protection Agency Bureau of Outdoor Recreation, U. S. Department of the Interior National Park Service, U. S. Department of the Interior Bureau of Mines, U. S. Department of the Interior Public Health Service, U. S. Department of Health, Education, and Welfare Geological Survey, U. S. Department of the Interior Department of Geography and Anthropology, Louisiana State University Louisiana Department of Public Works Louisiana Department of Health 6. Draft Statement to CEQ: 9 July 1971 Final Statement to CEQ: 9 MAR 1372 August 1971 MERMENTAU RIVER, BAYOUS NEZPIQUE AND DES CANNES, LOUISIANA FINAL ENVIRONMENTAL STATEMENT 1 . Project description. The project is located in southwest Louisiana near the towns of Lake Arthur and Jennings and is designed to improve navigation in the Mermentau River and Bayous Nezpique and des Cannes between the Gulf Intracoastal Waterway (GIWW) and Interstate 10 Highway. Impediments to navigation include the many sharp bends requiring reduced speeds to negotiate and restrictions on the size of tows imposed by existing channel dimensions and the vertical clearance provided by the Louisiana State Highway 14 bridge at Lake Arthur. Improvements authorized by the River and Harbor Act of 1965 and described in House Document Number 239, 89th Congress, include: enlargement and realignment of channels on Bayous Nezpique and des Cannes below Interstate 10 Highway crossings to a depth of 12 feet and a width of 125 feet, with five cutoffs on each bayou; enlargement and realign­ ment of the existing channel in Mermentau River above the GIWW to provide a channel 12 feet deep and 200 feet wide through Lake Arthur and 12 feet deep and 125 feet wide with nine cutoffs above Lake Arthur; and Federal participation in the cost of replacing the existing Louisiana State Highway 14 bridge at Lake Arthur with a new bridge having a vertical clearance of 50 feet above high water and a horizontal clearance of not less than 200 feet, with apportionment of the cost between the bridge owner and the United States in accordance with the principles of Section 6, Public Law 647, Seventy-sixth Congress, as amended. The channel clearances of all other bridges across the project channels are adequate for navigation. The Mermentau River Basin and the authorized improvements are shown on the three inclosed maps. A general design memorandum for the project has been approved. The benefit-cost ratio of the project based on the $6,731,000 cost estimate is 1.15. 2. Environmental setting without the project. The Mermentau River is formed by the confluence of Bayous Nezpique and des Cannes 2 miles above the town of Mermentau, Louisiana, from whence it flows about 72 miles to the Gulf of Mexico. The Mermentau Basin was formerly within the Mississippi and Red Rivers drainage systems. The northern part of the basin above the GIWW is comprised of uplands of Pleistocene origin and the southern part below the GIWW is comprised of prairie and coastal marsh of Recent deltaic origin. Beneath the entire study areo. is a sand and gravel aquifer known as the Chicot Reservoir which varies in thickness from a few feet to about 800 feet and in depth below the ground surface from about 50 to about 200 feet. That part of the Mermentau and its tributaries included in the project has incised into the Pleistocene sediments. Elevations in the Mermentau Basin range from 1 to 2 feet above m.s.l. (mean sea level) in the marshes to about 100 feet m.s.l. in the headwater area of Bayou Nezpique. Within the project area, ground elevations range from 1 to 2 feet above m.s.l. near the GIWW to a maximum of 20 to 25 feet above m.s.l. at the northern end of the project. Except for Bayou Lacassine, the tributaries of the Mermentau River rise in the uplands and generally follow tortuous channels through well-defined flood plains. Bayou Lacassine is formed in the swamps near Jennings by the junction of the East and West Forks of Bayou Lacassine and flows about 30 miles south through low prairie and marsh to Grand Lake. These streams flow through stable channels and carry little silt. Stages in the lower Mermentau Basin are partially controlled by four* structures which are designed to prevent the intrusion of salt water from the Gulf of Mexico and to maintain a stage sufficient to provide adequate water supplies for the irrigation of rice. Withdrawals for irrigation have lowered stages during dry periods to zero mean low gulf level. Conversely, the retention of water for irrigation of rice has resulted in flooding during periods of heavy rainfall. However, during the past 50 years, only the floods of August 1940 and May 1953 have caused flooding of major parts of the Mermentau Lisin. The upper part of the basin is extensively cleared for agricul­ ture and grazing. Remaining wooded areas on the higher ground are in upland pine and hardwoods. The stream flood plains are predominately in bottomland hardwoods. The prairie land is primarily grassland that is devoted to pasture and agriculture, with rice being the principal crop. The marshlands vary from completely fresh over most of the area to a highly saline band approximately 1 mile in width near the Gulf of Mexico. Marsh vegetation is determined primarily by water depth and salinity. Much of this marsh is used for grazing. The Mermentau River Basin contains valuable fish and wildlite resources. Habitat for migratory waterfowl is the most important resource, with large concentrations of ducks, geese, and coots annually overwintering in the prairies as well as the coastal marshes of the basin. Two major wildlife refuges are located within the basin. The 31,124-acre Lacassine National Wildlife Refuge and the 83,000-acre State-owned Rockefeller Wildlife Refuge are within the Mermentau Basin. Both have been intensively developed for waterfowl. The wetlands of the lower basin are also extensively used by other migratory birds such as snipe, rails, and gallinules. Fur animals are abundant, particularly in the lower basin, with muskrat and nutria leading in both value and numbers trapped. Alligators, an endangered species, remain common in the lower basin, with the largest numbers found on the two aforementioned refuges. The upper part of the Mermentau Basin, which includes the immediate project area, provides fair habitat for squirrels, quail, rabbits, and deer. The commercial and sport fishery resources of the basin are also of major importance. That part of the basin generally south of the Catfish Point Control Structure provides good harvests of shrimp, crabs, and finfishes, and also serves as nursery and spawning areas for various species which are harvested offshore. The remainder of the coastal wetlands between the GIWW and the Catfish Point Control Structure provides an excellent fresh water sport fishery. That part of the basin above the GIWW, which includes the immediate project area, provides a fair fresh water fishery. The U. S. Department of the Interior has advised the Corps of Engineers that a number of archaeological sites are located in the project area. There are no national parks or known historical sites in the area. The 1970 population of the parishes drained by the Mermentau Basin was 185,654. The largest towns are Crowley and Jennings with populations of 16,104 and 11,783, respectively. Transportation in the basin is provided by the Missouri Pacific and Southern Pacific Lines (both mainline railroads), numerous state highways, U. S. Highways 90 and 190, Interstate 10 Highway, and the GIWW and connecting waterways. Mineral production, consisting of oil and natural gas, is of major importance in and adjacent to the basin. Many access and pipeline canals have been constructed in the marsh by non-Federal interests in the exploitation of this resource. Industries in the area consist of rice mills, ship building plants, food processing plants, packing houses, machine shops, cotton compresses, building material plants, and canneries. In addition to rice, major crops include sweet potatoes and corn. The raising of livestock is also of major importance in the area economy.