Potential for water quality restoration through Mississippi River diversions

 

Michael G. Waldon, Ph.D., P.E.

University of Louisiana at Lafayette (retired), Currently Senior Hydrologist, Everglades Program Team, Loxahatchee National Wildlife Refuge, U.S. Fish and Wildlife Service, 10216 Lee Road, Boynton Beach, FL 33437, email: waldon@members.asce.org

 

Abstract:

Over the past 150 years in Louisiana, the Mississippi River System, including the Red and Atchafalaya Rivers, has been progressively isolated from the natural floodplain. This hydrologic isolation has provided flood control, and improved navigation. The river has been “controlled” by modifications including flood protection levees, training levees, jetties, dredging, spoil bank placement, floodway development, channel relocation, cut-offs, and control structures. This control has come at the price of reduction in water supply, water quality, and wetland ecosystem function. Coastal wetland land loss in Louisiana has resulted, in part, from loosing the river’s water, nutrients, and sediments. In this brief presentation, I will review two examples.

The Vermilion River achieved national notoriety in the 1970s as one of our nations most polluted rivers. The Vermilion River was once a distributary of the Atchafalaya River, and possibly the Red River, but was isolated from these sources by flood control projects that were completed in the 1930s. An amendment to the Mississippi River and Tributaries Act (MRT) authorized development of the Teche-Vermilion Freshwater Project to alleviate problems of water quantity and quality resulting from the MRT. Regular operation of the diversion initiated in 1983. Improvements in water quality of the Vermilion River have been documented following this flow augmentation.

The Atchafalaya River originates at the confluence of the Red River with Mississippi River diversion flow from the Old River Control Structures.  The U.S. Army Corps of Engineers attempts to maintain the flow at a 30/70 ratio, with 30 percent of the combined flow from the Red and Mississippi rivers flowing through the Atchafalaya Basin and the remaining 70 percent being carried by the Mississippi River. The Atchafalaya River Basin is the nation’s largest bottomland swamp.  As authorized under the MRT, the Atchafalaya Basin Floodway is bounded by protection levees to the east and west, roughly paralleling the River.  The floodway is approximately 125 miles long and 15 miles wide. The Atchafalaya Basin supports productive recreational and commercial fisheries, aquatic recreation, hunting, and non-consumptive recreation. Water quality issues include episodic low dissolved oxygen concentration, and localized excessive sedimentation. Flowing into the Gulf of Mexico through the Lower Atchafalaya River and the Wax Lake Outlet, the Atchafalaya River is now rapidly developing its delta. Increased Mississippi River diversion at times of intermediate discharge could provide improved water quality and productivity within the Atchafalaya Basin, while stimulating delta growth in Atchafalaya Bay. Diversion of flow to the less stratified coastal waters of Atchafalaya Bay would also reduce the development of hypoxia in the Gulf of Mexico.

 

Presented at: Coastal and Estuarine Wetland Restoration into the New Millennium: Improving Effectiveness, ASWM National Symposium and Workshop, Baton Rouge, Louisiana, June 2001.

 

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