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A Brief History of New Orleans Waterways and its Implications on Wetlands. Some of the information adapted from the work of S. Gagliano and W. Mitsch. The Mississippi River’s impact on New Orleans.
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A Brief History of New Orleans Waterways and its Implications on Wetlands. Some of the information adapted from the work of S. Gagliano and W. Mitsch
The Mississippi River’s impact on New Orleans • The present shape of Southeast Louisiana was formed over the last 7000 years from sediment deposited from the Mississippi River. • Building levees along the Mississippi, not just in Louisiana, with the intention of stopping flooding also stops the sediment deposition process. • The natural state or the river and its sediment deposition kept SE Louisiana above sea level.
With a few exceptions, most of the New Orleans area, including St. Bernard parish, is continuing to subside at an est. 4-6 mm/ yr. • Lack of sediment deposition • Ground water withdrawls (aquifer compaction) • Tectonic activity (faults) Louisiana State University
River Avulsion • As the Mississippi River caries sediment and silt southwards, the area around is built up. • Over Hundreds of years, the level of the river is elevated until it finally finds another course to the gulf. • The natural course of the river today is to merge with the Atchafalaya
Mississippi River Gulf Outlet • Idea conceived in the 1940s when New Orleans port officials requested the federal government build a safer, more efficient route. • Industrial Canal linking the Mississippi with Lake Pontchartrain built in 1923. • Among their concerns: • Route long, slow, and windy • Presence of sand bars provided some impedence • Losing business to Mobile, Tampa, and Especially Houston
Planning included the “Centroport”- an area around Almonaster Blvd. which would contain roads, rail, and an airport. • The Centroport failed to materialize except for the Jourdan Road Wharf. • Construction began in 1958 around the Industrial Canal at Paris Road and was completed in 1965. • The MRGO was operating in full capacity by 1968.
The 1956 Act of Congress authorizing the MRGO reads: • “The existing project for Mississippi River, Baton Rouge to the Gulf of Mexico, is hereby modified to provide for the Mississippi River-Gulf Outlet to be prosecuted under the direction of the Secretary of the Army and supervision of the Chief of Engineers, substantially in accordance with the Chief of Engineers, contained in House Document Numbered 245, eighty-second congress, at an estimated cost of $88,000,000…” • The MRGO was a relatively straight 76-mile long alternate passage to the 113 mile Mississippi River. • It was authorized to be 36-38 feet deep and 500-600 feet wide at the bottom.
This slide and the previous are courtesy of the Army Corp of Engineers.
By the 1990’s the average width of the MRGO was estimated at 1500 feet with estimates in some areas as high as 3000 ft. • Only 1-2 container vessels were using this channel when Katrina came in 2005.This at a 15 million per year maintenance cost. • It was estimated that had the wetlands in and surrounding the MRGO remained, the tidal surge would have overtopped the levies, but not destroy them.
