Setting stage for Mississippi River shift

Sediment buildup along the Lower Mississippi River could set the stage for a shift of the river into the Atchafalaya Basin, according to a study by an LSU research scientist. Sediment deposited on the river’s bottom north of Baton Rouge, La., and south of the Old River Control Structure, has reduced the river’s depth by nearly 30 feet and narrowed the channel by half a mile since the mid-1980s, according to hydrologist Yi-June Xu, affecting its flow capacity below Old River’s gates. The gates were built in stages by the Army Corps of Engineers beginning in the 1960s to prevent a flood from shifting the river’s flow into the Atchafalaya Basin. There’s been evidence of the river changing course in intervals at about every 1,500 years. The Atchafalaya would give the Mississippi a 150-mile shorter flow-route from Old River to the Gulf of Mexico. Some 36M metric tons of sediment increases the risk of a “mega flood” that could overflow structures and triggering a full flow into the Atchafalaya that may have major consequences for people and the state’s economy, according to the research. There are some 530M metric tons of sand on emerged river bars upstream from Old River to Vicksburg, Miss. If those were to be swept downstream, it could cause the river to jump its bank at Old River. Also, river-flow projections could increase by up to 60 percent by 2100 due to precipitation and urban-growth runoff risk factors. A river breakout through the Atchafalaya would be catastrophic for south Louisiana’s industries and would create a public water supply crisis for some 1.5M citizens in the New Orleans area and communities that draw drinking water from the river. An Atchafalaya Basin flood would more than likely overwhelm Morgan City, La. There’s one potential course of action: Mining sediments for use in Louisiana’s massive coastal restoration enterprise, but Xu cautions that the risks and challenges are immense. (Source: Work Boat 01/02/18)