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Historic Flooding Occurring on Lower Mississippi River
Monday, May 9, 2011

Historic Flooding Occurring on Lower Mississippi River

Record crests are moving down the Mississippi River from Cairo, Illinois, to the Gulf of Mexico. MG Michael J. Walsh, President of the Mississippi River Commission (MRC*), in charge of MR&T operations, released this statement: “We are currently experiencing the largest flood in the Watershed and in the history of the Mississippi River and Tributaries (MR&T) project. We are assisting locals in helping protect communities. As the highest crest in history works its way downstream, the last line of defense protecting life and livelihood is the proper operation of the MR&T project.”

The Corps of Engineers built the MR&T project after the devastating 1927 flood (that flood and its impact is well documented in the John Barry book “Rising Tide”). The MR&T project employs a variety of intensely managed engineering techniques, including an extensive levee system, floodways to divert excess flows past critical reaches to relieve pressure on levees, channel re-alignment and deepening, and pumping stations. Some of the features include bypasses, such as the Birds Point to New Madrid floodway where the Corps is required to open a levee on the Missouri side of the river to relieve pressure on the levee in Cairo, Illinois. This allows about a quarter of the river flow to leave the main channel and use the floodway to travel downstream to New Madrid before re-entering the main river. In the late 1920s and early 1930s, the Corps was directed to purchase flooding easements from the 130,000 acres of farmland in the Floodway so the Floodway could be operated when needed. Until this year, the last time the Birds Point floodway was operated was in 1937.

Other relief features are in place further downstream such as the Bonnet Carre’ Spillway, Morganza floodway, and the West Atchafalaya floodway. All of these are essentially relief valves for diverting flood flows from the main stem of the river in order for the levees along the main stem to be high enough to contain flows without overtopping. To put some perspective on the amount of flood flow in the Lower Mississippi river, the Project Design Flood at Cairo is over 2 million Cubic Feet per Second (cfs). At Vicksburg it is 2.7 million cfs. And above New Orleans it would be 3 million cfs IF flows were not diverted in the Atchafalaya floodway, which is designed to take half of that flow. The record flood crests this year are projected to exceed those of the past records from 1927, 1937, and 1973 in various spots along the river.

ASFPM has some of the documents about the MR&T and the Birds Point floodway on our web site. Click on this link Birds Point-New Madrid Floodway Information Paper.Additional documents are available on the MRC link below.

You can monitor the river gages yourself at various points on the river by going to http://www.rivergages.com/ (select Vicksburg District / Mississippi River and Passes for the Birds Point area).

*The Mississippi River Commission (MRC) was established by an Act of Congress on June 28, 1879. Congress charged the MRC with the mission to develop plans to improve the condition of the Mississippi River, foster navigation, promote commerce, and prevent destructive floods—perhaps the most difficult and complex engineering problem ever undertaken by the federal government up to that take. Today the MRC, which is headquartered in Vicksburg, Miss., provides water resources engineering direction and policy advice to the Administration, Congress, and the Army in a drainage basin that covers 41 percent of the United States and parts of two Canadian provinces by overseeing the planning and reporting on the improvements on the Mississippi River. http://www.mvd.usace.army.mil/mrc/

Compiled 5/9/2011 by the Association of State Floodplain Managers (ASFPM) www.floods.org





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