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Conference goers will certainly find themselves drawn to the Mississippi River. As NSTA participants stand along side the river and watch the amazing flow they will also have a chance to ponder the levee system.
The Mississippi River system drains and transports sediment from over thirty states and parts of Canada. The flooding of the Mississippi has been and continues to be vital to the creation of the |
wetlands of southern Louisiana through the sediments it carries. In the past, these sediments were deposited in the estuaries and marshes of southern Louisiana as the river flooded these areas. Alluvial rich soil revitalized the marshes by supplying nutrients for growth and soil for the natural development of new marsh. Presently, this type of beneficial flooding occurs far less frequently because of current flood control measures and the levee systems.
Levees are necessary structures for flood protection. The levees provide protection for inhabited areas in two respects: 1) levees along the Mississippi River prevent Mississippi River flood waters from escaping the channel; and 2) hurricane protection levees which surround communities to prevent hurricane storm surges from inundating an area, and allow water to be effectively pumped out of the area. The levee system was dramatically breached during hurricane Katrina and caused great suffering and widespread destruction of homes, community properties, businesses, etc.
Early settlements of the region were located on natural levees adjacent to the Mississippi River that were less likely to flood. As settlement continued, the limited amount of high ground that was available for settlement or agriculture production was depleted forcing later inhabitants to settle further back from the natural levees in the lower lying areas more susceptible to flooding. Settlers built levees along the Mississippi River to protect their homes and crops from flood danger because they recognized that flooding from the Mississippi would always be a problem.
The periodic input of sediment and water that is critical in the formation and maintenance of Louisiana's estuaries was lost when the channel of the Mississippi River was confined in place by massive constructed levees. The millions of tons of topsoil and nutrients that were historically deposited on these marshes during the annual spring floods of the Mississippi no longer are deposited due to the levee system. Instead, the channel of the Mississippi extends to the edge of the continental shelf and the sediments that once built the marshes are now deposited into deep water that precludes the formation of new marsh, or maintenance of existing marsh along the coast.
The levee system, while doing a good job of keeping water out, also does a good job of keeping water in, which is a problem because there is insufficient drainage for a heavy rainfall. Facilitation of drainage through pumping is an important aspect of the levee system especially during hurricane season since large storms bring large amounts of rain to the area. Runoff is now trapped inside the levees and has to be channeled into drainage canals and pumped out of the leveed areas. Pumps and pumping stations in low-lying areas control much of the excess always present.
--Jean May-Brett