Tuesday, 7 October 2008: 1:40 PM
George R. Brown Convention Center, Ballroom C
The continued rapid loss of wetlands on the Mississippi Rivera delta plain is the result of sediment starvation and rapid relative sea level rise. Dams upstream have reduced the sediment load reaching the Mississippi and Atchafalaya from 600 million metric tons to about 250 metric tons per year. On the Mississippi, continuous levees extend southward across the delta plain to near the mouth, eliminating renourishment of wetlands and shunting the river sediment to the edge of the continental shelf where it is lost. Wetlands are being lost at an average rate of more than 60 km2 per year with higher pulses during hurricanes. Water is about one meter deep across recently lost marshes and to two meters deep in earlier lost marshes. Global sea level rise is presently rising at 3 mm per year and subsidence across the delta is at 4-11 mm per year. Relative sea level is, thus, presently rising at 70-140 cm per century, and with global warming will likely be over 200 cm in the coming century.
To address the loss of wetlands, more than 30 international wetland scientists and engineers met in Louisiana in April, 2006 to seek consensus on a meaningful, long-lasting solution. They concluded fundamental changes are needed immediately, including reconfiguring the lower Mississippi river.
To retard wetland loss and begin rebuilding the delta plain three steps area urgently needed. (1) Abandon the present Mississippi ‘birdsfoot' outlet with new outlets between Myrtle Grove and Venice. This will retain much of the outflow on the shelf to be reworked shoreward. (2) Eliminate levee margins wherever possible and provide water/sediment diversions where levees must remain so to provide freshwater and sediment nourishment to existing marshes. (3) Once the above are in place, remove all possible upstream dams which have impounded decades of sediment.