Coastal Restoration In the Mississippi Delta - a Geo-Ecological Perspective

While the urgency of arresting and reversing coastal wetland loss in the Mississippi Delta has been recognized for decades, the issue has received widespread national attention only since the 2005 hurricane season. The numerous coastal restoration schemes that have been proposed increasingly converge on the critical need for large-scale river diversions that are capable of rebuilding substantial tracts of wetlands in strategically selected localities, within a reasonable (decadal) timeframe. We contend that fully restoring the wetlands that have been lost is not feasible, primarily due to the reduced sediment supply from the hinterland (mainly due to dam construction) and the expected increase in the rate of sea-level rise (current rates of sea-level rise on the U.S. Gulf Coast are at least four times higher than in the previous millennium). Nevertheless, we argue that river diversions have enormous potential and would be a dramatic improvement over the present situation where most of the Mississippi River sediment load is lost to the deep waters of the Gulf of Mexico. Detailed mapping of crevasse splays along the present river shows their abundance and testifies to the critical role of the Mississippi River in maintaining the health of the delta plain. Rebuilding wetlands in this fashion requires a better understanding of how rapidly crevasse splays aggrade and prograde, and how they interact with the subsurface in order to produce surface elevation gain. Studies of the late Holocene stratigraphic record of the Mississippi Delta show that compaction may accommodate as much as a third of newly introduced sediments, depending on the spatially variable subsurface architecture. Thus, we conclude that the time has arrived to go beyond the comparatively small diversion experiments and apply this method on a much larger scale.