SAN FRANCISCO, CALIFORNIA—The April and May 2011 floods along the Mississippi River were among the most damaging of the last century. But scientists hoped for a silver lining: evidence that floodwaters would inject a much-needed supply of sediments into to the region's rapidly eroding wetlands. Research presented here yesterday at the American Geophysical Union's fall meeting here, however, suggests mixed results from this "natural experiment." On the downside, satellite analyses, boat surveys, and sediment sampling revealed that the Mississippi River injected its sediment directly into the Gulf of Mexico, bypassing the wetlands. However, a plume of floodwaters diverted through the shallower, slower Atchafalaya Basin, a wetland connected to the Mississippi through the Morganza Spillway, distributed its sediments more widely among the coastal marshes. Although that's cause for hope, the mixed results suggest managers wishing to rebuild the wetlands by diverting the river's flow will need to think carefully about where to divert the waters.
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