Levees on the Mississippi River shield communities but accelerate loss of Louisiana wetlands

Over the last hundred years, the US Army Corps of Engineers constructed about 2,000 kilometres of levees along the lower Mississippi River, successfully preventing major flood damage to populated areas and agriculture. At the same time, USGS analysis indicates that these barriers have rerouted the river’s sediment load away from the delta, sending it into the deep Gulf of Mexico. The resulting sediment deficit has allowed coastal marshes to sink, leading to the loss of nearly 1,900 square miles of Louisiana shoreline from 1932 to 2010.

In response, federal and state programs are dredging millions of cubic yards of river sediment and pumping it into eroded wetlands, exemplified by the Upper Barataria Marsh Creation Project, which added 1,259 acres of new marsh and tidal ponds. Monitoring by NOAA Fisheries and The Water Institute shows rapid recolonization by native shrimp, crabs, fish and marsh plants. The effort is guided by a 20-year adaptive management plan overseen by the Louisiana Trustee Implementation Group and USGS scientists. While the restored area is modest compared with the total loss, it offers a template for rebuilding other parts of the delta.