Credit: M. Blum/NASA

Nature Geosci. 2, 488–491 (2009)

The Mississippi Delta is sinking, and to rebuild it some have proposed diverting the Mississippi River to carry sediment to coastal areas. But a new study shows that the delta's rivers don't have enough sediment to counter predicted sea-level rise.

Mike Blum and Harry Roberts, both then working at Louisiana State University in Baton Rouge, found that the rivers currently transport less sediment than the amount that was needed for delta formation. Sinking land and accelerating sea-level rise will submerge 10,500–13,500 square kilometres by 2100, they predict.

Even if sediment trapped in dams was freed, the duo found, the rivers still couldn't supply the 18–24 billion tonnes needed to keep the delta above water until the end of the century.