The Nile's floods poured alluvial soil onto the land and enriched the crop land

hidden on the Nile 2
Originally uploaded by ahmed the egyptian

Alluvial soil, aka silt, is extremely fertile. Once the Mississippi flooded, too, and created a fertile delta in Arkansas, Mississippi and Louisiana.

Today both the Mississippi and the Nile have been tamed by levees and dams. There's no more regular flooding.

But problems with the dam at Aswan and the loss of land around the mouth of the Mississippi have resulted from the changes.