A River's Three Stages

Geographers divide a river into three sections based on character. The upper course near the source is steep, fast, and narrow, cutting V-shaped valleys and waterfalls. The middle course widens as tributaries join, flowing through broader valleys with growing meanders.

The lower course is where the river reaches its widest and slowest. Here it deposits sediment, building floodplains and deltas. The Mississippi's bird's-foot delta — built entirely from sediment the river carried downstream — sprawls across roughly 2,000 square kilometers where the river finally empties into the Gulf of Mexico, about 160 kilometers below New Orleans.