River Channels

A channel is the long trough along which a river flows. When a river's channel winds or has a rough bed, friction slows the river down.

A river flows faster through a narrow, deep channel than a wide, shallow one because there is less friction. All river channels tend to wind, and the nearer they are to sea level, the more they wind. They form remarkably regular horseshoe-shaped bends called meanders.

Meanders seem to develop because of the way in which a river erodes and deposits sediments. One key factor in meanders is the ups and downs along the river called pools(deeps) and riffles(shallows).

The distance between the pools and riffles, and the size of meanders, are in close proportion to a river's width.

Another key factor in meanders is the tendency of river water to flow not only straight downstream but also across the channel. Water spirals through the channel in a corkscrew fashion called helicoidal flow.

Helicoidal flow makes water flow faster on the outside of bends, wearing away the bank. It flows more slowly on the inside, building up deposits called slip-off slopes.