A river runs through it

Erosion & rivers

River-related vocabulary You may recall the following terms. A tributary is a small stream that empties into a

larger river. A watershed is the land that water runs off from

into a river. A divide is an elevated region that separate

watersheds. The path a river follows is called the channel. The lengthening and branching of a river is called

headward erosion.

Stream Erosion Rivers form when

precipitation exceeds evapotranspiration.

The excess water then carries weathered soil and rock away, and forms a gully.

This also causes stream piracy, which is when one stream “captures” another and alters its channel.

Channel Erosion The edges of a stream are

called banks. The flow of a stream is

carrying other sediments – these are called loads.

The three types are suspended, bed, and dissolved loads.

The movement of these loads contributes to the erosion of sediments in the channel.

Discharge, gradient, and gaps The discharge is the

volume of water moved by a stream in a given time.

The gradient is the change in elevation of a stream from top to bottom.

A gap is a formation of a river through a mountain range, usually by the motion of isostatic adjustments.

River stages A young river has a fast

headward erosion, forming a V-shaped valley and waterfalls.

A mature river drains its watershed and usually only erodes its banks when it floods.

A mature river also bends and curves, and banks along these parts erode faster (these are called meanders). Abandoned meanders are called Oxbow lakes.

River stages An older river has a lower

gradient and lower discharge.

It usually deposits its loads along the bank and channel, forming a flat plain.

Movement of the earth’s crust can rejuvenate a river, and increase its gradient and/or discharge.

Reading and assignment Now read pages 247-251. The following

vocabulary will appear: Tributaries, watershed, divides, channel,

headward erosion, stream piracy, stream load (please also define suspended, bed, and dissolved loads), saltation, discharge, gradient, headwaters, water gap, wind gap, meanders, oxbow lake, rejuvenated.

Your homework will be to “glossarize” these words.