Stream Channels & Valleys

The longitudinal profile of a stream shows how the gradient (see Chapter 6 in the Lab Manual) gradually decreases from the head to the mouth of the stream.

The mouth is the base level for a stream – it limits the depth to which that stream can erode.

Over time, a stream adjusts its channel and longitudinal profile in response to changes in discharge, base level, and erodibility of the rock or sediment over which it flows.

Adjustments lead to a near balance between erosion and deposition along the stream course to produce a smooth longitudinal profile.

A stream that does not have a smooth profile erodes or deposits so as to attain one (waterfalls and rapids are eroded, lakes or ponds along the stream are filled in).

The size of the stream channel and the velocity & volume of water all increase downstream.

Discharge = volume of water per unit of time (velocity x cross-sectional area of channel) and the common units are m³/sec or ft³/sec.

As discharge increases so does all of its components – during flooding the velocity and channel size increase.

Stream velocity, channel area, and discharge are recorded at gaging stations on many streams throughout the USA.