The Formation of Stream Valleys

Lesson Transcript
Instructor: Margaret Cunningham

Margaret has taught many Biology and Environmental Science courses and has Master's degrees in Environmental Science and Education.

A stream valley is an elongated depression in the ground with water flowing at the lowest point. Learn what a stream valley is and explore how water, time, and erosion help form them. Updated: 09/28/2021

What Is a Stream Valley?

Next time you see a stream or river, take a minute and observe the water. Look at how fast the water is moving, the direction of the water, and how it has shaped the landscape around the waterway. Running water is very powerful and has the ability to drastically change the landscape around it. Most changes to the land are due to erosion, which is the movement of broken-down rock or soil from one place to another. The running water of a stream helps move particles from their original location to new areas.

When enough land is eroded, a stream can create a stream valley, which is a depression in the earth with water flowing at the lowest point. Stream valleys are also characterized by having a floodplain, which is the wide and level bottom of the valley. Floodplains are important because they designate the areas where the water will fill if the stream floods. Stream valleys can vary by the depth of the valley, the slope of the sides, and the size of the floodplain.

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The Formation of Stream Valleys

The formation of a stream valley is a long process. Over many years, the stream valley changes and develops due to an aging process. The aging process of a stream valley has three stages, including youth, maturity, and old age.

The youth stage occurs when a stream is located on an uplifted landmass. There is a steep gradient to the land and this causes vigorous and energetic water flow, which results in downward erosion. Stream valleys in the youth stage are often V-shaped, with steep sides, and they do not have any established floodplain yet. They are also characterized by having interrupted stream flow due to boulders, rapids, and waterfalls.

The maturity stage occurs when the stream erodes the valley and removes the boulders, rapids, and waterfalls. Instead of eroding downward, the stream begins to erode the sides of the valley. The valley gets wider and becomes more U-shaped. The valley becomes smoother and has a less steep gradient, which results in more gentle and slower moving water. A mature stream valley is also characterized by a stream with more sloping sides rather than steep sides. This characteristic leads to the formation of a large floodplain where water can escape if the stream becomes flooded.

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