Alluvial Channels: Definition & Types

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  • 0:01 Alluvial Channels
  • 1:36 Meandering Channels
  • 3:46 Braided Channel
  • 4:23 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

An alluvial channel is a water channel made up of loose sediments called alluvium. Learn about the types of alluvial channels, meandering channels and braided channels, and the characteristics that make them unique in this lesson.

Alluvial Channels

If you were on a hike and came up to a 'Y' in the road, would you take the path that was nicely worn and smooth or would you take the rocky and uneven path? In other words, would you take the easy or the hard path?

Well, if you were water, you would take the path of least resistance. In fact, water will go out of its way to take the easy path. This is why some waterways seem to meander, twist and flow in wild ways. These patterns of flow are seen in alluvial channels, which are water channels made up of loose sediments. The different types of alluvial channels and their unique characteristics are the focus of this lesson.

Alluvial channels have the ability to adjust and shift. This is because they consist of loose sedimentary materials known as alluvium. If you walk up to a stream, reach in and pull up a handful of silt, sand, pebbles and other particles, you would be holding alluvium.

These particles can be picked up in the flow of the stream and deposited downstream. If the stream is moving fast, the water has more force and causes erosion, or wearing away, of little sediment chunks from the banks of the channel. Consequently, if the water flow is slow, we see the settling of sediments, which is a process called deposition. This erosion and deposition explains how alluvial channels are able to change their shape or course over time.

Meandering Channels

There are a couple of different types of alluvial channels. One type is a meandering channel, or meandering stream. This is a channel that follows a winding course. If you look at a meandering stream from an airplane, it looks as if the stream cannot make up its mind which way it wants to go, so it keeps cutting back and forth through the valley, somewhat like a snake moving through the grass. It meanders because it is always trying to find the easiest path or low point to flow into.

As the channel curves, we see that the water on the outside of the bend moves faster than the water on the inner area. Therefore, erosion happens on the outer bend. This continual force chips away at the channel, forming a cut bank, which is defined as a small cliff on the outer bank of the channel caused by erosion. It is as if the stream is slowly sculpting its path through the landscape.

In contrast, the inner curve experiences calmer conditions that allow for the formation of a point bar, which is a collection of sediment materials along the inner curve of the channel caused by deposition. A point bar can be a nice place for fisherman to stand close to the stream without getting their feet wet.

Once a stream matures, the curves accentuate and can grow closer to each other. This increases the chance that the stream will cut through the landscape and we will see two bends joined by a new channel. This is called a meander cutoff. In essence, the waterway found an easier and shorter path and cut through. Of course, this isolates part of the stream.

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