8.2 Stream Types

Stream channels can be straight or curved, deep and slow, or rapid and choked with coarse sediments. The cycle of erosion has some influence on the nature of a stream, but there are several other factors that are important including gradient, discharge, and sediment load. A few key types of streams are described below.

Figure 8.2.1: The Cascade Falls area of the Kettle River, near Christina Lake, B.C. This stream cuts a deep narrow channel through the bedrock
Figure 8.2.1: The Cascade Falls area of the Kettle River, near Christina Lake, B.C. This stream cuts a deep narrow channel through the bedrock

Youthful streams that are actively down-cutting their channels tend to be relatively straight and are typically ungraded (meaning that rapids and falls are common). They also have steep gradients and steep and narrow V-shaped valleys—in some cases steep enough to be called canyons.

In mountainous terrain, such as that in western Alberta and B.C., steep youthful streams typically flow into wide and relatively low-gradient U-shaped glaciated valleys. The youthful streams have high sediment loads, and when they flow into the lower-gradient glacial valleys where the velocity isn’t high enough to carry all of the sediment braided patterns develop, characterized by a series of narrow channels separated by gravel bars.

Figure 8.2.2: Red River in Lake Clark National Park, Alaska, is an example of a sediment-laden braided stream. This braided stream transports glaciofluvial sediments from the Red Glacier, an alpine glacier formed on Iliamna Volcano (highest peak to the left of the stream), to Cook Inlet.
Figure 8.2.2: Red River in Lake Clark National Park, Alaska, is an example of a sediment-laden braided stream. This braided stream transports glaciofluvial sediments from the Red Glacier, an alpine glacier formed on Iliamna Volcano (highest peak to the left of the stream), to Cook Inlet.

Braided streams can develop anywhere there is more sediment than a stream is able to transport. One such environment is in mountainous areas, where streams carry glaciofluvial sediments from alpine glaciers (Figure 8.2.2). Another such environment is in volcanic regions, where explosive eruptions produce large amounts of unconsolidated material that gets washed into streams. Streams in the volcanic Mt. Meager area of southwestern British Columbia are good examples of this.

A meandering stream that occupies a wide, flat flood plain with a low gradient typically carries only sand-sized and finer sediments and develops a sinuous flow pattern. As you saw in Figure 8.1.1, when a stream flows around a corner, the water on the outside has farther to go and tends to flow faster. This leads to erosion of the cut banks on the outside of the curve, deposition on the inside, and formation of a point bar (Figure 8.2.3). Over time, the sinuosity of the stream becomes increasingly exaggerated, and the channel migrates around within its flood plain, forming a meandering pattern. As point bars develop over time, their surfaces form ridges called scroll bars. There is even evidence of these scroll bars and meandering channels on Mars (Figure 8.2.4)!

Figure 8.2.3: The confluence of the Alatna and Koyukuk Rivers near the western border of the Kanuti National Wildlife Refuge in Alaska. Both rivers pictured are examples of meandering streams, with sinuous channels, deposition of sediment on point bars, and erosion along the cut banks. Notice the narrow neck separating the channel in the foreground. When this neck is eventually eroded away, the meander in the foreground will be abandoned and will create an oxbow lake.
Figure 8.2.3: The confluence of the Alatna and Koyukuk Rivers near the western border of the Kanuti National Wildlife Refuge in Alaska. Both rivers pictured are examples of meandering streams, with sinuous channels, deposition of sediment on point bars, and erosion along the cut banks. Notice the narrow neck separating the channel in the foreground. When this neck is eventually eroded away, the meander in the foreground will be abandoned and will create an oxbow lake. [Image description]

A well-developed meandering river is shown in Figure 8.2.3. The meander in the middle of the photo has reached the point where the thin neck of land between two parts of the channel is about to be eroded through. When this happens, an oxbow lake will form. When an oxbow lake dries up, it leaves behind a curved meander scar filled with muddy sediment. 

At the point where a stream enters a still body of water—a lake or the ocean—sediment is deposited and a delta forms. The Fraser River has created a large delta, which extends out into the Strait of Georgia (Figure 8.2.5). Much of the Fraser delta is very young in geological terms. Shortly after the end of the last glaciation (10,000 years ago), the delta did not extend past New Westminster. Since that time, all of the land that makes up Richmond, Delta, and parts of New Westminster and south Surrey has formed from sediment from the Fraser River.

Figure 8.2.4: A sinuous channel in the Aeolis Planum region of Mars taken by the HiRISE camera on the Mars Reconnaissance Orbiter. Blue arrow indicates the sinuous channel-like form, and orange arrows indicate areas with scroll bars (curved ridges).
Figure 8.2.4: A sinuous channel in the Aeolis Planum region of Mars taken by the HiRISE camera on the Mars Reconnaissance Orbiter. Blue arrow indicates the sinuous channel-like form, and orange arrows indicate areas with scroll bars (curved ridges).
Figure 8.2.5: The delta of the Fraser River and the plume of sediment tFigure 8.2.5: The delta of the Fraser River and the plume of suspended sediment that extends across the Strait of Georgia in British Columbia. The land outlined in red has formed over the past 10,000 years.hat extends across the Strait of Georgia in British Columbia. The land outlined in red has formed over the past 10,000 years.
Figure 8.2.5: The delta of the Fraser River and the plume of suspended sediment that extends across the Strait of Georgia in British Columbia. The land outlined in red has formed over the past 10,000 years.

Image Descriptions

Figure 8.2.3 image description: A part of the Alatna River near its confluence with the Koyukuk River has curved around so sharply that it almost forms a circle before curving the other way again. Eventually, as the barrier between these two parts of the channel erodes, they will be joined and form an oxbow lake. [Return to Figure 8.2.3]

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A Practical Guide to Introductory Geology (2021-2022 Edition) Copyright © 2021 by Benjamin Daniels is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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