7.3 Stream Types

Steven Earle and Laura J. Brown

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.

photograph of the Cascade Falls
Figure 7.3.1 The Cascade Falls area of the Kettle River, near Christina Lake, B.C. This stream has a step-pool morphology and a deep bedrock channel.

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). As shown in Figures 7.3.1, youthful streams commonly have a pool morphology, meaning that the stream consists of a series of pools connected by rapids and waterfalls. They also have steep gradients and steep and narrow V-shaped valleys—in some cases steep enough to be called canyons.

In mountainous terrains, 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 7.3.2).

photograph of the braided channel of the Kicking Horse River
Figure 7.3.2 The braided channel of the Kicking Horse River at Field, B.C.
photograph of the braided channel of Meager Creek
Figure 7.3.3 The braided channel of Meager Creek in the Mt. Meager area

Braided streams can develop anywhere there is more sediment than a stream is able to transport. One 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 (Figure 7.3.3).

A 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. 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 banks on the outside of the curve, deposition on the inside, and the formation of a point bar (Figure 7.3.4). Over time, the sinuosity of the stream becomes increasingly exaggerated, and the channel migrates around within its flood plain, forming a meandering pattern.

photograph of the meandering channel of Bonnell Creek
Figure 7.3.4 The meandering channel of the Bonnell Creek, Nanoose, B.C. The stream is flowing toward the viewer. The sand and gravel point bar must have formed when the creek was higher and the flow faster than it was when the photo was taken.

A well-developed meandering river is shown in Figure 7.3.5. 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, another oxbow lake will form like the others in the photo.

aerial photograph of the meandering channel of Nowitna River
Figure 7.3.5 The meandering channel of the Nowitna River, Alaska. Numerous oxbow lakes are present and another meander cutoff will soon take place. [Image Description]

Exercise 13.4 Determining stream gradients

illustration mapping Priest Creek with elevations indicated
Figure 7.3.6 Elevations on Priest Creek at Kelowna, BC.

The gradient is the key factor controlling stream velocity, and of course, velocity controls sediment erosion and deposition. This map shows the elevations of Priest Creek in the Kelowna area (Figure 7.3.6). The length of the creek between 1,600 metres and 1,300 metres elevation is 2.4 kilometres, so the gradient is 300/2.4 = 125 metres per kilometre.

  1. Use the scale bar to estimate the distance between 1,300 metres and 600 metres and then calculate that gradient.
  2. Estimate the gradient between 600 and 400 metres.
  3. Estimate the gradient between 400 metres on Priest Creek and the point where Mission Creek enters Okanagan Lake.

 

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 7.3.7). 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. (You can see this in more detail at Geoscape Vancouver.)

aerial photograph of the Fraser River delta showing plume of sediment
Figure 7.3.7 The delta of the Fraser River and the plume of sediment that extends across the Strait of Georgia. The land outlined in red has formed over the past 10,000 years.

Image Descriptions

Figure 7.3.5 image description: A part of the Nowitna 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 7.3.5]

Media Attributions

  • Figures 7.3.1, 7.3.2, 7.3.4, 7.3.6: © Steven Earle. CC BY.
  • Figure 7.3.3: “Meager Creek” © Isaac Earle. CC BY.
  • Figure 7.3.5: “Nowitna river” by Oliver Kumis. CC BY-SA.
  • Figure 7.3.7: Delta of the Fraser River by NASA. Taken September 2011. Adapted by Steven Earle. Public domain.

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7.3 Stream Types Copyright © 2022 by Steven Earle and Laura J. Brown is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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