13.4 present Types

Stream networks can be right or curved, deep and slow, or rapid and choked with coarse sediments. The bike of erosion has some affect on the nature that a stream, however there are number of other components that space important.

You are watching: In a typical stream, where the gradient is steep, the discharge is _____.

Youthful streams that are proactively down-cutting their networks tend to be fairly straight and are typically ungraded (meaning the rapids and falls room common). As shown in figures 13.1 and also 13.18, youthful streams typically have a step-pool morphology, definition that the stream is composed of a collection of pools associated by rapids and waterfalls. They likewise have steep gradients and also steep and narrow V-shaped valleys — in some instances steep sufficient to be dubbed canyons.

Figure 13.18 The Cascade drops area that the Kettle River, near Christina Lake, B.C. This stream has actually a step-pool morphology and also a deep bedrock channel.

In such as mountain terrain, such as that in west Alberta and B.C., steep youthful streams commonly flow into vast and reasonably low-gradient U-shaped glaciated valleys. The youthful streams have actually high sediment loads, and also when they circulation into the lower-gradient glacial valleys wherein the velocity no high sufficient to carry all of the sediment, braided trends develop, defined by a series of narrow networks separated by gravel bars (Figure 13.19).

Figure 13.19 The braided channel of the Kicking steed River at Field, B.C.

Braided streams can build anywhere over there is an ext sediment than a present is able to transport. One such atmosphere is in volcanic regions, whereby explosive eruptions produce large amounts the unconsolidated product that it s okay washed right into streams. The Coldwater River next to Mt. St. Helens in Washington State is a great example of this (Figure 13.20).

Figure 13.20 The braided Coldwater River, Mt. St. Helens, Washington.

A stream the occupies a wide, flat flood plain with a low gradient commonly carries just sand-sized and also finer sediments and develops a sinuous flow pattern. Together you saw in number 13.14, when a present flows approximately a corner, the water top top the outside has farther to go and also tends to flow faster. This leader to erosion that the financial institutions on the outside of the curve, deposition on the inside, and also formation that a allude bar (Figure 13.21). End time, the sinuosity of the present becomes progressively exaggerated, and also the channel migrates roughly within its flood plain, developing a meandering pattern.

Figure 13.21 The meandering channel the the Bonnell Creek, Nanoose, B.C. The stream is flowing toward the viewer. The sand and also gravel allude bar have to have created when the creek was greater and the flow much faster than it was when the photograph was taken.

A well-developed meandering flow is displayed in number 13.22. The meander in the center of the photo has actually reached the allude where the thin neck that land between two parts of the channel is around to be eroded through. When this happens, one more oxbow lake will kind like the others in the photo.

Figure 13.22 The meandering channel the the Nowitna River, Alaska. Plenty of oxbow lakes are present and another meander cutoff will quickly take place.

Gradient is the key factor regulating stream velocity, and of course, velocity controls sediment erosion and also deposition. This map reflects the elevations of priest Creek in the Kelowna area. The size of the creek between 1,600 m and also 1,300 m key is 2.4 km, for this reason the gradient is 300/2.4 = 125 m/km.

1. Use the range bar to estimate the distance in between 1,300 m and also 600 m and then calculate the gradient.

2. Estimate the gradient between 600 and also 400 m.

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3. Calculation the gradient in between 400 m on monk Creek and the allude 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 also a delta forms. The Fraser flow has produced a large delta, i m sorry extends out right into the Strait the Georgia (Figure 13.23). Much of the Fraser delta is really young in geological terms. Soon after the finish of the last glaciation (10,000 year ago), the delta walk not expand past brand-new Westminster. Since that time, all of the land that makes up Richmond, Delta, and parts of new Westminster and also south Surrey has created from sediment from the Fraser River. (You deserve to see this in more detail in ~ Geoscape Vancouver http://www.cgenarchive.org/vancouver-fraserdelta.html.)

Figure 13.23 The delta that the Fraser River and also the plume of sediment the extends across the Strait that Georgia. The land outlined in red has developed over the past 10,000 years.