This is known as a radial drainage pattern.īecause streams erode more and remove more sediment where the stream gradient is higher, and deposit more sediment where the stream gradient is lower, a stream will develop a graded profile as shown. Streams will radiate in all directions from the center of a broad, high-elevation area, such as a composite cone. The stream valleys will bend sharply where they switch from following one joint set to another. As stream valleys develop in the joint system a rectangular drainage pattern develops, as shown in figure 3. The sets of joints typically intersect each other at high angles.
In some places the geology consists of a single type of rock that is resistant to erosion but the rock contains sets of parallel joints where it erodes more easily. This results in a trellis drainage pattern, as show in figure 2. If a region is underlain by layered formations of rock that have been folded, and the layers have different degrees of resistance to erosion, the stream valleys will tend to follow the layers of less resistant rock, and the layers of harder rock will become ridges. A dendritic drainage pattern is the most common type. If the geology underlying a stream system is fairly uniform-rocks equally resistant to erosion in all directions-a dendritic drainage pattern will develop, as shown in figure 1. Some types of rock are harder and more resistant to erosion than others.
The drainage pattern depends on the rock types and geologic structures underlying the stream system. Where the slopes are steepest and the hills the highest, the streams will be the most energetic and the rate of erosion will be fastest.Ī stream system that includes multiple tributaries exhibits a distinct drainage pattern as seen on a map. The higher the hill, the more gravitational energy there is to drive the stream. Streams flow downhill due to the force of gravity. Streams erode dirt and rocks, transport the sediment, and redeposit it in new locations, shaping the earth’s surface into a system of stream valleys. Most valleys on earth are the product of streams. Over longer intervals of time the same processes we’ve imagined on the construction site have built systems of streams and stream valleys on the surface of the earth. If not prevented, the channels may continue to deepen and erode soil from the construction site. A network of streams, including tributaries, has formed. Soon, the water excavates small channels, known as rills, in the dirt. At first the water saturates the ground and begins to flow downhill across the surface of the slope in a thin sheet. It is interesting to watch water on a recently bulldozed construction site with a slope. A small brook in a meadow and the Amazon River are both streams. \)Ī stream is flow of water, driven by gravity, in a natural channel, on land.
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