Chapter 3 Lecture Notes-Streams

Chapter 3 Lecture Notes-Streams - Prof. Jerry W. Kousen...

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Prof. Jerry W. Kousen ERTH100 Vincennes University Intro to Earth Science Streams and Drainage Systems Streams A stream is a body of water that carries rock particles and dissolved ions and flows down slope along a clearly defined path, called a channel . Thus, streams may vary in width from a few centimeters to several kilometers. Streams are important for several reasons: Streams carry most of the water that goes from the land to the sea, and thus are an important part of the water cycle. Streams carry billions of tons of sediment to lower elevations, and thus are one of the main transporting mediums in the production of sedimentary rocks. Streams carry dissolved ions, the products of chemical weathering, into the oceans and thus make the sea salty. Streams are a major part of the erosional process, working in conjunction with weathering and mass wasting. Much of the surface landscape is controlled by stream erosion, evident to anyone looking out of an airplane window. Streams are a major source of water and transportation for the world's human population. Most population centers are located next to streams. Geometry and Dynamics of Stream Channels The stream channel is the conduit for water being carried by the stream. The stream can continually adjust its channel shape and path as the amount of water passing through the channel changes. The volume of water passing any point on a stream is called the discharge . Discharge is measured in units of volume/time (m 3 /sec). Cross Sectional Shape - varies with position in the stream, and discharge . The deepest part of channel occurs where the stream velocity is the highest. Both width and depth increase downstream because discharge increases downstream. As discharge increases the
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cross sectional shape will change, with the stream becoming deeper and wider. Long Profile - a plot of elevation versus distance. Usually shows a steep gradient near the source of the stream and a gentle gradient as the stream approaches its mouth. Base Level - base level is defined as the limiting level below which a stream cannot erode its channel. For streams that empty into the oceans, base level is sea level. Local base levels can occur where the stream meets a resistant body of rock, where a natural or artificial dam impedes further channel erosion, or where the stream empties into a lake.
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When a natural or artificial dam impedes stream flow, the stream adjusts to the new base level by adjusting its long profile. In the example here, the long profile above and below the dam are adjusted. Erosion takes place downstream from the dam (especially if it is a natural dam and water can flow over the top). Just upstream from the dam the velocity of the stream is lowered so that deposition of sediment occurs causing the gradient to become lower. Velocity -
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Chapter 3 Lecture Notes-Streams - Prof. Jerry W. Kousen...

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