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2.) Cons, E.) Lifting Streams: Stream Rejuvenation, B.) The Work of Water:…
2.) Cons
reservoir sedimentation
the sediments that accumulate behind dams would have been deposited along coastal regions to help build and maintain coastal beaches. without these sediments, the beaches erode.
as reservoirs fill with sediments, their capacity to hold water decreases and sometimes disappears entirely, so that the useful life of the reservoir is limited.
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B.) Places of Deposition
sediments will settle out in the stream channel and accumulate when stream competence becomes insufficient to carry all the sediments that enter the stream.
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streams may lose energy after they flow through a steep-walled, V-shaped canyon that abruptly opens up onto a flat valley floor.
alluvial fan: a gently sloping accumulation of sediment deposited at the base of a mountain by an ephemeral stream in arid regions.
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Stream Drainage Patterns
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Deranged: forms on a surface that was recently covered by ice sheets.erosion by the glaciers leaves a landscape with many lakes and disorganized rivers connecting the lakes.
Radial: occurs on the flanks of volcanoes or conical mountains. streams flow outward away from a central point.
Rectangular: can form where bedrock jointing creates a linear, rectangular pattern and streams follow the joints.
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1.) Pros
water storage
dams deliver water by storing it in a reservoir and making it available at peak demand periods and in dry seasons.
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hydroelectricity
many large dams generate carbon-free hydroelectricity by using the kinetic energy of the water rushing out of the base of the dam to spin steek turbines that produce electrical energy.
transportation
former rivers are now a series of long, narrow lakes that allow large vessels to safely navigate the waterway.
recreation
water skiing, boating, fishing, swimming, and camping.
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How Stream Meanders Form
1.) a straight stream channel on a flat floodplain will develop meanders when the fastest flow, called the thalweg, increases erosion on one bank.
2.) a cut bank forms on the outside bend of a meander where flow velocity is highest. on the inside of a meander, where flow velocity is lowest, sediments are deposited to form a point bar.
3.) the meander loop deepens as erosion on the cut banks continues. as the meander deepens a meander neck forms.
4.) at the meander neck, a cutoff forms as the two meanders join. the abandoned stream channel creates an oxbow lake if it is filled with water, or a meander scar if it becomes dry.
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Headward Erosion
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2.) Rills migrate upslope through headward erosion, which deepens and lengthens them.
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16.4 VOCAB
flood - inundation by water in a region not normally covered by water, which results when stream discharge exceeds stream channel capacity.
flash flood - a flood that occurs with sudden, intense rainfall or dam collapse, often with little or no warning.
seasonal flood - a predictable period of flooding that occurs with seasonally heavy rain or snowmelt.
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2.) Seasonal Floods
seasonal floods follow prolonged rains that saturate the soil and inhibit more water from infiltrating the ground.
seasonal flooding poses less of a threat to human life than flash flooding because often the water rises slowly and there is ample time to evacuate.
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