Downstream Effects of Dams.docx

4 Pages

Earth & Environmental Sciences
Course Code
EESC 1158
Donald James

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Downstream Effects of Dams 1. Changed Hydrographs i. Less total flow ii. Fewer flood peaks iii. Lower high flow 2. Changed Sediment Load i. Sediment trapping in reservoir; clear water downstream ii. Flow changes ▯ transport changes iii. Can result in erosion or aggradation downstream 3. Changed Temperature 4. Changed Chemistry 5. Changed Habitat ▯ What happens on a given river depends on the size of the dam and how it is managed Rio Grande: Reduced total and flood flow i. Tributaries still deliver sediment to the river ii. Channel aggradation and narrowing: need to build levees to keep channel out of floodplain Platte River, NE: water supply for irrigation i. Braided, sand bedded, dynamic, adjustable ii. Pre-dam average: 18,000 ft3/s (510 m3/s) iii. Post-dam average: 2,500 ft3/s (71 m3/s) ▯ Dams/diversions reduce total flow Effects of reduced flow, Platte River i. Channel narrowing ii. Vegetation growth in channel area (due to lack of floods) iii. Stabilization of bars, channel pattern iv. Conversion from braided toward single channel morphology ▯ Loss of habitat in wide channels Snake River, ID-OR: Power Generation i. Little change in total or flood flow, large daily fluctuations ii. Sediment trapping behind dams, erosion of sandbar downstream from dams Power Generation Dams i. Little effect on flood peaks, total flow a. Little effect on competence and capacity ii. Daily flow fluctuations a. Wetting and drying of banks can enhance erosions iii. Lots of sediment trapping a. Erosion downstream due to sediment starved water b. Bed armoring by boulders and bedrock iv. Loss of habitat, recreation opportunities Sand Bar Erosion: loss of habitat, recreation opportunities Snake River: Dams block fish passage
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