Reservoirs Various Uses Irrigation electricity generation flood control
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Reservoirs
Various Uses Ø Irrigation, electricity generation, flood control, water supply (urban), improved navigation, fish culture, recreation, combination
Most are small Ø Built for irrigation by damming rivers in low rainfall (low runoff) areas
Reservoirs vs. Natural Lakes Much in common Ø Reservoirs usually have larger drainage basins for their size Ø Reservoirs usually younger Ø Reservoirs have greatest depth at dam Ø
Large Reservoirs Ø 3 types Ø Mainstream run-of- river Ø Tributary storage Ø Mainstream storage
Mainstream run-of-river Ø Used to generate electricity Ø Rapid flushing Ø Little or no stratification Ø No drawdown Ø Water release from deep outlet Ø Most river-like
Columbia River Grand Coulee Dam
Tributary storage reservoirs Ø Ø Ø Ø Built on smaller rivers Used for irrigation, flood control Slower flushing Stratified if deep enough Periodic drawdowns Surface outlet Most like natural lakes in area
Acton Lake, Ohio
Mainstream storage reservoirs Ø Intermediate in “position” between other types Ø More lotic during periods of high runoff Ø More lentic during other times
Mainstream storage reservoirs Ø Lie in well-defined river valleys Ø Exhibit pronounced longitudinal zonation
Mainstream storage reservoirs
Flushing rates Ø If flushing rate is greater than the doubling time of planktonic organisms, washout will occur Ø Poor development environment for plankton
Impacts on river Lentic system built into a lotic environment Ø Interferes with migration Ø
Prickett Dam, Michigan
Impacts on river Ø Modified timing, volume of discharge l Ø Interferes with life histories of biota Trapping materials behind dams l Creates erosional habitats downstream
Prickett Dam, Michigan
Impacts on river Largest threat – largescale water diversion for agriculture, especially in dryland areas Ø Reduced or zero discharge, loss of downstream wetlands, biota Ø
Drawdowns Necessary for dam maintenance Ø Increase flood capacity Ø Remove accumulated sediments Ø
Drawdowns Exposure, desiccation of littoral zone Ø Pronounced effects on biota Ø
Benefits and Costs Ø Benefits l l l Ø Development Agriculture Fisheries Costs l l Flooding Modified river reaches • Above, below