WATER Supply Use management
Sources of water • Groundwater • Aquifers • wells • Surface water • Rivers • Lakes • Streams • reservoirs
What does a healthy watershed provide? • Food for people, animals • Drinking water for people animals • Habitat for animals, plants • Temporary habitat for migratory birds • Cleaning air of some contaminants • Cleaning water of contaminants • Transportation • Recreation
Burning fossil fuels to make electricity. Boils water to turn generator Uses lots of water to condense the boiled water Much water lost to evaporation (consumptive) Still, much of the use is non-consumptive Water used in the plant is returned downstream Thermoelectric
Main impacts of irrigation • Waterlogging of soil • Salinization • Overdraft of groundwater • Main source of drinking water for ½ the US • If withdrawal > replenishment mining • Irrigation is mainly consumptive—water evaporates or transpirates and doesn’t return to source
HUGE: water-bearing sands, gravels under about 400,000 km2 from SD to TX Use in some places is 20 times greater than rate of replenishment Ogallala aquifer
Why are dams built? • Usually, many advantages cited. WHY? • Appeal to as many constituents as possible • Diversion of water for irrigation • Flood control • Recreation • Stable water supply • e.g. desert cities like LA and Las Vegas
Environmental impacts of dams • Loss of land and cultural resources • Riparian habitat lost • Sediment trapped behind dam. Why bad? • Reservoir fills up, reducing its life • Sediment would supply sand and nutrients • River below dam is unnatural (flows irregular)
Sedimentation problems with dams • Problem that faces all dams • Many trap nearly 100% of the sediment that washes down a river. • As sediment accumulates, reservoir can hold less water • but that was the point of the dam in the first place—to hold water!
What happens to rivers? • Colorado River near its source in Rocky Mt. Nat. Park.
Clean Water Act • Addresses surface water quality • Not directly groundwater or quantity • Tools to reduce pollutant discharges into waterways for "the protection and propagation of fish, shellfish, and wildlife and recreation in and on the water."
CWA • Passed in 1970 • Point pollution was early emphasis
CWA • Nonpoint source pollution now the big issue