Water and Water Pollution

Dams A dam is any obstruction placed in a river or stream to block the flow of water so that water can be stored in a reservoir Large losses of water through evaporation Flooded land destroys forests or cropland and displaces people Downstream flooding is reduced Downstream cropland and estuaries are deprived of nutrient-rich silt Migration and spawning of some fish are disrupted Provides water for year-round irrigation of cropland Reservoir is useful for recreation and fishing Can produce cheap electricity (hydropower)

Benefits of Dams Power generation Emissions reduction Crop irrigation Drinking water Flood control Shipping New recreational opportunities Hydroelectric dams—inexpensive energy Provide energy without burning fossil fuels Reservoir water can be withdrawn for irrigation purposes Can help to buffer against drought by providing storage Most reservoirs store water for cities to use Store seasonal surges (such as after a snow melt) and then can be gradually released Make it easier for ships to go than on a rocky river Fishing, boating, etc

Costs of dams Habitat alteration Decline in fisheries Population displacement Sediment capture Disruption of flooding Risk of failure Lost recreational opportunities Cause floods and modify river paths Fish that migrate to spawn may find dams as a barrier (ex) salmon) Flood farmland, and may force humans to move As the rivers slow, the sediments in the water settle to the bottom of the river and get trapped in the dam Floods actually help soil, and dams stop natural flooding—loss of topsoil Could fail—think xmen No whitewater rafting, etc

Three Gorges Dam Largest dam in the world—China

Three Gorges Damn

Aquifers

Desalination This is the removal of salt from seawater or other water of marginal quality

Aral Sea case study

Oxygen sag curve

Groundwater pollution Coal strip mine runoff Pumping well Waste lagoon Accidental spills Groundwater flow Confined aquifer Discharge Leakage from faulty casing Hazardous waste injection well Pesticides Gasoline station Buried gasoline and solvent tank Sewer Cesspool septic tank De-icing road salt Unconfined freshwater aquifer Confined freshwater aquifer Water pumping well Landfill