Water Use 12/4/08

Groundwater Groundwater is contained within aquifers (porous formations of rock, sand, or gravel that hold water) Groundwater is contained within aquifers (porous formations of rock, sand, or gravel that hold water) The upper layer (zone of aeration) contains pore spaces partially filled with waterThe upper layer (zone of aeration) contains pore spaces partially filled with water The lower layer (zone of saturation) has spaces completely filled with waterThe lower layer (zone of saturation) has spaces completely filled with water

Groundwater The boundary between these two zones is the water table The boundary between these two zones is the water table

Aquifers Confined aquifers—(artesian aquifer) exists when a water-bearing layer of rock is trapped between layers of less permeable substrate Confined aquifers—(artesian aquifer) exists when a water-bearing layer of rock is trapped between layers of less permeable substrate Unconfined aquifers—No upper layer to confine Unconfined aquifers—No upper layer to confine Readily recharged by surface waterReadily recharged by surface water

Aquifers

Groundwater Groundwater becomes surface water through spring and wells Groundwater becomes surface water through spring and wells Groundwater usually stays in aquifers for a long time Groundwater usually stays in aquifers for a long time The average age is estimated at 1400 yearsThe average age is estimated at 1400 years

Water distribution

Human water use Nations with arid climates use more freshwater for agriculture, and industrialized nations use more for industry Nations with arid climates use more freshwater for agriculture, and industrialized nations use more for industry Consumptive use—water is removed from an aquifer and is not returned Consumptive use—water is removed from an aquifer and is not returned Nonconsumptive use—water is not removed or only temporarily removed from an aquifer Nonconsumptive use—water is not removed or only temporarily removed from an aquifer Ex) Water for electricityEx) Water for electricity

Inefficient irrigation wastes water 60% more water is withdrawn for irrigation today than in % more water is withdrawn for irrigation today than in 1960 Irrigation can more than double crop yields Irrigation can more than double crop yields Only about 45% of the freshwater used for irrigation is taken up by plants Only about 45% of the freshwater used for irrigation is taken up by plants About 15-35% of water withdrawals for irrigation are unsustainable About 15-35% of water withdrawals for irrigation are unsustainable

Groundwater depletion 1/3 of the earth’s population relies on groundwater for its needs 1/3 of the earth’s population relies on groundwater for its needs If groundwater is withdrawn too quickly, the land above them may collapse If groundwater is withdrawn too quickly, the land above them may collapse May form sinkholes, areas where the ground gives way suddenlyMay form sinkholes, areas where the ground gives way suddenly

Water diversions Water diversions We change the flow of rivers for our ease of use We change the flow of rivers for our ease of use

Colorado River case study Colorado River basin includes some of the driest lands in the US Colorado River basin includes some of the driest lands in the US Has only a modest flow of water Has only a modest flow of water Legal pacts allocated more water for human us than the river can supply Legal pacts allocated more water for human us than the river can supply Since 1905, the amount of water has dropped dramatically because withdrawal has increased Since 1905, the amount of water has dropped dramatically because withdrawal has increased

Water wars! California diverts the flow of the Colorado River, reducing the flow by the time that it gets to Arizona California diverts the flow of the Colorado River, reducing the flow by the time that it gets to Arizona 261 rivers cross national borders 261 rivers cross national borders

Dikes and levees Long raised mounds of earth that are built to protect against floods Long raised mounds of earth that are built to protect against floods Sometimes make flooding worse by causing a backup of water Sometimes make flooding worse by causing a backup of water

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 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 Reservoir is useful for recreation and fishing Can produce cheap electricity (hydropower) Large losses of water through evaporation Large losses of water through evaporation Flooded land destroys forests or cropland and displaces people Flooded land destroys forests or cropland and displaces people Downstream flooding is reduced Downstream cropland and estuaries are deprived of nutrient-rich silt 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

Benefits of Dams (pg 447) Benefits of Dams (pg 447) 1. Power generation 2. Emissions reduction 3. Crop irrigation 4. Drinking water 5. Flood control 6. Shipping 7. New recreational opportunities

Costs of dams (pg 447) 1. Habitat alteration 2. Decline in fisheries 3. Population displacement 4. Sediment capture 5. Disruption of flooding 6. Risk of failure 7. Lost recreational opportunities

Three Gorges Dam Largest dam in the world—China Largest dam in the world—China

Three Gorges Damn

Three Gorges Dam Completed in 2003, will be filled in 2009 Completed in 2003, will be filled in 2009 Reservoir will hold 38 trillion L of waterReservoir will hold 38 trillion L of water Will generate hydroelectric powerWill generate hydroelectric power $25 billion dollar construction costs $25 billion dollar construction costs Flooding in 22 cities and 1.13 million people will be displaced Flooding in 22 cities and 1.13 million people will be displaced Flooding of archeological sitesFlooding of archeological sites

Some dams are being removed Can restore ecosystems and reestablish economically valuable fisheries Can restore ecosystems and reestablish economically valuable fisheries In 1998, the US Army Corps of Engineers said that it would no longer build large dams in the US In 1998, the US Army Corps of Engineers said that it would no longer build large dams in the US 500 dams have been removed in the US, most in recent years 500 dams have been removed in the US, most in recent years

Transferring water Water can be transported from water-rich to water-poor areas Water can be transported from water-rich to water-poor areas This practice has many benefits This practice has many benefits Also encourages unsustainable use of water in areas where water is not naturally supplied Also encourages unsustainable use of water in areas where water is not naturally supplied

California case study One of the world’s largest water transfer project is the California Water Project One of the world’s largest water transfer project is the California Water Project It uses a maze of dams, pumps, and aqueducts to transport water from northern to southern California It uses a maze of dams, pumps, and aqueducts to transport water from northern to southern California Southern California wants more water to support their large cities Southern California wants more water to support their large cities

California case study Southern California wants more water to support their large cities Southern California wants more water to support their large cities Northern California counter that this will degrade the river and cause pollution Northern California counter that this will degrade the river and cause pollution They also contend that much of the water is being wastedThey also contend that much of the water is being wasted

Aral Sea case study

Since 1960, enormous amounts of water has been transferred from the sea and its feeder rivers Since 1960, enormous amounts of water has been transferred from the sea and its feeder rivers Since 1961, the salinity has tripled and the water level has dropped 72 feet (90% water volume lost) Since 1961, the salinity has tripled and the water level has dropped 72 feet (90% water volume lost) 85% of the area’s wetlands have been eliminated, and ½ of the local bird and mammal species are gone 85% of the area’s wetlands have been eliminated, and ½ of the local bird and mammal species are gone

Aral Sea case study Winds are eroding the soil, and blowing the salty material to the Himalayas, causing the glaciers to melt Winds are eroding the soil, and blowing the salty material to the Himalayas, causing the glaciers to melt Local climate has been altered Local climate has been altered Many people are having health problems Many people are having health problems $600 million dollars has been spent to purify drinking water, improve irrigation, and build new dams/dikes $600 million dollars has been spent to purify drinking water, improve irrigation, and build new dams/dikes