Global River Basin Usage

2.4.1 How humans use water 1

Water Use by humansIncreasing Freshwater Supplies•Build dams & reservoirs to store runoff•Bring in surface water from another area•Withdraw ground water•Desalination – convert salt water to fresh water•Waste less water•Import food to reduce water use

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Various Water Retention SystemsEEn.2.4.1

Groundwater: Precipitation that infiltrates the ground and percolates downward through voids (pores, fractures, & crevices)

Zone of saturation: voids completely filled with water

Water table: located at the top of the zone of saturation

Aquifers: Porous, water-saturated layers of sand, gravel, or bedrock through which groundwater flows

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Wells

• Wells are a way to access water in an Aquifer• Over pumping can remove water from an aquifer faster than it is renewed by

precipitation.• Lowering of the water table when a well is drilled into aquifer (left)• A cone of depression(middle)• Excessive water removal continues, the water table falls & the aquifer is

depleted.

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Aquifer depletion from groundwater overdraft

Areas of greatest aquifer depletion from groundwater overdraft (top)

Ground subsidence (bottom)

Areas of greatest aquifer depletion from groundwater overdraft (top)

Ground subsidence (bottom)

Groundwater depletion prevention– Controlling population growth– Not planting water-intensive crops

such as cotton in dry areas– Shifting to crops that need less water

in dry areas– Developing crop strains that need

less water & are heat resistant– Wasting less irrigation water

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DamsPros of dams & reservoirs :Controlling floodsProducing hydroelectric powerSupplying water for irrigation, towns & citiesReservoirs also provide recreational activities, such as swimming, fishing, & boating

Cons of large dams & reservoirs•Reduces downstream flow, preventing water to reach the sea •Increased diversion of water is needed for irrigation for cities•Flood large areas of productive farmland & forests where the dam is built•The region’s entire ecosystem will be radically changed•Water pollution will increase because of the river’s reduced water flow•The reservoir fills up with sediment, making a flooding disaster more likely•Annual deposits of nutrient-rich sediments will be reduced and fish hatching reduced.

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Agricultural

• It is estimated that 69% of worldwide water use is for irrigation • It takes around 2,000 - 3,000 litres of water to produce enough food to

satisfy one person's daily dietary need.• To produce food for the now over 7 billion people who inhabit the planet

today, it requires the water that would fill a canal ten metres deep, 100 metres wide and 2100 kilometres long.

Agriculture

Above are some of the way’s that farmers are able to reduce their impact on water supplies

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Salt-Water Intrusion

• Saltwater intrusion occurs along coastal regions

• When the water table is lowered, the normal interface (dashed line) between fresh & saline groundwater moves inland (solid line) making groundwater drinking supplies unusable

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Water SuppliesWater prices rise as water supplies are being privatized worldwide. This results in:•Decreased ability of poor farmers & city dwellers to buy enough water to meet their needs•Transnational corporations are buying large supplies of water in water-short countries for resale at huge profits

•http://www.youtube.com/watch?v=TbCwZyJEb8Y

•Population and Water Demand video questions.docx

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