21.2 Groundwater Problems

• These include pollution, salt, and draining too much.

21.2 Other Effects of Groundwater Overpumping

• Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.

Figure 14-10

21.2 Groundwater Depletion: A Growing Problem

• The Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest).

Areas of greatest aquifer depletion from groundwater overdraft in the continental U.S.

Figure 14-8

21.2 Ogallala Aquifer

• This is the world’s largest known aquifer, and fuels agricultural regions in the U.S. It extends from South Dakota to Texas. It’s essentially a non-renewable aquifer from the last ice age with an extremely slow recharge rate. In some cases, water is pumped out 8 to 10 times faster than it is renewed. Northern states will still have ample supplies, but for the south it’s getting thinner. It is estimated that ¼ of the aquifer will be depleted by 2020.

21.1 Water Usage• Irrigation – watering crops• Industry – coolant (power plant)• Domestic and Municipal – drinking,

sewage, bathwater, dishwater & laundry

• Amount of water for which all people, animals and plants compete is < 1%– Industrial production increases

water use–Mass of water used 1000x total

production of minerals

21.1 Water Usage

21.1 Water Usage• Comparison of

population sizes and shares of the world’s freshwater among the continents.

21.2 Water Supply: A US Example

• Water supply at any point on the land surface depends on several factors in the hydrologic cycle,– including the rates of precipitation,

evaporation, transpiration– stream flow– subsurface flow

• Water budget– A model that balances the inputs, outputs,

and storage of water in a system.– Precipitation - evaporation = runoff

21.2 Water Supply: A US Example

• Amount of water vapor passing over the US every day ~ 152,000 million m3

– 10% falls as precipitation (66% of which is evaporated or transpired)

– Only 34% enters surface or groundwater

21.2 Groundwater Use and Problems

• ½ the people in the US use groundwater as a primary source of drinking water– 20% of water used– In many parts of the country

withdrawal from wells exceeds natural inflow• Overdraft• Nonrenewable resource• Problems include damage to river basins

and land subsidence

Global Water Problems

21.10 Global Water Shortage Linked to Food

Supply• Both surface water and groundwater are being stressed and depleted:– Groundwater in the United States, China,

India, Pakistan, Mexico, and many other countries is being mined• used faster than it is being renewed

– Large bodies of water—for example, the Aral Sea—are drying up.

– Large rivers, including the Colorado in the US and the Yellow in China, do not deliver any water to the ocean in some seasons or years.

21.10 Global Water Shortage Linked to Food

Supply• As human population grows there

is growing concern that there won’t be sufficient water to grow the food to feed 8-9 billion people.– Food shortage linked to water

resources a real possibility. – Water also linked to energy (fuel to

pump) as energy cost goes up so does cost of food.

21.10 Global Water Shortage Linked to Food

Supply• Solution

– Control human population growth– Conserve and sustain water resources– Need to be proactive now before

significant food shortages develop.

21.10 Impacts of Human Activities on Freshwater

Systems• Dams, cities, farmlands, and filled-in

wetlands alter and degrade freshwater habitats.– Dams, diversions and canals have

fragmented about 40% of the world’s 237 large rivers.

– Flood control levees and dikes alter and destroy aquatic habitats.

– Cities and farmlands add pollutants and excess plant nutrients to streams and rivers.

– Many inland wetlands have been drained or filled for agriculture or (sub)urban development.

21.10 Drinking Water Problems

21.10 Coliform Bacteria• The W.H.O. recommends

there be zero colonies of bacteria per 100ml of drinking water and 200 colonies per 100ml of swimming water. The average human excretes 2 billion organisms per day (see how easily untreated sewage can contaminate water?).

21.10 Oxygen Demanding Wastes

• These are organic wastes that can be decomposed by aerobic bacteria (causes lack of oxygen). Fish die as a result of a lack of oxygen.

21.10 Water-Soluble Inorganic Chemicals

• These include acids, salts, mercury, and lead. They make water unfit to drink.

21.10 Organic Material• These include oil, gas,

plastics, pesticides, and detergents.

21.10 Population Growth• Problems include over-

drawing fresh water, pollution, and over-building so that water can’t seep into the ground.

21.10 Sharing Water Resources

• There are water wars out west. California bought the water from the Colorado River, but Arizona wants it. Who owns it? The same thing is happening in Texas. More water rights are sold than the actual amount of water. How do you share water? This is a problem all over the world.

21.5 Water Management

21.5 Water Management• Management of water resources is

a complex issue that will become more difficult as demand for water increases in the coming years.– Especially in areas like the

Southwestern US and other semi arid regions

21.5 Dams and Reservoirs• Description: A dammed stream that can capture & store water from rain & melted snow.

• Benefits: Hydroelectric power; provides water to towns; recreation; controls floods downstream

• Problems: Reduces downstream flow; prevents water from reaching the sea (Colorado River) devastates fish life; reduces biodiversity.

Fig. 14-13a, p. 317

Provides water for year-round irrigation of cropland

Flooded land destroys forests or cropland and displaces people

Large losses of water through evaporationProvides

water for drinking Downstream

cropland and estuaries are deprived of nutrient-rich silt

Reservoir is useful for recreation and fishing

Risk of failure and devastating downstream flooding

Can produce cheap electricity (hydropower)

Downstream flooding is reduced

Migration and spawning of some fish are disrupted

Powerlines

Reservoir

DamPowerhouse

Intake

Turbine

21.7 China’s Three Gorges Dam

• There is a debate over whether the advantages of the world’s largest dam and reservoir will outweigh its disadvantages. (Opened June 2012)– The dam will be 2 kilometers long.– The electric output will be that of 18 large

coal-burning or nuclear power plants.– It will facilitate ship travel reducing

transportation costs.– Dam will displace 1.2 million people.– Dam is built over seismatic fault and already

has small cracks.

21.7 Dam Removal• Some dams are being removed for

ecological reasons and because they have outlived their usefulness.– In 1998 the U.S. Army Corps of Engineers

announced that it would no longer build large dams and diversion projects in the U.S.

– The Federal Energy Regulatory Commission has approved the removal of nearly 500 dams.

– Removing dams can reestablish ecosystems, but can also re-release toxicants into the environment.

21.7 Removal of Dams• Trapped sediment behind dams must be

dealt with in dam removal.– If released quickly it could damage

downstream ecosystem and fill pools.– Slower release minimizes damage.– Matilija Dam in Ventura County cost

$300,000 to build but 10 times that to remove.

• Removing dams is simple in concept but involves complex problems relating to sediment and water.

21.2 Desalinization• Description: Removing salt from salt water

• Benefits: Freshwater• Problems: Uses lots of energy; costs 3-5 times more money; what do we do with the salt?

21.5 Cloud Seeding

21.5 Harvesting Icebergs

•Description: Towing massive icebergs to arid coastal areas (S. California; Saudi Arabia)

•Benefits: freshwater •Problems: Technology not available; costs too high; raise temperatures around the earth.

21.5 Wasting Less Water in Agriculture

• Sixty percent of the world’s irrigation water is currently wasted, but improved irrigation techniques could cut this waste to 5-20%.

• Center-pivot, low pressure sprinklers sprays water directly onto crop.– It allows 80% of water to reach crop.– Has reduced depletion of Ogallala

aquifer in Texas High Plains by 30%.

21.4 Agricultural Use• Suggestions for conservation:

– Price agricultural water to encourage conservation

– Use lined or covered canals that reduce seepage and evaporation.

– Use computer monitoring and schedule release of water for maximum efficiency.

– Integrate the use of surface water and groundwater to more effectively use the total resource.

21.4 Agricultural Use– Irrigate at times when evaporation is

minimal, such as at night or in the early morning.

– Use improved irrigation systems, such as sprinklers or drip irrigation, that more effectively apply water to crops.

– Improve the soil to increase infiltration and minimize runoff.

– Encourage the development of crops that require less water or are more salt tolerant.

Center pivot

Drip irrigation

Gravity flow(efficiency 60% and

80% with surge valves)

Above- or below-ground pipes or tubes deliver water to individual plant roots.

Water usually comes from an aqueduct system or a nearby river.

(efficiency 90–95%)

(efficiency 80%–95%)Water usually pumped from underground and sprayed from mobile boom with sprinklers.

21.4 Water Conservation• The careful use and protection of

water resources– Involves the quantity of water used

and the quality– Important component of sustainable

water use– Expected that a number innovations

will reduce the total withdrawals

21.4 Conservation• Description: Saving the water we have • Methods: recycling; conserving at home; xeriscaping; fix leaks

• Benefits: Saves money; Saves Wildlife• Problems: bothersome to people; lack of caring; laziness

21.4 Industry and Manufacturing Use

• Water conservation measures that can be taken by industry:– Using cooling towers that use little or

no water– In-plant water treatment and

recycling

21.4 Perception and Water Use

• Perception of water is based partly on its price and availability.– If water is abundant and inexpensive,

we don’t think much about it. – If water is scarce or expensive, it is

another matter.– E.g. people in Tucson pay about 100%

more for water than people in Phoenix.• Tucson residence use less water per

person per day

21.5 Sustainability and Water Management

• From a water supply use and management perspective, sustainable water use defined as:– use of water resources by people in a

way that allows society to develop and flourish into an indefinite future

– W/o degrading the various components of the hydrologic cycle or the ecological systems that depend on it.

21.5 Sustainable Water Use

• General criteria:– Develop water resources in sufficient

volume to maintain human health and well-being.

– Provide sufficient water resources to guarantee the health and maintenance of ecosystems.

– Ensure minimum standards of water quality for the various users of water resources.

21.5 Sustainable Water Use

– Ensure that actions of humans do not damage or reduce long-term renewability of water resources.

– Promote the use of water-efficient technology and practice.

– Gradually eliminate water pricing policies that subsidize the inefficient use of water.

21.5 Groundwater Sustainability

• Sustainability involves a long term perspective– For groundwater even longer– Effects of pumping might not be seen

immediately– Long-term approach involves

balancing withdrawal with recharge