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Chapter 17

WATER USE

&

MANAGEMENT

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OUTLINE

• Hydrologic Cycle

• Major Water Compartments/Reservoirs

• Water Availability And Use

Types Of Water Use

• Freshwater Shortages

• Dams And Diversions

• Increasing Water Supplies

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2 ADDITIONAL READINGS

1. CASE STUDY – Page 374 CHINA’S SOUTH-TO-NORTH WATER DIVERSION

2. WHAT DO YOU THINK? Page 389 SHOULD WE REMOVE DAMS?

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WATER RESOURCES

• Hydrologic Cycle

• Describes the circulation of water as it:

Evaporates from land, water, and organisms (evapotranspiration from plants)

Enters the atmosphere

Condenses and precipitates back to the Earth’s surfaces

Moves underground by infiltration or overland by runoff into rivers, lakes and seas

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AVERAGE ANNUAL PRECIPITATION

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HYDROLOGIC CYCLE

• Solar energy drives the hydrologic cycle by

evaporating surface water.

EVAPORATION - changing liquid to a vapor

below its boiling point

SUBLIMATION - changing water between

solid and gaseous states without ever

becoming liquid

- Freezer burn, dry ice,

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HYDROLOGIC CYCLE

• HUMIDITY - amount of water vapor in the air

SATURATION POINT - when a volume of air

contains as much water vapor as it can hold

at a given temperature

RELATIVE HUMIDITY - amount of water vapor

in the air expressed as a percentage of the

maximum amount that can be held at that

temperature

Warm air can hold more water vapor than

cold air.

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HYDROLOGIC CYCLE

• DEW POINT - temperature at which

condensation occurs for a given amount of

water vapor

CONDENSATION NUCLEI - tiny particles that

facilitate condensation

- Smoke, dust, sea salt, spores

A cloud is an accumulation of condensed

water vapor in droplets or ice crystals. When

droplets become large/heavy enough, gravity

overcomes air currents and precipitation

occurs.

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Regions of Plenty and Regions of Deficit

• Three principal factors control global water

deficits and surpluses:

GLOBAL ATMOSPHERIC CIRCULATION –

circulation cells and prevailing wind belts

- Equator – moist air rises – tropical areas

- 300 dry air sinks – deserts form

PROXIMITY TO WATER SOURCES -

- Coasts are moderated by oceans/lakes

- Oceans provide moisture for winds

TOPOGRAPHY – changes with altitude,

proximity to mountains

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RAIN SHADOW

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Regions of Plenty and Regions of Deficit

• Mountains act as cloud formers and rain catchers.

Air rises on the windward side of a mountain, pressure decreases, and the air adiabatically cools.

- Eventually saturation point is reached, and moisture in the air condenses, rain falls on the windward side of the mountain.

Cool dry air descends and adiabatically warms, on the leeward side of the mountain

RAIN SHADOW EFFECT

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DISTRIBUTION OF THE WORLD’S WATER

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RESIDENCE TIME - the average length of time

during which a substance is in a given

location or condition

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MAJOR WATER COMPARTMENTS

• OCEANS

Together, oceans contain more than 97% of all liquid water in the world.

- Contain 90% of world’s living biomass

- Moderate temperature due to their circulation – gyres between continents

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MAJOR WATER COMPARTMENTS

GLACIERS, ICE, AND SNOW

2.4% of world’s water is classified as fresh.

90% in glaciers, ice caps, and snowfields

- As recently as 18,000 years ago, one-third of continental landmass was covered by glacial ice sheets.

Now, Antarctic glaciers contain nearly 85% of all ice in the world. (2 km thick)

Greenland, together with ice floating around the North Pole, is another 10%.

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MAJOR WATER COMPARTMENTS

GROUNDWATER

• Second largest reservoir of fresh water

INFILTRATION - process of water percolating through the soil and into fractures and permeable rocks

- ZONE OF AERATION - upper soil layers that hold both air and water

- ZONE OF SATURATION - lower soil layers where all spaces are filled with water

WATER TABLE - top of zone of saturation

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INFILTRATION

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GROUNDWATER • AQUIFERS - porous layers of sand, gravel, or

rock lying below the water table

ARTESIAN WELL- Pressurized aquifer that intersects with the surface (water flows out without pumping).

• RECHARGE ZONES - areas where water infiltrates into an aquifer

Recharge rate is often very slow.

- Groundwater is being removed faster than it can be replenished in many areas.

- Development (roads/buildings) block recharge zones

- Contamination of surface water and wells has polluted aquifers

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GROUNDWATER

AQUICLUDE – impervious layer of rock or clay

CONFINED AQUIFER – water trapped between

two aquicludes

Flow through an aquifer is generally VERY SLOW.

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MAJOR WATER COMPARTMENTS

RIVERS AND STREAMS

• Precipitation that does not evaporate or infiltrate into the ground runs off the surface, back toward the sea.

A measure of water volume carried by a river is DISCHARGE : The amount of water that passes a fixed point in a given amount of time

- Expressed as cubic feet/meters per second

Amazon – annual discharge (m3/sec) = 175,000

Mississippi - annual discharge (m3/sec) = 18,400

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MAJOR WATER COMPARTMENTS

LAKES AND PONDS

PONDS are considered small bodies of water

shallow enough for rooted plants to grow

over most of the bottom.

LAKES are deeper, inland depressions that

hold standing fresh water year-round.

Both ponds and lakes will eventually fill with

sediment, or be emptied by an outlet stream.

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MAJOR WATER COMPARTMENTS

WETLANDS (salt marshes, swamps, bogs)

• Play a vital role in hydrologic cycle

Dense plant growth stabilizes soil and slows surface runoff, allowing more aquifer infiltration.

Disturbance reduces natural water-absorbing capacity, resulting in floods and erosion in wet periods, and less water flow the rest of the year.

- 50% of U.S. wetlands are gone.

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MAJOR WATER COMPARTMENTS

• THE ATMOSPHERE

Among the smallest water reservoirs

- Contains < 0.001% of total water supply

- Has most rapid turnover rate

- Provides mechanism for distributing fresh

water over landmasses and replenishing

terrestrial reservoirs

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WATER AVAILABILITY AND USE

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WATER AVAILABILITY AND USE

RENEWABLE WATER SUPPLIES

• Made up of surface runoff plus infiltration into

accessible freshwater aquifers

Readily accessible, renewable supplies are

400,000 gal /person/year.

About two-thirds of water carried in rivers

and streams annually occurs in seasonal

floods too large or violent to be stored

effectively for human use.

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DROUGHT CYCLES

• Every continent has regions of scarce rainfall

due to topographic effects or wind currents.

Water shortages have most severe effect in

semiarid zones where moisture availability is

the critical factor in plant and animal

distributions.

- U.S. seems to have ~30 year drought cycle.

Dust Bowl in 1930s – caused by drought

and poor farming practices

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DROUGHT CYCLES

• Much of Western U.S. is still plagued by

drought and overexploitation of limited supply

of water.

• El Nino plays an important role in determining

when North America has drought.

• Global warming may make droughts more

frequent and severe.

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WATER CONSUMPTION < WITHDRAWAL

• WITHDRAWAL - total amount of water taken

from a source (river/aquifer) for any purpose.

Most withdrawn water is returned to its source.

• CONSUMPTION - fraction of withdrawn water

made unavailable for other purposes via

evaporation, absorption, chemical change, etc.

(is not returned to its source)

• DEGRADATION - Changes in water quality due

to contamination making it unsuitable for other

uses. ie: some water that is withdrawn (not

consumed) becomes polluted.

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WATER USE IS INCREASING

• Many societies have always treated water as an

inexhaustible resource.

Natural cleansing and renewing functions of

hydrologic cycle do not work properly if

systems are overloaded or damaged

Renewal of water takes time

Rate at which we are now using water makes

conservation necessary

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QUANTITIES OF WATER USED

• Human water use has been increasing about

twice as fast as population growth over the past

century, but impact varies with location.

Canada, Brazil, Congo withdraw less than

1% of their renewable supply per year.

In Libya & Israel, groundwater and surface

water withdrawals equal more than 100% of

the renewable supply. They are using faster

than can be replenished. Unsustainable!

U.S. uses 20% of renewable water/yr.

Although different regions have abundance

or shortages.

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WITHDRAWAL vs CONSUMPTION

COMPARE WITHDRAWAL & CONSUMPTION FOR

EACH CATEGORY.

WHICH HAS THE “BEST” RATIO AND WHICH IS

“WORST” ECOLOGICALLY?

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AGRICULTURAL WATER USE

• Water use is divided into 3 categories:

AGRICULTURAL, DOMESTIC & INDUSTRIAL

• Worldwide, AGRICULTURE water use:

- Total water Withdrawal rate of 60%

- Consumption rate of 85%.

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ARAL SEA

once the

fourth largest

inland body

of water in

world, has

been drained.

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LAKE CHAD in northern Africa went from

400,000 sq. km to less than 1,000 sq. km.

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WATER USE IN AGRICULTURE

IRRIGATION CAN BE INEFFICIENT.

Flood or furrow irrigation

Half of water can be lost

through evaporation.

Flood irrigation used to

remove salts from field, but

salt contaminates streams

Sprinklers have high evaporation.

Drip irrigation releases water

near roots, conserving water.

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DOMESTIC WATER USE

Worldwide, DOMESTIC water use accounts for

about 20% of water withdrawals.

• Consumption rate of 10%

• Where sewage treatment is unavailable, water

is degraded

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INDUSTRIAL WATER USE

• Worldwide INDUSTRY accounts for 20% of

global freshwater withdrawals.

Small portion is consumed, but degradation

is a large problem

Power production: Withdrawal of 50-70%

Mining produces the highest portion of

degraded water

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FRESHWATER SHORTAGES

• U.N. estimates a billion people lack access to

safe drinking water.

2.6 billion lack acceptable sanitation.

• At least 45 countries, mostly in Africa and the

Middle East, are considered to have serious

water stress.

• Urban areas generally have more access to

potable water than rural areas.

• Many developing countries lack a delivery

system. Women transport water from sources

to their homes.

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FRESHWATER SHORTAGES

• Water shortages could lead to wars as population grows and climate change dries up some areas. (An underlying cause of the Darfur genocide is water scarcity.)

• Page 385-386 – several examples of “conflicts”

over water rights.

(Kenya, Sudan, Chad, India vs Pakistan, Turkey vs Iraq)

• Multinational corporations are moving to take control of water supplies in many countries.

• Global warming may make water shortages much worse in many parts of the world.

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DAMS AND DIVERSIONS – “POSITIVES”

• Dams store runoff in lakes/reservoirs

• Historically, water has been dammed/diverted

for thousands of years

• Before 1900 there were 250 high dams (15 m) in

the world; today there are more than 45,000.

• In the U.S. dams are built by Army Corps of

Engineers and Bureau of Reclamation

Provide cheap hydroelectric power

Create jobs

Reduce flooding

Allow farming on lands that would otherwise

be too dry

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DAMS AND DIVERSIONS – “NEGATIVES”

Drown free flowing rivers

Submerge farmlands and towns

Increase “standing water” increases disease

Change aquatic habitats for native species

Dams can fail, causing catastrophic floods

1889 - Johnstown flood (city just east of Pittsburgh, PA) killed 2,200 people when dam broke.

1975 - After monsoon rains 45 dams failed in China killing 230,000.

Three Gorges Dam on Yangtze in China is built on a seismic fault. 100 million people live downstream.

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DAMS AND DIVERSIONS

• Army Corps of Engineers announced in 1998

that it would no longer be building large dams

and would be removing some older dams to

restore natural habitat

• Currently 75,000 large dams in the US

• Sediment carried by rivers eventually fills up

dams

• Lakes behind dams lose huge amounts of water

through evaporation and seepage (Consumption)

• Downriver habitats lose nutrients and beaches

suffer erosion as sediment is no longer

available

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DAMS AND DIVERSIONS

• Diversion projects can dry up rivers

Yellow River in China is dry 226 days per year

due to diversions

Colorado River in the U.S. is so depleted that

most of the year no water reaches the mouth

of the river in the Sea of Cortez

Mono Lake has been depleted to send water

to Los Angeles. Salinity of water doubled,

killing the brine shrimp that fed huge flocks

of migratory birds

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DAMS AND DIVERSIONS

• Dams interfere with spawning of fish

Salmon, trout, sturgeon

• Adults can not swim upstream – fish

ladders can be built to allow fish to

bypass the dam

• Young fish swimming downstream die in

the hydroelectric turbines – many species

are now bred in hatcheries and trucked

downstream below the dams.

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DAMS AND DIVERSIONS

CANADA:

2 hydro-electric companies have diverted 4

major rivers causing flooding of the tundra and

boreal forest

First Nations people have lost traditional

hunting and fishing areas

Mercury has seeped out of flooded rocks

causing poisoning in people and wildlife

Loss of permafrost

Some of the energy produced is exported to the

US as “renewable” energy

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DEPLETING GROUNDWATER

Groundwater is the source of nearly 40% of fresh water in the U.S.

On a local level, withdrawing water faster than it can be replenished leads to a CONE OF DEPRESSION in the water table.

Heavy pumping can deplete an aquifer.

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THE OGALLALA

AQUIFER

• Underlies 8 states between Texas and North Dakota • Wells have dried up and whole towns are being abandoned • Will take thousands of years to refill

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DEPLETING GROUNDWATER

• Withdrawing large amounts of groundwater in a

small area causes porous formations to

collapse, resulting in SUBSIDENCE (settling).

SINKHOLES form

when an underground

channel or cavern

collapses.

Can results in the

permanent loss of an

aquifer.

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SALTWATER INTRUSION can occur along

coastlines where overuse of freshwater

reservoirs draws the water table low enough to

allow saltwater to intrude.

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INCREASING WATER SUPPLIES

• SEEDING CLOUDS (controversial)

Introducing hygroscopic salts into the

atmosphere as condensation nuclei

• DESALINATION - removing salt from ocean

water or brackish water to get fresh water

Three to four times more expensive than

most other sources

DISTILLATION - evaporation and

re-condensation of water

REVERSE OSMOSIS – forcing water under

pressure through a semi-permeable

membrane. (produces concentrated wastes)

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DOMESTIC CONSERVATION

• Estimates suggest we could save as much as half of domestic water usage without change in lifestyle

Largest domestic use is toilet flushing

- Can use low volume toilets or waterless composting

- Anaerobic digesters use bacteria to produce methane gas from waste

Significant amounts of water can be reclaimed and recycled.

Purified sewage effluent

San Diego pumps water from sewage plant directly into drinking reservoir

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DOMESTIC CONSERVATION

• Use water efficient appliances (washers, shower heads)

• Water lawns less, use native plants

• Repair leaks

• Collect rainwater for irrigation of lawns

• Take shorter showers, install motion detecting faucets/timed faucets

• Use GREY WATER for fields, lawns, toilets

Grey-water is water from sinks, washing machines, baths. It does not contain human feces and is relatively uncontaminated and can be reused.

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DOMESTIC GREY-WATER SYSTEM

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PRICE MECHANISMS AND WATER POLICY

• Through most of U.S. history, water policies have generally worked against conservation.

In well-watered eastern states, water policy was based on RIPARIAN USE RIGHTS. (If you had access to a river, you could use the water.)

In drier western regions where water is often a limiting resource, water law is based primarily on prior APPROPRIATION RIGHTS. (The first people to “claim” the water had rights to it. These rights could be bought and sold as a commodity)

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PRICE MECHANISMS AND WATER POLICY

• In most federal reclamation projects, customers

were only charged for immediate costs of water

delivery.

Dam and distribution system costs were

subsidized.

Underpriced water in some areas amounted

to a subsidy of $500,000 per farm per year.

• Growing recognition that water is a precious

and finite resource has changed policies and

encouraged conservation across the U.S.

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PRICE MECHANISMS AND WATER POLICY

• Charging a higher proportion of real costs to

users of public water projects has helped

encourage conservation.

• Conservation has been successful. U.S. today

uses 10% less water than in 1980 but has 37

million more people.

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Think about what goes into

producing each of the

following products. What

processes use the water?