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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?
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