Transcript Understanding Our Environment

Water Use and Management
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Outline
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Hydrologic Cycle
Major Water Compartments
Water Availability and Use
 Types of Water Use
Freshwater Shortages
 Depleting Groundwater
Increasing Water Supplies
Water Management and Conservation
 Price Mechanisms
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WATER RESOURCES
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Hydrologic Cycle
Describes the circulation of water as it:
 Evaporates from land, water, and
organisms. (Transpires from plants)
- Enters the atmosphere.
 Condenses and precipitates back to
the earth’s surfaces.
 Moves underground by infiltration
or overland runoff into rivers, lakes
and seas.
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Average Annual Precipitation
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Hydrologic Cycle
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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
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Hydrologic Cycle
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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.
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Hydrologic Cycle
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Dew Point - Temperature at which
condensation occurs for a given amount of
water.
 Condensation Nuclei - Tiny particles that
facilitate condensation.
- Smoke, dust, sea salt, spores.
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Balancing the Water Budget
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Oceans account for 86% of total evaporation.
 Ninety percent of water evaporated from
the ocean falls back on ocean as rain.
- Remaining 10% is carried by prevailing
winds over continents.
 Without oceans to absorb and store heat,
and wind currents to redistribute the heat
in latent energy of water vapor, the earth
would undergo extreme temperature
fluctuations.
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Regions of Plenty and Regions of Deficit
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Three principal factors control global water
deficits and surpluses.
 Global atmospheric circulation
 Prevailing Winds
 Topography
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Regions of Plenty and Regions of Deficit
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Mountains act as cloud formers and rain
catchers.
 Air sweeps up the windward side of a
mountain, pressure decreases, and the air
cools.
- Eventually saturation point is reached,
and moisture in the air condenses.
 Rain falls on the mountaintop.
 Cool, dry air descends and warms,
absorbing moisture from other
sources. (Rain Shadow)
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Rain Shadow
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MAJOR WATER COMPARTMENTS
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Oceans
 Together, oceans contain more than 97%
of all liquid water in the world.
- Contain 90% of world’s living biomass.
- Moderate earth’s temperature.
 Average residence time of water in the
ocean is about 3,000 years.
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Major Water Compartments
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Glaciers, Ice, and Snow
 2.4% of world’s water is classified fresh.
- 90% in glaciers, ice caps, and snowfields.
 As recently as 18,000 years ago, onethird of continental landmass was
covered by glacial ice sheets.
 Now, Antarctic glaciers contain
nearly 85% of all ice in the world.
 Sea ice comes from ocean water, but
salt is excluded during freezing.
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Major Water Compartments
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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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Water Compartments
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Groundwater
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Aquifers - Porous layers of sand, gravel, or
rock lying below the water table.
 Artesian - Pressurized aquifer intersects
the surface. (Water flows without pumping)
Recharge Zones - Area where water
infiltrates into an aquifer.
 Recharge rate is often very slow.
- Presently, groundwater is being removed
faster than it can be replenished in many
areas.
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Groundwater
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Major Water Compartments
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Rivers and Streams
 Precipitation that does not evaporate or
infiltrate into the ground runs off the
surface, back toward the sea.
- Best 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.
 Usually expressed as cubic feet per
second.
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Major Water Compartments
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Lakes and Ponds
 Ponds are generally considered small
bodies of water shallow enough for rooted
plants to grow over most of the bottom.
 Lakes are 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
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Wetlands
 Play a vital role in hydrologic cycle.
- Lush plant growth stabilizes soil and
retards surface runoff, allowing more
aquifer infiltration.
 Disturbance reduces natural waterabsorbing capacity, resulting in floods
and erosion in wet periods, and less
water flow the rest of the year.
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Major Water Compartments
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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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Renewable Water Supplies
 Made up of surface runoff and infiltration
into accessible freshwater aquifers.
- 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.
 Readily accessible, renewable
supplies are 400,000 gal /person/year.
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Drought Cycles
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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.
 Climatic changes such as global
warming may alter cycles.
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Types of Water Use
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Withdrawal - Total amount of water taken
from a source.
Consumption - Fraction of withdrawn water
made unavailable for other purposes (Not
returned to its source).
 Degradation - Change in water quality due
to contamination making it unsuitable for
desired use.
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Types of Water Use
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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.
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Quantities of Water Used
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Human water use has been increasing about
twice as fast as population growth over the
past century.
 Annual renewable water supply in U.S.
amounts to an average of 2.4 million
gallons/person/year.
- Now withdraw one-fifth of this amount.
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Agricultural Water Use
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Worldwide, agriculture claims about twothirds of total water withdrawal and 85% of
consumption.
 In many developing countries, agricultural
water use is extremely inefficient and
highly consumptive.
- Drip irrigation is a promising technology.
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Groundwater Withdrawals for Irrigation
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Domestic and Industrial Water Use
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Worldwide, domestic water use accounts for
about one-fifth of water withdrawals.
 Only about 10% of consumption.
- Grown in proportion with urban
populations.
Industry accounts for 20% of global
freshwater withdrawals.
 Range from 5% to 70%.
- Small proportion is consumed, but
degradation is a problem.
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FRESHWATER SHORTAGES
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Estimated 1.5 billion people lack access to
an adequate supply of drinking water.
 Nearly 3 billion lack acceptable sanitation.
A country where consumption exceeds more
than 20% of available, renewable supply is
considered vulnerable to water stress.
 Globally, water supplies are abundant, but,
along with capital resources, are unevenly
distributed.
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A Precious Resource
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Currently, 45 countries, most in Africa or
Middle East, are considered to have serious
water stress, and cannot meet the minimum
essential water requirements of their citizens.
 More than two-thirds of world’s households
have to retrieve water from outside the
home.
- Sanitation levels decline when water is
expensive.
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Depleting Groundwater
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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,
- On a broader scale, heavy pumping can
deplete an aquifer.
 Ogallala Aquifer
 Mining non-renewable resource.
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Depleting Groundwater
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Withdrawing large amounts of groundwater
in a small area causes porous formations to
collapse, resulting in subsidence.
 Sinkholes form when an underground
channel or cavern collapses.
 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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Cone of Depression and Saltwater Intrusion
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INCREASING WATER SUPPLIES
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Seeding Clouds
 Condensation Nuclei
Towing Icebergs
 Cost
Desalination
 Most common methods are distillation and
reverse osmosis.
- Three to four times more expensive than
most other sources.
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Increasing Water Supplies
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Dams, Reservoirs, Canals and Aqueducts
 Common to trap excess water in areas of
excess and transfer it to areas of deficit.
 Environmental Costs
- Upsets natural balance of water systems.
 Ecosystem Losses
- Loss of wildlife habitat.
 Reservoir Size
 Water Quality
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Dams, Reservoirs, Canals and Aqueducts
Displacement of People
- Three Gorges Dams in China is forcing
relocation of over a million people.
 Evaporation, Leakage, Siltation
- Evaporative losses from Lake Mead and
Lake Powell on the Colorado River is
about 2 billion m3 per year.
- Dams slow water flow, allowing silt
(nutrients) to drop out.
 Loss of Free-Flowing Rivers
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WATER MANAGEMENT AND
CONSERVATION
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Watershed Management
 Watershed - All the land drained by a
stream or river.
- Retaining vegetation and ground cover
helps retard rainwater and lessens
downstream flooding.
 Additionally, retaining crop residue on
fields reduces flooding and minimizing
plowing and forest cutting on steep
slopes protects watersheds.
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Domestic Conservation
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Estimates suggest many societies could
save as much as half of current domestic
water usage without great sacrifice or serious
change in lifestyle.
 Largest domestic use is toilet flushing.
- Small volume of waste in large volume
of water.
- Significant amounts of water can be
reclaimed and recycled.
 Purified sewage effluent.
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Price Mechanisms and Water Policy
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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.
 In drier western regions where water is
often a limiting resource, water law is
based primarily on prior appropriation
rights.
- Fosters “Use it or Lose it” policies.
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Price Mechanisms and Water Policy
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In most federal reclamation projects,
customers were only charged for immediate
costs of water delivery.
 Dam and distribution system costs were
subsidized.
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
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Charging a higher proportion of real costs to
users of public water projects has helped
encourage conservation.
In 1999, the Canadian government passed
federal legislation banning bulk water export.
- Water is “too precious” to be treated like
other commodities.
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Summary
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Hydrologic Cycle
Major Water Compartments
Water Availability and Use
 Types of Water Use
Freshwater Shortages
 Depleting Groundwater
Increasing Water Supplies
Water Management and Conservation
 Price Mechanisms
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