Chapter 21: Water Supply, Use
and Management
Water
• To understand water, we must understand its
characteristics, and roles:
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Water has a high capacity to absorb and store heat.
Water is the universal solvent.
Water has a high surface tension.
Water is the only compound whose solid form is lighter
than its liquid form.
– Sunlight penetrates water to variable depths, permitting
photosynthetic organisms to live below the surface.
A Brief Global Perspective
• We are facing a growing global water
shortage linked to the food supply.
• Global hydrologic cycle
– Transfers water from the atmosphere, to land,
to oceans and back to atmosphere
– 97% in oceans
– 2% in ice
– Only 0.001% in atmosphere
A Brief Global Perspective
• At Earth’s surface water can be found in
liquid, solid or gaseous form.
– Residence time varies from a few days to
thousands of years
• 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
Groundwater and Streams
• Groundwater refers to the water below the
water table
– Where saturated conditions exist
– Locations where surface waters move into the
ground are recharge zones
– Places where it flows or seeps out are discharge
zones (points)
– Area where water seeps through pore spaces
known as vadose zone
Groundwater and Streams
• Aquifer is an underground zone from which
groundwater can be obtained
– When water is pumped from an aquifer forms a
cone of depression
Streams
• Effluent stream
– Flow is maintained during the dry season by seepage
– Perennial stream
• Influent stream
– Entirely above the water table and flows only in direct
response to precipitation
– Ephemeral stream
• A given stream can have reaches that are both or
intermittent at varying times of year.
Interactions Between Surface
Water and Groundwater
• Should be considered part of the same
resource.
• Nearly all surface water environments have
linkages w/ ground water
– E.g. withdrawal of groundwater can lower
stream flow or lake levels
– Pollution can spread from one source to the
other
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
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
Precipitation and Runoff Patterns
• In developing water budgets for water
resources management it is useful to
consider annual precipitation and runoff
patterns.
– Potential problems can be predicted in areas
where average runoff and precip low
– Total storage of runoff not possible because of
evaporative losses
Droughts
• Because there are large annual and regional
variations in stream flow, even areas with
high precipitation and runoff may suffer
from droughts.
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
Desalination as a Water Source
• Seawater is 3.5% salt
• Desalination- a technology to remove salt
from water
– Must be reduces to 0.05% to be fresh water
– Requires large amount of energy, tied to fuel
prices
– Has place value- price increases quickly with
transport distance
– Discharge may affect local salinity
Water Use
• Off-stream use
– Refers to water removed from its source for use
– May be returned to source after use
– Or consumptive use- water enters tissues,
product or evaporates during use and not
returned
Water Use
• In-stream use
– The use of the river for navigation,
hydroelectric power, fish and wildlife habitats,
and recreation.
– Multiple uses can create controversy
Water Use
• Another problem with off stream use is how
much water can be removed w/o damaging
the stream ecosystem.
– E.g. Aral Sea. Diverting water for agriculture
caused sea to dry up
– Surface area of sea reduces 90% in 50 years
Aral Sea
• Salt content of the water has increased
• Dust storms from dry salt flats
• Climate changes
– Winters colder, summers warmer
– Loss of fishing and decline of tourism
Transport of Water
• Ancient civilizations constructed canals and
aqueducts to transport water
– From distant river to where it is needed
• In modern civilization water moved from
areas of abundant rain and snow fall to
areas of high usage
– E.g. California moves water from north to south
– E.g. New York City has had to obtain water
from farther and farther away
Some Trends in Water Use
• Withdrawal of surface water far exceeds
withdrawal of groundwater
• Since 1980 use has decreases and leveled
off
– Suggests improvement in water management
and conservation
Some Trends in Water Use
• Trends in freshwater withdrawals by wateruse categories suggests that:
– 1. The major uses of water are for irrigation and
the thermoelectric industry.
– 2. Water use for irrigation increased from 19501980. It decreased and leveled off from 19852000
• due to better irrigation efficiency, crop type and
higher energy costs.
Some Trends in Water Use
– 3. Water use by thermoelectric industry
decreased slightly in 1980, and stabilized in
1985.
• Due to reticulating water for cooling
– 4. Water for public and rural supplies continued
to increase through the period from 1950 to
2000
• presumably related to the increase in human
population.
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
Agricultural Use
• Improved irrigation could reduce
agricultural withdrawals by 20 to 30%
– Tremendous savings because ag is the biggest
user
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.
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.
Domestic Use
• Accounts for about 10% of total national
water withdrawals
– But concentrated in urban areas
– May pose major local problems
Domestic Use
• Water use can be substantially reduced by:
– In semiarid regions, replace lawns with
decorative gravels and native plants.
– Use more efficient bathroom fixtures.
– Turn off water when not absolutely needed.
– Flush the toilet only when really necessary.
– Fix all leaks quickly.
Domestic Use
– Purchase dishwashers and washing machines
that minimize water consumption.
– Take a long bath rather than a long shower.
– Sweep sidewalks and driveways.
– Using gray water to water vegetation.
– Water lawns and plants at cool times to reduce
evaporation.
Domestic Use
– Use drip irrigation and place water-holding
mulch around garden plants.
– Plant drought-resistant vegetation.
– Learn how to read the water meter to monitor
for unobserved leaks and record your
conservation successes.
– Use reclaimed water
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
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
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.
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.
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.
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
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
Water Management
• Options for minimizing potential problems:
– Alternating water supplies and managing
existing supplies better
– Towing icebergs
– As price goes up many innovative programs are
possible.
Variable-water-source approach
A Master Plan for Water
Management
• New management philosophy is that surface
water and groundwater are both subject to
natural flux with time.
– In wet years, there is plenty of surface water,
and the near-surface groundwater resources are
replenished.
– During dry years, specific plans to supply water
on an emergency basis must be in place and
ready to use.
A Master Plan for Water
Management
• Advanced planning may include
– Drilling to wells that are presently isolated
– Reuse of waste water
– Develop surface water and use groundwater in
dry years
– In wet years pump excess surface water
underground to recharge groundwater
Water Management and the
Environment
• Often a good deal of controversy surrounds
water development
– Dams, canals, wetlands modification
– Resolution of development involves input from
a variety of government and public groups
Wetlands
• Wetlands is a comprehensive term for
landforms such as salt marshes, swamps,
bogs, prairie potholes, and vernal pools.
– Common feature is that they are wet at least
part of the year
– Have a particular type of vegetation and soil
Wetlands
• Wetlands - defined as areas that are inundated by
water or where the land is saturated to a depth of a
few cm for at least a few days per year.
• Three major components used to determine the
presence of wetlands are:
– Hydrology
– Type of vegetation
– Type of soil.
Natural Service Functions of
Wetlands
• Freshwater wetlands are a natural sponge for
water.
– Reducing flooding.
• Many freshwater wetlands are important as areas
of groundwater recharge or discharge.
• Wetlands are one of the primary nursery grounds
for fish, shellfish, aquatic birds, and other animals.
• Wetlands are natural filters that help purify water.
Natural Service Functions of
Wetlands
• Wetlands are often highly productive and are
places where many nutrients and chemicals are
naturally cycled.
• Coastal wetlands provide a buffer for inland areas
from storms and high waves.
• Wetlands are an important storage site for organic
carbon.
• Wetlands are aesthetically pleasing to people.
Wetlands
• Freshwater wetlands are threatened in many
areas.
– Over the past 200 years > 50% of all wetlands
have disappeared, 90% of freshwater wetlands
– Diked, drained or filled
– SF bay estuary considered the most modified
by human activity
Wetlands
• Mississippi River delta includes major
coastal wetlands
– Historically maintained by flooding
– Accretion processes counter natural subsidence
– If accretion decreases area of open water
increases and wetland in reduced
– Levees block sediments and costal wetlands are
being lost
Restoration of Wetlands
• Number of projects have attempted to
restore wetlands.
– In freshwater marshes recovery linked to
availability of water
– Salt marshes more complex
– EPA of 1969 states if wetlands destroyed by
development must be replaced elsewhere
Restoration of Wetlands
• Constructing wetlands to clean up ag waste
– Natural ability to remove excess nutrients,
break down pollutants, and cleanse water.
– In Florida, human-made wetlands designed to
intercept and hold nutrients so they don’t
damage the Everglades.
Dams and the Environment
• Dams and their accompanying reservoirs
generally are designed to be multifunctional
structures.
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Used for recreational activities
Generating electricity
Providing flood control
Ensuring a more stable water supply
• Often difficult to reconcile various uses at a
given site.
Dams and the Environment
• The environmental effects of dams include
the following:
– Loss of land, cultural resources, and biological
resources in the reservoir area.
– Larger, dams and reservoirs produce a potential
serious flood hazard should they fail
– Storage behind the dam of sediment that would
otherwise move downstream to coastal areas.
Dams and the Environment
– Downstream changes in hydrology and in
sediment transport that change the entire river
environment and the organisms that live there.
– Fragmentation of ecosystems above and below
a dam.
– Restrict movement upstream and downstream
or organic material, nutrients and aquatic
organisms.
Dams and the Environment
• Many people vehemently against building
new dams.
– But if present water use practices continue we
will need new dams.
– Few acceptable sites for dams
– Expensive to build and operate, many people
don’t want tax dollars spent on subsidized
water.
Canals
• Water from upstream reservoirs may be
routed downstream by way of natural water
ways or canals and aqueducts.
– Not hydrologically the same as creeks
– Smooth, steep banks; water moves fast
– Canals can spread and carry disease
• schistosomiasis
Removal of Dams
• Recent dam removals include
– Edwards Dam in Maine
– Marmot Dam in Oregon
– After removal both river saw return of fish as
they migrated upstream
• Large fish runs transport nutrients upriver
from ocean to forest ecosystems.
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.
Channelization and the
Environment
• Channelization of streams consists of
straightening, deepening, widening,
clearing, or lining existing stream channels.
– Engineering technique that has been used to
control floods, improve drainage, control
erosion, and improve navigation
Channelization and the
Environment
• Adverse environmental effects, including the
following:
– Degradation of the stream’s hydrologic qualities;
• nearly all riffle flow, resulting in loss of important fish
habitats.
– Removal of vegetation along the watercourse, which
removes wildlife habitats and shading of the water.
– Downstream flooding where the channelized flow ends.
– Damage or loss of wetlands.
– Aesthetic degradation.
Channelization and the
Environment
• Case study in problems w/ Channelization
– Kissimme River in Florida
– Meandering river turned into straight ditch
– Failed to provide flood protection, damaged
wildlife habitat, water quality problems and
aesthetic degradation.
– In 1990 efforts to restore river began.
The Colorado River: Water Resources
Management and the Environment
• The history of the Colorado River
emphasizes linkages among physical,
biological, and social systems that are at the
heart of environmental science.
– Major river of the southwestern US
– Ends in the Gulf of California
The Colorado River
• For its size has a modest flow but is one of
the most regulated and controversial bodies
of water in the world.
– Total flow was apportioned among various
users in 1922
– No water allowed for environmental purposes
– Water rarely flows into the Gulf, all stored and
used upstream.
• Damaged delta
The Colorado River
• Two largest reservoirs- Hoover Dam and
Glen Canyon Dam
– Stored about 80% of total in the basin
– Represents a buffer of several years water
supply.
– Changing hydrology of the river changed other
aspects
• Rapids, sediment load, and vegetation
The Colorado River
• Record snowmelt in the Rocky Mountains
in 1983 forced the release of water from
Glen Canyon Dam
– Three times normal but similar to spring floods
before the dam was built.
– Beneficial to the river, highlighted the
importance of floods in maintaining a natural
state.
The Colorado River
• As an experiment “flood” waters released in
1996
– Two weeks at full flood
– As a result 55 new sandbars formed and 75% of
existing sandbars increased in size, rejuvenated
marshes and backwaters.
– Hailed a success; hoped that what was learned
can help restore other river impacted by dams.
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.
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.
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.