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					     Chapter 7
Water: Hydrologic Cycle and
        Human Use

Death of the Aral Sea

• Located in present-day Kazakhstan and
• 1930’s it was decided that the area
  surrounding the sea could be used to
  grow cotton.
• By 1960, millions of acres of land were
  irrigated using water from the two large
  rivers that fed the Aral Sea.
• The sea began to shrink
  Aral Sea Impacts
• Salinity increased as water was not
  – Hurt the 60,000 employee fishery industry.
  – 3x saltier than the ocean.
• Lost 90% of it’s original volume.
• Many health impacts for the people as the
 dried salt/pesticide/fertilizer/herbicide
 laden dust is carried by winds
  – Increased cancer, higher infant mortality
• Local climate changed, growing season
 shortened, switch from cotton to rice
Other dry runs:

• Aral sea not unique:
  – Rio Grande shorter because of withdraw for
    domestic use and irrigation.
  – Colorado river almost completely drained
    before it can reach Mexico leaving a dried
    baked mud area in the gulf of California.
  – Dead Sea is being diverted by Israel and
    Jordan. May disappear by 2050 without any
    action taking place to prevent it.
Lesson 7.1

• Objectives for the chapter (Threefold)
1. To understand the natural water
   cycle, its capacities, and its
2. To understand how we are over
   drawing certain water sources and
   to understand the consequences
3. To understand how water must be
   handled if we are to achieve
   sustainable supplies
Water is fundamental to life

• Earth has about 325 million cubic miles/
 covers about 71 % of its surface
  – 97.5% of this water is salt water
• Fresh water- water that has a salt content of
  less than 0.1%
• 97.5% Salt water
• 2.5% Fresh water
  – 1.7% Polar ice caps and glaciers
  – .77% Accessible fresh water
Where does the 0.77% fresh
water come from?
• Lakes
• Wetlands
• Rivers
• Groundwater
• Biota
• Soil
• Atmosphere
• Human societies must draw fresh water
  for energy through hydroelectric,
  transportation, recreation, waste
  processing, and habitats for aquatic
  plants and animals.
• Over the past two centuries these uses
  have led us to try to control the water
  through infrastructure: dams, canals,
  reservoirs, sewer systems, treatment
  plants, water towers, etc.
What water does for land:

• Provides drinking water, water for
  industry, and water to irrigate crops.
• Bodies of water provide energy through
  the hydroelectric power and control
  flooding by absorbing excess water.
• There are two ways to consider
 water issues:
 –Quantity (this chapter)
   •On the Global water cycle and how it
    works, on the technolgies we use to
    control and manage its use, and on
    public policy
 –Quality (chapter 17)
   •Water pollution and its consequences,
    on sewage treatment technologies, and
    on public policy for dealing with
    pollution issues.
             Section Two
         The Hydrologic Cycle:
Natural Cycle, Human Impacts
Water cycle or Hydrologic cycle
- Hydrologic Cycle:
 - Consists of water rising to the
   atmosphere through either
   evaporation or transpiration and
   returning to the land and
   oceans through condensation
   and precipitation.
   - Water vapor-green water
   - Liquid water-blue water
• Humidity- amount of water vapor
 in the air
  –measured as relative humidity
   (amount of water vapor as a %
   of what the air can hold at a
   particular temperature)
•Humidity increases as air warms
           decreases as air cools
Water cycle
Water Terms
•Table 7-1 page 172
•Add the following terms:
Physical Processes and Loops
4 Physical Processes     3 Physical Loops
•   Evaporation          • Evapotranspiration loop
•   Condensation            – Evaporates and returns as
•   Precipitation
                         • Surface runoff loop
•   Gravitational flow      – Water runs across the ground
                              surface and becomes part of the
                              surface water system
                         • Ground water loop
                            – Water infiltrates, percolates down
                              to join the ground water traveling
                              through aquifers and then exiting
                              through seeps, springs, or wells
Green House Gas
•Water is a powerful
 greenhouse gas: it provides
 about 2/3 of the total
 warming from all
 greenhouse gases.
• Microscopic liquid or solid particles
  originating from land and water surfaces
  that attract water vapor and promote the
  formation of droplets of moisture (AKA-
  condensation nuclei)
May originate naturally through volcanic
  eruption, wind-stirred dust and soil, and
  sea salts or may occur anthropogenically
  through sulfates, carbon, and dust.
Natural water purification
•One very important aspect of
 evaporation & condensation is water
  •When water in an ocean or lake
  evaporates, only the water
  molecules leave the surface. May
  pick up impurities again as it falls.
  •Water turn over in the atmosphere
  happens every 10 days, so water is
  constantly being purified.
Ground Water
• Water that infiltrates the ground has two alternatives.
   1. It may be held in the soil and returned
      to the atmosphere through one of the
      following methods…

• Transpiration: air picks up water vapor from
    vegetation    (green water flow)
•   Evaporation: Air picks up water vapor from the soil
    (green water flow)
•   Evapotranspiration: the combination of the two above

    2. Or it may percolate (blue water
Salt Lakes

• Created as salts are picked up and carried
 to inland lakes the same way that they are
 carried to the ocean.
Hadley Cell
Rising air over the equator is pushed from beneath by
more rising air causing a “spill over” to the North and
South. The two halves of the system (rising and
falling air) make up the Hadley cell
Rain Shadow

• Causes rising and falling air currents when
 moisture laden trade winds encounter
 mountain ranges
• Layers of porous material through which
 groundwater moves through.
  – Hold 99% of the liquid fresh water
  – The rest is found in lakes, wetlands and rivers
Surface Runoff and Ground
• Both are blue water systems.
• Both are the usual focus for
  human resource management.
• Infiltration-runoff ratio: the
  amount that soaks in compared to
  the amount that runs off
Human Impacts
•Four categories that either
 directly or indirectly impact
 the water cycle:
 –Changes to Earth’s surface
 –Changes to Earth’s climate
 –Atmospheric pollution
 –Withdraws for human use
• As land is cleared or
 overgrazed, the pathway for
 the water cycle shifts from
 infiltration and groundwater
 recharge to runoff.
 –Consequences include flooding,
  decreased ground water,
  increased salinization, loss of
Section Three
 Water: A Resource to Manage,
  a Threat to Control
 Major Uses
• Table 7.2
• Homes/industry:
  –washing and flushing away wastes.
  –Irrigation. (consumptive)
• We use less water today than in
 1975…even though population has
Water Usage
Consumptive                   Nonconsumptive
• The applied water does      • Water is returned to its
  not return to the water       source
  source                         – Electric power generation
   – Irrigation                  – Industrial use
   – Other agricultural use      – Domestic use (public and
Trends in water use:
• US: industry followed by agriculture by
• World: agriculture, industry, domestic
• Europe: similar to US
• South America & Africa: agriculture,
  domestic, industry
• Asia: similar to world pattern of use

• Figure 7-11 page 179
• US: 40% ground, 60% surface for
  domestic use.
• Developing countries: 90% of the waste
  water is released directly to surface
  waters without treatment…cholera, etc.
  1.1 billion people drink this unsafe water.

         Saris used to
         filter cholera in
Technologies for water collection

• Industrialized countries:
  – dams are built across rivers to create
    reservoirs (hole water in times of excess flow
    and can be drawn out in times of lower flow).
  – Water is piped to treatment plants.
  – Water is distributed through the water system
    to homes, schools, and industry.
  – Water is collected by sewage-treatment plant,
    retreated, and sent back out for distribution
Municipal Water Treatment
 • Figure 7-13 page 180.
  –Know the steps of the water
   treatment plant…Alum, mixing
   tank, settling basin, sand filter,
   lime/fluoride added, distribution.
 Dam Impacts
• US: 75,000 dams at least six feet in
  height, another 2 million smaller
• Fresh water habitats lost, increased
  salt concentration, etc.
Glen Canyon
• Closed its gates in 1963 (meaning it
  became operational).
• Stores excess water in Lake Powell
• Spans the Colorado River at Lee’s Ferry,
  AZ, just above Grand Canyon National
• Operated by Federal Bureau of
• Generates hydropower and stores water
  for distribution to CA, NE, AZ, and Mexico.
Glen Canyon Continued

• A study in the late 1980’s to early 1990’s
  concluded that the operation of the dam
  had greatly impacted the downstream
  ecology and its recreational resources.
• 1996, Secretary of the Interior issued new
  rules that established minimum and
  maximum water-release rates (GCMRC)

• 1996
• Secretary of the Interior, Bruce Babbitt
• Grand Canyon Monitoring and Research
• Provides scientific monitoring for the
  dam’s operations and operates within the
  guidelines of adaptive ecosystem
• Outcome: successful
Dam building around the world

• US: 75,000 dams at least 6 feet in height
  and an estimated 2 million other smaller
• Around the world: more than 45,000
  large dams (50ft high).
  – 3,000 of these contain storage reservoirs with
    volumes greater than 25 billion gallons, 120
    million acres of land and containing more than
    1,500 mi3 of water

• CALFED Bay-Delta Program
  – Established to “develop and implement a lon-
    term comprehensive plan that will restore
    ecological health and improve water
    management for beneficial uses of the Bay-
    Delta System”
  – Bay-Delta is a huge estuary in the San
    Francisco Bay.
Ground Water
• Can be nonrenewable, such is the
 case for the Ogallala aquifer.
 –Originally charged during the last
  ice age melt (fossil water).
 –Used to irrigate 1/5 of US land.
  Cannot recharge at a fast enough
  rate to be sustainable.
 Falling water table
• Wet lands dry up.
• Structural support is lost.
  –Land subsistence.
  –Sink holes.
  –Salt water intrusion (figure 7-18 page
• Land subsidence is
 where ground water
 has leached into
 cavities in the ground,
 helping to support the
 above lying rock and
 soil. As the water
 table drops, the
 support is lost. This is
 the gradual settling of
 the land.
            • Type of land subsidence that
Sink hole    happens rapidly and
Salt water intrusion
• Results from dropping water tables.
• Springs of outflowing ground water may
 lie under the ocean. As long as the water
 table is high it will maintain enough head
 pressure in the aquifer and water will flow
 into the ocean. When tables are low the
 pressure is not enough and ocean water
 flows backward into the aquifer
Salt water intrusion
Section Four
Water Stewardship:
Public Policy Challenges
How is there not enough?

• If the water cycle is sufficient to provide
  water for all human needs, why do some
  go without?
  – Not distributed evenly
  – Scarcity of water in many parts of the world
  – Deficit in infrastructure
  – Expanding populations
How can we make water
use sustainable:
1. Capture more runoff
2. Gain better access to groundwater
3. Desalt seawater
   (microfiltration/reverse osmosis)
4. Conserve present supplies by using
   less water. (drip irrigation)
 Why build dams?

 • Combination of flood control, water
  storage, and hydropower.

Three Georges Dam
Three Georges Dam
• Yangtze River in China
• Completed in 2006
• Largest hydroelectric project in the world
• Generates 22,000 MW of electricity
• More than 1.2 million people have been
• Critics point to the huge human,
  ecological, and aesthetic costs of the dam
  and claim alternative sources of energy
  are cheaper
US Dam Removal

• 500 dams have already been removed in
  the US and many await the same fate.
• Pros for removal: reestablish historic
  fisheries and reestablish the river for
  recreational and aesthetic value
• Cons: massive sediment from upriver that
  will be washed downstream, difficult.
Wild and Scenic Rivers Act

• 1968
• Keeps rivers labeled as “wild and scenic”
  from being dammed or affected by other
  harmful operations.
• 11,300 miles of rivers have been
  protected, 60,000 more miles are eligible.
• Like national parks, they need supporters
  and defenders such as the organization
  American Rivers
Threats to irrigated agriculture

• Greatest: ground water depletion
  – Happening in many parts of the world
• Other threats: pollution from fertilizers,
  pesticides, animal wastes, and industrial
Genetically modify plants?
• Scientists are trying to modify plants to be tolerant of
•   The trend however is to desalinate until this is an
    actual possibility.
•   Desalinating: microfiltration (reverse osmosis)-great
    pressure forces seawater through a membrane filter
    fine enough to remove salt…and distillation-
    evaporation and recondensation of water vapor
•   Under the best circumstance it costs $2 per 1,000
    gallons (2-4 x’s as much as US city dwellers pay but
    by far cheaper than bottled water
•   Cost efficient for city dwellers but not for crop owners
    who need to irrigate.
Water used per day per person

• Developing nation: 1 gallon (includes
  cooking and washing)
• US: 100 gallons per person per day
  – If all indirect uses such as irrigation are added
    in it goes up to 1,300 gallons
Agricultural water conservation
• Drip irrigation: network of
  plastic pies with pin holes
  in them that literally drip
  water at the base of the
• Treadle pump: works like
  an exercise machine
  pumping water from just a
  few feet below the
Municipal water conservation
• Flushing 3-5 gallons
• Showering 2-3 gallons per minute
• Laundry 20-30 gallons per load
• Conserve: fix leaky faucets, low-flow
  shower heads and faucets, replace lawns
  with xeriscaping, ban use of water during
  draughts, gray-water recycling.

• Landscaping with desert species that
 require no extra watering (lawn
US water policy

• No US water policy 
• Clean water act and its subsequent
  amendments authorize the US EPA to
  develop programs and rules to carry out
  its mandate for oversight of the nation’s
  water quality.
• EPA does not deal with water quantity.
Issues to be addressed
• The last time a water policy report was issued
  was in 1950 by Harry S. Truman
• The issues that need to be addressed by a
  water policy report…7 on page 190
  – Promote efficiency
  – Water subsidies reduced or eliminated
  – Polluters charged according to effluents
  – Watershed management
  – Regulate dam operations
  – International development aid
  – More research and monitoring

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