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Chapter 7 Water: Hydrologic Cycle and Human Use. Introduction. The Aral Sea. Death of the Aral Sea. Located in present-day Kazakhstan and Uzbekistan. 1930’s it was decided that the area surrounding the sea could be used to grow cotton.

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Chapter 7 Water: Hydrologic Cycle and Human Use

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death of the aral sea
Death of the Aral Sea
  • Located in present-day Kazakhstan and Uzbekistan.
  • 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
Aral Sea Impacts
  • Salinity increased as water was not replenished
    • 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
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.
Objectives for the chapter (Threefold)
  • To understand the natural water cycle, its capacities, and its limitations
  • To understand how we are over drawing certain water sources and to understand the consequences
  • 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
Where does the 0.77% fresh water come from?
  • Lakes
  • Wetlands
  • Rivers
  • Groundwater
  • Biota
  • Soil
  • Atmosphere

How do we use it?

  • 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
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
Section Two

The Hydrologic Cycle:

Natural Cycle, Human Impacts

water cycle or hydrologic cycle
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 terms
Water Terms
  • Table 7-1 page 172
  • Add the following terms:
    • Potable
    • Gray
    • Black
physical processes and loops
Physical Processes and Loops

4 Physical Processes

3 Physical Loops

Evapotranspiration loop

Evaporates and returns as precipitation

Surface runoff loop

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

  • Evaporation
  • Condensation
  • Precipitation
  • Gravitational flow
green house gas
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
Natural water purification
  • One very important aspect of
  • evaporation & condensation is water
  • purification.
    • 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.

    • 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 terms.
    • Or it may percolate (blue water


salt lakes
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
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
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 water
Surface Runoff and Ground Water:
  • 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
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 biodiversity
section three
Section Three

Water: A Resource to Manage, a Threat to Control

major uses
Major Uses
  • Table 7.2
  • Homes/industry:
    • washing and flushing away wastes. (nonconsumptive)
    • Irrigation. (consumptive)
  • We use less water today than in 1975…even though population has increased.
water usage
Water Usage



Water is returned to its source

Electric power generation

Industrial use

Domestic use (public and self-supplied)

  • The applied water does not return to the water source
    • Irrigation
    • Other agricultural use
trends in water use
Trends in water use:
  • US: industry followed by agriculture by domestic
  • 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 Bangladesh.

technologies for water collection
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
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
Dam Impacts
  • US: 75,000 dams at least six feet in height, another 2 million smaller structures.
  • Fresh water habitats lost, increased salt concentration, etc.
glen canyon
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 Park.
  • Operated by Federal Bureau of Reclamation.
  • Generates hydropower and stores water for distribution to CA, NE, AZ, and Mexico.
glen canyon continued
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 center
  • Provides scientific monitoring for the dam’s operations and operates within the guidelines of adaptive ecosystem management.
  • Outcome: successful
dam building around the world
Dam building around the world
  • US: 75,000 dams at least 6 feet in height and an estimated 2 million other smaller structures.
  • 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
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
Falling water table
  • Wet lands dry up.
  • Structural support is lost.
    • Land subsistence.
    • Sink holes.
    • Salt water intrusion (figure 7-18 page 184).
  • 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.
sink hole
Sink hole
  • Type of land subsidence that happens rapidly and dramatically
salt water intrusion
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
section four
Section Four

Water Stewardship:

Public Policy Challenges

how is there not enough
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
How can we make water use sustainable:
  • Capture more runoff
  • Gain better access to groundwater aquifers
  • Desalt seawater (microfiltration/reverse osmosis)
  • Conserve present supplies by using less water. (drip irrigation)
why build dams
Why build dams?
  • Combination of flood control, water storage, and hydropower.

Three Georges Dam

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 displaced
  • Critics point to the huge human, ecological, and aesthetic costs of the dam and claim alternative sources of energy are cheaper
us dam removal
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
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
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 chemicals.
genetically modify plants
Genetically modify plants?
  • Scientists are trying to modify plants to be tolerant of salts.
  • 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
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
Agricultural water conservation
  • Drip irrigation: network of plastic pies with pin holes in them that literally drip water at the base of the plant.
  • Treadle pump: works like an exercise machine pumping water from just a few feet below the surface.
municipal water conservation
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 replacement)
us water policy
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
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