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.
• 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
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:
• 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
WATER: A VITAL RESOURCE
• Objectives for the chapter (Threefold)
1. To understand the natural water
cycle, its capacities, and its
limitations
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:
• 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:
–Potable
–Gray
–Black
Physical Processes and Loops
4 Physical Processes 3 Physical Loops
• Evapotranspiration loop
• Evaporation
– Evaporates and returns as
• Condensation
precipitation
• 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.
Aerosols
• Microscopic liquid or solid particles
originating from land and water surfaces
that attract water vapor and promote the
formation of droplets of moisture (AKAcondensation 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
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.
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
terms.
2. Or it may percolate (blue water
system).
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
Aquifers
• 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:
• 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
Deforestation
• 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
Water: A Resource to Manage,
a Threat to Control
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
Consumptive
• The applied water does
not return to the water
source
– Irrigation
– Other agricultural use
Nonconsumptive
• Water is returned to its
source
– Electric power generation
– Industrial use
– Domestic use (public and
self-supplied)
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
Sources
• 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
• 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
structures.
• 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
Park.
• Operated by Federal Bureau of
Reclamation.
• 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)
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
• 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
• CALFED Bay-Delta Program
– Established to “develop and implement a lonterm comprehensive plan that will restore
ecological health and improve water
management for beneficial uses of the BayDelta 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
184).
Subsidence
• 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
• Type of land subsidence that
happens rapidly and
dramatically
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
aquifers
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
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
• 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
chemicals.
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 distillationevaporation 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
plant.
• Treadle pump: works like
an exercise machine
pumping water from just a
few feet below the
surface.
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.
xeriscaping
• Landscaping with desert species that
require no extra watering (lawn
replacement)
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