2. USING DAMS AND RESERVOIRS
TO SUPPLY MORE WATER
• Large dams and reservoirs can produce
cheap electricity, reduce downstream
flooding, and provide year-round water for
irrigating cropland, but they also displace
people and disrupt aquatic systems.
3. Water Needs in West
• Dams are
used to
create
reservoirs
for water
diversion for
western
states
4. Dams and Diversion
• Dams disrupt ecosystems above and
below the dam
• Less water flows through river system
Less water available for use downstream
• Floods the area behind the dam
Disrupts biota and human settlements
• Sediment builds up behind the dam
• Lack of sediment downstream creates
erosion
5. Fig. 14-13a, p. 317
Provides water
for year-round
irrigation of
cropland
Flooded land
destroys forests
or cropland and
displaces people
Large losses of
water through
evaporation
Provides
water for
drinking Downstream
cropland and
estuaries are
deprived of
nutrient-rich silt
Reservoir is
useful for
recreation
and fishing
Risk of
failure and
devastating
downstream
flooding
Can produce
cheap
electricity
(hydropower)
Downstream
flooding is
reduced
Migration and
spawning of
some fish are
disrupted
6. Issues with Diversion
• Natural river
channels reduced or
enclosed
• Diversion of water
eliminates viability of
town
• Water dries up
before the river
reaches the sea
through Mexico
7. Issues with Irrigation
• Irrigation
causes
Salinization
of soil – as
water
evaporates
leaves salt
behind
8. DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES
• Removing salt from seawater by current
methods is expensive and produces large
amounts of salty wastewater that must be
disposed of safely.
– Distillation: heating saltwater until it evaporates,
leaves behind water in solid form.
– Reverse osmosis: uses high pressure to force
saltwater through a membrane filter.
9. DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES
• Seeding clouds with tiny particles of
chemicals to increase rainfall towing icebergs
or huge bags filled with freshwater to dry
coastal areas have all been proposed but are
unlikely to provide significant amounts of
freshwater.
10. INCREASING WATER SUPPLIES
BY WASTING LESS WATER
• We waste about two-thirds of the water we
use, but we could cut this waste to 15%.
– 65-70% of the water people use throughout the
world is lost through evaporation, leaks, and
other losses.
– Water is underpriced through government
subsidies.
– The lack of government subsidies for improving
the efficiency of water use contributes to water
waste.
11. INCREASING WATER SUPPLIES
BY WASTING LESS WATER
• Sixty percent of the world’s irrigation water is
currently wasted, but improved irrigation
techniques could cut this waste to 5-20%.
• Center-pivot, low pressure sprinklers sprays
water directly onto crop.
– It allows 80% of water to reach crop.
– Has reduced depletion of Ogallala aquifer in
Texas High Plains by 30%.
12. Fig. 14-18, p. 325
Center pivot
Drip irrigation
Gravity flow
(efficiency 60% and
80% with surge
valves)
Above- or below-
ground pipes or tubes
deliver water to
individual plant roots.
Water usually comes from
an aqueduct system or a
nearby river.
(efficiency 90–95%)
(efficiency 80%–95%)
Water usually pumped
from underground and
sprayed from mobile
boom with sprinklers.
13. Fig. 14-19, p. 326
Solutions
Reducing Irrigation Water Waste
• Line canals bringing water to irrigation ditches
• Level fields with lasers
• Irrigate at night to reduce evaporation
• Monitor soil moisture to add water only
when necessary
• Polyculture
• Organic farming
• Don't grow water-thirsty crops in dry areas
• Grow water-efficient crops using drought
resistant and salt-tolerant crop varieties
• Irrigate with treated urban waste water
• Import water-intensive crops and meat
14. Solutions: Getting More Water for
Irrigation in Developing Countries
– The Low-Tech Approach
• Many poor farmers in
developing countries
use low-tech methods
to pump groundwater
and make more
efficient use of rainfall.
Figure 14-20
15. Fig. 14-21, p. 327
Solutions
Reducing Water Waste
• Redesign manufacturing processes
• Repair leaking underground pipes
• Landscape yards with plants that
require little water
• Use drip irrigation
• Fix water leaks
• Use water meters
• Raise water prices
• Use waterless composting toilets
• Require water conservation in water-
short cities
• Use water-saving toilets, showerheads,
and front loading clothes washers
• Collect and reuse household water to
irrigate lawns and nonedible plants
• Purify and reuse water for houses,
apartments, and office buildings
• Don't waste energy
16. Fig. 14-25, p. 333
What Can You Do?
Water Use and Waste
• Use water-saving toilets, showerheads, and faucet aerators.
• Shower instead of taking baths, and take short showers.
• Stop water leaks.
• Turn off sink faucets while brushing teeth, shaving, or washing.
• Flush toilets only when necessary.
• Wash only full loads of clothes or use the lowest water-level for
smaller loads.
• Use recycled (gray) water for lawn, gardens, house plants,
car washing.
• Wash a car from a bucket of soapy water, and use the hose for
rinsing only.
• If you use a commercial car wash, try to find one that recycles its
water.
• Replace your lawn with native plants that need little if any watering
and decorative gravel or rocks.
• Water lawns and gardens in the early morning or evening.
• Sweep or blow off driveways instead of hosing off with water.
• Use drip irrigation and mulch for gardens and flowerbeds.
