managing groundwater and surface water supplies

1. Managing Groundwater andManaging Groundwater and
Surface Water SuppliesSurface Water Supplies

2. TOO LITTLE FRESHWATERTOO LITTLE FRESHWATER
 Our water options are:Our water options are:

Get more water from aquifersGet more water from aquifers

Manage river water with dams and reservoirsManage river water with dams and reservoirs

Transport waterTransport water

Desalinate ocean waterDesalinate ocean water

Waste less waterWaste less water

3. WITHDRAWING GROUNDWATERWITHDRAWING GROUNDWATER
TO INCREASE SUPPLIESTO INCREASE SUPPLIES
 Almost 25% of world’s water is from aquifersAlmost 25% of world’s water is from aquifers
 Most aquifers are renewable resources –Most aquifers are renewable resources –
unless water is removed faster thanunless water is removed faster than
replenished or contaminatedreplenished or contaminated
 Groundwater depletion is a growing problemGroundwater depletion is a growing problem
mostly from irrigationmostly from irrigation

At least one-fourth of the farms in India are beingAt least one-fourth of the farms in India are being
irrigated from over-pumped aquifers.irrigated from over-pumped aquifers.

4. Fig. 14-7, p. 313
Trade-Offs
Withdrawing Groundwater
Advantages Disadvantages
Useful for drinking
and irrigation
Aquifer depletion from
overpumping
Available year-
round
Sinking of land
(subsidence) from
overpumping
Exists almost
everywhere
Polluted aquifers for
decades or centuries
Renewable if not
overpumped or
contaminated
Saltwater intrusion into
drinking water supplies
near coastal areas
Reduced water flows
into surface waters
No evaporation
losses
Cheaper to extract
than most surface
waters
Increased cost and
contamination from
deeper wells

5. Groundwater Pumping in SaudiGroundwater Pumping in Saudi
Arabia (1986 – 2004)Arabia (1986 – 2004)
 Green dots – irrigation systems from theGreen dots – irrigation systems from the
nonrenewable aquifernonrenewable aquifer
 Brown dots – wells that have gone dryBrown dots – wells that have gone dry
Figure 14-9Figure 14-9

6. Case Study: Overpumping the OgallalaCase Study: Overpumping the Ogallala
 OgallalaOgallala – the world’s largest aquifer– the world’s largest aquifer

7. Case Study: Overpumping the OgallalaCase Study: Overpumping the Ogallala
 OgallalaOgallala – under 8 states– under 8 states

Allows productive agriculture in Great PlainsAllows productive agriculture in Great Plains

NonrenewableNonrenewable

Pumped 10 – 40X faster than rechargePumped 10 – 40X faster than recharge

Government subsidies encourage farming andGovernment subsidies encourage farming and
therefore depletion of aquifertherefore depletion of aquifer

Contaminated with fertilizers and pesticidesContaminated with fertilizers and pesticides

8. Effects of Groundwater OverpumpingEffects of Groundwater Overpumping
 Loss of springsLoss of springs

Water tables fall, springs disappearWater tables fall, springs disappear

Reduced habitat and biodiversity at wetlandsReduced habitat and biodiversity at wetlands

9. Effects of Groundwater OverpumpingEffects of Groundwater Overpumping
 Land subsidenceLand subsidence – sinking or collapsing of– sinking or collapsing of
land when aquifer depleted – damagesland when aquifer depleted – damages
infrastructure – recharge impossibleinfrastructure – recharge impossible

11. Land subsidence in Mexico CityLand subsidence in Mexico City

12. Effects of Groundwater OverpumpingEffects of Groundwater Overpumping
 SinkholesSinkholes form when theform when the
roof of an undergroundroof of an underground
cavern collapses after beingcavern collapses after being
drained of groundwaterdrained of groundwater

13. Effects of Groundwater OverpumpingEffects of Groundwater Overpumping
 Saltwater intrusionSaltwater intrusion – contamination of– contamination of
freshwater aquifers near coastal areas withfreshwater aquifers near coastal areas with
saltwatersaltwater

15. Tapping Deep AquifersTapping Deep Aquifers
 May contain enough water to provide forMay contain enough water to provide for
billions of people for centuriesbillions of people for centuries
 Major concernsMajor concerns

NonrenewableNonrenewable

Little is known about the geological andLittle is known about the geological and
ecological impacts of pumping deep aquifersecological impacts of pumping deep aquifers

Some flow beneath more than one countrySome flow beneath more than one country

Costs of tapping are unknown and could be highCosts of tapping are unknown and could be high

17. Using Isotope Hydrology toUsing Isotope Hydrology to
Understand AquifersUnderstand Aquifers
 Isotope hydrologyIsotope hydrology – use of chemical– use of chemical
“fingerprints” to identify origins, age, size,“fingerprints” to identify origins, age, size,
flow and fate of water in aquifersflow and fate of water in aquifers
 Helps manage aquifersHelps manage aquifers

18. Managing Surface WaterManaging Surface Water
 DamDam – structure built across a river to control– structure built across a river to control
its flowits flow
 ReservoirReservoir – artificial lake behind dam– artificial lake behind dam

19. USING DAMS AND RESERVOIRSUSING DAMS AND RESERVOIRS
TO SUPPLY MORE WATERTO SUPPLY MORE WATER
 Large dams and reservoirs:Large dams and reservoirs:

Produce cheap electricity, reduce downstreamProduce cheap electricity, reduce downstream
flooding, provide year-round water for irrigatingflooding, provide year-round water for irrigating
cropland and communities, recreationcropland and communities, recreation

Displace people (40 – 80 million) and disruptDisplace people (40 – 80 million) and disrupt
aquatic (upstream and downstream) andaquatic (upstream and downstream) and
terrestrial ecosystems, fill up with sediment, loseterrestrial ecosystems, fill up with sediment, lose
water due to evaporation and seepagewater due to evaporation and seepage
 > 45,000 large dams worldwide, 22,000 in> 45,000 large dams worldwide, 22,000 in
China, 70,000 large and small in U.S.China, 70,000 large and small in U.S.

21. Figure 14-13Figure 14-13

22. Case Study: The Colorado Basin – anCase Study: The Colorado Basin – an
Overtapped ResourceOvertapped Resource
 The Colorado River has so many dams andThe Colorado River has so many dams and
withdrawals that it often does not reach thewithdrawals that it often does not reach the
oceanocean

14 major dams and reservoirs, and canals14 major dams and reservoirs, and canals

Water is mostly used in desert area of the U.S.Water is mostly used in desert area of the U.S.
(in rain shadow of CA mountains) – farms,(in rain shadow of CA mountains) – farms,
ranches, communities, recreation – L.A. Sanranches, communities, recreation – L.A. San
Diego, Las VegasDiego, Las Vegas

Provides electricity from hydroelectric plants forProvides electricity from hydroelectric plants for
30 million people (1/1030 million people (1/10thth
of the U.S. population)of the U.S. population)

23. The Colorado River BasinThe Colorado River Basin
 Drainage basinDrainage basin
equals > one-equals > one-
twelfth of thetwelfth of the
land area of theland area of the
lower 48 stateslower 48 states

24. Case Study: The Colorado Basin – anCase Study: The Colorado Basin – an
Overtapped ResourceOvertapped Resource
 Lake Powell, isLake Powell, is
the secondthe second
largest reservoirlargest reservoir
in the U.S.in the U.S.
 It hosts one ofIt hosts one of
the hydroelectricthe hydroelectric
plants located onplants located on
the Coloradothe Colorado
RiverRiver

25. Case Study: The Colorado Basin – anCase Study: The Colorado Basin – an
Overtapped ResourceOvertapped Resource
 Major problems:Major problems:

Includes some of driest lands in U.S. and MexicoIncludes some of driest lands in U.S. and Mexico

Modest water flow for its sizeModest water flow for its size

Legal pacts (1922, 1944) allocate more water forLegal pacts (1922, 1944) allocate more water for
human uses than river can supporthuman uses than river can support

Water flow has dropped because of withdrawalWater flow has dropped because of withdrawal
for urban and agricultural uses (including waterfor urban and agricultural uses (including water
intensive crops like rice, cotton and alfalfa)intensive crops like rice, cotton and alfalfa)

Often doesn’t reach sea – habitat loss, sedimentOften doesn’t reach sea – habitat loss, sediment
deprivation for delta wetlands and forestsdeprivation for delta wetlands and forests

26. Case Study:Case Study:
China’s Three Gorges DamChina’s Three Gorges Dam
 Debate – advantages > disadvantages ?Debate – advantages > disadvantages ?

World’s largest dam and reservoir – 2.3 km longWorld’s largest dam and reservoir – 2.3 km long
crossing Yangtze Rivercrossing Yangtze River

Electric output = 18 large coal-burning or nuclearElectric output = 18 large coal-burning or nuclear
power plantspower plants

Prevents floodingPrevents flooding

Facilitates ship travel, reduces transportation costsFacilitates ship travel, reduces transportation costs

Displaced 1.2 million people, lost cultural sitesDisplaced 1.2 million people, lost cultural sites

Built over seismic fault and has small cracks.Built over seismic fault and has small cracks.

27. Three Gorges DamThree Gorges Dam

28. Three Gorges DamThree Gorges Dam

29. Dam RemovalDam Removal
 Some dams removed for ecological reasonsSome dams removed for ecological reasons
and because they outlived usefulnessand because they outlived usefulness

1998 – U.S. Army Corps of Engineers announced1998 – U.S. Army Corps of Engineers announced
that it would no longer build large dams andthat it would no longer build large dams and
diversion projects in U.S.diversion projects in U.S.

The Federal Energy Regulatory Commission hasThe Federal Energy Regulatory Commission has
approved the removal of nearly 500 damsapproved the removal of nearly 500 dams

Removing dams can reestablish ecosystems, butRemoving dams can reestablish ecosystems, but
is expensive and can re-release toxic sedimentsis expensive and can re-release toxic sediments

31. What Happens When You
Demolish Two 100-Year Old Dams