Global Water ResourcesJanuary 27, 2014

Properties of Water Due to Hydrogen Bonding

Stores heat/doesn’t change temperature easily

Dissolves many compounds Capillary Action Expands when frozen Evaporation takes lots of energy Water filters out harmful UV rays Exist over a wide temperature range

Availability of Freshwater

Only 0.02% of all water is available as liquid freshwater

Comparison: Population vs. water usage

Fig. 14-2, p. 307

ContinentPercent of world's water resources and population

Asia60.5%

36%

Africa10%

8%Europe

North and Central America 7.3%

South America and Caribbean 6.4%

26%

15%

5%Oceania

11.3%

0.5%

14%

Per Capita Water Use

Global Water Use

Case Study: Who Should Own and Manage Freshwater Resources There is controversy over whether water

supplies should be owned and managed by governments or by private corporations.

How Would You Vote? Should private companies own or

manage most of the world's water resources? a. No. Democratically elected governments, which are

accountable to the voters, should own and manage water resources.

b. Qualified yes. Governments should own the water, but expert private companies should manage it.

c. Depends. Each case must be decided independently. The record on private versus public ownership is mixed.

d. Yes. Private companies have more expertise and experience in managing water resources than most government bureaucrats.

Surface Water - Watersheds Watershed: An

area of land where all surface runoff goes to the same place (drainage basin)

Determined by landscape (mountains, etc.)

Land Use activities in one part of the watershed will affect other parts of the watershed.

Fig. 14-3, p. 308

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined Recharge Area

Runoff

Flowing artesian well

Recharge Recharge Unconfined Unconfined AquiferAquifer

Stream Well requiring a pumpInfiltration Water

table LakeInfiltration

Unconfined aquifer

Confined aquiferConfining impermeable rock layer Confining impermeable rock layer

Less permeable Less permeable material such as claymaterial such as clay

Ground Water Water table

the level below which the ground is saturated with water.

Aquifer a body of permeable rock that can hold and/or

move groundwater. Renewable Resource?

unless water is removed faster than it is replenished or if they are contaminated.

Problems Subsidence

Gradual caving in or sinking of land can be caused by water mining

Salt-water Intrusion Pollution Subsidence: San

Joaquin Valley

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

Salt Water Intrusion Contaminates

freshwater wells and groundwater

Groundwater The

Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest).

Fig. 14-12, p. 316

Solutions

Groundwater Depletion

Prevention Control

Waste less water Raise price of water to discourage waste

Subsidize water conservation

Ban new wells in aquifers near surface waters

Tax water pumped from wells near surface waters

Buy and retire groundwater withdrawal rights in critical areas

Do not grow water-intensive crops in dry areas

Set and enforce minimum stream flow levels

Dams & Reservoirs Large dams and reservoirs can

produce cheap electricity reduce downstream flooding provide year-round water for irrigating

cropland

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

Dams, Reservoirs and Aqueducts: Good or Bad?

Three Gorges Dam, China

Aral Sea,Russia

Case Study: Colorado Basin