APES Chapter 14 Water Resources
Water’s Unique Properties • Hydrogenbonding • Liquid over wide temperature range • Changes temperature slowly • High heat of evaporation • Great dissolving power • Helps regulate pH • Adhesion and cohesion • Expands when it freezes
Freshwater Readily accessible freshwater Groundwater 0.592% Biota 0.0001% Lakes 0.0007% Rivers 0.0001% 0.014% Ice caps and glaciers 1.984% Soil moisture 0.0005% Atmospheric water vapor 0.0001% Supply of Water Resources Fig. 14-2 p. 314
What is Surface Water? • Precipitation that does not infiltrate the ground or return to the atmosphere by evaporation. • Example: A watershed (drainage basin) is a region from which water drains into a stream, lake, reservoir, wetland, or other body of water.
What is Groundwater? • Precipitation that infiltrates into the ground and percolates downward through spaces between soil and rock. • Near the surface, these voids contain little moisture. • Deeper, in the zone of saturation, the voids are completely filled with water.
The water table is located at the top of the zone of saturation. • Porous, water-saturated layers of sand, gravel , or rock are called aquifers. • An area of land through which water passed downward into an aquifer is the rechargearea. • If water is withdrawn from an aquifer faster than it can recharge the aquifer will become depleted.
Flowing artesian well Precipitation Evaporation and transpiration Well requiring a pump Evaporation Confined Recharge Area Runoff Aquifer Stream Infiltration Water table Lake Infiltration Unconfined aquifer Confined aquifer Less permeable material such as clay Confirming permeable rock layer Ground Water Fig. 14-3 p. 315
United States Agriculture 38% Power cooling 38% Industry 11% Public 10% Use of Water Resources • Humans use about 50% of reliable runoff • Agriculture • Industry • Domestic • Power plants Fig. 14-5 p. 316
Acute shortage Adequate supply Shortage Metropolitan regions with population greater than 1 million What causes freshwater shortages? • Dry climate • Drought • Desiccation • Water stress Fig. 14-7 p. 317
How can we increase Freshwater Supplies? • Build dams and reservoirs • Bring in water from another area • Withdraw groundwater • Waste less water • Import food to reduce water use
Building Dams Advantages Disadvantages Large water loss through evaporation Land lost Migration and spawning of some fish disrupted No nutrient-rich silt downstream of dam • Control flooding • Produce hydroelectric power • Supply water for towns and cities • Provide recreational activities such as fishing and boating
Downstream cropland and estuaries are deprived of nutrient-rich silt Flooded land destroys forests or cropland and displaces people Large losses of water through evaporation Downstream flooding is reduced Reservoir is useful for recreation and fishing Provides water for year-round irrigation of cropland Can produce cheap electricity (hydropower) Migration and spawning of some fish are disrupted Using Dams and Reservoirs to Supply More Water Fig. 14-9 p. 319
Transferring water form another area Advantages Disadvantages Degrade rivers Deplete groundwater Threaten fisheries • Supplies water for agricultural, domestic, and industrial needs
Tapping Groundwater Advantages Disadvantages Water table lowering Aquifer depletion Intrusion of salt water into aquifers Reduce stream flow May be contaminated by septic tanks or industrial activities • Year round supply • Not lost by evaporation • Less expensive to develop than surface water sources
Desalination Advantages Disadvantages Very expensive Produces large quantities of wastewater • Can provide fresh water from very abundant salt water
How Can We Use Water More Efficiently? • Reduce losses due to leakage • Reform water laws • Improve irrigation efficiency (Fig. 14-18 p. 330) • Improving manufacturing processes • Water efficient landscaping • Water efficient appliances
Too Much Water: Floods • Natural phenomena • Aggravated by human activities • Renew and replenish Reservoir Dam Levee Flood wall Floodplain Fig. 14-22 p. 332
Solutions: Achieving a More Sustainable Water Future • Efficient irrigation • Water-savingtechnologies • Improving water management See Fig. 14-25 p. 336