Chapter 13 Water Resources Post Reading Discussion

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2a. What percentage of the earth’s freshwater is available to us? 0.024% Back to Contents

2b. Define groundwater, zone of saturation, water table, and aquifer. Water that infiltrates the ground through spaces in soil, gravel, and rock; found in the zone of saturation below the water table. Zone where all available pores in soil and rock in the earth’s crust are filled with water. Upper surface of the zone of saturation. Geological layers of underground caverns and porous layers of sand, gravel, or bedrock through which groundwater flows.

Back to Contents Fig. 13-3, p. 316

2c. Define surface water, surface runoff, and watershed (drainage basin). Freshwater from precipitation and snowmelt that flows across the earth’s land surface and into rivers, streams, lakes, wetlands, estuaries, and ultimately the oceans. Precipitation that does not infiltrate the ground or return to the atmosphere by evaporation. Land from which surface water drains into a particular river, lake, or other body of water. Back to Contents

2d. Distinguish between surface runoff and reliable surface runoff. Surface runoff we can generally rely on as a source of freshwater. Back to Contents

3a. How is most of the world’s water used? 70%, irrigation of crops 20%, industry 10%, municipal and domestic Back to Contents

3b. Describe the availability an use of freshwater in the United States. More than enough renewable, but unevenly distributed and much is contaminated by ag- and industrial use. The East: most used for energy production, power plant cooling, and manufacturing. In arid and semi-arid West: most (85%) used for irrigation. Half of water come from ground; rest, from rivers, lakes and reservoirs. Hotspots (see Figure 13-5, p. 318) Back to Contents

3d. What is drought and what are its causes and harmful effects? Condition in which an area does not get enough water because of lower than normal precipitation or higher than normal evaporation from higher temperatures. Causes: below normal rainfall, falling water tables (such as when ground water is overused), and climate change. Dries soils, reduces stream flows, decreases tee growth and biomass, lowers NPP, reduces crop yields, and can shift biomes towards savannas and deserts. Back to Contents

4a. What are the advantages and disadvantages of withdrawing groundwater? Back to Contents Fig. 13-7, p. 321

4b. Describe the problems with groundwater depletion in the world and in the U.S., esp. the Ogallala Aquifer. Water tables fall ½ billion people fed on grain grown with ground water In U.S., groundwater withdrawn 4x faster than recharge. Serious overdrafts in lower half of Ogallala Aquifer; CA’s Central Valley (Fig. 13-9, p. 322) – Loses of ecological and agricultural productivity/loss of natural capital and ecological services. Back to Contents

4c. Describe ways to prevent or slow groundwater depletion. Back to Contents Fig , p. 324

5a. What is a dam? A structure built across a river to control the river’s water flow. Back to Contents

5b. What is a reservoir? Artificial lake behind a dam. Back to Contents

5c. What are the advantages and disadvantages of large dams and reservoirs? Back to Contents Fig , p. 325

5d. What ecological services do rivers provide? Back to Contents Fig , p. 270

6a. Describe the California Water Project and the controversy over this water transfer project. Dams, pumps and aqueducts transport water from water-rich northern CA to water-poor southern CA’s heavily populated ag-regions and cities. Southern CA wants more water for crops and LA and San Diego. Northern CA argues that Sacramento River is degraded cause or reduced flow, threatening fisheries and reduces river’s ability to flush pollutants out of San Francisco Bay; much of water sent south is wasted.

Back to Contents Fig , p. 330

6b. Describe the Aral Sea disaster. Back to Contents

7a. Define desalinization and distinguish between distillation and reverse osmosis. Removal of dissolved salts from ocean water or from brackish water in aquifers or lakes or domestic use. Heating saltwater until it evaporates. Also called microfiltration; use high pressure to force saltwater though a membrane filter with pores small enough to remove salt. Back to Contents

7b. What are the limitations of desalinization and how might they be overcome? Limitations: – High cost and large energy footprint – Kill many marine organisms – Concentrated brine needs to be disposed of Obstacles – New filtering technologies – Desalinization off-shore Back to Contents

8a. What percentage of the world’s water is unnecessarily wasted and what are causes of such waste? 65-70% Causes – Evaporation, leaks, and other losses – Low cost – Lack of subsidies for improving the efficiency of water use. Back to Contents

8b. Describe four irrigation methods and describe ways to reduce water waste in irrigation in developed and developing countries. Flood irrigation, gravity flow Center-pivot, low pressure sprinkler Drip or trickle irrigation, also called micro- irrigation. Rainwater harvesting Polyculture farming, agroforestry, and fog- cather nets. Back to Contents

8c. List ways to reduce water waste in industry and homes. Back to Contents Fig , p. 336

8d. List ways to use water more sustainably. Back to Contents Fig , p. 337

8e. Describe ways in which you can reduce your use and waste of water. Back to Contents Fig , p. 338

9a. What is a floodplain and why do people like to live on floodplains? Area adjacent to rivers where streams overflow the normal channels. – Include highly productive wetlands, provide natural flood control, maintain water quality, and recharge groundwater. People live there because of fertile soils, ample water for irrigation, transportation and recreation, and flat land suitable for crops, buildings, highways and railroads. Back to Contents

9c. List three human activities that increase the risk of flooding. Removal of water-absorbing vegetation (see Fig , p. 339) Draining and building on wetlands Burning fossil fuels and clearing forests Back to Contents

9e. How can we reduce the risk of flooding? Back to Contents Fig , p. 340