Chapter 18: Water Supply, Use and Management

1. Chapter 18:Water Supply, Use and Management

2. Overview • Water • Water Supply - A US Example • Water Use • Water Conservation • Sustainability and Water Management • Wetlands • Dams and the Environment • Global Water Shortage Linked to Food Supply

3. Water • Water’s characteristics: • High capacity to absorb and store heat • Universal solvent • High surface tension • Only compound whose solid form is lighter than its liquid form • Permits sunlight penetration water, allowing photosynthetic organisms to live below the surface

4. A Brief Global Perspective • We are facing a growing global water shortage • Linked to the food supply • Global hydrologic cycle • Water can be liquid, solid or gas • Transfers water from the atmosphere, to land, to oceans, and back to atmosphere • Residence time varies from a few days to thousands of years

6. The Hydrologic Cycle

7. A Brief Global Perspective • Where is water globally? • 97% in oceans, 2% in ice, 0.001% in atmosphere • 99% of all water on earth is unavailable or unusable (salt) to plants and animals • Water is the most use resource on earth • Mass of water used 1000x the total production of minerals • This is only increasing with greater industrial production and technology

8. Groundwater and Streams • Groundwater - • Water located below the water table • saturated conditions • Recharge zones • Locations where surface waters move into the groundwater • Discharge zones • Locations where water flows or seeps out of groundwater • Vadose zone • Area where water seeps through pore spaces

9. Groundwater and Streams • Aquifer • Underground zone from which groundwater can be obtained • Cone of Depression • Forms in water table elevation when water is pumped from an aquifer

11. Streams • Effluent stream • Flow is maintained during the dry season by seepage into channel from subsurface • Perennial stream - flows all year • Influent stream • Entirely above the water table and flows only in direct response to precipitation • Ephemeral stream • A stream can have reaches that are both of these, or intermittent at varying times of year

12. Interactions Between Surface Water and Groundwater • Should be considered part of the same resource • Nearly all surface water environments have linkages with ground water • Ex: withdrawal of groundwater can lower stream flow or lake levels • Pollution can spread from one source to the other

14. Water Supply: A US Example • Water supply depends on several factors in the hydrologic cycle • Rates of precipitation, evaporation, transpiration • Stream flow • Subsurface flow • Water budget • Model that balances the inputs, outputs, and storage of water in a system • Precipitation – evaporation = runoff

16. Water Supply: A US Example • Amount of water vapor passing over the US every day ~ 152,000 million m3 • 10% falls as precipitation • 66% of which is evaporated or transpired • Only 34% enters surface or groundwater

18. Useful in developing water budgets for water resources management Potential problems can be predicted in areas with: Low average runoff Low precipitation Total storage of runoff not possible because of evaporative losses Precipitation and Runoff Patterns

19. Droughts • Areas with high precipitation and runoff may suffer from droughts • Large annual and regional variations in stream flow

20. Groundwater Use and Problems • Half the US population use groundwater as a primary source of drinking water • Groundwater accounts for 20% of water used in US • In many parts of the US, withdrawal from wells exceeds natural inflow • Overdraft • Mining a nonrenewable resource • Problems include damage to river basins and land subsidence

22. Water Use • Off-stream use • Refers to water removed from its source for use • May be returned to source after use • Consumptive use- water is not returned to its source • Plant or animals water use (evaporates in the tissue, or is used to make new organs) • Industrial use

23. Water Use • In-stream use • Water left in its source for use • Navigation, hydroelectric power, fish and wildlife habitats, and recreation • Multiple uses can create controversy

24. Water Use • Problem with off-stream use • How much water can be removed without damaging the stream ecosystem? • Ex: Aral Sea • Diverting water for agriculture caused sea to dry up • Surface area of sea reduced 90% in 50 years

27. Aral Sea • Climate changes • Winters colder, summers warmer • Loss of fishing and decline of tourism • Salt content of the water has increased • Dust storms from dry salt flats

28. Transport of Water • Ancient civilizations • Constructed canals and aqueducts to transport water • In modern civilization • Water moved from areas of abundant rain and snow fall to areas of high usage • Examples • California moves water from north to south • New York City has imported water from nearby areas for more than 100 years

29. Some Trends in Water Use • Withdrawal of surface water far exceeds withdrawal of groundwater • Since 1980 use has decreased and leveled off • Suggests improvement in water management and conservation

31. Some Trends in Water Use • Trends in freshwater withdrawals by water-use categories suggests: • Major uses of water are for irrigation and the thermoelectric industry • Water use for irrigation increased from 1950–1980, but decreased and leveled off from 1985–2000 • Due to better irrigation efficiency, crop type and higher energy costs

32. Some Trends in Water Use • Water use by thermoelectric industry decreased slightly in 1980, and stabilized in 1985. • Due to recirculating water for cooling • Water for public and rural supplies continued to increase through the period from 1950 to 2000 • Presumably related to the increase in human population

34. Water Conservation • Careful use and protection of water resources • Involves both quantity and quality of water • Important component of sustainable water use • Three components • Agricultural Use • Domestic Use • Industrial Use

35. Agricultural Use • Agriculture is biggest user of water • Improved irrigation could reduce agricultural withdrawals by 20 to 30% • Suggestions for conservation • Price agricultural water to encourage conservation • Use lined or covered canals that reduce seepage and evaporation

36. Agricultural Use • Suggestions for conservation (cont’d) • Use computer monitoring and schedule release of water for maximum efficiency • Integrate the use of surface water and groundwater to more effectively use the total resource • Irrigate at times when evaporation is minimal

37. Agricultural Use • Suggestions for conservation (cont’d) • Use improved irrigation systems that more effectively apply water to crops • Sprinklers or drip irrigation • Improve the soil to increase infiltration and minimize runoff • Encourage the development of crops that require less water or are more salt tolerant

38. Agriculture in 1990

39. Agriculture in 2020

40. Domestic Use • Accounts for about 10% of total national water withdrawals • But concentrated in urban areas • May pose major local problems

41. Domestic Use • Ways to reduce water use • In semiarid regions, replace lawns with decorative gravels and native plants • Use more efficient bathroom fixtures • Turn off water when not needed • Flush the toilet only when necessary • Fix all leaks quickly

42. Domestic Use • Ways to reduce water use (cont’d) • Purchase efficient dishwashers and washing machines • Take a long bath rather than a long shower • Sweep sidewalks and driveways • Using gray water to water vegetation • Water lawns and plants at cool times to reduce evaporation

43. Domestic Use • Ways to reduce water use (cont’d) • Use drip irrigation and place water-absorbing mulch around garden plants • Plant drought-resistant vegetation • Use the water meter to monitor for unobserved leaks • Use reclaimed water

44. Industry and Manufacturing Use • Water conservation measures that can be taken by industry • Using cooling towers that use little or no water • In-plant water treatment and recycling

45. Sustainability and Water Management • Sustainable water use definition • Use of water resources by people in a way that allows society to develop and flourish into an indefinite future • Use of water without degrading the various components of the hydrologic cycle or the ecological systems that depend on it

46. Sustainable Water Use • General criteria • Develop water resources in sufficient volume to maintain human health and well-being • Provide sufficient water resources to guarantee the health and maintenance of ecosystems • Ensure minimum standards of water quality for the various users of water resources

47. Sustainable Water Use • General criteria (continued) • Ensure that actions of humans do not damage or reduce long-term renewability of water resources • Promote the use of water-efficient technology and practice • Gradually eliminate water pricing policies that subsidize the inefficient use of water

48. Groundwater Sustainability • Sustainability involves a long term perspective • For groundwater even longer • It takes a long time to regenerate groundwater • Effects of pumping might not be seen immediately • Long-term approach involves balancing withdrawal with recharge

49. Water Management • Management of water resources is a complex issue • Will become more difficult as demand for water increases • Options for minimizing potential problems • Alternating water supplies and managing existing supplies better • Towing icebergs • As price goes up many innovative programs are possible

50. Variable-water-source approach