1. Chapter 21: Water Supply, Use and Management

2. Water To understand water, we must understand its characteristics, and roles: –Water has a high capacity to absorb and store heat. –Water is the universal solvent. –Water has a high surface tension. –Water is the only compound whose solid form is lighter than its liquid form. –Sunlight penetrates water to variable depths, permitting photosynthetic organisms to live below the surface.

3. A Brief Global Perspective We are facing a growing global water shortage linked to the food supply. Global hydrologic cycle –Transfers water from the atmosphere, to land, to oceans and back to atmosphere –97% in oceans –2% in ice –Only 0.001% in atmosphere

4. Groundwater and Streams Groundwater refers to the water below the water table where saturated conditions exist –Locations where surface waters move into the ground are recharge zones –Places where it flows or seeps out are discharge zones –Area where water seeps through pore spaces known as vadose zone

5. Groundwater and Streams Aquifer is an underground zone from which groundwater can be obtained –When water is pumped from an aquifer it forms a cone of depression

6. Streams Effluent stream –Flow is maintained during the dry season by seepage –Perennial stream (flows all year) Influent stream –Entirely above the water table and flows only in direct response to precipitation –Ephemeral stream (doesn’t flow all year)

7. Interactions Between Surface Water and Groundwater Should be considered part of the same resource and linked together. –Withdrawal of groundwater can lower stream flow or lake levels –Pollution can spread from one source to the other

8. Water Supply: A US Example Water budget –A model that balances the inputs, outputs, and storage of water in a system. –Precipitation - evaporation = runoff US Example –10% of water vapor falls as precipitation –66% of that is evaporated –34% enters the groundwater or surface water supply

9. Groundwater Use and Problems ½ the people in the US use groundwater as a primary source of drinking water –20% of all water used –In many parts of the country withdrawal from wells exceeds natural inflow Overdraft Nonrenewable resource Problems include damage to river basins and land subsidence

11. Desalination as a Water Source Seawater is 3.5% salt Desalination - a technology to remove salt from water –Must be reduced to 0.05% to be fresh water –Requires large amount of energy  tied to fuel prices –Has place value  price increases quickly with transport distance –Discharge (waste) may affect local salinity

12. Water Use Off-stream use –Refers to water removed from its source for use –May be returned to source after use Consumptive use – water used by plants, animals, or industry –Enters tissues or evaporates –Not returned to source

13. Water Use In-stream use –The use of the river for navigation, hydroelectric power, fish and wildlife habitats, and recreation. –Multiple uses can create controversy

14. Water Use Another problem with off stream use is how much water can be removed w/o damaging the stream ecosystem. –Aral Sea  Diverted water for agriculture caused sea to dry up –Surface area of sea reduced 90% in 50 years

16. Transport of Water Water is moved from areas of abundant rain and snow fall to areas of high usage –California moves water from north to south –New York City has had to obtain water from farther and farther away

17. Some Trends in Water Use Trends in freshwater withdrawals by water- use categories suggests that: –1. The major uses of water are for irrigation and the thermoelectric industry. –2. Water use for irrigation has decreased and leveled off from 1985-2000 Due to better irrigation efficiency, crop type and higher energy costs.

18. Some Trends in Water Use –3. Water use by thermoelectric industry stabilized in 1985. Due to reticulating water for cooling –4. Water for public and rural supplies continued to increase through 2000 Presumably related to the increase in human population.

21. Water Conservation The careful use and protection of water resources –Involves the quantity of water used and the quality

22. Agricultural Use Improved irrigation could reduce agricultural withdrawals by 20 to 30% –Tremendous savings because ag is the biggest user

23. Agricultural Use: Conservation –Price agricultural water to encourage conservation –Use lined or covered canals that reduce seepage and evaporation. –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, such as at night or in the early morning. –Use improved irrigation systems, such as sprinklers or drip irrigation, that more effectively apply water to crops. –Improve the soil to increase infiltration and minimize runoff. –Encourage the development of crops that require less water or are more salt tolerant.

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

27. Domestic Use: Conservation –In semiarid regions, replace lawns with decorative gravels and native plants. –Use more efficient bathroom fixtures. –Turn off water when not absolutely needed. –Flush the toilet only when really necessary. –Fix all leaks quickly. –Use drip irrigation and place water-holding mulch around garden plants. –Purchase dishwashers and washing machines that minimize water consumption. –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. –Plant drought-resistant vegetation. –Use reclaimed water

28. 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

29. Perception and Water Use Perception of water is based partly on its price and availability. –If water is abundant and inexpensive, we don ’ t think much about it. –If water is scarce or expensive, it is another matter. –People in Tucson pay about 100% more for water than people in Phoenix. Tucson residence use less water per person per day

30. Sustainable Water Use General criteria: –Maintain human health and well-being. –Maintenance of ecosystems. –Ensure minimum standards of water quality –Do not damage or reduce long-term renewability of water resources. –Promote the use of water-efficient technology –Eliminate water pricing policies that subsidize the inefficient use of water.

31. Variable-water-source approach

32. A Master Plan for Water Management Advanced planning may include –Drilling to wells that are presently isolated –Reuse of waste water –Develop surface water and use groundwater in dry years –In wet years pump excess surface water underground to recharge groundwater –Towing icebergs

33. Wetlands Wetlands is a comprehensive term for landforms such as salt marshes, swamps, bogs, prairie potholes, and vernal pools. –Common feature is that they are wet at least part of the year –Have a particular type of vegetation and soil

34. Natural Service Functions of Wetlands Reducing flooding. Groundwater recharge or discharge. Nursery grounds for fish, shellfish, aquatic birds, etc. Wetlands are natural filters that help purify water. Nutrients and chemicals are naturally cycled. Coastal wetlands provide a buffer for inland areas from storms and high waves. Storage site for organic carbon. Wetlands are aesthetically pleasing to people.

35. Wetlands Freshwater wetlands are threatened in many areas. –Over the past 200 years > 50% of all wetlands have disappeared, 90% of freshwater wetlands –Diked, drained or filled –SF bay estuary considered the most modified by human activity –Mississippi Delta is decreasing

36. Dams and the Environment Dams and their accompanying reservoirs generally are designed to be multifunctional structures. –Used for recreational activities –Generating electricity –Providing flood control –Ensuring a more stable water supply Often difficult to reconcile various uses at a given site.

37. Removal of Dams Trapped sediment behind dams must be dealt with in dam removal. –If released quickly it could damage downstream ecosystem and fill pools. –Slower release minimizes damage. –Matilija Dam in Ventura County cost $300,000 to build but 10 times that to remove. Removing dams is simple in concept but involves complex problems relating to sediment and water. Increased fish migration has been shown after removal

38. Canals Water from upstream reservoirs may be routed downstream by way of natural water ways or canals and aqueducts. Not hydrologically the same as creeks Smooth, steep banks; water moves fast Canals can spread and carry disease (schistosomiasis)

39. Channelization and the Environment Adverse environmental effects, including the following: –Degradation of the stream ’ s hydrologic qualities; nearly all riffle flow, resulting in loss of important fish habitats. –Removal of vegetation along the watercourse, which removes wildlife habitats and shading of the water. –Downstream flooding where the channelized flow ends. –Damage or loss of wetlands. –Aesthetic degradation.

40. Global Water Shortage Linked to Food Supply As human population grows there is growing concern that there won ’ t be sufficient water to grow the food to feed 8-9 billion people. –Food shortage linked to water resources a real possibility. –Water also linked to energy (fuel to pump) as energy cost goes up so does cost of food.