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Ch. 14and 19 Water Resources and Water Pollution
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How much freshwater is available and where is it?
97.4% of water is in the ocean, 2.6% is freshwater and of that amount, Most is locked in icecaps leaving .014% available for use
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Readily accessible freshwater
Biota 0.0001% Rivers Atmospheric water vapor 0.001% Lakes 0.007% Soil moisture 0.005% Groundwater 0.592% Ice caps and glaciers 1.984% 0.014% Fig. 13.2, p. 296
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United States China Agriculture 41% Agriculture 87% Power cooling 38%
Public 6% Industry 7% Industry 11% Public 10% Fig. 13.5, p. 298
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Water use (cubic kilometers per year)
5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 1900 1920 1940 1960 1980 2000 Water use (cubic kilometers per year) Total use Agricultural use Industrial use Domestic use Year Fig. 13.4, p. 298
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1 automobile 400,000 liters (106,000 gallons) 1 kilogram cotton
aluminum 9,000 liters (2,800 gallons) 1 kilogram grain-fed beef 7,000 liters (1,900 gallons) 1 kilogram rice 5,000 liters (1,300 gallons) 1 kilogram corn 1,500 liters (400 gallons) 1 kilogram paper 880 liters (230 gallons) 1 kilogram steel 220 liters (60 gallons) Fig. 13.6, p. 298
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What causes water shortages?
Dry climate Drought Desiccation Water stress (low per capita availability due to population growth) 30 countries containing 500,000 million people have chronic water shortages There is enough water, but often it is wasted, polluted, is in areas where it is hard to get to. Two-thirds of the world live in water poverty where they do not have water coming into the home.
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Competition for the World’s Water
Cities are outbidding farmers for water supplies from rivers and aquifers Some countries are importing grain as a way to reduce their water needs More crops are being used for biofuels increasing water demand.
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Average annual precipitation (centimeters)
0-25 0-25 25-50 25-50 50-75 50-75 Fig. 13.7a, p. 299
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Acute shortage Adequate supply Shortage
Metropolitan regions with population greater than 1 million Fig. 13.8b, p. 299
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Europe North America Asia Africa South America Australia Stress
High None Fig. 13.8, p. 300
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How can water supplies be increased?
Building dams and reservoirs Importing water Withdrawing groundwater Desalination improved efficiency
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Dams and reservoirs Pros: Can capture and store water
The water can be released as desired Control flooding downstream Supply irrigation water year around Provide electricity
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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 Provides water for year-round irrigation of cropland Reservoir is useful for recreation and fishing Can produce cheap electricity (hydropower) Migration and spawning of some fish are disrupted Fig. 13.9, p. 301
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Cons: Silting behind the dam robs the downstream of nutrients Loss of silt destroys deltas Causes flooding behind the dam They can fall down Disturbs species like salmon Causes landslides and earthquakes
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Case Study: The Colorado River
Water laws in the Western United States are governed by prior appropriation: “First in time, first in right”, which means the first to use the water has the first rights. On the Colorado River the Indians and the Ranchers were the first. The Colorado is divided into two parts: * Upper Basin: Wyoming, Utah, Colorado, New Mexico * Lower Basin: Arizona, Nevada and California
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Case Study: The Colorado River
In 1922 water was allocated to these states by the Colorado River compact, in 1944 Mexico was allocated water The problem was that the amount of water was overestimated by 33%, so when all the states start taking their water, there will not be enough
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IDAHO WYOMING Dam Aqueduct or canal Salt Lake City Upper Basin
Grand Junction Lower Basin Denver UPPER BASIN UTAH COLORADO Lake Powell Grand Canyon Glen Canyon Dam Las Vegas NEW MEXICO Boulder City ARIZONA CALIFORNIA Albuquerque Los Angeles LOWER BASIN Palm Springs Phoenix 100 mi. San Diego Yuma 150 km Mexicali Tucson All-American Canal Fig , p. 304 Golf of California MEXICO
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The Science of Groundwater
Groundwater: rain that infiltrates the ground and percolates downward through spaces in soil, water and rock Below a certain level the spaces are completely filled with water, called the zone of saturation . The top of this zone is the water table. Aquifer: porous layers of sand, gravel and rock through which water flows. Recharge rate: how fast an aquifer can refill. Can take thousands of years.
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Tapping Groundwater Pros: Supplies 50 % of drinking water
Supplies 40% of irrigation Usually very high quality
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Tapping Groundwater Aquifer depletion: currently US is withdrawing groundwater at 4x it’s replacement rate Aquifer subsidence: sinking of land due to water removal Salt water intrusion: removing too much groundwater causes salt water to seep into aquifers
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Evaporation and transpiration
Flowing artesian well Precipitation Unconfined Aquifer Recharge Area 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 Confining permeable rock layer Fig. 13.3, p. 297
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Major irrigation well Well contaminated with saltwater Water table
Sea Level Salt water Fresh groundwater aquifer Interface Interface Saltwater Intrusion Normal Interface Fig , p. 308
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Original water table Initial water table Cone of depression Lowered water table Fig , p. 307
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High Moderate Minor or none
Groundwater Overdrafts: High Moderate Fig a, p. 308 Minor or none
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High Moderate Minor or none
Subsidence: High Moderate Fig b, p. 308 Minor or none
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Case Study: Ogallala Aquifer
The Ogallala aquifer stretches from Texas north to North Dakota. It was deposited over several thousand years during the last ice age. It is the largest aquifer in North America. It is non-renewable because it has a very slow recharge rate. One quarter of it will be depleted by This is because the farmers get tax breaks for depleting it. In the Midwest there is no such thing as water conservation.
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WYOMING SOUTH DAKOTA NEBRASKA KANSAS COLORADO OKLAHOMA NEW MEXICO
Less than 61 meters (200 ft) meters ( ft) More than 183 meters (600 ft) (as much as 370 meters or 1,200 ft. in places) NEBRASKA KANSAS COLORADO OKLAHOMA NEW MEXICO TEXAS Miles 100 160 Fig , p. 309 Kilometers
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Water Transfer Pros: Using tunnels, aqueducts and pipes to transport water from watersheds to water poor areas Allows for year-around irrigation of cropland in arid regions Has allowed L.A. to become what it is.
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Water Transfer Robs other areas of water
Can be environmentally harmful to areas where the water is being removed Threatens fisheries Causes rivers to flow backwards Takes away the flushing action of rivers Lowers the level of inland seas and lakes Causes inland seas to become more salty and produces salt rain from blowing salt Hard on native species
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Areas already harmed: Aral Sea in Russia Mono Lake in California
Sacramento River delta
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KAZAKHSTAN 2000 1989 1960 UZBEKISTAN TURKMENISTAN
ARAL SEA 1989 1960 UZBEKISTAN TURKMENISTAN Fig , p. 305
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CALIFORNIA NEVADA Shasta Lake UTAH Sacramento River Oroville Dam and Reservoir Feather River Lake Tahoe North Bay Aqueduct Sacramento San Francisco Hoover Dam and Reservoir (Lake Mead) South Bay Aqueduct Fresno Colorado River Los Angeles Aqueduct San Luis Dam and Reservoir ARIZONA California Aqueduct Central Arizona Project Santa Barbara Colorado River Aqueduct Los Angeles Phoenix Salton Sea San Diego Tucson Fig , p. 306 MEXICO
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Desalination Removing salt from ocean water by distillation or reverse osmosis Problem is that it requires large amounts of energy and it is very expensive
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Improved Efficiency 60-70% of water is wasted worldwide
Why is water wasted: * artificially low prices in the US * government subsidies * outdated laws governing water supplies * water management in watersheds is divided into too many different hands.
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Wasting Less Water in Irrigation
Currently we use flood irrigation or gravity flow, which wastes 50% of water Drip irrigation delivers water directly to plants with a 80-90% efficiency Center-pivot-mobile boom moves over crops 70-80% efficient
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Gravity Flow Drip Irrigation Center Pivot
(efficiency 60% and 80% with surge valves) Water usually comes from an aqueduct system or a nearby river. Drip Irrigation (efficiency 90–95%) Above- or below-ground pipes or tubes deliver water to individual plant roots. Center Pivot (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA sprinkler) Water usually pumped from underground and sprayed from mobile boom with sprinklers. Fig , p. 311
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Lining canals bringing water to irrigation ditches
Leveling fields with lasers Irrigating at night to reduce evaporation Using soil and satellite sensors and computer systems to monitor soil moisture and add water only when necessary Polyculture Organic farming Growing water efficient crops using drought-resistant and salt-tolerant crop varieties Irrigating with treated urban waste water Importing water intensive crops and meat Fig , p. 313
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Wasting Less in Industry
Recycling water in the manufacturing process Many companies already do this because it saves them money and they do not get government kickbacks on water like farmers do Also companies have to pay for the amount of stuff that goes down the sewer
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Wasting Less in Businesses and Homes
Low flush toilets Low flow shower heads Xeriscaping Fix leaky pipes Reusing gray water in homes and to water lawns
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Too much water-Floods Floodplain: the natural overflow area of a river, these are very productive areas with nutrient rich soils Floods are natural thing- they enrich the soil, recharge groundwater and refill wetlands Humans make flooding worse by removing vegetation, draining wetlands and living on floodplains
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Reservoir Dam Levee Floodplain
wall Floodplain Fig , p. 314
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Evaporation increases
Oxygen released by vegetation Diverse ecological habitat Evaporation increases Trees reduce soil erosion from heavy rain and wind Agricultural land Steady river flow Leaf litter improves soil fertility Tree roots stabilize soil and aid water flow Vegetation releases water slowly and reduces flooding Fig a, p. 316 Forested Hillside
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Evapotranspiration decreases
Tree plantation Evapotranspiration decreases Roads destabilize hillsides Ranching accelerates soil erosion by water and wind Winds remove fragile topsoil Agriculture land is flooded and silted up Gullies and landslides Heavy rain leaches nutrients from soil and erodes topsoil Rapid runoff causes flooding Silt from erosion blocks rivers and reservoirs and causes flooding downstream Fig b, p. 316 After Deforestation
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Extremely severe Very severe Moderately severe Somewhat severe
Fig , p. 317 Not severe
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Not depleting aquifers Preserving ecological health of aquatic systems
Preserving water quality Integrated watershed management Agreements among regions and countries sharing surface water resources Outside party mediation of water disputes between nations Marketing of water rights Wasting less water Decreasing government subsides for supplying water Increasing government subsides for reducing water waste Slowing population growth Fig , p. 317
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