Water: A Limited Resource

Chapter 14

Chapter 14Water: A Limited Resource

Domestic water in Lagos, Nigeria: in many less developed countries, access to safe, clean water use is limited and expensive. Poor residents of large towns often pay more for water than do the wealthy, spend a much larger fraction acquiring itAnd use part of their limited supply boiling it.

Overview of Chapter 14• Importance of Water– Hydrologic Cycle

• Water Use and Resource Problems– Too Much Water– Too Little Water

• Water Problems in US and Canada• Global Water Problems– Sharing Water Resources

• Water Management– Providing Sustainable Water Supply

• Water Conservation

Importance of Water• Cooking• Washing• Use large amounts for:– Agriculture– Manufacturing– Mining– Moderates our climate– Allows organisms to

survive– Energy production– Waste disposal

• Use of freshwater is increasing

Properties of Water• Composed of 2 Hydrogen and 1

oxygen• Exists as solid, liquid or gas• Polar– One end has (+) charge, one end has (-)

charge• Forms Hydrogen bond between 2

water molecules– H-bonds define water’s physical

properties1.High heat capacity2.High melt/freeze pt, high boil3.Universal solvent4.Adhesive and cohesive (cohesive sticks

to other water molecule and adhesive is attaches to other surface)

Hydrologic Cycle

Major Water Compartments• Glaciers, Ice, and Snow– 2.6% of world’s water is classified fresh.– 0.5 % is groundwater• 0.014% readily accessible freshwater

(lakes, rivers, groundwater).– As recently as 18,000 years ago, one-third of

continental landmasses were covered by glacial ice sheets.» Now, Antarctic glaciers contain nearly 85% of all ice

in the world.– Sea ice comes from ocean water, but salt is excluded

during freezing.

MAJOR WATER COMPARTMENTSOceans

– Together, oceans contain more than 97% of all liquid water in the world.• Contain 90% of world’s living biomass.• Moderate earth’s temperature.

– Average residence time of water in the ocean is between 100 days to 3,000 years. (range)

Major Water Compartments

• Groundwater- water below the water table– Second largest reservoir of fresh water.• Infiltration - Process of water percolating

through the soil and into fractures and permeable rocks.–Zone of Aeration - Upper soil layers that

hold both air and water.–Zone of Saturation - Lower soil layers

where all spaces are filled with water.»Water Table - Top of Zone of Sat.

Major Water Compartments

• Wetlands– Play a vital role in hydrologic cycle.• Lush plant growth stabilizes soil and retards

surface runoff, allowing more aquifer infiltration.–Disturbance reduces natural water-

absorbing capacity, resulting in floods and erosion in wet periods, and less water flow the rest of the year.

WATER AVAILABILITY AND USE• Renewable Water Supplies– Made up of surface runoff and infiltration into

accessible freshwater aquifers.• About two-thirds of water carried in rivers and

streams annually occurs in seasonal floods too large or violent to be stored effectively for human use.–Readily accessible, renewable supplies are

400,000 gal /person/year.

Major Water Compartments

• The Atmosphere– Among the smallest water reservoirs.• Contains < 0.001% of total water supply.• Has most rapid turnover rate.• Provides mechanism for distributing fresh

water over landmasses and replenishing terrestrial reservoirs.

Freshwater Terminology

• Surface water– Precipitation that remains on the surface and does not seep into

soil• Runoff

– Movement of surface water to lakes, rivers, etc.• Watershed (drainage basin)

– Land area that delivers water into a stream or river system• Groundwater

– Freshwater under the earth’s surface stored in aquifers• Aquifer

– Underground caverns and porous layers of sand, gravel and rock in which groundwater is stored

Distribution of Water

• Only % of water on earth is freshwater

• % is in the form of ice!

• Only ~% of water on earth is available freshwater

Properties of Water

• Water is never completely pure in nature

• Seawater• Many substances

water dissolves cause water pollution

Aquifers

• In unconfined aquifers, the layers of rock above are porous and allow surface water directly above them to seep downward, replacing the aquifer content. The upper limit of an unconfined aquifer, below which the ground is saturated with water, is the water table.

• A confined aquifer or artesian aquifer is a groundwater storage area between impermeable layers of rock. The water in a confined aquifer is trapped and is often under pressure. Its recharge area may be hundreds of kilometers away.

Water use and Resource Problems

• The greatest use of water worldwide is agriculture

• Irrigation accounts for 71% of the world’s total consumption

• Industry 20%• Domestic and Municipal use 9%

Water Resource Problems

• Three categories• Too much• Too little• Poor quality/contamination

Too Much Water

• Flooding– Both natural and human-induced

• Modern floods are highly destructive because humans:– Remove water-absorbing plant cover from soil– Construct buildings on floodplains

• Floodplain– Area bordering a river channel that has the

potential to flood

Role of Forests

• Forests trap and absorb precipitation to provide nearby lowlands with some protection from floods. If woodlands are cut it can result in floods and also erosion.

• What the soil cannot absorb, spill over its banks onto the flood plain.

• When an area is developed for human use, much of the water-absorbing plant cover is removed. Buildings and paved roads do not absorb water so runoff is greater.

Case in PointThe Floods of 1993

• http://www.youtube.com/watch?v=ZIXioecWiJs• Refer also to page number 314 and 315 in your text

book.

Floodplain

• Government restrictions on building– Levees can fail

o Rather than rebuild levees adjacent to rivers, experts suggest allowing some flooding of floodplains during floods• (next slide)

Left: Traditional levees adjacent to river

Right: Suggested levee style, set back from river

Recent Floods

• River cresting figures

SLIDESHOW

where

Too Little Water

• Typically found in arid land• Problems– Drought– Overdrawing water for irrigation purposes– Aquifer depletion• Subsidence• Sinkholes

Aquifer depletion from porous sediments causes subsidence or sinking of the land above it. Some areas of the San Joaquin Valley in California have sunk almost 10m. In the past 50 years.The limestone bedrock of Florida erodes as groundwater moves through it, sometimes causing a sinkhole, a large surface cavity or depression where an underground cave roof has collapsed.Saltwater intrusion occurs along coastal areas when groundwater is depleted faster than it recharges. Well water in these areas becomes too salty for human consumption.

Too Little Water

• Problems (continued)– Saltwater Intrusion

Water Problems In US and Canada

• US has a plentiful supply of freshwater

• Many areas have a severe shortages because of– Geographical

variations– Seasonal variations

Water Problems in US and Canada• Water shortages in West and Southwest• Water is primarily used for irrigation, municipal, commercial and industrial

uses.– Water is diverted and transported via aqueducts

Mono Lake

• Rivers and lakes that are largely formed from snowmelt in the Sierra Nevada Range replenish Mono Lake.

• Mono lake is becoming saltier as water is removed by evaporation.

• Beginning in 1941, much of the surface water that fed Mono Lake was diverted to Los Angeles 442 km away. As the water level dropped increased salinity adversely affected brine shrimp and alkali fly population. This in turn affected the bird population which fed on the shrimp and flies.

• Dust storm from the exposed lakebed began to pose health hazard and violation of federal air pollution standards.

Mono lake

Solution –Mono Lake Problem

• A court order halted water diversions from Mono Lake in 1989, and in 1994, the state of California worked out an agreement on Mono Lake- less water will be diverted to Los Angeles, and Mono Lake will be allowed to return to about 72% of its original volume.

• The city of Los Angeles is using state funds to develop water conservation and reclaimed water projects to replace water supplies from Mono lake.

Colorado River Basin

Colorado River Basin

– Provides water for 27-million people– Numerous dams for Hydropower– As a result of diversion for irrigation and other uses in

the United States, the Colorado river Usually dries up before reaching the Gulf of California in Mexico.

– The lower Colorado is increasingly saltier as it flows toward Mexico.

– Colorado River no longer reaches ocean– In 2003 California agreed to withdraw no more water

from the Colorado river than the Colorado River Compact Permits.

Delaware: A State without water?

• Delaware has no water source that originate within its boundaries and no major lake to serve its inhabitants. It shares Christina River Basin, which provides water for both Newark and Wilmington, with parts of Pennsylvania and Maryland. There are restriction as to how much water can be withdrawn from Christina River Basin.

• Conservation-based pricing: water supply pricing structures that reward consumers for using less water. these often come in the form of low prices for water use up to some level, and stepped up prices as use increases.

Water Problems in US and Canada-Groundwater

• Aquifer Depletion

Aquifer depletion

• In certain areas of Louisiana and Texas, removal of too much groundwater resulted in intrusion of salt water from the Gulf of Mexico.

• Saltwater intrusion from the Pacific Ocean has occurred along parts of the California coast, along coastal areas of Puget Sound in Washington State and in certain areas of Hawaii.

• Florida and Northeast and Mid-Atlantic states also have saltwater intrusion.

Ogallala Aquifer

• Farmers on the High Plains rely on water from the Ogallala aquifer the largest groundwater deposit in the world..

• In some areas farmers are drawing water from the Ogallala Aquifer 40 times faster than nature replaces it, which has lowered the water table more than 30 m. in these places higher pumping costs have made it too expensive to irrigate.

• Population decline as farms fail during dry spells

Global Water Problems

• Amount of freshwater on planet CAN meet human needs– BUT, it is unevenly distributed and some places lack stable

runoff• Problems:– Climate Change– Drinking Water– Population Growth– Sharing Water Resources Among Countries– Stable run off: the share runoff from precipitation that can

be depended on every month and is low in India.

Water and Climate Change

– Climate change affects the type and distribution of precipitation. It is expected to increase in some areas while it drops in others.

– Potential issues:• Reduced snowfall will impact water resources

downstream• Sea level rise will cause saltwater intrusion into drinking

water supplies

Drinking Water Problems

– Many developing countries have insufficient water to meet drinking and household needs

• Population Growth and water problems– Increase in population means an increase in

freshwater requirements– Limits drinking water available– Limits water available for agriculture (food)

Sharing Water Resources Among Countries

– Rhine River Basin (right)• Countries upstream discharged

pollutants into river• Countries downstream had to pay

to clean the water before they could drink it• In 1950 the five countries(France,

Switzerland, Luxemburg, Germany and Netherlands) formed the International Commission for Protection of the Rhine (ICPR) to deal with water issues related to the Rhine River.

Contd..

• In 1986 a severe chemical spill in Switzerland dumped 30 tons of dyes herbicides, fungicides, insecticides and mercury into the river. the spill galvanized the ICPR, which initiated a 15-year Rhine Action Plan.

• As a result long-absent fishes have returned to the river, including Atlantic Salmon which returned in 1990 after a 30-year absence. ICPR is now working on bank restoration, flood control, and cleaning up remaining polutants.

Aral Sea

• Water diversion for irrigation has caused sea to become too saline• The Soviet Union diverted water from Amy Darya and

the Syr Darya –1950• In 1960 the Aral sea, once the largest freshwater lake,

declined in area and the total volume is down by 80% its biological diversity disappeared.• Health problems-tuberculosis to anemia, kidney

disease and cancers.

Aral Sea

1967 1997

As water was diverted fro irrigation, the sea level subsided.

Potentially Volatile International Water Situations

• Mekong River Basin shared between Pakistan and India.

• India and Bangladesh quarrel over the Ganges river.

• Slovakia and Hungary both depend on the Danube River.

Jordan River

• It supplies water to Israel, Jordan, the West Bank, and Gaza Strip. Water use is increasing because of population growth and economic activity in the region,

• Differential access between Israeli settlers on the West Bank, who use four to five times as much water as do neighboring Palestinians, may be a significant source of conflict.

Nile River

• Egypt uses most of the Nile’s water even though 10 nations share the Nile River Basin. Ethiopia and Sudan are expanding their use of the Nile River’s flow to meet the demands of their supply at a time when its population is increasing.

• The United Nations engineered an international water-use agreement among the Nile River countries to help diffuse this potentially dangerous water situation.

Water Management

• Main Goal: Provide sustainable supply of high-quality water– Requires humans to use resource carefully

• Dams and Reservoirs• Water Diversion Projects• Desalinization• Seeding Clouds – Condensation Nuclei (addition of chemicals)

• Towing Icebergs– Cost

Dams and Reservoirs

• Benefits:– Ensure year-round supply

of water with regulated flow

– Generate electricity– Provide recreational

activities• Disadvantages– Alter the ecosystem– Reduce sediment load

Dams and Reservoirs

• Salmon Population in Columbia R. very low due to dams that impede migration

• Fish ladders help, but are not effective enough. They help migratory fishes to bypass dams in their migration upstream.Read page numbers 326-328 to have better understanding on the impact of dam on ecosystem and organisms

Dams and Reservoirs• Glen Canyon Dam

– Regulated flow has changed ecosystem• To rectify situation

– Canyon has been flooded several times– Small floods compared to natural floods– Still helps rebuild habitat

Water Diversion Projects

• Requires diverting water to areas that are deficient by pumping through a system of aqueducts

• Much of CA’s receives its water supply from diverted water from Northern CA

• Controversial and expensive

Desalinization

• Removal of salt from ocean or brackish water• Two methods: – Distillation- salt water is evaporated, and water

vapor is condensed into freshwater (salt left behind)

– Reverse Osmosis- involves forcing salt water through a membrane permeable to water, but not salt

• Very expensive

Water Conservation

• Reducing Agricultural Water Waste– Agriculture is very inefficient with water– Microirrigation- irrigation that conserves waster

by piping to crops through sealed systems• Also called drip or trickle irrigation

Water Conservation

• Reducing Industrial Water Waste– Stricter laws provide incentive to conserve water• Recycling water within the plant

– Water scarcity (in addition to stricter pollution control requirements) will encourage further industrial recycling

– Potential to conserve water is huge!

Water Conservation

• Reducing Municipal Water Waste

• Gray Water– Can be used to flush

toilets, wash car or water lawn

• Water saving household fixtures

• Government incentives

Conserving at Home

• Install water-saving shower heads and faucets• Install low-flush toilets• Fix leaky fixtures• Purchase high efficiency appliances• Modify personal habits• Use the dishwasher instead of washing by

handRead You can make a difference: Page number 332 Conserving water at home