Water: A Limited Resource

Overview Water Unit• 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– Energy production– Waste disposal

• Use of freshwater is increasing

Composition/Properties of Water

• Composed of 2 Hydrogen and 1 oxygen

• Exists as solid, liquid or gas• High heat capacity• Polar– One end has (+) charge, one

end has (-) charge• Forms Hydrogen bond

between 2 water molecules– H-bonds define water’s

physical properties

Properties of Water

• Water is never completely pure in nature

• Seawater (left) contains many dissolved ions

• Majority being Na+ and Cl- which is why it is “salty”

Recall Water circulates around the earth through the Hydrologic Cycle

Distribution of Water

• Only 2.5% of water on earth is freshwater

• 2% is in the form of ice!

• Only ~0.5% of water on earth is available freshwater

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

Freshwater Aquifer

Water Use and Resource Problems

• Fall into Three Categories– Too much water– Too little water– Poor quality/contamination (discussed in Chapter

22)

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

Effects of Urbanization: Urban vs. Pre-Urban Floodplains

Floodplain• Government restrictions on building based on the fact that

– Levees can fail…(ex. New Orleans)

o Rather than rebuild Rather than rebuild levees adjacent to levees adjacent to rivers, experts suggest rivers, experts suggest allowing some flooding allowing some flooding of floodplains during of floodplains during floodsfloods

• (next slide)(next slide)

Left: Traditional Left: Traditional levees adjacent to levees adjacent to riverriver

Right: Suggested Right: Suggested levee style, set levee style, set back from riverback from river

Case-In-Point Floods of 1993 (pg286)

Extreme flooding of the mississippi brings back the age old debate. Should the Govt. restore old levees or allow the areas to return back to a more normal state in order to mitigate the flooding?

Too Little Water

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

Too Little Water (coastal)

• Problems (continued)– Saltwater Intrusion

Water Problems In US and Canada

• US has a plentiful supply of freshwater

• But many areas have a severe shortage there are also

– Geographical variations

– Seasonal variations

Water Problems in US and Canada• B/C of Water shortages in West and Southwest

– Water is diverted and transported via aqueducts

Water Problems in US and Canada- Surface Water

• Mono Lake (Eastern CA)– Rivers and streams that once fed this lake are diverted

to Los Angeles (275mi away)– Becoming highly saline– Court ordered water diversion reduction

• Colorado River Basin– Provides water for 27-million people– Numerous dams for Hydropower– Colorado River no longer reaches ocean– See pg. 291

Colorado River bed in Mexico

Water Problems in US and Canada-Groundwater

• Aquifer Depletion

Aquifer depletion is a wide-spread problem in the US, particularly in the high plains, California and Southern Arizona

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

Global Water Problems

• Water and Climate Change– Climate change affects the type and distribution of

precipitation– Potential issues:• Reduced snowfall will impact water resources

downstream• Sea level rise will cause saltwater intrusion into

drinking water supplies and coastal migration inward which will tax those sources of water

Global Water Problems

• Drinking Water Problems– Many developing countries have insufficient water

to meet drinking and household needs

• Population Growth– Increase in population means an increase in

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

is needed more to feed the increased population

Global Water Problems

• 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

– Aral Sea (next slide)• Water diversion for irrigation has

caused sea to become too saline

Aral Sea in Kazakstan

19671967 19971997

Similar to the problems which face Mono Lake

Total volume is down by 80% and all 24 fish species are gone

Global Water Problems

• Potentially Volatile International Water Situations– Jordan River

• Supplies water to Israel, Jordan, the West Bank and the Gaza Strip• Increased population growth in the area is straining the resource

– Nile River• Ten nations share the Nile River including Egypt, Ethiopia, and Sudan• Ethiopia and Sudan are expanding in population• Almost all of Egypts water comes from the Nile so they are becoming

imperiled

Water Management

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

• Three main techniques:– Dams and Reservoirs– Water Diversion Projects– Desalinization

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• 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

Dams and Reservoirs

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

• Fish ladders help (right slide), but are not effective enough

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

• Definition: 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

Distillation Example

Reverse Osmosis Example

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 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: What you can do

• Install water-saving shower heads and faucets (Eco-shower)

• Install low-flush toilets• Fix leaky fixtures• Purchase high efficiency appliances• Modify personal habits• Use the dishwasher instead of washing by

hand