WATER RESOURCESUNIT 7CHAPTERS 13 & 20

WATER SUPPLY

97.4% of water is SALT WATER Most of the other 2.6% is found in glaciers,

ice caps, and deep underground Only 0.014% of water is actually available

for us to use!

SURFACE WATER

Does not percolate into the ground or evaporate

Also called surface runoff

Land area this water flows into a body of water from is known as the watershed or drainage basin

RUNOFF

Reliable runoff is the amount of runoff we can count on to be there year after year for us to use

GROUND WATER Water that has percolated into tiny

cracks and crevices of soil

GROUND WATER Zone of aeration: close to the surface, contains mixture of air and water

Zone of saturation: lower layers, fully saturated with waterWe drill wells down to

this layer Water table: at top of

Z of S, falls in dry weather, rises in wet weather

AQUIFERS

AQUIFERS

Porous, water-saturated layers of sand, gravel, bedrock (limestone) through which groundwater flows

Watertight layers of rock/ clay lie at the bottom of an aquifer so water doesn’t leak out

AQUIFERS

Most are replenished through natural recharge (rain that percolates through the soil)

Some have lateral recharge (water from streams flow sideways into aquifer)

Some are classified as “fossil aquifers” and are non-renewable

AQUIFERS Aquifers provide

water for 25% of people

Is renewable as long as the aquifer is not contaminated

Water tables are falling worldwide

DEEP AQUIFERS

Deeper than 0.5 mi Water deposits thousands to millions

of years old! Can run under several countries

Could support us for a long time if we could reach it

DEEP AQUIFERS

Drawbacks? Would be very expensive to tap into No idea what (if any) ecological

impacts might be Who owns the water? Who has the rights to use it?

WATER USE

Withdrawl: is the amount of water we take out of nature to use for whatever

Some of it gets returned to its source We use about 34% of reliable runoff

each year

WATER USE

What do we use water for? 70%= irrigation 20%= industry 10%= residences

Water use varies by region

INDUSTRIAL USE

Use drinking quality water to flush & dilute wastes!

Becomes low quality water no one wants to use after that

MANAGING INDUSTRIAL USE

Decrease amount of waste Ban discharge of toxic waste into

water systems Rely on composting toilets Use sludge produced by treatment

plants as a fertilizer Use natural ways to treat sewage

(living systems)

WATER MANAGEMENT

Who should be in charge of our water resources?

Private companies? or Governments? or a combination of the two?

WATER MANAGEMENT

Almost all are owned by the government

MOST water resources are managed by local governments

In some areas private businesses are allowed to MANAGE public water resources (public-private partnership)

WATER MANAGEMENT

Why let private businesses run things?

How much should the gov’t regulate private businesses running public utilities?

Public utilities like water can be focus of a terrorist attack- shouldn’t we have the government in charge???

WATER MANAGEMENT

UK in 1980’sPM Margaret Thatcher turned over the

water supply to private companiesResulted in disaster

UK in 1990’sPM Tony Blair imposed tighter restrictions

& controls and fixed everything

TOO LITTLE WATER

What causes water shortages?

1. Dry climate2. Drought3. Desiccation4. Water stress

WATER SHORTAGES

Desiccation: drying of exposed soil

Water stress: low per capita availability of waterWater stressed: vol of r.r. per person

drops below 1700 cubic m/ yearWater scarcity: vol of r.r. per person

drops below 1000 cubic m/ year

WATER SHORTAGES

Some people have lots of water & some people don’t

Rivers can be far from population & agricultural centers

Short periods of rainfall Lakes & rivers have shrunk due to too

much water being withdrawn

WATER SHORTAGES In –ing countries ~1.5

billion people lack adequate supplies of safe water

In some countries some women spend hours a day hauling water

Where safe water is in short supply, hygiene & basic sanitation are often neglected

WATER WASTE

We waste about 2/3 of the water we use

If we can reduce water waste we can meet our water needs

HOW TO REDUCE WATER WASTE

Charge more for water!Keeping the price low for consumers tricks

us into thinking there is more water available than there really is

Reduce gov’t water subsidies for corporations & farmersForce to use more efficient methods of

irrigation & manufacturing Give subsidies for increasing water

efficiencyThanks for saving water! Have some

money!

IRRIGATION EFFICIENCY

60% of irrigation water does NOT reach crops or contribute to food production

IRRIGATION METHODS

1. Flood irrigation: uses more water than plants need*Loses 40% of water*Water comes from aqueducts or rivers

IRRIGATION METHODS

2. Center pivot low-pressure sprinklers*80% to 95% (with LEPA) efficient!

3. Low-energy precision application sprinklers (LEPA)*Sprays water closer to ground

IRRIGATION METHODS

4. Soil moisture detectors*only water plants when they need it

IRRIGATION METHODS

5. Drip irrigation*MOST EFFICIENT*Network of perforated tubes installed at or below ground level*Allows water to be delivered in small & steady rates

XERISCAPING

Use of native plants for landscaping that require less water

Reduces water, fertilizer, & pesticide use

DESALINATION

Removing dissolved solids (salts) from ocean or brackish water

DESALINATION

120 countries have desalination plants Makes less than 0.3% of the world’s

water Middle Eastern countries produce 60%

of that US produces about 20%

DESALINATION METHODS

Distillation: heating water until it evaporates and then collecting that vapor and recondensing it.

Reverse osmosis: pump sea water at high pressure through a thin membrane with pores that allow water but not salts throughWe do this here in Tampa

PROBLEMS WITH DESALINATION

Takes a LOT of energy

What do we do with all the leftover brine?

CLOUD SEEDING

Force rain clouds to form by putting dry ice or particles of chemicals in the atmosphere

Forces it to rain/ snow in dry areas

China did this before the 2008 Olympics

CLOUD SEEDING PROBLEMS

Not many clouds in dry areas Not much evidence this actually works Adds lots of chemicals to the

environment Who owns clouds & has the right to

seed them?

ICEBERG TOWING

Proposed idea Tow icebergs to water

stressed areas and keep them offshore

Could pump water onshore for agricultural and residential use

Another similar idea is to fill giant plastic bags with water and do the same thing.

DAM!

Estimated 800,000 dams are built on all the world’s rivers

Purpose?Capture and store runoffControl floodingGenerate electricitySupply irrigation waterRecreation

THOSE DARN DAMS

Increases reliable runoff Can reduce downstream flow to

nothing Prevents rivers from reaching the sea ½ of the worlds rivers go dry for part

of the year due to dams!

THOSE DARN DAMS

Displace people Floods areas that

are productive land Endanger

freshwater fish species & environments

Can actually cause a greater loss of water

Reservoirs fill up with silt and become useless

TOO MUCH WATER!

Floods are caused by too much rain and rapid snow melt

Water in a river/ stream overflows & spills into the surrounding area known as the floodplain

FLOODPLAINS

People like living here! Fertile soil from flooding events Close to rivers Land is mostly flat

FLOODING POSITIVES

Deposits nutrient rich soils onto the floodplains

Recharges groundwater

Replenishes wetlands

FLOODING NEGATIVES

Kills lots of people & animals

Lots of property damage

Can cause mudslides

HUMAN IMPACTS

We remove water absorbing plants from river banks

We drain wetlands We live in floodplains We alter the paths of rivers

CAN WE PREVENT FLOODING?

Not totally, but we can try to lessen the effectsStraighten & deepen streams by

channelizationBuild levees & floodwallsBuild damsPreserve/ restore wetlands