WATER RESOURCES UNIT 7 CHAPTERS 13 & 20
Jan 03, 2016
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