Chapter 14
Water: A Limited Resource
Overview of Chapter 14
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Importance of Water
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Water Use and Resource Problems
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Sharing Water Resources
Water Management
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Too Much Water
Too Little Water
Water Problems in US and Canada
Global Water Problems
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Hydrologic Cycle
Providing Sustainable Water Supply
Water Conservation
Importance of Water
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Cooking
Washing
Use large amounts
for:
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Agriculture
Manufacturing
Mining
Energy production
Waste disposal
Use of freshwater
is increasing
Properties of Water
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Composed of 2 Hydrogen
and 1 oxygen
Exists as solid, liquid or gas
High heat capacity
Polar
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One end has (+) charge, one
end has (-) charge
Forms Hydrogen bond
between 2 water molecules
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H-bonds define water’s
physical properties
Properties of
Water
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Water is never
completely pure
in nature
Content of
seawater (left)
Many
substances
water dissolves
cause water
pollution
Hydrologic Cycle
(units are km3 & km3 per year)
Hydrologic Cycle:
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Evaporation – Transpiration: adds water vapor
to the atmosphere
Condensation onto condensation nuclei (dust):
turns water vapor into liquid water droplets
(clouds)
Precipitation – large water droplets (or snow,
hail, etc) fall to earth’s surface
Hydrologic Cycle…continued
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Infiltration – water seeps into the pores in rock
and soil, becomes groundwater, which flows
slowly back to oceans, lakes, rivers, or wetlands
Runoff – water flows across surface into rivers
& streams, wetlands, lakes, and then back to
oceans.
Groundwater – the underground reservoir of
water, flows due to gravity
Distribution of
Water
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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
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Surface water
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Runoff
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Land area that delivers water into a stream or river
system
Groundwater
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Movement of surface water to lakes, rivers, etc.
Watershed (drainage basin)
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Precipitation that remains on the surface and does not
seep into soil
Freshwater under the earth’s surface stored in
aquifers
Aquifer
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Underground caverns and porous layers of sand, gravel
and rock in which groundwater is stored
Freshwater Aquifer
Water Use and Resource Problems
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Fall into Three Categories
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Too much water
Too little water
Poor quality/contamination (discussed in Chapter 22)
Too Much Water
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Flooding
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Modern floods are highly destructive because
humans:
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Both natural and human-induced
Remove water-absorbing plant cover from soil
Construct buildings on floodplains
Floodplain
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Area bordering a river channel that has the potential
to flood
Urban vs. Pre-Urban Floodplains
Floodplain
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Government restrictions on building
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Levees can fail
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
Case-In-Point Floods of 1993
Too Little Water
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Typically found in arid land
Problems
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Drought
Overdrawing water
for irrigation
purposes
Aquifer depletion
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Subsidence
Sinkholes
NOTE: shown are center-pivot irrigation
circles…each one is the result of long pipes
that extend along the radius from the center
of the circle to the edge…rotating slowly to
spray the crops.
Too Little Water
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Problems (continued)
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Saltwater Intrusion
Water Problems In US and Canada
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US has a
plentiful supply
of freshwater
However, water
is NOT
uniformly
distributed, so
many areas
have severe
shortages
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Geographical
variations
Seasonal
variations
Water Problems in US and Canada
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Water shortages in West and Southwest
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Water is diverted and transported via aqueducts
Water Problems in US and Canada- Surface Water
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Mono Lake (Eastern CA)
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Colorado River Basin
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Rivers and streams that once fed this lake are
diverted to Los Angeles (275mi away)
Becoming highly saline
Court ordered water diversion reduction
Provides water for 27-million people
Numerous dams for Hydropower
Colorado River no longer reaches ocean
Delaware – a state without water
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Use of conservation-based pricing, in which
consumers are rewarded for conserving water is
helping water managers meet needs
Colorado River bed in Mexico
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Water Problems in US and CanadaGroundwater
Aquifer Depletion
Global Water Problems
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Amount of freshwater on planet CAN meet
human needs
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BUT, it is unevenly distributed and some places lack
stable runoff
Problems:
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Climate Change
Drinking Water
Population Growth
Sharing Water Resources Among Countries
Global Water Problems
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Water and Climate Change
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Climate change affects the type and distribution of
precipitation
Potential issues:
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Reduced snowfall will impact water resources downstream
Sea level rise will cause saltwater intrusion into drinking
water supplies
Global Water Problems
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Drinking Water Problems
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Many developing countries have insufficient water to
meet drinking and household needs
The World Health Organization estimates that about
1.1 billion people lack access to safe drinking water!
Population Growth
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Increase in population means an increase in
freshwater requirements
Limits drinking water available
Limits water available for agriculture (food)
Global Water Problems
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Sharing Water Resources
Among Countries
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Rhine River Basin (right)
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Countries upstream discharged
pollutants into river
Countries downstream had to
pay to clean the water before
they could drink it
Aral Sea (next slide)
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Water diversion for irrigation
has caused sea to become too
saline
Aral Sea
1967
1997
Global Water Problems
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Potentially Volatile International Water
Situations
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Jordan River
Nile River
Water Management
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Main Goal: Provide sustainable supply of highquality water
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Requires humans to use resource carefully
Dams and Reservoirs
Water Diversion Projects
Desalinization
Dams and Reservoirs
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Benefits:
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Ensure year-round supply of
water with regulated flow for
those near dam
Generate electricity
(hydroelectric power)
Provide recreational activities
(flooded area used by boaters,
fishermen, etc.
Can provide flood protection
Can reduce flood damage
Dams and Reservoirs
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Disadvantages: Alter the
ecosystem by:
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Creates a still water
ecosystem rather than flowing
water
Reduce sediment load
downstream, Increased
sediment trapped upstream
behind dam
Raise temp of water behind
dam
Lowers oxygen levels behind
dam, restricts flow, etc.
Dams and Reservoirs
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Glen Canyon Dam
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Regulated flow has changed ecosystem (destroyed
sandbars which were bird nesting grounds)
To rectify situation
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Canyon has been flooded several times
Small floods compared to natural floods
Still helps rebuild habitat
Dams and Reservoirs
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Salmon Population in
Columbia R. very low
due to dams that
impede migration
Fish ladders help, but
are not effective
enough
Water Diversion Projects
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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
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Removal of salt from ocean or brackish
water
Two methods:
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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
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Reducing Agricultural Water Waste
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Agriculture is very inefficient with water
Microirrigation- irrigation that conserves waster by
piping to
crops through sealed
systems
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Also called drip or
trickle irrigation
Water Conservation
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Reducing Industrial Water Waste
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Stricter laws provide incentive to conserve water
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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
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Reducing Municipal
Water Waste
Gray Water
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Can be used to flush
toilets, wash car or
water lawn
Water saving
household fixtures
Government
incentives
Conserving at Home
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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 hand