Transcript Water - PlattScience

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 Clwhich 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
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
(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 CanadaGroundwater
• 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
Similar to
the
problems
which face
Mono Lake
1967
1997
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 highquality 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