overview of chapter 13 - napa valley college of chapter 13 ... due to dams that block migration
TRANSCRIPT
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Chapter 13Water: A Limited Resource
Overview of Chapter 13
Importance of Water
Water Use and Resource Problems
Global Water Problems
Water Management
Water Conservation
Importance of Water
Cooking & washing
Agriculture
Manufacturing
Mining
Energy production
Waste disposal
Demand for water is increasing
California Rice
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Properties of Water
H2O (two hydrogen atoms and one oxygen atom)
Exists as solid, liquid, or gas
High heat capacity
Polar
Forms Hydrogen bonds between water molecules
H-bonds define water’s physical properties
Properties of Water
Water is never completely pure in nature
Content of seawater (left)
Water dissolves many substances
Some cause water pollution
Distribution of Water on Earth
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
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Hydrologic Cycle
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
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Water Use and Resource Problems
Three general categories
Too much water
Too little water
Poor quality/contamination
Too Much Water
Flooding
Regular natural phenomenon
Human activities can alter flood characteristics
Floods are highly destructive in developed areas
Humans have removed water-absorbing plant cover from soil
Humans construct buildings on floodplains
Floodplain
Area bordering a river channel that has the potential to flood
Rather than rebuild levees adjacent to rivers, experts suggest allowing some flooding of floodplains during floods
Floodplain
Government restrictions on building on floodplains
Levees fail
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Left: Traditional levees adjacent to river
Right: Suggested levee style, set back from river
Floodplain
The Napa River
The Napa River (New Year’s Flood)
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The Napa River (New Year’s Flood)
The Napa River (New Year’s Flood)
The Napa River (New Year’s Flood)
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Where does the water go?Natural ground cover
Where does the water go?10%-20% Impervious surface
Where does the water go?35%-50% Impervious surface
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Where does the water go?75%-100% Impervious surface
Too Little Water
Typically found in arid land
Problems
Drought
Overdrawing water for irrigation
Aquifer depletion
Ground subsidence
Water Distribution in North America
The U.S. has a plentiful supply of freshwater
However, many areas have severe shortages
Geographical variations
Seasonal variations
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Water shortages in West and Southwest
Water is diverted and transported via aqueducts
Water Distribution in US
The Colorado River is diverted so much that the channel goes dry in Mexico before entering the sea
Water Diversion Projects
Water diverted to areas that are deficient
Much of Southern CA receives its water supply from diverted water from Northern CA
Controversial and expensive
California’s Aqueduct System
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Dams and Reservoirs
Benefits:
Ensure year-round supply of water with regulated flow
Generate electricity
Provide recreational activities
Disadvantages
Alter the ecosystem
Water temperature, fish migration, etc.
Traps sediment
Dams and Reservoirs
Salmon populations along west coast have been greatly reduced due to dams that block migration
Fish ladders help but are not effective enough to compensate for the altered river system
Global Water Problems
Water and Climate Change
Climate change affects the type and distribution of precipitation
Water content in snowpack
Timing
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Global Water Problems
Amount of freshwater on planet can meet current human needs
However, it is unevenly distributed and some places lack reliable sources
Desalination
Removal of salt from water
Two main methods:
Distillation- saltwater is evaporated and condensed
Reverse Osmosis- saltwater forced through a selective membrane, which allows water through but not salt
Both methods are very expensive and energy-intensive
Distillation
Reverse Osmosis Unit
Water Conservation
Reducing Agricultural Water Waste
American agriculture has historically been very inefficient with water
Drip (or trickle) irrigation greatly improves water efficiency
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Water Conservation
Gray Water
Recycled wash water for non-human contact
Can be used to flush toilets and for irrigation
Water-efficient fixtures
Government incentives
Rebates, tax breaks, etc.
Conserving at Home and Work
http://www.h2ouse.org/
http://www.saveourh2o.org/