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Water Resources
Chapter 9
Water, water, everywhere…
• Most (97%) of Earth’s
water is saltwater
• Of the 3% that is
freshwater, <1% is
available for us
• The rest is frozen or
deep underground
Groundwater
• Aquifer – groundwater is located in small
spaces within permeable layers of rock
and sediment
• Unconfined aquifer – porous rock + soil;
water can move in and out freely
• Confined aquifer – surrounded by
impermeable layers
– Springs or artesian wells
Groundwater…
• Water table – the uppermost level of
water saturation in the soil
• Groundwater recharge – water from
precipitation that percolates back into the
soil
Groundwater…
• Pumping water out of the ground faster
than it can be recharged will cause a drop
in the water table
• Wells near the coastline can suffer from
saltwater intrusion as the freshwater is
infiltrated with ocean water
Surface Water
• Streams, rivers, ponds, lakes, wetlands
• 3 largest rivers based on volume:
1. Amazon in South America
2. Congo in Africa
3. Yangtze in China
• Human settlement and impacts
– Transportation
– Irrigation
– Agriculture
Surface water…
• Lakes – surface area versus depth and
volume determine size
• Classification of lakes:
1. Oligotrophic
•
Low nutrient levels = low productivity
2. Mesotrophic
•
Moderate productivity
3. Eutrophic
•
Highly productive
Surface water…
• Wetlands – help to offset flooding during
periods of heavy rainfall
• Also are very useful at absorbing
pollutants
Atmospheric water
• Drought – lack of rainfall
– Harm ecosystems and humans
– Also impact soil:
• Harder for nutrients to cycle
• Dried soil more vulnerable to wind erosion
• Flooding – too much rainfall
– Also cause crop and property damage
– Ground has been paved
• Excess water can’t soak in
Humans alter water availability
• Flood control/prevention:
– Levees
•
•
•
•
•
Mississippi River (New Orleans)
Black Warrior River (Northport)
Floodwaters move downstream
Encourages development of floodplain
Risk of collapse or breach
– Dikes
• Levees for ocean waters
• The Netherlands
Humans alter water availability…
• Dams – cross rivers to produce a reservoir
– Water used for consumption, generation of
electricity, flood control, recreation
– Environmental issues:
• Disrupt ecosystems during construction
• Interfere with natural flow of water
• Silt behind the dam
Humans alter water availability…
• Aqueducts – carry water to another place
– New York City & Los Angeles
– Environmental issues
• Disruption of ecosystem during construction
• Less water available in ecosystem feeding the
aqueduct
• Can cause international disputes
Humans alter water availability…
• Desalination – making saltwater fresh
– Distillation: boiled water leaves salt behind,
steam is captured and cooled to condense
• Requires a lot of energy
– Reverse osmosis: water is forced through a
membrane which blocks the salt
• More efficient and less costly
• Brine – super salty water waste
Water use
• Agriculture
– Irrigation: considerations – cost, amount of
evaporation
•
•
•
•
Furrow ~ 65% efficient
Flood ~ 70-80% efficient
Spray ~ 75-95% efficient
Drip > 95%
– Hydroponic agriculture
Water Use…
• Industry
– Electrical generation:
• In the U.S. ~ ½ of all water used goes toward
generating electricity
• Hydroelectric generation returns water to source
• Thermoelectric power plants use water to cool the
system and it leaves as water vapor
– Refining metals and making paper
• Gallons used per kg made:
• Copper 116, Aluminum 108, Steel 68, paper 33
Water Use…
• Households ~ 10% of all water used in
U.S.