Water-and-Water-Resources by huangyuarong

VIEWS: 6 PAGES: 54

									 Chapter 13
Water Resources
           Importance of Water
• Covers 71% of Earth’s surface
   – 97% by volume is found in the ocean
   – 3% is fresh water (2.997% in glaciers and ice
     caps)
   – 0.024% freshwater easily accessible in
     groundwater, lakes, streams, etc.
• Water is constantly recycled via the hydrologic
  cycle .
     Freshwater Availability
• Canada has 0.5% of the world
  population but has 20% of available
  freshwater.
• China has 20% of the world population
  but only 7% of available freshwater
• Asia has 60% of the world population
  but 30% of the available freshwater
  Important Properties of Water
• Hydrogen Bonds – creates the adhesive and
  cohesive forces of water
  – Causes water to exist as a liquid over a wide
    temperature range
• Water has a high heat capacity
  – Protects organisms from heat fluctuations
  – Moderates Earth’s climate
  – Good coolant for engines, power plants, etc.
• Dissolves a variety of compounds (polarity)
  – “universal solvent”
• Ionizes which maintains pH (H+, OH-)
• Filters out UV light
• Expands by 10% when frozen, so it floats
                 Groundwater
• Groundwater –
  precipitation that
  penetrates downward
  through geologic features
  and enters the water table
• Zone of Saturation - below
  the water table surface
  where voids (spaces
  between rock) are filled
  with water
• Water Table - the surface
  of the zone of saturation
• Zone of Aeration – above
  the water table surface
  where voids are not filled
  with water
               Groundwater
• Aquifer - porous sand, gravel or bedrock
  through which groundwater flows
• Recharge area - an area of land through
  which water passes downward or laterally
  into an aquifer
  – Natural recharge (via percolation) or lateral
    recharge (recharge from the side)
• Water mining - removal of water from an
  aquifer that exceeds its replenishment
Groundwater
                Surface Water
• Surface runoff: water that flows into streams,
  lakes, and reservoirs
  – Reliable runoff: stable source of water not lost to
    seasonal flooding and is available for human use
  – 1/3 of all runoff is reliable; 2/3 is lost.
• Watershed (drainage basin): region from
  which water drains into a stream, lake, or
  reservoir
     World’s Reliable Runoff?
• In the last century, the population is tripled.
• Global water withdrawal has increased 7x;
  per capita withdrawal has increased 4x
• We currently withdrawal 34% of the
  world’s reliable runoff.
• It could reach 70% by 2025 but at this rate
  it could reach as high as 90%.
       How do we use our water?
• Current usage of water withdrawals
  – 70% is used for irrigation (agriculture)
  – 20% is used for industry
  – 10% is used for city and residential
  Interesting Factoids: It takes
    2400 bathtubs of water to make one car.
    25 bathtubs of water to make a t-shirt
    37 gallons of water to produce one cup of coffee
     US Freshwater Resources
• Much available water is:
  – In the wrong place at the wrong time (flooding,
    drought)
  – Contaminated by agricultural and industrial
    waste/practices
       Water Use in the U.S.


• ½ the water in the US comes from groundwater
• Water tables in 48 states is dropping quickly.
• 36 states will suffer water shortages by 2013
  due to
  – Population growth & Urban sprawl
  – Drought, rising temperatures
  – Excessive use
          US Water Problems
       Eastern US             Western US
• Water used for:      • Water used for:
  energy production,     irrigation (85%)
  cooling, and         • Water Problems:
  manufacturing          – Shortage of runoff due
• Water Problems:          to low precipitation,
  – Flooding               high evaporation rates,
                           and prolonged drought
  – Occasional urban
    shortages
  – pollution
Population and Water Resources
   Developed Countries      Developing Countries
• People live where       • Settle where water is
  climate is more           prevalent
  favorable               • Dry seasons make
• Water is imported         crops difficult to grow
  from other watersheds   • Too expensive to
                            irrigate
   Using Dams and Reservoirs
• Purpose – capture and store runoff and
  release it as needed for flood control,
  producing hydroelectric power, supplying
  water
• Problems – can reduce downstream flow to
  a trickle; can reduce biodiversity; can
  destroy habitats
 Causes of Freshwater Shortages
• Dry Climate
• Drought – over 21 days of lowered precipitation
  and increased evaporation
• Desiccation – drying of soil due to activities like
  deforestation and overgrazing
• Water Stress – lower per capita availability of
  water; have more people who are using limited
  water sources

About 41% of the world’s population lives in countries
        that are water-scarce or water-stressed
What’s the answer to the increasing
    water shortage problem?
• Withdraw groundwater?
• Build dams or reservoirs that store runoff?
• Bring in surface water from another
  location?
• Convert salt water to freshwater through
  desalinization?
• Waste less water?
• Import food to reduce water use?
    Problems with Groundwater
           withdrawals
Groundwater over-pumping can cause land to sink, and
contaminate freshwater aquifers near coastal areas with
saltwater
Sinkholes
Provides water   Flooded land
for year-round   destroys forests or
irrigation of    cropland and
cropland         displaces people

                   Large losses of
                   water through
                   evaporation
Provides
water for
drinking          Downstream
                  cropland and
Reservoir is      estuaries are
useful for        deprived of
recreation and    nutrient-rich silt
fishing

                      Risk of failure
Can produce           and
cheap                 devastating
electricity           downstream
(hydropower)          flooding
Downstream
flooding is          Migration and
reduced              spawning of
                     some fish are
                     disrupted

                      Fig. 13-12 p. 325
      The Colorado River Basin
• 1400 miles of river through 7 states into the Gulf
  of California.
• Has 14 major dams and canals that irrigate
  farmlands.
• Supplies water to some of the driest land in the
  rain shadow of the mountains.
Hoover Dam
Hoover Dam – Ansel Adams
Hoover Dam from above
Hoover Dam inlets
Hoover Dam
             Case Study:
      China’s Three Gorges Dam
Benefits:
• The World’s largest hydroelectric dam, which
  will reduce China’s dependency on coal.
• Reduction in CO2 emissions.
• Facilitate the movement of cargo ships.
• Built to prevent flooding that killed 4000 in 1998.
    China’s Three Gorges Dam
Problems:
• Many freshwater fish and plants endangered or
  extinct.
• Cost is about $25 billion dollars.
• The reservoir will flood 1,350 villages and
  displace 5.4 million people.
• Reduces nutrient rich sediments from going
  downstream.
• Built on a fault line.
• Over time, it will develop into a large sewer.
Three Gorges Dam
Three Gorges Dam construction
Three Gorges Dam
       California Water Project
• A massive transfer of water from water-rich northern
  California to water-poor southern California is
  controversial.

• Southerners need the water for irrigation of water thirsty
  crops like rice and alfalfa.

• Northerners complain that the project will degrade the
  Sacramento River and fisheries. Decreased water flow
  reduces the ability of the river to flush out San Francisco
  Bay. They also complain that Southerners are wasting the
  water.
       Other Water Transfers
• Aral Sea
  – Water was diverted
    for irrigation
  – Due to dry climate
    and high
    evaporation rates,
    the Aral Sea has
    shrunk and salinity
    increased.
North Aral Sea recovery 2005-07
     China’s South-North Water Transfer
                   Project
• China spent $62.5
  billion to build canals,
  reservoirs, dams and
  pumping stations to
  transfer water from the
  Yangtze River to the
  north to Beijing.
                   Desalination
• Distillation: Heating water until it evaporates.

• Reverse osmosis: Forcing water through a
                   filter to remove salt.

Problems:
• Desalination is very expensive
• Produces briny wastewater.
• Reverse osmosis water reduces soil salinization on
   irrigated crops.
  Using Water More Sustainably
Currently 65-70% of water people use throughout the
world is wasted through evaporation, leaks and other
losses.

It’s thought that if we can reduce the water loss by 15%,
we can meet the world’s water needs in the future.

Reasons for water waste
       Water is cheap
       No government subsidies for conserving water.
      Improving Irrigation Efficiency

• 60% of the world’s irrigation water never
  reaches the target crop.

More efficient irrigation methods:
• Gravity Flow = 60 – 80% efficient
• Drip irrigation = 90 – 95% efficient
• Center-pivot, low pressure sprinklers sprays water directly
  onto crop. 80% efficient, but can be up to 95% efficient with
  LEPA (low energy, precision application) sprinklers.
                           Drip irrigation
                       (efficiency 90–95%)


     Gravity flow
 (efficiency 60% and
   80% with surge
         valves)




                                                                  Center pivot
                                                           (efficiency 80%–95%)
                                                           Water usually pumped
                               Above- or below-ground      from underground and
                               pipes or tubes deliver      sprayed from mobile
Water usually comes from       water to individual plant   boom with sprinklers.
an aqueduct system or a        roots.
nearby river.
Getting More Water for Irrigation in
       Developing Countries
      The Low-Tech Approach
                 • low-tech methods to
                   pump groundwater
                 • Harvesting rainwater
     Raising the Price of Water:
    A Key to Water Conservation
• We can reduce water use and waste by raising
  the price of water while providing low lifeline
  rates for the poor.
  – When Boulder, Colorado introduced water meters,
    water use per person dropped by 40%.
                         What Can You Do?
                         Water Use and Waste
• Use water-saving toilets, showerheads, and faucet aerators.
• Shower instead of taking baths, and take short showers.
• Stop water leaks.
• Turn off sink faucets while brushing teeth, shaving, or washing.
• Flush toilets only when necessary.
• Wash only full loads of clothes or use the lowest water-level for smaller
  loads.
• Use recycled (gray) water for lawn, gardens, house plants, car
  washing.
• Wash a car from a bucket of soapy water, and use the hose for rinsing
  only.
• If you use a commercial car wash, try to find one that recycles its water.


• Replace your lawn with native plants that need little if any watering and
  decorative gravel or rocks.
• Water lawns and gardens in the early morning or evening.
• Sweep or blow off driveways instead of hosing off with water.
• Use drip irrigation and mulch for gardens and flowerbeds.
               Reducing Flood
 Natural phenomena               Aggravated by
 Renew and replenish              human activities
                                    Flood zone
               Reservoir

                           Dam

               Levee        Flood
                            wall
  Floodplain
                                                 Fig. 15.24, p. 327
        TOO MUCH WATER




• Comparison of St. Louis, Missouri under
  normal conditions (1988) and after severe
  flooding (1993).
                                         Figure 14-22
         Water Conservation
• The average American uses 90 gallons of water
  each day. European-53 and Sub-Saharan
  Africa-5
• Fix leaks, replace old toilets (trade ins),
  efficient washers (50% less water and energy).
• A switch to water efficient appliances family of
  4- save 23,000 gallons a year.
•

								
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