Water Use and Management

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Water Use and Management

• Chapter 19

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Outline

• Hydrologic Cycle
• Major Water Compartments
• Water Availability and Use
• Types of Water Use
• Freshwater Shortages
• Depleting Groundwater
• Increasing Water Supplies
• Water Management and Conservation
• Price Mechanisms

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WATER RESOURCES

• Water, liquid and solid, covers more than 70 of
  worlds surface.
• More than 370 billion billion gallons.

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Hydrologic Cycle

• Describes the circulation of water as it
• Evaporates from land, water, and organisms.
  (Transpires from plants)
• Enters the atmosphere.
• Condenses and precipitates back to the earths
  surfaces.
• Moves underground by infiltration or overland
  runoff into rivers, lakes and seas.

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Hydrologic Cycle
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Hydrologic Cycle

• Solar energy drives the hydrologic cycle by
  evaporating surface water.
• Evaporation - Changing liquid to a vapor below
  its boiling point.
• Sublimation - Changing water between solid and
  gaseous states without ever becoming liquid.
• Freezer Burn

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Hydrologic Cycle

• Humidity - Amount of water vapor in the air.
• Saturation Point - When a volume of air contains
  as much water vapor as it can hold at a given
  temperature.
• Relative Humidity - Amount of water vapor in the
  air expressed as a percentage of the maximum
  amount that can be held at that temperature.

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Hydrologic Cycle

• Dew Point - Temperature at which condensation
  occurs for a given amount of water.
• Condensation Nuclei - Tiny particles that
  facilitate condensation.
• Smoke, dust, sea salt, spores.

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Rainfall and Topography

• Mountains act as cloud formers and rain catchers.
• Air sweeps up the windward side of a mountain,
  pressure decreases, and the air cools.
• Eventually saturation point is reached, and
  moisture in the air condenses.
• Rain falls on the mountaintop.
• Cool, dry air descends and warms, absorbing
  moisture from other sources. (Rain Shadow)

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Rainfall and Topography
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Desert Belts

• Evaporation is highest near the equator as direct
  sunlight produces the greatest heat budgets.
• Air at the equator rises, cools, and falls as
  rain, forming rainforests at the equator.
• Cooler, drier air descends along Tropics of
  Cancer and Capricorn.
• Causes evaporative losses and creates deserts.

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Precipitation Patterns
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Balancing the Water Budget

• Oceans account for 86 of total evaporation.
• Ninety percent of water evaporated from the ocean
  falls back on ocean as rain.
• Remaining 10 is carried by prevailing winds over
  continents.

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MAJOR WATER COMPARTMENTS

• Oceans
• Together, oceans contain more than 97 of all
  liquid water in the world.
• Contain 90 of worlds living biomass.
• Moderate earths temperature.
• Average residence time of water in the ocean is
  about 3,000 years.

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Major Water Compartments

• Glaciers, Ice, and Snow
• 2.4 of worlds water is classified fresh.
• 90 in glaciers, ice caps, and snowfields.
• As recently as 18,000 years ago, one-third of
  continental landmass was covered by glacial ice
  sheets.
• Now, Antarctic glaciers contain nearly 85 of all
  ice in the world.
• Sea ice comes from ocean water, but salt is
  excluded during freezing.

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Major Water Compartments

• Groundwater
• Second largest reservoir of fresh water.
• Infiltration - Process of water percolating
  through the soil and into fractures and permeable
  rocks.
• Zone of Aeration - Upper soil layers that hold
  both air and water.
• Zone of Saturation - Lower soil layers where all
  spaces are filled with water.
• Water Table - Top of Zone of Sat.

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Groundwater
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Groundwater

• Aquifers - Porous layers of sand, gravel, or rock
  lying below the water table.
• Artesian - Pressurized aquifer intersects the
  surface. (Water flows without pumping)
• Recharge Zone - Area where water infiltrates into
  an aquifer.
• Recharge rate is often very slow.
• Presently, groundwater is being removed faster
  than it can be replenished in many areas.

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Groundwater
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Major Water Compartments

• Rivers and Streams
• Precipitation that does not evaporate or
  infiltrate into the ground runs off the surface,
  back toward the sea.
• Best measure of water volume carried by a river
  is discharge.
• The amount of water that passes a fixed point in
  a given amount of time.
• Usually expressed as cubic feet per second.

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Major Water Compartments

• Lakes and Ponds
• Ponds are generally considered small bodies of
  water shallow enough for rooted plants to grow
  over most of the bottom.
• Lakes are inland depressions that hold standing
  fresh water year-round.
• Both ponds and lakes are will eventually fill
  with sediment, or be emptied by an outlet stream.

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Major Water Compartments

• Wetlands
• Play a vital role in hydrologic cycle.
• Lush plant growth stabilizes soil and retards
  surface runoff, allowing more aquifer
  infiltration.
• Disturbance reduces natural water-absorbing
  capacity, resulting in floods and erosion in wet
  periods, and less water flow the rest of the year.

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Major Water Compartments

• The Atmosphere
• Among the smallest water reservoirs.
• Contains lt 0.001 of total water supply.
• Has most rapid turnover rate.
• Provides mechanism for distributing fresh water
  over landmasses and replenishing terrestrial
  reservoirs.

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WATER AVAILABILITY AND USE

• Renewable Water Supplies
• Made up of surface runoff and infiltration into
  accessible freshwater aquifers.
• About two-thirds of water carried in rivers and
  streams annually occurs in seasonal floods too
  large or violent to be stored effectively for
  human use.
• Readily accessible, renewable supplies are
  400,000 gal /person/year.

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Drought Cycles

• Every continent has regions of scarce rainfall
  due to topographic effects or wind currents.
• Water shortages have most severe effect in
  semiarid zones where moisture availability is the
  critical factor in plant and animal
  distributions.
• US seems to have 30 year drought cycle.
• Climatic changes such as global warming may alter
  cycles.

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Types of Water Use

• Withdrawal - Total amount of water taken from a
  source.
• Consumption - Fraction of withdrawn water made
  unavailable for other purposes (Not returned to
  its source).
• Degradation - Change in water quality due to
  contamination making it is unsuitable for desired
  use.

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Types of Water Use

• Worldwide, humans withdraw about 10 of total
  annual renewable supply.
• Many societies have always treated water as an
  inexhaustible resource.
• Natural cleansing and renewing functions of
  hydrologic cycle do not work properly if systems
  are overloaded or damaged.

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Quantities of Water Used

• Human water use has been increasing about twice
  as fast as population growth over the past
  century.
• Average amount of withdrawn worldwide is about
  170,544 gal/person/year.
• Annual renewable water supply in US amounts to an
  average of 2.4 million gallons/person/year.
• Now withdraw one-fifth of this amount.

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Global Water Use Growth
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Water Use By Sector

• Worldwide, agriculture claims about 69 of total
  water withdrawal.
• In many developing countries, agricultural water
  use is extremely inefficient and highly
  consumptive.
• Worldwide, industry accounts for about 25 of all
  water use.
• Cooling water for power plants is single largest
  industrial use.

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FRESHWATER SHORTAGES

• Estimated 1.5 billion people lack access to an
  adequate supply of drinking water.
• Nearly 3 billion lack acceptable sanitation.
• A country where consumption exceeds more than 20
  of available, renewable supply is considered
  vulnerable to water stress.
• Globally, water supplies are abundant, but, along
  with capital resources, are unevenly distributed.

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A Precious Resource

• Currently, 45 countries, most in Africa or Middle
  East, are considered to have serious water
  stress, and cannot meet the minimum essential
  water requirements of their citizens.
• More than two-thirds of worlds households have
  to retrieve water from outside the home.
• Sanitation levels decline when water is expensive.

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Depleting Groundwater

• Groundwater is the source of nearly 40 of fresh
  water in the US.
• On a local level, withdrawing water faster than
  it can be replenished leads to a cone of
  depression in the water table,
• On a broader scale, heavy pumping can deplete an
  aquifer.
• Ogallala Aquifer
• Mining non-renewable resource.

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Depleting Groundwater
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Depleting Groundwater

• Withdrawing large amounts of groundwater in a
  small area causes porous formations to collapse,
  resulting in subsidence.
• Sinkholes form when an underground channel or
  cavern collapses.
• Saltwater intrusion can occur along coastlines
  where overuse of freshwater reservoirs draws the
  water table low enough to allow saltwater to
  intrude.

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Saltwater Intrusion
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INCREASING WATER SUPPLIES

• Seeding Clouds
• Condensation Nuclei
• Towing Icebergs
• Cost
• Desalination
• Most common methods are distillation and reverse
  osmosis.
• Three to four times more expensive than most
  other sources.

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Increasing Water Supplies

• Dams, Reservoirs, Canals and Aqueducts
• Common to trap excess water in areas of excess
  and transfer it to areas of deficit.
• Environmental Costs
• Upsets natural balance of water systems.
• Ecosystem Losses
• Loss of wildlife habitat.
• Reservoir Size
• Water Quality

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Dams, Reservoirs, Canals and Aqueducts

• Displacement of People
• Three Gorges Dams in China will force relocation
  of over a million people.
• Evaporation, Leakage, Siltation
• Evaporative losses from Lake Mead and Lake Powell
  on the Colorado River is about 1km3 per year (264
  billion gallons).
• Dams slow water flow, allowing silt (nutrients)
  to drop out.
• Loss of Free-Flowing Rivers

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WATER MANAGEMENT AND CONSERVATION

• Watershed Management
• Watershed - All the land drained by a stream or
  river.
• Retaining vegetation and ground cover helps
  retard rainwater and lessens downstream flooding.
• Additionally, retaining crop residue on fields
  reduces flooding and minimizing plowing and
  forest cutting on steep slopes protects
  watersheds.

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Domestic Conservation

• Estimates suggest many societies could save as
  much as half of current domestic water usage
  without great sacrifice or serious change in
  lifestyle.
• Largest domestic use is toilet flushing.
• Small volume of waste in large volume of water.
• Significant amounts of water can be reclaimed and
  recycled.
• Purified sewage effluent

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Typical US Household Water Use
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Price Mechanisms and Water Policy

• Through most of US history, water policies have
  generally worked against conservation.
• In well-watered eastern states, water policy was
  based on riparian use rights.
• In drier western regions where water is often a
  limiting resource, water law is based primarily
  on prior appropriation rights.
• Fosters Use it or Lose it policies.

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Price Mechanisms and Water Policy

• In most federal reclamation projects, customers
  were only charged for immediate costs of water
  delivery.
• Dam and distribution system costs were
  subsidized.
• Growing recognition that water is a precious and
  finite resource has changed policies and
  encouraged conservation across the US.

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Price Mechanisms and Water Policy

• Charging a higher proportion of real costs to
  users of public water projects has helped
  encourage conservation.
• In 1999, the Canadian government passed federal
  legislation banning any bulk water export.
• Water is too precious too be treated like other
  commodities.

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Summary

• Hydrologic Cycle
• Major Water Compartments
• Water Availability and Use
• Types of Water Use
• Freshwater Shortages
• Depleting Groundwater
• Increasing Water Supplies
• Water Management and Conservation
• Price Mechanisms

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