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Water Use and Management

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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

• 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 earth’s surfaces. Moves underground by infiltration

or overland runoff into rivers, lakes and seas.

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Average Annual Precipitation

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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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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. Without oceans to absorb and store heat,

and wind currents to redistribute the heat in latent energy of water vapor, the earth would undergo extreme temperature fluctuations.

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Regions of Plenty and Regions of Deficit

• Three principal factors control global water deficits and surpluses. Global atmospheric circulation Prevailing Winds Topography

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Regions of Plenty and Regions of Deficit

• 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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Rain Shadow

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MAJOR WATER COMPARTMENTS

• Oceans Together, oceans contain more than 97%

of all liquid water in the world.- Contain 90% of world’s living biomass.- Moderate earth’s 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 world’s 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 Saturation.

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Water Compartments

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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 Zones - 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 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 < 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.

- U.S. 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 unsuitable for desired use.

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Types of Water Use

• 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. Annual renewable water supply in U.S.

amounts to an average of 2.4 million gallons/person/year.

- Now withdraw one-fifth of this amount.

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Agricultural Water Use

• Worldwide, agriculture claims about two-thirds of total water withdrawal and 85% of consumption. In many developing countries, agricultural

water use is extremely inefficient and highly consumptive.

- Drip irrigation is a promising technology.

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Groundwater Withdrawals for Irrigation

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Domestic and Industrial Water Use

• Worldwide, domestic water use accounts for about one-fifth of water withdrawals. Only about 10% of consumption.

- Grown in proportion with urban populations.

• Industry accounts for 20% of global freshwater withdrawals. Range from 5% to 70%.

- Small proportion is consumed, but degradation is a problem.

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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 world’s 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 U.S.. 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

• 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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Cone of Depression and 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 is forcing

relocation of over a million people. Evaporation, Leakage, Siltation

- Evaporative losses from Lake Mead and Lake Powell on the Colorado River is about 2 billion m3 per year.

- 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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Price Mechanisms and Water Policy

• Through most of U.S. 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 U.S..

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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 bulk water export.

- Water is “too precious” to 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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