chapter 21: water supply, use and management

Chapter 21: Water Supply, Use and Management

Water

• To understand water, we must understand its characteristics, and roles:– Water has a high capacity to absorb and store heat.

– Water is the universal solvent.

– Water has a high surface tension.

– Water is the only compound whose solid form is lighter than its liquid form.

– Sunlight penetrates water to variable depths, permitting photosynthetic organisms to live below the surface.

A Brief Global Perspective

• We are facing a growing global water shortage linked to the food supply.

• Global hydrologic cycle– Transfers water from the atmosphere, to land,

to oceans and back to atmosphere– 97% in oceans– 2% in ice– Only 0.001% in atmosphere

A Brief Global Perspective

• At Earth’s surface water can be found in liquid, solid or gaseous form.– Residence time varies from a few days to

thousands of years

• Amount of water for which all people, animals and plants compete is < 1%– Industrial production increases water use– Mass of water used 1000x total production of

minerals

Groundwater and Streams

• Groundwater refers to the water below the water table– Where saturated conditions exist– Locations where surface waters move into the

ground are recharge zones– Places where it flows or seeps out are discharge

zones (points)– Area where water seeps through pore spaces

known as vadose zone

Groundwater and Streams

• Aquifer is an underground zone from which groundwater can be obtained– When water is pumped from an aquifer forms a

cone of depression

Streams

• Effluent stream– Flow is maintained during the dry season by seepage

– Perennial stream

• Influent stream– Entirely above the water table and flows only in direct

response to precipitation

– Ephemeral stream

• A given stream can have reaches that are both or intermittent at varying times of year.

Interactions Between Surface Water and Groundwater

• Should be considered part of the same resource.

• Nearly all surface water environments have linkages w/ ground water– E.g. withdrawal of groundwater can lower

stream flow or lake levels– Pollution can spread from one source to the

other

Water Supply: A US Example

• Water supply at any point on the land surface depends on several factors in the hydrologic cycle,– including the rates of precipitation, evaporation,

transpiration– stream flow– subsurface flow

• Water budget– A model that balances the inputs, outputs, and storage

of water in a system.– Precipitation - evaporation = runoff

Water Supply: A US Example

• Amount of water vapor passing over the US every day ~ 152,000 million m3

– 10% falls as precipitation (66% of which is evaporated or transpired)

– Only 34% enters surface or groundwater

• In developing water budgets for water resources management it is useful to consider annual precipitation and runoff patterns.– Potential problems can be predicted in areas

where average runoff and precip low– Total storage of runoff not possible because of

evaporative losses

Precipitation and Runoff Patterns

Droughts

• Because there are large annual and regional variations in stream flow, even areas with high precipitation and runoff may suffer from droughts.

Groundwater Use and Problems

• ½ the people in the US use groundwater as a primary source of drinking water– 20% of water used– In many parts of the country withdrawal from

wells exceeds natural inflow• Overdraft• Nonrenewable resource• Problems include damage to river basins and land

subsidence

Desalination as a Water Source

• Seawater is 3.5% salt• Desalination- a technology to remove salt

from water– Must be reduces to 0.05% to be fresh water– Requires large amount of energy, tied to fuel

prices– Has place value- price increases quickly with

transport distance– Discharge may affect local salinity

Water Use

• Off-stream use– Refers to water removed from its source for use– May be returned to source after use– Or consumptive use- water enters tissues,

product or evaporates during use and not returned

Water Use

• In-stream use– The use of the river for navigation,

hydroelectric power, fish and wildlife habitats, and recreation.

– Multiple uses can create controversy

Water Use

• Another problem with off stream use is how much water can be removed w/o damaging the stream ecosystem.– E.g. Aral Sea. Diverting water for agriculture

caused sea to dry up– Surface area of sea reduces 90% in 50 years

Aral Sea

• Salt content of the water has increased

• Dust storms from dry salt flats

• Climate changes– Winters colder, summers warmer– Loss of fishing and decline of tourism

Transport of Water

• Ancient civilizations constructed canals and aqueducts to transport water – From distant river to where it is needed

• In modern civilization water moved from areas of abundant rain and snow fall to areas of high usage– E.g. California moves water from north to south– E.g. New York City has had to obtain water

from farther and farther away

Some Trends in Water Use

• Withdrawal of surface water far exceeds withdrawal of groundwater

• Since 1980 use has decreases and leveled off– Suggests improvement in water management

and conservation

Some Trends in Water Use

• Trends in freshwater withdrawals by water-use categories suggests that:– 1. The major uses of water are for irrigation and

the thermoelectric industry.– 2. Water use for irrigation increased from 1950-

1980. It decreased and leveled off from 1985-2000

• due to better irrigation efficiency, crop type and higher energy costs.

Some Trends in Water Use

– 3. Water use by thermoelectric industry decreased slightly in 1980, and stabilized in 1985.

• Due to reticulating water for cooling

– 4. Water for public and rural supplies continued to increase through the period from 1950 to 2000

• presumably related to the increase in human population.

Water Conservation

• The careful use and protection of water resources– Involves the quantity of water used and the

quality– Important component of sustainable water use– Expected that a number innovations will reduce

the total withdrawals

Agricultural Use

• Improved irrigation could reduce agricultural withdrawals by 20 to 30%– Tremendous savings because ag is the biggest

user

Agricultural Use

• Suggestions for conservation:– Price agricultural water to encourage

conservation – Use lined or covered canals that reduce seepage

and evaporation.– Use computer monitoring and schedule release

of water for maximum efficiency.– Integrate the use of surface water and

groundwater to more effectively use the total resource.

Agricultural Use

– Irrigate at times when evaporation is minimal, such as at night or in the early morning.

– Use improved irrigation systems, such as sprinklers or drip irrigation, that more effectively apply water to crops.

– Improve the soil to increase infiltration and minimize runoff.

– Encourage the development of crops that require less water or are more salt tolerant.

Domestic Use

• Accounts for about 10% of total national water withdrawals– But concentrated in urban areas– May pose major local problems

Domestic Use

• Water use can be substantially reduced by:– In semiarid regions, replace lawns with

decorative gravels and native plants.– Use more efficient bathroom fixtures.– Turn off water when not absolutely needed.– Flush the toilet only when really necessary.– Fix all leaks quickly.

Domestic Use

– Purchase dishwashers and washing machines that minimize water consumption.

– Take a long bath rather than a long shower.– Sweep sidewalks and driveways.– Using gray water to water vegetation. – Water lawns and plants at cool times to reduce

evaporation.

Domestic Use

– Use drip irrigation and place water-holding mulch around garden plants.

– Plant drought-resistant vegetation.– Learn how to read the water meter to monitor

for unobserved leaks and record your conservation successes.

– Use reclaimed water

Industry and Manufacturing Use

• Water conservation measures that can be taken by industry:– Using cooling towers that use little or no water– In-plant water treatment and recycling

Perception and Water Use

• Perception of water is based partly on its price and availability.– If water is abundant and inexpensive, we don’t

think much about it. – If water is scarce or expensive, it is another

matter.– E.g. people in Tucson pay about 100% more for

water than people in Phoenix.• Tucson residence use less water per person per day

Sustainability and Water Management

• From a water supply use and management perspective, sustainable water use defined as:– use of water resources by people in a way that

allows society to develop and flourish into an indefinite future

– W/o degrading the various components of the hydrologic cycle or the ecological systems that depend on it.

Sustainable Water Use

• General criteria:– Develop water resources in sufficient volume to

maintain human health and well-being.– Provide sufficient water resources to guarantee

the health and maintenance of ecosystems.– Ensure minimum standards of water quality for

the various users of water resources.

Sustainable Water Use

– Ensure that actions of humans do not damage or reduce long-term renewability of water resources.

– Promote the use of water-efficient technology and practice.

– Gradually eliminate water pricing policies that subsidize the inefficient use of water.

Groundwater Sustainability

• Sustainability involves a long term perspective– For groundwater even longer– Effects of pumping might not be seen

immediately– Long-term approach involves balancing

withdrawal with recharge

Water Management

• Management of water resources is a complex issue that will become more difficult as demand for water increases in the coming years.– Especially in areas like the Southwestern US

and other semi arid regions

Water Management

• Options for minimizing potential problems:– Alternating water supplies and managing

existing supplies better– Towing icebergs– As price goes up many innovative programs are

possible.

Variable-water-source approach

A Master Plan for Water Management

• New management philosophy is that surface water and groundwater are both subject to natural flux with time. – In wet years, there is plenty of surface water,

and the near-surface groundwater resources are replenished.

– During dry years, specific plans to supply water on an emergency basis must be in place and ready to use.

A Master Plan for Water Management

• Advanced planning may include– Drilling to wells that are presently isolated– Reuse of waste water– Develop surface water and use groundwater in

dry years– In wet years pump excess surface water

underground to recharge groundwater

Water Management and the Environment

• Often a good deal of controversy surrounds water development– Dams, canals, wetlands modification– Resolution of development involves input from

a variety of government and public groups

Wetlands

• Wetlands is a comprehensive term for landforms such as salt marshes, swamps, bogs, prairie potholes, and vernal pools.– Common feature is that they are wet at least

part of the year– Have a particular type of vegetation and soil

Wetlands

• Wetlands - defined as areas that are inundated by water or where the land is saturated to a depth of a few cm for at least a few days per year.

• Three major components used to determine the presence of wetlands are: – Hydrology

– Type of vegetation

– Type of soil.

Natural Service Functions of Wetlands

• Freshwater wetlands are a natural sponge for water.– Reducing flooding.

• Many freshwater wetlands are important as areas of groundwater recharge or discharge.

• Wetlands are one of the primary nursery grounds for fish, shellfish, aquatic birds, and other animals.

• Wetlands are natural filters that help purify water.

Natural Service Functions of Wetlands

• Wetlands are often highly productive and are places where many nutrients and chemicals are naturally cycled.

• Coastal wetlands provide a buffer for inland areas from storms and high waves.

• Wetlands are an important storage site for organic carbon.

• Wetlands are aesthetically pleasing to people.

Wetlands

• Freshwater wetlands are threatened in many areas.– Over the past 200 years > 50% of all wetlands

have disappeared, 90% of freshwater wetlands– Diked, drained or filled – SF bay estuary considered the most modified

by human activity

Wetlands

• Mississippi River delta includes major coastal wetlands– Historically maintained by flooding– Accretion processes counter natural subsidence– If accretion decreases area of open water

increases and wetland in reduced– Levees block sediments and costal wetlands are

being lost

Restoration of Wetlands

• Number of projects have attempted to restore wetlands.– In freshwater marshes recovery linked to

availability of water– Salt marshes more complex– EPA of 1969 states if wetlands destroyed by

development must be replaced elsewhere

Restoration of Wetlands

• Constructing wetlands to clean up ag waste– Natural ability to remove excess nutrients,

break down pollutants, and cleanse water.– In Florida, human-made wetlands designed to

intercept and hold nutrients so they don’t damage the Everglades.

Dams and the Environment

• Dams and their accompanying reservoirs generally are designed to be multifunctional structures. – Used for recreational activities – Generating electricity – Providing flood control– Ensuring a more stable water supply

• Often difficult to reconcile various uses at a given site.

Dams and the Environment

• The environmental effects of dams include the following:– Loss of land, cultural resources, and biological

resources in the reservoir area.– Larger, dams and reservoirs produce a potential

serious flood hazard should they fail– Storage behind the dam of sediment that would

otherwise move downstream to coastal areas.

Dams and the Environment

– Downstream changes in hydrology and in sediment transport that change the entire river environment and the organisms that live there.

– Fragmentation of ecosystems above and below a dam.

– Restrict movement upstream and downstream or organic material, nutrients and aquatic organisms.

Dams and the Environment

• Many people vehemently against building new dams.– But if present water use practices continue we

will need new dams.– Few acceptable sites for dams– Expensive to build and operate, many people

don’t want tax dollars spent on subsidized water.

Canals

• Water from upstream reservoirs may be routed downstream by way of natural water ways or canals and aqueducts.– Not hydrologically the same as creeks– Smooth, steep banks; water moves fast– Canals can spread and carry disease

• schistosomiasis

Removal of Dams

• Recent dam removals include – Edwards Dam in Maine – Marmot Dam in Oregon– After removal both river saw return of fish as

they migrated upstream

• Large fish runs transport nutrients upriver from ocean to forest ecosystems.

Removal of Dams

• Trapped sediment behind dams must be dealt with in dam removal.– If released quickly it could damage downstream

ecosystem and fill pools.

– Slower release minimizes damage.

– Matilija Dam in Ventura County cost $300,000 to build but 10 times that to remove.

• Removing dams is simple in concept but involves complex problems relating to sediment and water.

Channelization and the Environment

• Channelization of streams consists of straightening, deepening, widening, clearing, or lining existing stream channels.– Engineering technique that has been used to

control floods, improve drainage, control erosion, and improve navigation

Channelization and the Environment

• Adverse environmental effects, including the following:– Degradation of the stream’s hydrologic qualities;

• nearly all riffle flow, resulting in loss of important fish habitats.

– Removal of vegetation along the watercourse, which removes wildlife habitats and shading of the water.

– Downstream flooding where the channelized flow ends.– Damage or loss of wetlands.– Aesthetic degradation.

Channelization and the Environment

• Case study in problems w/ Channelization– Kissimme River in Florida– Meandering river turned into straight ditch– Failed to provide flood protection, damaged

wildlife habitat, water quality problems and aesthetic degradation.

– In 1990 efforts to restore river began.

The Colorado River: Water Resources Management and the Environment

• The history of the Colorado River emphasizes linkages among physical, biological, and social systems that are at the heart of environmental science.– Major river of the southwestern US– Ends in the Gulf of California

The Colorado River

• For its size has a modest flow but is one of the most regulated and controversial bodies of water in the world.– Total flow was apportioned among various

users in 1922– No water allowed for environmental purposes– Water rarely flows into the Gulf, all stored and

used upstream. • Damaged delta

The Colorado River

• Two largest reservoirs- Hoover Dam and Glen Canyon Dam– Stored about 80% of total in the basin– Represents a buffer of several years water

supply.– Changing hydrology of the river changed other

aspects• Rapids, sediment load, and vegetation

The Colorado River

• Record snowmelt in the Rocky Mountains in 1983 forced the release of water from Glen Canyon Dam– Three times normal but similar to spring floods

before the dam was built.– Beneficial to the river, highlighted the

importance of floods in maintaining a natural state.

The Colorado River

• As an experiment “flood” waters released in 1996– Two weeks at full flood– As a result 55 new sandbars formed and 75% of

existing sandbars increased in size, rejuvenated marshes and backwaters.

– Hailed a success; hoped that what was learned can help restore other river impacted by dams.

Global Water Shortage Linked to Food Supply

• Both surface water and groundwater are being stressed and depleted:– Groundwater in the United States, China, India,

Pakistan, Mexico, and many other countries is being mined

• used faster than it is being renewed

– Large bodies of water—for example, the Aral Sea—are drying up.

– Large rivers, including the Colorado in the US and the Yellow in China, do not deliver any water to the ocean in some seasons or years.

Global Water Shortage Linked to Food Supply

• As human population grows there is growing concern that there won’t be sufficient water to grow the food to feed 8-9 billion people.– Food shortage linked to water resources a real

possibility. – Water also linked to energy (fuel to pump) as

energy cost goes up so does cost of food.

Global Water Shortage Linked to Food Supply

• Solution– Control human population growth– Conserve and sustain water resources– Need to be proactive now before significant

food shortages develop.