Chapter 21

Water Supply, Use and Management

Basic information• Water has a high capacity to absorb and store heat.

– Solar energy warms the oceans, stores huge amts of heat which transfers to the atmosphere producing weather

• Water is the universal solvent

• Water has a high surface tension

• Capillary Action of water

• Water is the only compound whose solid is less dense than its liquid form.– Ice floats

• Sunlight penetrates water to differing depths– Photosynthesis below the surface for both plants and

photosynthetic animals

General Stats• 97% of the earth’s water is in the oceans

• 2% is in the ice caps and glaciers

• 99% of Earth’s water in the natural state is unavailable or unsuitable for human use.

• Water is scarce in some parts of the world (ie: Middle East & N. Africa)

• U.S. Water Resource Council estimates that water use in the U.S. by 2020 may exceed surface water resources by 13%

Groundwater and Streams

Define the following terms:groundwater, water table, recharge

zone, discharge zone, vadose zone, aquifer, cone of depression, effluent stream, perennial stream, influent stream, ephemeral stream

Copy Figure 21.2 – Neat and Colorful : )Groundwater and Surface Water Flow System

(Page 436)

Water Supply• Depends on several factors in ;the

hydrologic cycle– Rates of precip., Evaporation, transpiration,

stream flow and subsurface flow

• Water Budget – the model used to balance inputs, outputs and storage and understand water supply

United States• US:Avg water usage=100gal/person/day

• Europe: 50gal/person/day

• SubSahara: 5gal/person/day

• Ex: Missouri River flows at 8.4 trill.gal/yr– It could handle 230 mill Americans

• This is not considering precip, runoff patterns,

• Evaporation and droughts

Surface-Groundwater Interactions

• Withdrawal of groundwater reduces stream flow, lowers lake levels and can change the quality of surface waters.

• Can change a effluent stream from perennial to an intermittent influent stream.

• Diversion of surface water may deplete groundwater resources. (This may increase conc. Of dissolved chemicals in the groundwater due to lack of dilution from infiltrated surface water.

Groundwater Use & Problems• Nearly 50% of people in US use groundwater as

their primary drinking source – this accounts for 20% of all water that is used.

• In many parts of US – groundwater withdrawal exceeds natural inflow – OVER-DRAFT

• It can then be thought of as a non-renewable resource – It is being MINED– Causes damage to river ecosystems and

subsidence

Ogallala Aquifer• High Plains Aquifer – South Dakota to

Texas

• 400,000 km2

• Tremendous amt. of groundwater, however in some areas it is being used at 20X the replacement rate

• Most severe area are ones in which irrigation was first used in the 1940’s

• WATER SHORTAGE !!!

Groundwater sustainability and management

• For groundwater : effective mgmt. for sustainability is long process.

• Withdrawal must be balanced with recharge

• Surface water is more easily managed:– Recharge is shorter

• As demand for water increases - so does MANAGEMENT

• To minimize water supply problems:– Locate alternative water supplies

– Manage existing supplies better

– Consideration to “out of the box” ideas• Towing icebergs

• Importing water

• Permanent conservation methods

• Use reclaimed water

Water Use• Off-stream use:

– water removed from it’s source for use and then returned (industrial processes)

• Consumptive use – an off-stream use: water is consumed by plants or animals

• Must balance the amt. of water withdrawn with the health of the ecosystem

• In-stream use: – the use of rivers for navigation, hydroelectric

power generation, fish and wildlife habitats and recreation• Each use requires different conditions

Wetlands• Areas that are inundated by water or where

the land is saturated to a depth of a few centimeters for at least a few days per year

• Wetlands serve a variety of functions that benefit ecosystems and people

Natural Functions of Wetlands• Natural sponge for water – During high river flow:

store water, reducing downstream flow. Following a flood: slowly release water

• Groundwater recharge• Primary nursing ground for many animals• Natural filter that helps purify water• Highly productive. Many nutrients and chemicals

are recycled• Buffer for inland areas• Storage site for organic matter

Wetlands

• Wetlands are threatened in many areas

• 50 - 60% of wetlands in the US have disappeared in the last 200 yrs.– Diking & draining for agriculture– Leveeing– Filling in for building

Louisiana Wetlandshttp://projects.propublica.org/louisiana

•

Dam impacts

Pro’s and Cons of Dams

•

Benefits of Dams 

Water storage  Flood control Floods affected the lives of 65 million people

between 1972 and 1996.Irrigation Dams contribute to 12-16% of world food

production.Electrical Power Generation 19% of the worlds total electricy supply, in 150

countries.  24 countries depend on dams for 90% of their power supply.  

Improved navigation Stabilized annual flowsImproved domestic water availability In 1990, over a billion people had access to less than

the minimum required of 50 litres per person per day.

Recreation Fishing cab be improved esp. in lakes but also in rivers with introduced species, leisure (e.g., boating on lakes, extended rafting season on the Colorado River)

Ecological Increased riparian vegetation if dam discharges are steady

 

Negative issues with DamsEcological disruption Fragmentation of 60% of the worlds rivers;

 Disruption of movement of species (e.g., destruction of up to 75% of riparian bird species on the Colorado) Destruction of riparian vegetation if discharges are irregular, e.g., peak-power of flood control types of operations; loss of beaches and marshes

Groundwater table effects  

Sedimentation behind dams  

Erosion downstream by sediment-starved waters  

Flucuation vs. steady releases Flucuations strand fish, reduce habitat for larval native fishes; deny access to tributaries;

Clogging of rivers Peak floods required to clear channel may be eliminated

 

Canals

• Water is routed by use of canals or aqueducts.

• Water is deceptively fast in main canals: hazard for swimming

• Unanticipated environmental problems:– Ex: Nile River, Egypt– Snails that carry: schistosomiasis (Snail Fever)

Channelization and the Environment

• Channelization: – An engineering technique that consists of

straightening, deepening, widening, clearing, or lining existing stream channels

– Purpose:• Control floods, improve drainage, etc.

Environmental Effects of Channelization

• Degradation of streams hydrology – loss of fish habitats

• Removal of vegetation – removes wildlife habitats

• Flooding downstream

• Damage or loss of wetlands – drains water

• Aesthetic degradation

Read & Summarize & Copy

• Read section 21.9, The Colorado River: Water Resources Management and the Environment

• Summarize in paragraph form or bullets

• Pages 453-458

• Copy Figure 21.19 (page 456)

Sustainable Water Use

• The use of water resources by people in a way that allows society to develop and flourish into an indefinite future without degrading the various components of the hydrologic cycle or the ecological systems that depend on it

How can water be sustained?• Develop water resources in sufficient volume to

maintain health and well being• Ensure minimum standards of water quality• Ensure that human actions do not damage the

long-term renewability• Promote water-efficient technology• Gradually eliminate water pricing policies that

subsidize the inefficient use of water

Water Conservation

• Review the water conservation methods on page 444-445 of your text.

• Write down 5 conservation methods you had not heard of…..

Desalination as a Water Source

• Desalination: a technology to remove salt from water

• Reduce salt to 0.05% from 3.5% (sea water)• Produce 5-8 million gallons per day• Increased cost – several times that of traditional

water supply• Salty water is discharged from plants – affecting

other ecosystems