Chapter 21

Water Supply, Use and Management

Water is Unique

• High heat capacity (climate)• Universal solvent (dissolves compounds)• High surface tension (physical and biological

process)• Solid lighter than liquid (impact biosphere)• Sunlight penetrates to various depths

(biosphere)

Groundwater and Streams• Groundwater

– Water found below the Earth’s surface, within the zone of saturation, below the water table

– Water table, recharge zones, discharge zones, aquifer, cone of depression

• Effluent Stream (perennial)– A type of stream where flow is maintained during the

dry season by groundwater seepage into the channel

• Influent Stream (epheremal)– A type of stream that is everywhere above the

groundwater table and flows in direct response to precipitation

Water Supply: A U.S. Example

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

water in a system.– precipitation=evapotranspiration and runoff– Defines the natural variability and availability of water

• Over 99% of the Earth’s water is unavailable or unsuitable for beneficial human use

• It is expected that the total water withdrawn from streams and groundwater in the U.S will decrease but the consumptive use will increase

Precipitation and Runoff

• Arid and Semiarid areas

• Runoff not stored• shortages• Droughts:

– large annual and regional variations in stream flow

• Groundwater Use and Problems:– nearly ½ US

population use GW as primary source for drinking water

– “overdraft”

Desalination as a Water Source

• Desalination: a technology to remove salt from water

• Increased cost• “Place value”• Environmental impacts

– discharge– damage ecosystems

Water Use

• Off-stream use:– water removed from it's source for use

• Consumptive use: – consumption by plants and animals or used in

industrial processes

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

power generation, fish and wildlife habitats and recreation (Example – Aral Sea)

Transport of Water

• Often moved long distances from areas of abundant rainfall and snow to areas of increased usage

• Example: New York City– Hudson River

• paved areas increase surface runoff to sea

– 1842: 1st large dam produced– 1900: 2nd dam produced

Water Conservation

- the careful use and protection of water resources

- Agricultural Use- Domestic Use- Industry and Manufacturing Use- Perception and Water Use

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

Sustainable Water Use

• General criteria includes:– develop water resources in sufficient volume– guarantee health and maintenance of ecosystems– ensure minimum standards of water quality for

various user of water resources– ensure actions of humans don't damage or reduce

long-term renewability of water resources– promote use of water-efficient technology– gradually eliminate water pricing policies that

subsidize inefficient use of water

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• Groundwater recharge• Nursery grounds• Natural filters• Highly productive and places where nutrients

and chemicals are recycled• Buffer zones• Storage site for organic carbon• Aesthetically pleasing

Dams and the Environment

• Proponents of:– recreation; generating electricity; flood control

• Environmental effects:– loss of land and biological resources; sediment

disruption; downstream changes in hydrology and sediment transport; fragmenting ecosystems

• Few accept sites for new dams• Economical effects:

– expensive to guild and operate

Removal of Dams

• Edwards Dam, August, Maine– fish migration

• Glines Canyon Dam, Washington (2010)– fish– beaches at river's

mouth

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.

Adverse environmental effects:

• Degradation of the stream's hydrologic qualities

• Removal of vegetation along the watercourse• Downstream flooding where the channelized

flow ends• Damage of loss of wetland• Aesthetic degradation

Flooding

• The most universal natural hazard in the world

• The frequency and severity are increased by urbanization

• Avoid building on floodplains• Most common control - Dams

Colorado River: Management and Environment

• Most regulated and controversial

• 7 U.S. states and Mexico (1922)– allocated no water

for environmental purposes

• Today:– ecosystems of lower

river and delta are damaged

– canals and aqueducts– “input” uncertainties

• winter precipitation; snow-melt; t-storms

– Hoover and Glen Canyon Dams

Global Water Shortage Linked to Food Supply

• Groundwater being mined (faster than renewed)– U.S., China, India, Pakistan and Mexico

• Large bodies of water dried up– Aral Sea

• Large rivers– waters to oceans

• Water demand tripled in past ½ century– agriculture