Environmental Engineering Reference
In-Depth Information
TAble 4.2
Water Balance in the United States (Billion Gallons per Day)
Precipitation 4250
Evaporation and transpiration 3000
Runoff 1250
Withdrawal 410
Irrigation 240
Industry (principally utility cooling) 130
Municipal 30
Consumed (principally irrigation loss) 90
Returned to streams 220
Sources:
Wolman, A.,
Water Resources: A Report to the Committee on
Natural Resources
, NAS-NRC Publ. No. 1000-B, National
Research Council, National Academy of Sciences,
Washington, DC, 1962. USGS,
Water Use Trends for 2000
,
U.S. Geological Survey, Washington, DC, 2000 (
www.
Specific sources of surface water include
• Rivers
• Streams
• Lakes
• Impoundments (manmade lakes made by damming a river or
stream)
• Very shallow wells that receive input via precipitation
• Springs affected by precipitation (low or quantity directly depen-
dent upon precipitation)
• Rain catchments (drainage basins)
• Tundra ponds or muskegs (peat bogs)
Surface water has advantages as a source of potable water. Surface water
sources are usually easy to locate; unlike groundwater, finding surface water
does not require a geologist or hydrologist. Normally, surface water is not
tainted with minerals precipitated from the Earth's strata. Ease of discovery
aside, surface water also presents some disadvantages. Surface water sources
are easily contaminated with microorganisms that can cause waterborne
diseases and are polluted by chemicals that enter from surrounding runoff
and upstream discharges. Water rights can also present problems.
As we have said, most surface water is the result of surface runoff. The
amount and flow rate of this surface water are highly variable for two
main reasons: (1) human interference, and (2) natural conditions. In some
cases, surface water quickly runs off land surfaces. From a water resources
