Introduction - Hydro-Environmental Analysis: Freshwater Environments - page 7

by Figure 1.4, consumptive demands vary widely across the United States, partly as a function of
water-use patterns, and they also vary widely in comparison with the available supply. For example,
in the eastern United States, consumptive use is a relatively small fraction of the available supply,
while water use in the arid West often approaches or exceeds the available supply.
The demands also vary between speciic water uses, including the following:

• Livestock

• Irrigation

• Domestic

• Public water supply

• Thermoelectric cooling

• Mining

• Aquaculture

• Industrial uses

As illustrated in Figure 1.5, of these uses in 2005, thermoelectric power (49%), irrigation (31%),
public water supply (11%), and industrial demands (4%) combined to make up 95% of the total U.S.
water demands. In 2000, irrigation in California accounted for 20% of all irrigation in the United
States (Hutson et al. 2000).
The demands also vary between surface water and groundwater supplies. Of the total demands,
approximately 79% were surface water withdrawals in 2000. Of the demands for groundwater,
68% were for irrigation (Hutson et al. 2000). Total irrigation withdrawals in the United States are
illustrated by Figure 1.6.
The total demands increased from approximately 180 to 408 billion gallons per day (681 billion
to 1.5 trillion L day -1 ) during the period between 1950 and 2000 (Hutson et al. 2000). Changes also
occurred in the distribution of these demands during that period, as illustrated by changes in the
distribution of irrigated lands (Figure 1.7).
Total demands have also changed with the growing U.S. population, as illustrated by a compari-
son of changes in the population and public supply withdrawals between 1950 and 2000 (Figure 1.8).

1.3 PATTERNS IN WATER MANAGEMENT IN THE UNITED STATES
The earth's total water supply is large and it is usually the distribution of water in time and space
that is the problem. The quantity and quality of water are rarely “just right” at any speciic time or
location. Water is commonly in excess or in short supply and/or its quality limits or precludes its use.
The pattern of water management and use has varied with time in the United States. Historic fed-
eral laws focused on protecting waters for navigation and other human usages, while state and local
laws focused on “who owns the water.” Conventional water management in the United States has
focused on the control or manipulation of water supplies. Traditional management has included the
construction of dams and levees to control excess water; the construction of dams to contain water
for water supply, power generation, and other uses; and the construction of conduits of various kinds
to redistribute water or provide for commercial uses. Often, traditional water resource engineering
projects have also focused on design to withstand the impacts of excess water.
Often, historical water management projects or practices did not take into full consideration the
environmental impact of those projects or practices. One consequence is that many of the past gen-
erations' water management solutions have become today's or the future's water management prob-
lems. For example, many engineering projects today are attempting to reverse the impact of past
engineering projects. Examples include projects for reducing or removing low regulation structures
such as dams and canals; removing legacy contaminates (DDT, dioxins, PCBs, etc.) from waterbod-
ies; restoring the natural low and biota of waterbodies, which were impacted by past projects; and
mitigating the impact of excess use of groundwater, which has resulted in depletion and contamina-
tion of aquifers, land subsidence, and decreased lows in surface waters.