Environmental Engineering Reference
In-Depth Information
electricity with steam-driven turbine generators. In order to cool water using a condenser, water
may be withdrawn from a source, circulated through heat exchangers, and then returned to a surface
waterbody (once-through cooling). This practice results in an increase in the release temperature
over the inluent temperature, and this temperature increase may often be detrimental to some sys-
tems. In the 2003 temperature TMDL completed by the Georgia Environmental Protection Division
(Georgia EPD 2003) for the Chattahoochee River, it was determined that once-through cooling
operations resulted in violations of Georgia's temperature standard, with the resulting recommen-
dation to remove the power plant heat loads from the river. In many areas, once-through cooling is
being replaced by evaporating a portion of the cooling tower water and transferring the resultant
heat into the air, which is a consumptive use.
The licensing or permitting of abstractions by state regulatory agencies is the primary method
of control. However, the form and administration of these regulations differ widely. In part, this
may be due to differences in the fundamental water rights resource doctrines adapted by states or
regions, such as the doctrine of prior appropriation, also known as the “Colorado doctrine” of water
law, common in western states, based on “irst in time, irst in right” as opposed to the riparian
water rights in most eastern states. In the riparian rights system, based on English common law,
water is allocated based on ownership of the land about its source.
One common dificulty in the regulation of lows, and the licensing or permitting of abstractions,
is determining how much water there is to allocate. In order to manage water systems it is usually
necessary to establish a water balance or water budget to determine all water sources and sinks.
Instream lows are commonly measured in the United States by agencies such as the U.S. Geological
Survey. However, information is often not available for sources and sinks due to tributary sources,
precipitation and iniltration, nonpoint source runoff, point sources and abstractions, evapotranspi-
ration, or exchanges of surface and groundwater, all of which are components of the total low and
may impact the effective management of a river or a stream. An additional complication is that the
lows, along with the sources and sinks, vary with time at a variety of timescales. Healy et al. (2007)
provide additional information and guidance on developing a water budget.
An additional complication is indirect abstractions due to groundwater uses. The pumping of
groundwater, such as for municipal and agricultural uses, results in a depression in the original
water table of the aquifer, as illustrated in Figure 3.30.
The area or zone of inluence depends on the rate of pumping and the characteristics of the
aquifer, but it can extend over many miles and the depth of the depression can be many feet. The
Area of influence
Well
Cone of depression
Aquifer
Groundwater flow
FIGURE 3.30 Cone of depression of groundwater. (From Cornell Cooperative Extension, Cornell University,
1988. With permission.)
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