Environmental Engineering Reference
In-Depth Information
8.5
Environmental Conservation
8.5.1
Water Conservation and Flood Control
Resources and Hazards
Aspects
Groundwater is an important natural resource, and, especially in areas of low rainfall, its
availability is often critical to the growth and even survival of cities. Overextraction results
in a number of detrimental effects:
The water table declines and the cost of extraction increases, and often the qual-
ity decreases as well so that treatment is required. In some cases, it is conceivable
that groundwater could cease to be a viable source of water supply.
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In areas with marginal rainfalls, a desert environment could be created where
one did not previously exist, thereby degrading the ecosystem in general, and
increasing the incidence of erosion.
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Land subsidence has occurred in many areas (see
Section 10.2),
which results in
increased flooding incidence as well as surface faulting.
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Along seacoasts, groundwater pollution is caused by saltwater intrusion.
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Other aspects of conservation related to water are:
Pollution resulting from surface and subsurface disposal of liquid and solid
wastes
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Increased erosion and siltation resulting from uncontrolled land development
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Increased flooding incidence resulting from overdevelopment of floodplains
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Salinization and destruction of croplands resulting from irrigation
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Environmental Planning
Conservation of water and protection against floods and other undesirable effects such as
erosion require comprehensive regional environmental planning.
Case Study: Pima County, Arizona
Introduction
A study of the impact of urbanization on the natural environment in the semiarid climate
of Tucson, Arizona, and the adjacent area of Canada del Oro was made to determine
the measures that could be taken to minimize the impact and protect the public (Hunt,
1974).
Background
The city of Tucson is situated in a basin at an elevation of about 2000 ft above sea level,
bounded on three sides by mountains rising to as high as 10,000 ft above sea level. In the
valley, up to 2000 ft of sediments have filled over the basement rock.
One hundred years ago, according to reports, water was plentiful in the basin, lush
grass covered the valley floor, and water flowed all year in the Santa Cruz River. Even in
1984, the average precipitation in the basin was 12 in. (300 mm) and as much as 30 in.
(750 mm) in the nearby mountains. However, the Santa Cruz winds its way through the
