Civil Engineering Reference
In-Depth Information
Adequacy of supply
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Channel changes, shoal and bar formation, and silting
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Availability of water to intake ports at all river stages and at all stream flows
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Accessibility to intake for maintenance at all river stages and at all seasons
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Location of the intake with respect to the city to be served
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Navigation requirements
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100-year flood level
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Need for storage dam, either in-channel or off-channel, and detention provided
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Foundation conditions
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Structural stability and safety of dams
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Protection from rapid currents, wind, ice, boats, floating material, waves, and
bottom sediment
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Water-depth, and ability to draw water from different depths
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Distance from service roads and a source of electric power
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Protection from vandalism
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Even in the absence of upstream discharges of municipal wastewater, there are
public health factors to be considered in intake location. Storm runoff that makes up
stream flow may contain almost any of the contaminants included in drinking water
standards. The concentrations of these substances can be restricted by proper location
and operation of intakes. The protection of raw water supplies is discussed elsewhere
in this chapter under ''Watershed Management.''
In making case-by-case judgments of the minimum distance between the points of
wastewater discharge and water supply intake, some of the items to be considered
include:
Stream flow and quality
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Quantity and quality of treated wastewater to be discharged
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Potential water quality improvement by stream purification processes, including
dilution, reaeration, adsorption, sedimentation, and biological die-off
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Pollution from sources other than municipal wastewater, including industries,
storm runoff, agriculture, and miscellaneous nonpoint sources
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Raw water quality at intake under most adverse conditions
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Water treatment provided
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Relationship between wastewater effluent characteristics and safe drinking water
requirements
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Risk assessment of intake siting options
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PRETREATMENT OF SURFACE WATER SUPPLIES
Surface water supplies, whether from rivers or reservoirs, often contain impurities or
characteristics that may best be removed prior to conventional water treatment. Res-
ervoirs contain algae and other microscopic organisms that can cause taste and odor
problems. Anaerobic conditions may develop near the bottom of reservoirs causing
