Civil Engineering Reference
In-Depth Information
the same. If the conservation program addresses only inside uses, this simply reduces
the quantity of water that flows to a wastewater treatment facility.
ALTERNATIVE SOURCES
Potential supply sources include:
Surface water (rivers, reservoirs, and lakes)
•
Conjunctive use of surface and groundwater
•
Imported water (canals, pipelines from distant sources)
•
Groundwater (wells or sub-irrigation)
•
Wastewater (agricultural returns, wastewater, power plants, gray water)
•
Stormwater
•
Conservation and demand management
•
Seawater and brackish water
•
The source selected is a key factor in determining the nature of the required puri-
fication, transmission, and storage facilities. The supply must provide a reliable quan-
tity of water for the long-term needs of the community, and preferably will have quality
that minimizes the amount of treatment required. A detailed evaluation of all alternative
sources should be made to compare yield, reliability, quality, treatment, collection, and
distribution costs. Some of the general advantages and disadvantages of the alternative
sources are discussed below.
Surface Water Supplies
The majority of the water served in the United States is derived from surface supplies,
which require treatment to make them suitable for use as public water supplies. It is
increasingly difficult, because of easier access and greater recreational use of streams,
lakes, and watersheds, and urban, agricultural, and industrial development, for unfil-
tered surface water from protected watersheds to meet the federal drinking water reg-
ulations.
The quality of lake water is not as consistent as the quality of groundwater, but is
more consistent than that of river water. The turbidity of river water may change
rapidly during a heavy rainstorm, or from runoff due to melting snows. Lake water
quality may change from wind-generated currents or when thermal stratification oc-
curs. If the lake freezes over, the dissolved oxygen may be depleted in portions of the
lake, with the result that the bottom deposits become anaerobic and many compounds
become soluble. Many lakes and reservoirs have substantial quantities of iron, and
occasionally manganese, in their bottom deposits. Normally they are of no particular
importance to water engineers because they are oxidized and precipitated, or chelated,
with organic compounds. However, when the bottom deposits in the relatively shallow
areas of the lake become suspended because of wind-induced currents, these deposits
can enter the intakes.
