Civil Engineering Reference
In-Depth Information
CHAPTER 27
Storage
INTRODUCTION
Finished-water storage is an essential element serving several functions in any large
public water supply system.
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It is primarily used to provide water to meet peak daily
and emergency water system demands. Using storage to meet peak demands through-
out the day reduces the required sizes and design capacities of other water system
elements, such as sources of supply, treatment plants, pump stations, and transmission
mains. Storage also helps to maintain uniform pressures throughout the service area.
Finally, storage provides a reserve supply that can be drawn on during emergencies
such as power outages, fires, and equipment failures. Storage volume requirements for
these functions are typically classified as operating, equalizing, fire and / or emergency,
and dead storage volumes. These individual volume components are considered in
combination to determine the total volume of storage capacity that is required for any
system.
CAPACITY
General
In all but the very smallest water service areas, the costs for constructing and operating
water storage facilities are partially or totally offset by reduced costs for building and/
or reductions in operating costs for other parts of the water system. Many state reg-
ulatory agencies have requirements for minimum distribution storage volumes.
Adequate storage volumes also can serve to improve local fire insurance ratings and
reduce fire insurance premiums. Capacity requirements of storage tanks comprise sev-
eral component volumes:
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Operating Storage.
The volume of storage between the ''pump on'' and ''pump
off'' levels in the tank is normally being used when the sources of supply pumps to
the storage tank are off. The pumps supplying the tank will typically be started when
the tank has drained to ''pump on'' level sensor.
•
Equalizing Storage.
This storage component is used when the source pump ca-
pacity is less than the peak system demands. The storage is needed so that water
production facilities can operate at a relatively constant rate. The volume is determined
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