CEMP-E
EI 11C103
1 March 1997
CHAPTER 2
TYPES OF STORAGE
1. GENERAL. Required storage capacity at military installations is met by use of elevated or ground
storage. Elevated storage, feeds the water distribution system by gravity flow. Storage which must be
pumped into the system is generally in ground storage tanks. Clearwell storage, which is usually part of a
water treatment plant, is not included in computing storage unless sufficient firm pumping capacity is
provided to assure that the storage can be utilized under emergency conditions, and then only to the extent
of storage in excess of the 24-hour requirements of the treatment plant. Clearwell storage is used to supply
peak water demand rates in excess of the production rate, and to provide a reservoir for plant use, filter
backwash supply, and water supply to the system for short periods when plant production is stopped
because of failure or replacement of some component or unit of treatment.
2. GROUND STORAGE.
a. General. Ground storage is usually located remote from the treatment plant but within the distribution
system. Ground storage is used to reduce treatment plant peak production rates and also as a source of
supply for pumping to a higher pressure level. Such storage for pumping is common in distribution systems
covering a large area, because the outlying service areas are beyond the range of the primary pumping
facilities.
b. Type. Ground storage tanks or reservoirs, below ground, partially below ground, or constructed
above ground level in the distribution system, may be accompanied by pump stations if not built at
elevations providing the required system pressure by gravity. However, if the terrain permits, this design
location of ground tanks at elevation sufficient for gravity flow is preferred. Reservoirs are the most
common type of water storage structure and are categorized as being ground supported with a flat bottom
and a height no greater than its diameter. Concrete reservoirs are generally built no deeper than 6-7.5
meters (20-25 feet) below ground surface. If rock is present, it is usually economical to construct the
storage facility above the rock level. In a single pressure level systems, ground storage tanks should be
located in the areas having the lowest system pressures during periods of high water use. In multiple
pressure level systems, ground storage tanks are usually located at the interface between pressure zones
with water from the lower pressure zones filling the tanks and being passed to higher pressure zones
through adjacent pump stations.
3. ELEVATED STORAGE
a. General. Elevated storage is provided within distribution system to supply peak demand rates and
equalize system pressures. In general, elevated storage is more effective and economical than ground
storage because of the reduced pumping requirements, and the storage can also serve as a source of
emergency supply
since system pressure requirements can still be met temporarily when pumps are out of service.
b. Type. The most common types of elevated storage are elevated steel tanks and standpipes. An
example of a conventional elevated steel tank is given in figure 2-1. In recent years, elevated tanks
supported by single pedestals, such as shown in figure 2-2, have been constructed where aesthetic
considerations are an important part of the design process. (See American Water Works Association
AWWA D100 (appendix A).)
c. Standpipe. A standpipe is a tall cylindrical tank normally constructed of steel or reinforced concrete.
They are ground supported, flat bottom, cylindrical tanks with heights greater than their diameter. Only the
portion of the storage volume of a standpipe that meets the requirements of paragraph d below is
considered useful storage for pressure equalization purposes. The lower portion of the storage acts to
2-1
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