FLOOD02698

• County: Statewide
• Basin: Statewide
• Title: Hydrologic Engineering Methods for Water Resources Development Volume 7
• Date: 2/1/1976
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

If the flood control space in the reservoir below the "normal full

.
pool elevation" (top of flood control pool) is relatively large in pro-
portion to the spillway design flood volume. the initial pool level

assumed in flood routing studies can have a major influence on estimates

of spillway discharge requirements and surcharge heights. Some considera-

tions in selecting initial stages are quoted below from Corps of Engineers

manuals.

As a general rule there is no reliable rational way of estimating

the initial reservoir level that is likely to prevail at the ueginning of
the spillway design flood, except when the storage space is so small as
to assure frequent filling. If a long period of streamflow records is
available, hypothetical reservoir regulation studies will provide some
index to reservoir elevation probabilities. but even these computed rela-
tions may be greatly altered in the future if changing conditions result
in substantial alterations in the reservoir regulation plan (as is often
the case). In addition, reallocations of flood control space to some
other use in the future may result in higher pool levels at the beginning
of the spillway design flood. In any case, an unusual sequence of floods
can result in filling all or a major portion of the flood control space
in a reservoir immediately before the beginning of the spillway design

flood.

In view of the uncertainties involved in estimating initial reser-
voir levels that might reasonably be expected to prevail at the beginning
of the spillway design flood, it has been common practice in studies pre-
pared by the Corps of Engineers to assume the reservoir is initially
filled to the "normal full pool level" if routing of representative major

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