Chapter 5 - Publications, US Army Corps of Engineers

EM 1110-2-1701
31 Dec 1985
SSR is its complexity. Because of the large amount
required to do daily studies for long time periods,
routings are based on weekly or monthly intervals.
of weekly or monthly average flows is satisfactory.
of computer time
most sequential
Generally, the use
Where using
weekly or mnthly intervals results in an energy estimate that is
substantially in error (see Section 5-6b(4)), SSR studies should be
made using daily flows for all or part of the period of analysis.
(3) The sequential streamflow routing method is described in
Sections 5-8 through 5-14.
d. flvbrid~ The hybrid method combines features of bth
the duration curve and SSR methods. Historical streamflow and
reservoir elevation data for the period of record are obtained either
from historical records or from an existing SSR analysis (such as an
operational study performed for evaluating existing project
functions). Power output is computed sequentially for each interval
in the period of record, and the resulting data is compiled into
duration curve format for further evaluation. The hybrid method was
developed primarily to investigate the addition of power at existing
projects where head varies independently of flow. This includes flood
control storage projects and projects with conservation storage
regulated for non-power purposes. The hybrid method is usually faster
than an SSR routing but slower than the flow-duration curve method.
The hybrid method is described in Section 5-15.
(1) ~ For very preliminary or screening studies, the
flow-duration method can be used for almost any project, although
energy estimates for projects with storage or where head varies
independently of flow must be viewed with caution. Following is a
discussion of the methods that would normally be used for the various
types of projects.
(2) aun-of-mer Pro~ For the typical run-of-river
project, where head is essentially fixed (high head projects) or where
head varies with discharge (low head projects), the flow-duration
method is generally the best choice. Where head varies independently
of flow, the hybrid method should be used. SSR can also be used, but
is usually not selected for single projects because the daily flow
analysis required to get accurate results for run-of-river projects is
usually too time consuming. However, it is often desirable to use SSR
to analyze run-of-river projects that are operated as a part of a
system which also includes storage projects. An alternative to the
latter would be to use streamflows from an existing system SSR study
as input for a flow-duration or hybrid analysis.
5-8