FLOOD09784

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Routing of Floods Through River Channels
• Date: 3/1/1960
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EM 111~:!-U08
1 Mauh 1960

H4. BASIC FLOOD.ROUTING PROCEDURE. The flood-routing equation (28) is solved con-
veniently for each routing' period by a simple graphical method using a sliding device on the R-D curve.
Plate No.6 illustrates graphically the satisfaction of equation (28) and also illustrates the sliding device
which is similar to a flood-routing device proposed by Steinqerg,1O An example of the application of
the slide and working curve in routing an inflow hydro graph for an initial working discharge of 31,000 cfs,
X=0.2, and ~t= 1.0 day is illustrated by the tabulation and descri'ption of procedure shown on the
same plate. The routing can be accomplished also by use of a specially constructed slide rule as shown
in plate No.7. The slide rule setting shown is for the first step of the routing illustrated by the tabulation
on plate No.6, The scaled distances on the upper scale, for any value of working discharge, correspond
to values of R=S(I-X)+0.5 D~t. The routing procedure also could be accomplished entirely by
computation methods.

H5. ROUTING PROCEDURE INVOLVING AN INDEPENDENT VARIABLE. An example of the
routing procedure for the case in which the independent variable is tributary inflow, which is assumed
to be known and independent of conditions on the main stream, is shown on plate No.8. The family
of R-D curves on plate No, 8 represents the effect of tributary discharges on main stream storage and
outflows, Although the routing could 'be accomplished by a graphical procedure, as described in para-
graph 3-04, with an added operation involved in interpolation to satisfy the conditions imposed by known
values of the tributary inflow at the beginning and el)d of each routing interval, the routing may be
accomplished just as readily by.c,omputation. The computation procedure is illustrated on plate No.8.

3-06. ROUTING PROCEDURE AT A MAJOR JUNCTION. As mentioned in paragraph 2-07, no
completely adequ.lte procedures have been developed for routing at a major junction when the flows in
two branches of a river mutually affect the flow conditions. A trial and error procedure described by
Gilcrest' is illustrated herein, Two sets of working curves, prepared as described in p8rugraph 3-03, arc
represented by the two eharts in plate No, 9. A computational procedure, rather than graphical proce-
dure, is recommended for such a routing and is illustrated on plate No.9. The table in this illustration
is used for recording the inflows, average inflows,working valu~s R, working discharges D, and ou.t-
flows 0 of each branch, the outflows being combined to yield the outflow from the reach. As is shown,
the trial-and-error procedure may require several trials for each routing pcriod to arrive at values of
outflow satisfying all the requirements.

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CHAPTER 4
RESERVOIR-LAG METHOD OF FLOOD ROUTING

4-0L . RESERVOIR-LAG METHOD. It is desirable ill some flood-routing operations to develop
quickly a hydrograph at a downstream station. The 'upstream hydro graph may he routed by t.he
reservoir-lag met.hod and then combined with runoff hydrographs developed from unit hydrographs
for the t.ributary area between stations. The reservoir-lag met.hod assumes the effects of all the vaUey
storage may be reproduced by a.lesser amount of reservoir-type storage if an adjustment is made for
travel time. The procedure consists, therefore, of routing the inflow hydrograph through some amount.
of reservoir-type storage by any of the many available methods and then translating this outflow hydro-
graph a time interval T, to the downstream station. If the coefficient method of reservoir-type rout.ing
is used, X is zero and the problem consists of selecting T, and K, giving a reasonable reproduct.ion of
hydro graphs at the dov."Ilstream station. The subscript s, for storage, is applied to K to differentiate
this coefficient from that of the basic coefficient method of routing, In this met.hod K. should approxi-
mately equal the coefficient K of the basic method minus the selected value T,. Reseryoir-Iag methods
are described by Meyer,' by Clark 1 and by F. F. Snyder in a discussion t.o Clark's paper. Until some
procedures become available to relate T, and K, with channel characteristics, the lag method will be
subject to the same limitations as the methods previously desCribed.

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