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<br />The first equation above is based upon the effective length of an <br />incremental volume, namely, the distance by which the <br />mean end area is multiplied to obtain the original volume. Equation 2 shows it is <br />possible to estimate the subsequent volume having the same effective length as the <br />original volume. In Equation 3, the effective length cancels out and the constant <br />factor (also referred to as "ratio") obtained is simply a ratio of the original volume to <br />the sum of the original end areas. Substituting the factor f for this ratio, Equation 4 <br />becomes the simplified formula for computing volumes. Once determined for a unit, <br />this factor is assumed constant and is applied in computations for all future <br />sedimentation surveys. <br /> <br />Capacity computations require 3 or 4 (depending upon whether or notthe <br />analysis being performed is the initial capacity computation for the reservoir) <br />successive computer programs, all developed in the Omaha District. The output from <br />each program serves as an input file to the program that follows. <br /> <br />The first program uses digitized/planimetered surface areas at given <br />contour elevations for each segment of the reservoir to compute original segment ' <br />volumes at incremental elevations (Vo in the above equations). These volumes are <br />combined with original cross section end areas (A' 0 and A"o above), computed from <br />another program, to calculate subsegment ratios (the constant factor f in Equations <br />3 and 4) using a third program. This surface area-to-volume-to-ratio procedure needs' <br />to be run only for the original capacity computations of each reservoir since the <br />computed ratios are assumed to remain constant for all subsequent resurveys. The <br />remaining program i.n the series combines reservoir subsegment and segment volumes <br />to compute total reservoir volume versus elevation. For all future resurveys the <br />reservoir storage-elevation relationship is updated (to account for sediment deposition) <br />by multiplying the new segment end areas by the original constant factor (Equation <br />4). <br /> <br />3. ELEVATION-OUTFLOW RELATIONSHIP. <br /> <br />Elevation outflow relationships should be developed for each control <br />structure and composited for use in the Modified Puis routing method. These include <br />the low level outlet, spillway and flow over the top of dam if the outlet works and <br />spillway capacity are inadequate to pass the inflow flood. Simplified procedures for <br />developing elevation discharge rating curves for each control structure are discussed <br />in the following paragraphs. <br /> <br />7-76 <br /> <br />. <br />