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<br />.., <br /> <br />. <br /> <br />\.~ <br /> <br />~roloqie Consi~rAtlons. <br />A common practice for hv"raulic analysis i.s to use the fl~ hy<'lroqrllph <br />ceak discharqe valll"s for the backwat..r calculations and iqnore the faet that in <br />most ea9~S t~ peaks of the hY"roqraphs ~ not occur at th.. same time. In many <br />cases the effp.ct of this assumption on the calculat..~ water surfaee profile is <br />well witllin t~ aceuracy for profile ealculfttions. Most RBC-2 mo"els are <br />assemblP-rl in this mann..r. Wh",n it com..s to ~ solit flow an~lYsis, the effect of <br />using t~ peak "ischapoes as steady flow shoul" not ~ iqnore~. <br />The REC-2 solit flow I'lption, as a default, reduces all "ischarge values <br />downstream from a snlit flow r..acll by the calculat"," split flow values. For <br />examole, if 1000 cfs is lost at the headwaters of a stream, the Drogram will <br />reduc.. a~l t~ ~ischarqes bv 1000 cfs all tile way <'lownstream to the start of <br />monel I'lr to the section n~r where the us..r has speeifi..d tltat it returns. <br />Tlte only way to "etermine the yaliditv of re<'lucino tile "l.scharqes in this manner <br />is to look at the entire l1ydroqraph, to see how tile loss from the split flow <br />effects the Deak M~charqes tlownstre8lll. It may be that the peak <'lischarge <br />further downstream will onlY he partially ..ffeete" by tile split flow loss. '!'he <br />peak discharges tlownstr..am may be more deoendent on the timing of tributapy and <br />local inflows. <br />To illustrate this prolllem, the following simple example is presentpd. As <br />shown on Fiqure 4, the l~er Main Stem has a solit fow reach 1ust upstream frnm <br /> <br /> <br />the confluence with Tributary No 1. Fiqure 5 is a plot of tile original <br /> <br />hydroqraphs for the Upoer Main Stem, Tributary No l, an" their cnmhinl'!!<'l <br /> <br /> <br />bydrographs on tile Lower Main Stem. If flows that exceed 3000 efs on the UPper <br /> <br /> <br />Main Stem are InRt, t~en the modifie" hydroqraphs plott.... on Figure 6 occur. <br /> <br />15 <br /> <br />~ <br />