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<br />In divided flow, such as flow around islands, flow from the main <br />channel divides and follows two (or more) separate channels before <br />rejoining downstream. The division of discharge between the channels <br />must be such that the energy losses for each branch are equal. The <br />proper division of discharge to achieve equal energy loss in each <br />branch usually requires several trials. <br /> <br />In a spill, flow escapes from the main flow channel over some <br />terrain feature that acts as a hydraulic control section. The amount <br />of spill may be governed by several factors such as the geometry of <br />the control section at the point of the spill, and the water surface <br />elevation or energy grade elevation of the main channel at the control <br />section. Flow through the control section may be either nonnal depth <br />flow or weir flow. Spills may totally or partially return to the main <br />flow at a downstream location, or they may be completely lost. <br />Computation of spill discharges requires iteration, since the amount <br />of flow lost through the spill affects water surface elevations in the <br />main channel, which affect the amount of the spill. This may be done <br />manually or automatically using the Split Flow Option of the HEC-2 <br />computer program. <br /> <br />To account for changed conditions and to simplify the hydraulic <br />models, significant changes were made from the models used in the 1989 <br />SFH study. These changes and the configuration of the new hydraulic <br />model are given in detail below. The layout of the various hydraulic <br />models used in this study are shown on Figure 2. <br /> <br />The Cache La <br />restationed from <br />restationing was <br />the 1987 Flood <br /> <br />Poudre River channel in . thestu:ly reach <br />that used in the 1989 study. The origin of <br />taken from the stream station of Horsetooth Road <br />Insurance Study for Larimer County (Reference <br /> <br />was <br /> <br />the <br /> <br />in <br /> <br />4) . <br /> <br />5 <br /> <br />i . <br />