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<br />4.4 <br /> <br />correspondi ng gri del ements. The enhanced reso'l Ilt ion provi ded by the 25-foot <br />square fan apex grid system eliminated the need for defining a discrete channel <br />within individual grid elements as was done in the overall fan grid system. <br />The potential effects of an obstruction to the channel at the fan apex were <br />invest igated. An obstructed channel flood :w;nario WitS silllul ated for the <br />without-berm condition. This was accomplished by preventing flow from occurring <br />toward the east or south through grid elements numbers 13 and 19. Essentially, <br />all flow was forced out of the channel and towards the eastern side of the apex <br />under the conditions simulated by this scenario. <br /> <br />4.2 Hydraulic ModelinQ Results <br />Maximum flood depths and velocities for 100~year return period water flood <br />and mud flow at the apex of the Cornet Creek alluvial fan were defined for each <br />of the two flood scenarios analyzed. In the following sections the results for <br />each flood scenario are summarized. <br /> <br />4.2_1 Water Flood <br />4.2_1.1 With-Berm Flood Scenario <br />Hydraulic modeling results at the alluvial fan apex for the water flo.od, <br />unobstructed channel, with-berm flood scenario are presented on Figures 4.3 and <br />4.4. In general, the water flood follows th(~ existing channel al ignment of <br />Cornet Creek. The existing berm contains most Df the flood discharge. Minor <br />overflow to the historic channel on the eastern half of the fan is observed in <br />this simulation. <br />Figure 4.3 delineates the maximum depth contours predicted. The maximum <br />depth along the channel within the apex is less than 4 feet. Shallow overflow <br />from the channel toward the east side of the fan is predicted. Maximum depths <br />are predicted to be less than I foot over most of the eastern half of the fan. <br />In a few grid elements on the eastern side of the fan depths of up to 4.5 feet <br />were pn;dicted due to the influence of local topographic depressions and <br />constrictions caused by structures. <br />Figure 4.4 illustrates the maximum velocity contours over the fan apex. <br />Velocities up to 30 feet per second (fps) are predicted for the existing channel. <br />Velocities less than 6 fps are predicted to occur in overbank areas and in the <br />historic channel on the eastern half of the fan. <br />