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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />14 <br /> <br />Decrease tn Depth <br /> <br />Figure 3 indicates that for a flow of 5,000 cfs, the water surface elevation wlll be <br /> <br />reduced about two feet if the entrance to the existing concrete arch railroad culvert <br /> <br /> <br />Is Improved as shown In FIgure 4. <br /> <br />With the Ketner Reservoir Improvements in place, the peak flow rate upstream of <br />the railroad 10 1,510 de. Uelng Figure 3, thlo flow rote tranolateo to a water sur- <br />face elevation of 5362.8, based on the Improved Inlet curve. ThIs is the same elev- <br />ation given by the the 1986 study results. All this means is that the HEC-2 model <br />formulation is not as accurate as the hand calculated depth-outflow relationship. <br />The HEC-2 model uses only the orIfice equation to estimate the upstream depth. <br /> <br />STORAGE VOLU"E UPSTREA" OF THE CI.S RAILROAD <br /> <br /> <br />There Is another improvement that should be made to the models used In the 1986 <br /> <br /> <br />FHAD study. The existing HEC-l model does not incorporate the storage volume that <br /> <br /> <br />presently exists upstream of the railroad culvert, whIch wlll tend to reduce the <br /> <br />depth of water upstream of the culvert. <br /> <br />If the lOa-year flood event had occurred at the time that the 1986 study was being <br /> <br /> <br />conducted, the water surface elevatIon upstream of the rallroad culvert would not <br /> <br /> <br />have been 5365.0, but would have been severa 1 feet lower. <br /> <br />This Is because a portion of the runoff volume would have been temporarily detained <br /> <br /> <br />upstream of the rallroad culvert. This water would be used to form the temporary <br />