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<br />Tom Smith <br />Oak Creek Floodplain and Floodway - Florence, Colorado <br />FEMA LMMP Contract No. EMW-90-C-3132 <br />Page 3 <br /> <br />program shows the flow shifting from overbank to overbank even though that is not physically <br />possible based on the topography. This shifting also occurs when defining the floodplain with <br />one model. The attached drawings show a version of the limits of the floodway based on a single <br />HEC-2 model. <br /> <br />For comparison, we have defined the floodway using the three separate HEC-2 models. The <br />floodplain is encroached from the outside limits (i.e. from the left in the left overbank model and <br />from the right in the right overbank model). Based on the hydraulic analysis, if the floodplain is <br />encroached from the left, additional flow will spill from the left overbank model into the main <br />channel model. If the floodplain is encroached from the right, additional flow will spill from the <br />right overbank model into the main channel model. Also, increasing the flow in the main <br />channel will cause additional spill into the right overbank model upstream of 3rd Street Thus, <br />the floodplain is encroached from the left and right with the flow spills balanced until a one foot <br />rise is reached in the left overbank and right overbank, or main channel model. The revised flow <br />splits are shown on Figure 2. A draft version of the limits of the flood way based on this <br />approach are outlined on the attached drawings. Using this approach, the floodway table will be <br />separated into three sections: the right overbank, left overbank, and main channel. <br /> <br />Using either of these two approaches, the floodway would be significantly different than the <br />currently regulated floodway. We would appreciate your guidance, comments, and direction <br />regarding the delineation of the floodplain and floodway. <br /> <br />We would appreciate your comments on the hydraulic analysis and the floodway delineation <br />before we proceed with finalization of the study. Due to the budget, we will not be able to <br />resubmit the study if the hydraulic analysis is not accepted initially; thus, it is important to <br />receive your comments in advance so that the initial submittal will be acceptable to FEMA. <br /> <br />If you have any questions or require further information regarding the hydraulic analysis, do not <br />hesitate to call. <br /> <br />Sincerely, <br /> <br />LOVE & ASSOCIATES, INe. <br /> <br />Sheila A. Beissel, P.E. <br /> <br />Reviewed by <br /> <br />David J. Love, P.E. <br /> <br />SAB/DJL:jg <br />enclosures <br /> <br />cc: Dr. John Liou, P.E., P.L.S. - FEMA, Region VIII <br /> <br />/ <br /> <br />