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<br />Tom Sm.th <br />Oak Cree,k Floodplain aad F100dway . Florence, Colorado <br />FEMA LMMP Contract No. EMW-90-C-3132 <br />Page 3 <br /> <br />p:ogram shows the t10w shifting from overbaak to overbaak even though that is not physically <br />possible based on the topography. This shifting also occurs when defIning the floodplain with <br />Ole model. The attached drawings show a version of the limits of the floodway :Jased on a single <br />HEC-2 model. <br /> <br />FJr COffiJarison, we: have defined the floodway using the thtee separate HEC-2 models. The <br />floodplaia 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 em the hydraulic analysis, if the floodplain is <br />encroached from thi: 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 ~.dditional spill into the right overbank model upstream of 3rd Street. Thus, <br />!t,e floodplain is encroached from the left aad right with the flow spills balanced unill a one foot <br />rise is reached in the left overbank aad right overban~:, 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 />s"paratec. into thtee sections: the right overbank, left ove::bank, and main channel. <br /> <br />Using ei:her of these two approaches, the floodway' would be significantly different than the <br />currently regulated floodway. We would appreciace your guidance, commen::s, and direction <br />re:garding the delineation of the floodplain aad flood way <br /> <br />We wou,d appreciate your comments on the hydraulic aaalysis aad the floodway delineation <br />bdore 'We proceed with finalization of the study. Due to the budget, we wiU not be able to <br />r"submit the study if the hydraulic analysis is not accepted initially; thus, it is important to <br />r(:ceive your comments in advaace so that the initial submittal will be acceptable to FEMA. <br /> <br />If you have any questions or require further informmion regarding the hydraulic analysis, do not <br />hesitate to call. <br /> <br />Sincerely, <br /> <br />LOVE & ASSOCIATES, INC. <br /> <br />-------. <br />Sheila A. B,~i.ssel, P,E, <br /> <br />Reviewed by <br /> <br />David ]., Love, P.E. <br /> <br />SAB/Dn_:jg <br />enclosun:s <br /> <br />cc: Dr. John Liou, P.E., P.L.S. - FEMA, Region VITI <br />