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<br />Flood Insurance Study Report Data <br />Flood Insurance Study - Florence, Colorado <br />Page 4 <br /> <br />If the Oak Creek floodplain were to be defined using one model which includes the main chaanel <br />and overbanks as opposed to thtee separate models, the HEC--2 program shifts the flow in the <br />overballks aad m.ain chaanel from one overbank to the other. From examining the topography in <br />the area, the flow caanot physically shift from one overbank to another; thus, a single model would <br />not realistically define the floodplain. <br /> <br />4.0 FLOODPLAIN MANAGEMENT APPLICATIONS <br /> <br />4.1 FlooQplain Boundaries (maps used) <br /> <br />1) City of Florence, Fremont County, Colorado; Scale 1" = 100'; Contour Interval <br />= 2' (Reference 1). <br /> <br />4.2 Floodwav.s, <br /> <br />Ploodway computations: Due to the complicated J100dplain hydraulics, a submittal package was <br />sent to FEMA's technical evaluation contractor (Michael Baker, Jr., Inc.) on August 3, 1992. This <br />submittal requested a determination on which floodway analysis method would be technically <br />acceptable for this project. No ruling was issued as to which method would be most acceptable. <br />Please refer to the correspondence section of this dDcument for the August 3, 1992 submittal <br />package. <br /> <br />On November 4, 1992 at the intermediate CCO meeting, the alternate floodways were presented to <br />the City. The City was reluctant to accept any of the alternate delineated floodways because the <br />new USACE hydrology decreased the 100-year discharge by more thaa 20 percent, however each <br />alternate floodway was larger thaa that published in the effective FIS. The City requested that II <br />map be developed showing Base Flood Elevations and areas of shallow :f1ooding so that II <br />deterrnination could be made on the floodwa.y based upon a cle:ar understanding of the depths of <br />flow in the 100-year floodplain. <br /> <br />The majority of the right aad left overbank flows caa Ix: classifie:d as shallow Hooding. Therefore, <br />the floodway was defined using only the main channel model with only the 100-year main chaanel <br />flows. The floodway was first estimated by using HEC-2 Encroachment Method 4 aad was then <br />smoothed by USirlg maaual encroachments (Method 1). <br />