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Peak discharge-drainage area relationships for the streams studied by detailed methods are shown in Table 4, "Summary of Discharges." 3.2 Hydraulic Analyses Analyses of the hydraulic characteristics of flooding from the sources studied were carried out to provide estimates of the elevations of floods of the selected recurrence intervals. Users should be aware that flood elevations shown on the FIRM represent rounded whole-foot elevations and may not exactly reflect the elevations shown on the Flood Profiles or in the Floodway Data tables in the PIS report. Flood elevations shown on the FIRM are primarily intended for flood insurance rating purposes. For construction and/or floodplain management purposes, users are cautioned to use the flood elevation data presented in this FIS in conjunction with the data shown on the FIRM. Water-surface elevations (WSELs) of floods of the selected recurrence intervals for all steams studied by detailed methods with the exception of the South Platte River, were computed using the USACE HEC-2 step-back water computer program (Reference 53). For the South Platte River, the WSELs of floods of the selected recurrence intervals were computed using the NRCS WSP2 computer program (Reference 54). These profiles and elevations were compared with historic floods, and the flood stages were then determined. City of Arvada The basis of the hydraulic analysis utilized is from the Major Drainageway Planning Report and from the UDFCD plans entitled "Ralston Creek Flood Hazard Area Delineation Study" (Reference 55). City of Edgewater The drainageway between Depew Street and Sheridan Boulevard was studied to provide estimates of the elevation of the lOO-year flood. For the HEC-2 program, topographic data were taken from a topographic map with 1.0 foot contour intervals prepared by Greiner Engineering Sciences, Inc. and checked to ensure conformance with mapping standards (Reference 56). Field surveying was also conducted by Wright Water Engineers. From this topographic map, a total of 15 cross sections were digitized and used as data for the computer analysis. An analysis of flow in the stormwater channel between Ingalls Street and Depew Street is based on the Manning's Equation to estimate normal depth. A step-backwater analysis was used where necessary to reflect obstructions, such as culverts. Where bends occur in the channel, superelevation of the flow has been calculated and included in the WSELs. Culverts have been analyzed to determine the control condition, inlet or outlet control. Because of irregular and poorly defined channels for street and overland flows in the area upstream on Ingalls Street and 20th A venue, the resulting 1 DO-year floodplain for this area is not as well defined. Updated aerial mapping was used to determine "channel" cross sections and WSELs in this area. 30