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through the various channel reaches. routing was chosen using typical storage/discharge relationships. The Modified Puls Method for channel stream c ross-secti ons for deve 1 opi ng norma 1 depth Hydraulic runs were completed for the 10-year, 50-year, 100-year, and SOD-year events for streams analyzed in the Flood Insurance Study. Hydraulic runs were completed for the 2-year, 5-year, 10-year, 50-year and 100-year events for stream analyzed in this study. However, only the 10-year and 100-year water surface profiles are reported in this study. The only major transbasin diversion modelled in the Flood Insurance Studies was the Broadway diversion of Fourmile to Wonderland. In this diversion, 400 cfs was taken from Fourmile Creek and added to Wonderland. The Fourmile diSCharges were not reduced since improvements may eliminate the diversion in the future. Irrigation ditches cross each of the drainageways at various locations. In many cases, siphons, aqueducts, or pipes are used at the crossings. However, Goose, Elmer's Twomile, and Bluebell Canyon Creeks discharge directly into ditches. For this hydrologic analysis, it was assumed that the ditches would be full to capacity while crossing the basins, and storm runoff was therefore assumed to flow directly across the irrigation ditches. In addition, a floodway was computed for all streams under study. This floodway is based on the City of Boulder criteria allowing for no more than a one-half foot rise in the water surface elevation with encroachment during the 100-year event, and no encroachment in areas where velocities exceed 2 feet per second or depths exceed 2 feet. Table 6 presents a summary of all peak discharge results. the streams are shown in Figures 6 through 11. Typical shown in Fi gure 12. Discharge profiles fOr flood hyd rographs are The floodplains for the 100-year event were then delineated on the topographic mapping using the computed water surface profile. The floodplains and water surface profiles are presented on Sheets 1 through 31. Hydraulics Culvert or bridge blockage was considered at each crossing structure. The degree of blockage was determined by field inspection by the City of Boulder Staff. Table 7 presents the estimate of blockage at major crossings for the drainageways included in this study. The water surface profiles for all streams under study were computed using the HEC-2 computer model (Reference 8). Cross section information for streams completed as part of the Flood Insurance Studies was obtained using photogrammetric techniques, by utilizing digitized sections from the aerial photography used to prepare the two foot contour mapping. Cross sections fOr streams analyzed under this study were taken directly from the two foot contour mapping. flOODPLAIN DESCRIPTIONS The extent of flooding in overbank areas varies throughout each study reach. A description of the 100-year flOOdplain for each of the eleven streams follows. Bear Canyon Creek Geometric measurements and invert elevations for bridge and culvert crossings were obtained in the field as required. Photographs were taken of each crossing and a sketch of the crossing was prepared showing appropriate dimensions. This material is on file as back up information to the project. During these field investigations, estimates of roughness coefficients, i.e. Mannings "n" values, were also noted. The upstream portion of Bear Canyon Creek experiences shallow flooding. From the upstream study limit to Lehigh Street, the floodplain ranges in width from 50 to 150 feet. Although the area is fairly well developed, flood damage to properties is light, as the floodplain is narrow and buildings are usually not located close to the stream channel. Three buildings are affected by the floodplain within this section of the creek. 13