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<br />~ <br /> <br />one that involves water or sewage treatment plants. The SOD-year flood <br />event can be used to provide an upper level of safety. <br /> <br />2. Flood Elevation: Water surface elevations for the lO-year, 2S-year, <br />50-year, 100-year, and SOD-year floods, as determined at each cross- <br />section, may be found in Table 3 - "Flood Frequency-Elevation and <br />Discharge Data". The flood profile data (sheets 1P through 2SP) show a <br />graphical relationship of water surface elevations along the stream <br />reaches for the given frequencies, Selected typical cross-sections from <br />different reaches within the study area are shown on sheets 1X through <br />3X. <br /> <br />The flood profiles may be used in areas where controversy arises over the <br />100-year flood boundary shown on the Flood Plain Maps, Since the flood <br />profile exhibits give the water surface elevation at a specific point on <br />the reference line, the flood elevations can be surveyed on the ground to <br />alleviate any discrepancies on the base map, <br /> <br />3. Flooded Areas: Flood plain maps, sheets 1 through 7, show the <br />boundary of the 100-year flood plain. The flood plain boundary was <br />plotted using flood contour elevations and stationing from the plotted <br />flood profiles. This was done at elevation intervals compatible with the <br />map contour intervals. Flood contours are shown as wiggly lines at two- <br />foot intervals and perpendicular to the direction of flow. <br /> <br />B. HYDROLOGY <br />The watersheds that produce runoff to Four-Mile Creek in Canon City are <br />large in size (total area: 434 sq. miles). The Mud Gulch's watersheds <br />are much smaller (total area: 3.61 sq. miles). Slopes range from 3 <br />percent to 20 percent and greater, <br /> <br />The Four-Mile Creek flows southerly out of the pike National Forest; <br />whereas, the Mud Gulch flows southerly out of a small local drainage. <br />They both join the Arkansas River at Canon City. The NRCS TR-20 <br />(Computer Program for Project Formulation Hydrology) was used in <br />frequency flow calculations for Mud Gulch. Four-Mile Creek's discharges <br />were computed by regional analysis. <br /> <br />Snow Melt Analvsis - The effect of snow melt on runoffs was investigated, <br />The U.S. Army Corps of Engineers computer program HEC-l was used to test <br />the contribution snow melt made to peak discharges, Results show that <br />snow melt is not a contributing factor to runoff frequencies of 10-year <br />or greater, which is the primary concern of this study. This implies <br />that significant runoff is coming from rainfall events. As a <br />consequence, only rainfall generated runoff is considered in developing <br />peak discharge-frequency values included herein. <br /> <br />FreQUency Analvsis - Initially, frequency discharges for Four-Mile Creek <br />were determined by the Log Pearson Type III frequency analysis (Bulletin <br />17B) of the USGS stream gage data (the gage is located on Four-Mile <br />Creek, 3100 ft from the Arkansas River), but the results were inadequate <br />because the data record of Four-Mile watershed did not include sufficient <br />historical peaks. Further research in the archives of the Canon City <br />Historical Society, in an attempt to recover the missing records, did not <br />yield any result. <br /> <br />7 <br />