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<br />. <br /> <br />. <br /> <br />. <br /> <br />Frequency Rainfall Distribution <br /> <br />The 24-hour storm was divided into IS-minute intervals and arranged according to the NRCS <br />rainfall distribution pattern Type 11 for Colorado. This pattern places the most intense period of <br />rainfall in the 49th IS-minute pattern. The HEC-I computer program arranged the 24-hour storm <br />precipitation over each watershed. <br /> <br />Channel Routing <br /> <br />The Albuquerque District used the Muskingum-Cunge procedure for channel routing of flood <br />hydrographs in the HEC-I computer model. Computer routing through channels employed eight- <br />point cross sections that are a composite of data from the USGS 7-1/2" quadrangle maps and field <br />measurements. The Albuquerque District considered an n-value from 0.025 to 0.05 appropriate for <br />the arroyo channels; the n-values ranged from 0.03 to 0.10 for overbank areas. <br /> <br />Two detention structures exist within the study area. A strip mine dam is located at the <br />downstream end of Subarea lOin the Coal Creek watershed, and Spring Dam is located at the <br />downstream end of Subarea MOC-I near Yorkville in the Oak Creek watershed. The elevation, <br />storage, and discharge data were obtained for each structure from local records and field <br />reconnaissance, and both structures are modeled within the HEC-I computer program. <br /> <br />STUDY RESULTS AND RECOMMENDATIONS <br /> <br />Tables 7 and 8 list the peak discharges generated by the HEC-I computer model at selected <br />concentration points on Coal Creek, Oak Creek, and contributing tributaries. In some cases, the <br />Colorado Water Conservation Board identified the need for additional concentration points beyond <br />the scope of the HEC-I model; therefore, an interpolation based on the weighted area of the subareas <br />was performed to obtain the corresponding discharges at the additional concentration points. The <br />interpolated concentration points listed in Tables 7 and 8 are marked with an asterisk. <br /> <br />The purchase and placement of operational stream and staff gages is strongly recommended. <br />Gages are needed to monitor flood depths as well as collect data for more accurate hydrologic and <br />hydraulic modeling. In addition to many other uses, gages are necessary to ensure flood <br />preparedness effectiveness. Hydrologic modeling results performed without calibration to many <br />years of stream gage data are potentially inaccurate. Until long-term stream gage data is available <br />for Oak Creek and Coal Creek and their tributaries, this report presents the best available hydrologic <br />analysis. <br /> <br />9 <br />