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<br />. <br /> <br />.) <br /> <br />. <br /> <br />DRAFT SOUTH PLAITE RIVER TRIBUTARIES HYDROLOGY REPORT <br /> <br />FOUR MILE CREEK, HORSE CREEK, WEST CREEK, AND TROUT CREEK <br /> <br />As a result, the long-term sub-basiri hydrologic conditions were detennined to be the <br />most appropriate condition for which to establish hydrology for the four tributaries. As <br />the final step in the coordination procc::ss between the USGS and Moser & Associates, the <br />USGS provided the long-term sub-basin RCN, lag time, and initial abstraction <br />characteristics. These characteristics were then used to determine the hydrologic results <br />outlined below. <br /> <br />2.1 Rainfall <br /> <br />To simulate the 10-, 25-, 50-, 100- and 500-year recurrence interval storm events in <br />HEC-HMS, the user hyetograph meteorological model was used. <br /> <br />To obtain the rainfall hyetographs fhr the model, Urban Drainage and Flood Control <br />District (UDFCD) rainfall criteria was used to determine the design storm distribution for <br />the 2-hour event. This criteria suggests that a 2-hour storm event be used for drainage <br />basin areas from 5 to 10 square miles. Therefore, the 2-hour storm event was applied to <br />the Four Mile Creek drainage basin, which has an drainage area of 8.35 square miles. <br /> <br />One-hour point rainfall depths for thc~ various return periods were determined from the <br />Douglas County Drainage and Tech][}ical Criteria Manual. Zone III depths from the <br />Douglas County criteria manual were used. These depths were then distributed over a 2- <br />hour storm period based on UDFeD criteria. <br /> <br />To obtain the 25-, and 500-year recurrence interval rainfall depths, procedures outlined in <br />the NOAA Atlas were used. See Appendix A. Table 1 summarizes the 2-hom design <br />storm distribution used for the Four Mile Creek Basin. <br /> <br /> <br />Page 5 <br />