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<br />increases to approximately 60 percent (p in 10). The analyses reported <br />herein reflect flooding potentials bas~d on conditions existing in the <br />community at the time of completion of this study. Maps I;1nd flood <br />elevstions will be amended periodically'to reflect future changes. <br /> <br />3.1 Hydrologic Analyses <br /> <br />Since no stream gage data was available for the streams studied, a <br />rainfall-runoff analysis was conducted on the watersheds to <br />determine the flood discharges. This was accomplished by using the <br />Colorado (UD&FCD) CUHP rainfall-runoff computer program to develop <br />the storm hydro graphs (Reference: 6) and the U. S. Army Corps of <br />Engineers HEC-1 flood hydro graph Fackage computer program for the <br />, <br />stream and reservoir routings (R"ference 7). For this analysis, <br />basin characteristics which def:\.ne the size, shape and runoff <br />characteristics of the watershed ~s well as rainfall amounts based <br />on the selected recurrence intervals (obtained from the NOAA atlas <br />of precipitation Reference '8) are used to compute flood <br />hydro graphs for various design points in the basin. All stream and <br />reservoir routings were accomp~ished using the Modified Pulse <br />Method. <br /> <br />Since there was a lack of SOO-yea~ precipitation data, the SOO-year <br />frequency storm runoff values at each design point were calculated. <br />The logarithmic values of th~ 10-, SO-, and 100-year peak <br />discharges were fit to a regression line by method of least <br />squares. The SOO-year discharges were analytically extrapolated <br />from the regression line based upon a log-normal probability <br />relationship. For more detailed information see the final <br />hydrologic analysis report for: Big Dry Creek and Tributaries <br />prepared by Greiner Engineering, iJanuary 1984. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic char~cteristics of flooding from the <br />sources studied were carried qut to provide estimates of the <br />elevations of floods of the selected recurrence intervals. The <br />analyses in this report refl~ct flooding potential based on <br />existing land use conditions in ~he community as of December 1983. <br />Map and flood elevations will b'e amended periodically to reflect <br />future changes. <br /> <br />For all streams studied, the water-surface elevations for floods of <br />the selected recurrence intervalS were computed using the U.S. Army <br />Corps of Engineers HEC-Z Step-backwater computer program (Reference <br />9) . <br /> <br />6 <br />