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35.14AO.9214, where A is the area to the point of interest in square miles. Figure 3 displays the results of this analysis. The USGS published equation for the northwest region of Colorado, which includes the Gunnison and Colorado Rivers, is QIOO = 104.7Ao624. There are four equations published by the CWCB for the Colorado River basin. The most applicable equation for the Grand Junction area is the equation for the Lower Gunnison River. As you know, the equation for the Lower Colorado River is not available from CWCB at this time. The Lower Gunnison River equation, QIOO = 180.8Aos", is based on tributaries of the Gunnison River downstream of the City of Gunnison, including Mesa County, using drainage areas between 2 and 8,000 square miles. Of the CWCB equations, this equation results in the largest estimate of I DO-year discharges for the range of area sizes applicable to the Leach CreekIHorizon Drive drainage basin. In addition, this equation is an upper envelop of the ICON developed and USGS published equations. Figures 4 and 5 display the four equations discussed above and the results of our preliminary rainfall-runoff models for the Leach CreekIHorizon Drive drainage basins. Clearly the lower rainfall results in discharges that compare more favorably with results of all the regression equations. Appendix C contains supporting information for this analysis. CONCLUSION Figures I or 2 clearly indicate the NOAA Atlas 2 depth-duration-frequency values are significantly higher than the rainfall data support. The Log-Gumbel curve for the 24-hour data is a very good fit. The results of the rainfall-runoff modeling also indicate the NOAA Atlas 2 rainfall depths are high compared to the published regional regression curves. We would appreciate your expeditious review of this information. If you have any questions please give me a call. Sincerely, ICON Engineering, Inc. Mike Vinson, P.E. cc: Mr. Trent Prall, P.E. City of Grand Junction, CO