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F and flows to 5320 feet at the stream flow gaging station in Harvard Park. The slope was determined using the weighted-average method and was found to be 0.0083 feet per foot (ftIft). Harvard Gulch is a highly developed, primarily residential neighborhood. It has been essentially fully developed for the past 20 years with very little modification. The effective percent imperviousness in this investigation was found to be a major point of contention. The USGS reports that the basin consists of 72 percent residential, 17 percent commercial, and 11 percent open space for an effective imperviousness of 27 percent (OFR 82-872). A comprehensive 1983 USGS report based it's determinations on low-altitude aerial photographs and found the imperviousness to be 31 percent (WRI 83- 4138). The Urban Drainage Criteria Manual published by the UDFCD recommends a 40-45 percent imperviousness for medium density fully developed residential basins (USDCM, 1984). The infiltration rateof precipitation on pervious surfaces is another key parameter that is not always clearly defined. The UDFCD gives recommended values for Horton's equation based on the Soil Conservation Service (SCS) hydrologic soil group. Groups C and D are the most common within the metropolitan area. Zarrie,lIo reported Harvard Gulch to be primarily group B soils, which have a high initial infiltration rate. SCS soil surveys were not consulted for this investigation. Depression retention was estimated to be 0.35 inches on pervious surfaces (lawn grass) and 0.065 inches on impervious surfaces (sloped roofs) based on the Urban Storm Drainage Criteria Manual recommendations. CUHP CALIBRATION The CUHP program can be calibrated in many ways. The intention of this investigation was to apply a calibration method that has the most application to the real situations encountered by industry. In most cases, engineers do not have the benefit of unit hydrograph information. To compound circumstances, as illustrated in the previous discussion, the hydrologic parameters of the basin are often subject to debate. CUHP assumes that there is a one-to-one relationship between the return period of precipitation and the return period of runoff. In other words, the 50-year rainstorm event will produce the 50-year runoff event. The 2-, 5-, 10-, 50-, and 1 DO-year 1-hour precipitation depths for the Denver metropolitan area have been established by the UDFCD (table 3). Therefore, it stands to reason that the runoff for Harvard Gulch should 'track' those statistical events. A frequency analysis of the peak flow through Harvard Gulch was computed based on the annual maximum series (AMS) from the period of 1981-1999 presented in table 4. Application and Evaluation of CUHP Page 8 of 52