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I I I I I I I I I I I I I I I I I I I (1974). Hansen and others (1978), and Jarrett and otherS-(in review) noted that maximum rainfall amounts in eastern Colorado are located on or near the crest of the Palmer Divide (fig. 1). Jarrett and others (in review) analyzed extreme rainstorm data for eastern Colorado (McKee and Doesken, 1997) with respect to topographic relief. They found maximum rainfall amounts exceed 12 inches for convective storm in areas of high topographic relief (crest of the Palmer Divide, isolated ridges and buttes, Raton Mesa, Cheyenne Ridge, and the foothills); maximum rainfall was less than about 10 inches for convective storms in areas of low topographic relief. About 75 percent of the high plains of eastern Colorado has local relief of less than about 300 ft in less than 3 miles. It is important to note that localized cells of maximum rainfall in Eastern Colorado are extremely localized (fig. 1; Follansbee and Spiegel, 1937; Follansbee and Sawyer, 1948; Matthai, 1969; Snipes and others, 1974; Hansen and others, 1978; Hansen and others, 1988), and also that the maximum cells primarily resulted from different storms. Flood data for basins in eastern Colorado that have relatively low TR, which most likely would not have a substantial orographic enhancement to precipitation, also are shown on figure 4. Low TR data plot on or below the envelope curve of maximum flooding for Cherry Creek and substantially below "other" Palmer Divide streams having high topographic relief (fig. 4) and support the hypothesis that topography enhances rainfall-producing floods. 2. The two largest rainstorms (1935 and 1965) in Colorado were located on the Palmer Divide (McKee and Doesken, 1997). The May 30-31, 1935 Hale-Cherry Creek rainstorm (Follansbee and Spiegel, 1937; Hansen and others, 1988) was reported to have produced up to 24 inches of rain in about 10 hours with two distinct rainstorm cells (fig. 1). One cell was located about 150 mi east of Denver near Hale in the Republican River basin (local relief about 300 ft), and a second cell was reported over the headwaters of Cherry Creek basin. Jarrett and others (in review) reviewed 1935 rainfall-bucket survey data and rainfall data for stations near the Palmer Divide. They found that maximum rainfall estimates for both cells were measured in stock tanks, which are used to store water for animals. Approximately 6 to 10 inches of rain fell in the week preceding May 30, 1935. Jarrett and others (in review) suggest that it is very unlikely preceding rainwater was emptied from the stock tank, particularly during a severe drought period (Collins and others, 1991), and concluded the May 30-31,1935 total rainfall amount was about 14 to 18 inches for each cell. Flood discharges from these revised rainfall amounts are more consistent with maximum flood discharges for the 1965 storm, which had similar rainfall amounts but larger flood discharges than in 1935 (Matthai, 1969). Historical records indicate significant flooding did not occur in 1935 in Cherry Creek (U.S. Army Corps of Engineers, 1976) nor in Running Creek (Water Resources Consultants, 1979). The 1935 Cherry Creek cell apparently was misnamed and should be referred to as the Kiowa- Bijou cell, which did have large rainfall amounts and extreme flooding in 1935 (Matthai, 1969). The location of maximum rainfall in 1935 and 1965 was on the divide between Kiowa and Bijou Creeks (fig. 1) where local relief is about 300 to 500 ft in less than a mile. The June 16-17, 1965 rainstorm did not produce significant rainfall nor any flooding in the headwaters of Cherry Creek and Running Creek (Matthai, 1969; Water Resources Consultants, 1979). The peak discharge was 1,000 ft3/S in Cherry Creek near Franktown (06712000) on June 16, 1965 at 1945 hrs, but occurred after the flood peak at the Melvin gage; the flood of 7