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<br />grasses, with Gambel oak and ponderosa pine trees. The tablelands <br />vegetation is mainly western wheatgrass, junigrass, mounta1n <br />meehley, and Gambel oak. <br /> <br />2.3 Principal Flood Problems <br /> <br />Douglas County is located in an area that is prone to very <br />intense rainfall. sometimes of cloudburst magnitude. Floods have <br />resulted from storms covering large areas with heavy general rain- <br />fall as well as from storms covering small areas with extremely <br />intense rainfall. Floods generally occur from May through August. <br />The upland areas are characterized by dissected topographic relief <br />with steep stream slopes. Floods are characterized by rapid <br />rises, high maximum discharges, short durations, and comparatively <br />low volumes of total runoff. <br /> <br />The roadways that cross the streams and obstruct floodflows are <br />the most significant factor affecting flooding in the area. Other <br />manmade objects, such as buildings, cars, and fences, as well as <br />the natural vegetation of the flood plains, cause flow obstruc- <br />tion. <br /> <br />The following accounts of flooding on the South platte River, Plum <br />Creek, and Cherry Creek area are representative of typical floods <br />for which information is available. <br /> <br />Three separate floods occurred during May and June 1864. The <br />first originated in the Cherry Creek and Plum Creek basins, <br />occurring during the night of May 19-20, 1864, and was caused <br />primarily by a cloudburst in the upper part of those basins. On <br />the morning of May 20, the flood inundated the lower portions of <br />Denver at a depth of 1 to 5 feet, leaving great deposits of sand <br />and gravel. <br /> <br />Records indicate that 2.08 inches of rain occurred during a 2-hour <br />period on July 14, 1912. The heaviest precipitation occurred be- <br />tween Franktown and a point approximately 5 miles north of Denver, <br />the center was located near Parker. The rainfall started around <br />3 p.m. and continued until around 5 p.m. Cherry Creek crested <br />around 10 p.m. and had a peak discharge of 25,000 cubic feet per <br />second (cfs) in Denver. The Cherry Creek Flood Commission <br />estimated that runoff occurred from an area of approximately 200 <br />square miles. Flood damages in the reach between Franktown and <br />the site of the existing Cherry Creek Dam and Reservoir totaled <br />$554.000. <br /> <br />In June 1921. the rainfall.extended east of the mountains for a <br />considerable distance, and the plains tributaries as well as those <br />in the mountains contributed flow into the South Platte River. No <br />gaging stations were being maintained at the mouths of the trib- <br />utaries. This flood caused the South platte River to rise approx- <br />imately 7 feet in Denver. The local press estimated that approxi- <br />mately 500 houses were inundated and many families were forced to <br /> <br />9 <br />