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I I I I I I '. I I I I I I I I I I I I 3 "The stream valleys in the Sand Creek basin upstream from Buckley Field are narrow and steep-sided, averaging one-fourth mile wide or less. From Buckley Field downstream, the valleys broaden and flatten to average from one-half mile to more than 1 mile wide. Stream slopes are rather steep throughout the basin. Stream gradients on Sand Creek range from 25 feet per mile upstream from Buckley Field to about 26 feet per mile downstream from Buckley Field. Through the metropolitan area, Sand Creek is generally characterized by a broad flat-bottomed sandy channel with low steep banks. Grass, brush, and trees occupy portions of. the immediate overflow area. The Sand Creek channel width from Buckley Field to its mouth ranges from 30 to 250 feet." (From Reference No.3) Related Studies Three reports concerning flood hazards associated with Sand Creek have been published by the Corps of Engineers. The first was a flood plain information report published in 1964 (Ref. 2). The rains and floods of 1965 indicated the need to revise this study. The revision was published in 1971 (Ref. 4). An interim report which discussed possible flood control measures was published in 1969 and revised in 1972 (Ref. 3). The hydrologic and hydraulic data contained in this report were developed by the Corps of Engineers, Omaha District as a part of a present study entitled, "Metropolitan Denver and South Platte River and Tributaries Study. " The flood discharges contained in this report are significantly lower than the discharges published in the 1971 flood plain information report. The differences in discharge are attributed to the utilization of more sophisticated hydrologic and hydraulic modeling techniques. Development in the Flood Plain The Sand Creek flood pl ain upstream from Chambers Road in Aurora and Arapahoe County is relatively undeveloped, with the exception of a portion of a mobile home park and isolated buildings. Urban development is more prevalent downstream of Chambers Road. A large residential development called Morris Heights lies in the flood plain near the confluence of Sand and Toll Gate Creeks. Down- stream from Morris Heights the flood plain is crossed by two runways at Stapleton International Airport in Denver. In Commerce City, Interstate Highway 270 closely parallels the north bank of the channel. Urban development consists of many commercial and industrial buildings. In addition to the runways, 17 roads and five railroads cross the Sand Creek flood plain. Two major irrigation ditches, the Burlington Ditch and the Highline Canal, also cross Sand Creek. Substantial portions of the Sand Creek flood plain remain undeveloped. Unless sound regulatory measures are applied, the flood damage potential will undoubteply increase in future years. - HISTORICAL FLOODS - Sand and Toll Gate Creeks have experienced major floods in 9 years since 1896. These floods occurred in 1896, 1912, 1917, 1921, 1933, 1938, 1948,.1957, and 1965. Because the basins were esentially undeveloped prior to 1941, no flood discharges or descriptions are available for the first six floods. Descriptions of the 1948, 1957, and 1965 floods were printed in Reference 3 and are reprinted below. "Flood of 30 May 1948. In the 1 ate afternoon and eveni ng of 30 May 1948, a severe rain and hailstorm occurred over Sand Creek and over the area east of Denver. Lowry Air Force Base recorded rainfall of 2.32 inches with two periods of 1 inch per hour. The storm produced 8 inches of rainfall at its center in 4 hours.