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<br />and on the east-west trending drainage divide between the South Platte River and <br />Arkansas River northeast of Colorado Springs (Henz, 1974). Temporally, cloudbursts <br />~enerally occur in the afternoon.or early evening of unusually warm days. Ninety <br />percent of cloudburst storms occur between May and September, with strong modes <br />during the first week in June and the first week in August (Hansen and others, 1978). <br />The most distinctive historic floods occurred in the Front Range area in 1935 <br />(Kiowa and Bijou Creek), 1936 (Bear Creek and tributaries), 1965 (South Platte <br />River and tributaries), and 1976 (Big Thompson River and tributaries). <br />Floods generated by cloudburst rainstorms are characteristically flashy, short <br />in duration, small in total volume, but very high in instaneous peak. The effects <br />of flooding on streams in the Great Plains are different than those of mountain <br />channels. Plains streams have broad floodplains where floodwaters spread out. This <br />results in rapid reductions in flood-peak stages downstream because of valley storage. <br />These conditions also favor deposition of sediment. As much as 12 feet of sediment <br />was deposited on the floodplains of West Bijou Creek during the flash flood of June, <br />1965. Many trees were uprooted and channels widened by bank cutting. Much <br />damage occurs at bridge crossings where flooding and backwater occur because of the <br />constriction of the channel and floodplain. Channel scour of sand-bed streams can <br />be extensive, and can undermine bridge and embankment supports. <br />On the night of May 21, 1978, a flash flood destroyed a wooden train bridge <br />across Kiowa Creek, a north-flowing tributary of the South Platte River east of <br />Denver. A standard gage Union Pacific locomotive along with most of its cars <br />plunged into the torrent of water. A few days later, a search was begun for the <br />locomotive using long metal rods driven into the dry sand channel. The project <br />was soon abandoned, and to this day the locomotive remains to be recovered. <br />In the foothills, stream valleys are narrow and confined by bedrock walls. <br />Towns and villages are constrained topographically to build on floodplains and/or <br /> <br />-2- <br /> <br />. <br /> <br />. <br /> <br />. <br />