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willows and cottonwoods. There ,'lre irrigated pasturelands III lhe! Parachute Creek valley north of town. 2.3 Principal Flood Problems Most floods on Parachute Creek are caused by rapid snowmelt from mountainous regions of the upper Parachute Creek basin during late May to early July. There is also potential for floods resulting from rainfall occurring on top of melting snow as well as from summer thunderstorms. Snowmelt floods are characterized by moderate peaks, large volumes of runoff and long durations whereas floods from summer thunderstorms have larger peaks but smaller volumes and shorter durations. Between the Colorado River and the D&RG Railroad, the channel meanders through agricultural and industrial tracts which have some residential areas interspersed. Between the railroad and the westbound lanes of Interstate Highway 70 0-70), the channel is straight and relatively deep. The railroad bridge constitutes the primary potential obstruction to flood flows in this reach. Upstream of 1-70, the channel is confined between residential areas and a commercial strip along U.S. Highway 6. The stream was channelized as the town grew up on its banks. Within this reach, the U.S. Highway 6 bridge is the most significant hydraulic obstruction. Overflow of the creek from a 500-year flood would subject the main business sector of town to floodwaters which can only be directed back to the main channel by the highway and railroad embankments. Water which flows over the railroad embankment will not re-enter Parachute Creek but will flow in a southerly direction to the Colorado River. The Colorado River is a braided river subject to flood flows of relatively long duration and large volume resulting from melting snow. The study reach of the Colorado River within the town is approximately 2 stream miles in length and slopes at an average 0.l9 percent. The floodplain meanders along the southern boundary of the town and reaches up to about 1/2 mile in width in certain areas. Portions of the overbank areas are used for gravel mining. The south bank of the river rises steeply and forms a substantial barrier for flood flows, while the north bank rises more gently and subjects portions of the town to periodic inundation. Significant historical discharges measured at USGS Gage No. 09093000 on Parachute Creek are listed below (Reference l): Date Discharlle. (cfs) May l8, 1979 August 19, 1977 July 3l, 1976 May 5, 1952 May 20, 1922 944 2,3l0 2,600 912 795 4