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- I . however, ettenu~tes rapidly on the South Platte RIver downstream from the contributIng trIbutaries due to valley storage of the floodwater. The general rainstorm floods result from ralofa' lover areas of largo arelll extent. RIl1nf/.11 from this type of storm fIlay <)Cellr over several days. Because of this time duratIon, the affected streoms rise relatively slow; sometimes ovor Il period of several days. The duration of the flood period alSO Is someti~s of con- Siderable length. Because of the large arear extent of raInfall, more tributaries contribute to the peak discharge on the South Platte River. This results In increasIng discharge progressIvely downstream oyer 1l considerable length of the South Platte River. However, downstream from the contributing trlbut~ries, the effects of valley storage cause flood discharge attenuation. Erosive effects can be considerable in the event of any flood regardless of its origin. Floods resulting from Intense rainstorms typically create severe erosion damages in a short period of time due to the relatively large peak discharge and high velocity of the floodwater. Erosion d~mages from snowmelt or general rainstorm floods usually result from prolonged exposure of the floodwater because of the long duration typical of these floods. Intense rainstorm floods as well as genera! rainstorm floods have occurred On the South Platte RIVer. Examples of the intense storms are the 1965 events on Plum Creek and BIJou Croek and the 1916 event on the Big Thompson River. Examples of the larger more generalized storms are the 1969 and 1973 events producing flooding on the South Platte River. Table 2 AnnualPeakO!schargeforthe 1/2/ South Platte River near Weldona, Colorad~ Oate Dlscharqe tc.f.s.l " '" 1951 14,200 27 '" 1958 8,840 6 J," 1961 1,140 " J," 1965 18,800 10 J," 1969 11,000 14 M 1910 14,000 2BApr 1911 1,400 BMay 1973 26,800 l! From U.S.G.S. Gaging Station located 400 feet downstream from Colorado State Htghway 144 and 2.8 miles southeastofWaldona. 2/ Only those years having a peak discharge of 5,000 c.f.s. or greater are Indicated. For periOd of gaging record, s~a table I. . , , P,,:;tFlood:; Several floods have occurred along the South Platte River in Morgan and Washin~ton Counties. Tables 2 through 4 indicate yearly peak discharges experienced at the three stream gaging stations oper- etn~ in the ~~~t by the U. S. GAOloglr.~1 Survny In Morgan r~unty. . , ,