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heavy vegetation encroaching upon channel banks. The flood plains are largely undeveloped for both streams, and the soils are of the Argiborolls-Rock Outcrop and Cyroboralfs-Rock Outcrop Associations (Reference 4). The Cache La poudre River flow~ in a southeasterly direction through Larimer County. Development along the Cache La POudre River flood plain is minor at the present ~ime with only a few residential and commercial structures. The channel in the studied section is approxi- mately 160 feet wide and 7 feet deep, with the gradient varying from 28 feet per mile in the upper parts of the study area and 16 feet per mile in the lower parts. The soils within the Cache La POudre River study area consist of the Fluvaquents-Fluvents Associa- tion (Reference 4). Black Canyon Creek was studied from its confluence with Big River upstream approximately 1,4 miles to McGregor Avenue. upstream 0.4 mile of this study reach is in Lar.imer County. Thompson The 2.3 Principal Flood Problems Major floods on the streams are caused by intense rainfall from localized thunderstorms over the basins. The floods caused by such events will characteristically have high peak discharges of short duration for all of the mountain-area streams. Floods on the streams in the plains area~ are normally of a longer duration with less velocity and considetable channel storage. Flooding can also occur as a result of rapid spring snowmelt. These floods characteristically are of longer duration. Significant floods have occurred on the streams within the county in past years. The most significant flood within the county occur- red on the Big Thompson River,' July 31 to August 1, 1976. This flood was one of the worst natural disasters in the history of Colorado. Intense precipitation over an approximate 60-square- mile area between Lake Estes, and Drake, with rainfall depths up to 12 inches, generated a flood discharge of approximately 31,200 cubic feet per second (cfs) at the mouth of the canyon. ~his flood is known to have taken 139 lives. Property damage was estimated at $16.5 million, while hundreds of people were left homeless. Over 200 residential structure's were damaged or destroyed by the flood, while nearly 1,200 land parcels were adversely affected (Reference 5). Floods on the ~ig Thompson River caused damage in 1864 and 1894, but no discharge or damage estim~tes were recorded. Floods also occurred on the B~g Thompson River in 1919, 1923, 1945, and 1949 with discharges'of 8,'000, 7,000, 7,600, and 7,750 cfs, respectively. The 1976 flood 'is depicted in Figures 2 through 6. .. ~ Notable floods on the Cache La POudre River in the study area occur- red in 1844, 1864, 1884, 1891, 1904, 1923, and 1930. There were apparently three large floods 'of comparable size in 1864, 1891, 6