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vegecacion encroaching upon channel banks. The flood plains are largely undeveloped for boch screams, and che soils are of che Argiborolls-Rock Ouccrop and Cyroboralfs-Rock Ouccrop Associations (Reference 4). The Cache La Poudre River f~ows in a soucheascerly direccion chrough Larimer County. Development along' che Cache La Poudre River flood plain is minor aC che presenc cime wich only a few residential and commercial scruCCures. The channel in che studied section is approximately 160 feec wide and 7 feec deep, with the gradient varying from 28 feeC per mile in che upper parts of the scudy area and 16 feet per mile in the lower parts. The soils within the Cache La Poudre River scudy area consisc of Che Fluvaquents-Fluvents Associacion (Reference 4). Black Canyon Creek was scudied from ics confluence with Big Thompson River upscream approximacely 1.4 miles co McGregor Avenue. The upsCream 0.4 mile of chis study reach is in Larimer County. 2.3 Principal Flood Problems Major floods on che sCreams are caused by incense rainfall from localized chunderscorms over the basins. The floods caused by such evenCs will characceristically have high peak discharges of short duration for all of the mountain-area screams. Floods on che streams in che plains areas are normally of a longer duracion with less velocicy and considerable channel storage. Flooding can also occur as a resulc of rapid spring snowmelt. These floods characteristically are of longer duration. Significanc floods have occurred on che sCreams within the county in pasc years. The most significanc flood wichin che county occurred on the Big Thompson River, July 31 co August 1, 1976. This flood was one of the worst natural disascers in the hiscory of Colorado. Incense precipitacion over an approximate 60-square-mile area becween Lake Esces and Drake, with rainfall depths up co 12 inches, generated a flood discharge of approximacely 31,200 cubic feet per second (cfs) at che mouth of che canyon. This flood is known to have taken 139 lives. Property damage was escimated at $16.5 million, while hundreds of people were left homeless. Over 200 residencial sCructures were damaged or destroyed by the flood, while nearly 1,200 land parcels were adversely affected (Reference 5). Floods on che Big Thompson River caused damage in 1864 and 1894, but no discharge or damage estimaces were recorded. Floods also occurred on the Big Thompson River in 1919, 1923, 1945, and 1949 wich discharges of 8,000, 7,000, 7,600, and 7,750 cfs, resp~ccively. The 1976 flood is depicced in Figures 2 through 6. Notable floods on the Cache La Poudre River in the scudy area occurred in 1844, 1864, 1884, 1891, 1904, 1923, and 1930. There were apparencly chree large floods of comparable size in 1864, 1891, and 1904. All of these floods peaked near 21,000 cfs. The 1904 flood was probably che worsc flood in terms of dollar damage 6