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e e e. .. .. ,.., ~ L ( - 10 - The only flood event on Indian \'iash for which there is an adequate ___record of peak-flow and-an estimate of monetary damages is the flood. resulting fram the stonn of June 6, 1958. This stonn was concentrated in the upper watershed area with-very little_rainfall i~_ the principal damage areas located-downstream-frOIli the High LineCanat. The precipitation recorded at the U. S. Weather Bureau Station at the --- Grand Junction airport was -:0.63 -inch. In their '~eport on Flood of 6 June 1958 on Indian Wash, Grand Junction and Vicinity, Coloradd' dated August 1958, the U. S. Corps of Anny Engineers estimated the peak discharge was 2,700 c.f.s. in- the Indian Wash channel near. the High Line Canal flume-and the total-- damages to be about $25,000. The principal damage was to residences, business establishments, and streets as shown by p~otographs taken during and after the flood (see Plates 1, 2 and 3). ( The principal reason for the lack of reliable data concerning previous flood damages on Indian Wash is that the build-up of residential and commercial property in the area subject to damage has taken place fairly recently, mostly since about 1955. Consequently, floods that occurred at earlier dates were generally much less damaging than those occurring more recently. Urbanization of agricultural land in the damage area is continuing at a steady rate, and large floods occurring in the future will have a much higher damage potential than floods of similar size would have at the present time. . Sediment and Erosion Damage The higher peak discharges of floods on Indian Wash are accompanied by large amounts of sediment derived mainly fram highly erodible lands above the High Line Canal. The principal sediment damage results from the deposition of silt, sand, and other debris on lawns, parking lots, city streets, and in buildings, as well as on irrigated cropland and in irrigation and drainage ditches. Removal of sediment and debris fram lawns, streets, basements, and main floors of buildings in particular involves considerable expense to the City of Grand Junction and to private interests. Sheet, gully, and streambank erosion are all major sources of sedL~ent in the upper watershed area. They also act to reduce forage production on the rangeland. Sheet and gully erosion are most damaging in the areas where shale lies at or near the surface. Above the High Line Canal, channel entrenchment into alluvial floodplain deposits has occurred along Indian Wash and most of the larger tributaries. Downcutting is reaching stability, but widening or the channels through streambank erosion is still taking place.