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Show Craddock: Selt Lake 61 City Flood, 1945 No floods occurred in any of the experimental watersheds Farmington in which intensive headwater improvements had been made in recent years. On the night of August 19 when the most intense rainfall ever recorded in Utah fell on the mountain in this area, stream flow in masonry flume sections rose above base flow stage to' maximum instantaneous heights of 0.92 foot id Farmington Canyon, 1.11 feet in Parrish Creek, and 1.23 feet in Centerville Creek. These height stages are equivalent to dis charges of 11.6 cubic feet per second per square mile in Farming ton Canyon, 4.5 c.s.m. in Parrish Creek, and 3.9 c.s.m, in Cen terville Creek. These discharges are less than 0.5 percent of the calculated peak flows which issued from the Salt Lake City foothills. near .... .. .. . These comparative discharges are especially significant when Farmington Canyon and Parrish- Creek were among the several streams which produced destructive debris flows in the period 1923 1930, and that the. flood source areas ih the headquarters of those streams have since been improved by installation of contour trenches, artificial reseeding, and protection from grazing. Centerville Creek has never flooded destructively since settlement. This watershed has been carefully managed for many years and is almost completely covered by a dense mantle of vegetation and litter. it is considered that both .... CONCLUSIONS Evaluation of the observable and recorded evidence described above lead to the following conclusions: 1. The Salt Lake City flood was caused by a coincidence of high intensity rainfall and recently drastically impaired water shed conditions. 2. It is highly probable that no flood or at .most only minor run oH would have occurred if the plant and litter cover had not been impaired by previous abuse and the 1944; fire. 3. Because of the highly efficient gully system and deteri orated condition of the plant cover, storms of lesser magnitude than the one of August 19, will cause much run off and erosion so that debris floods of greater frequency and violence can be ex pected to occur from these watersheds in future years. 4. Prevalence of the highly inflammable cheatgrass on all of the lower slopes of the mountains north and east of "Salt Lake City has greatly increased the hazard of fires and of destructive floods. 5. Future floods in the Salt Lake City area can be mini mized by: (1) breaking up the gully system, (2) improvement of the plant cover, (3) prevention of watershed fires, and (<f) construction of channel improvements. .... .... .... .... .. f |
