Potential Sediment Yield From a Burned Drainage - An Example From the Wasatch Front, Utah

by Robert M. Robison, Utah County Geologist, Provo, United States,

Document Type: Proceeding Paper

Part of: Hydraulics/Hydrology of Arid Lands (H²AL)


Two debris flows hit Mapleton City, Utah, as a result of rainstorms on a steep drainage basin, which had recently been burned. Debris flow potential for the area was evaluated to determine if hazardous conditions existed. Also, the increase in sediment loss due to fire denudation of slopes could be observed in relation to similar contiguous unburned drainages. Numerical calculations for the burned drainage were based on accepted methods developed by the Pacific Southwest Inter-Agency committee (PSIAC, 1968). Yield estimates indicated about 4,700 yd3 (3,600 m3) of potentially available debris flow sediment. Reports addressing the potential for debris flows and possible mitigation measures were given to several government agencies. No action was taken before two thunderstorms hit several days later, which initiated debris flows. No specific path for the debris flows could be predicted, and the entire surface of the alluvial fan was considered at risk. The debris flows hit a residence, damaged fences, partially filled a canal, and covered several roads. Preliminary measurements by the U.S. Forest Service indicated that about 15,000 yd3 (11,500 m3) of sediments were deposited on the alluvial fan at the mouth of the drainage. However, an evaluation of 'retainable-sediments', that which would remain in a debris basin, was somewhat less, about 5,000 to 7,000 yd3 (3,800 to 5,400 m3), which is close to the volume predicted by the PSIAC calculations.

Subject Headings: Solids flow | Sediment | Drainage | Potential flow | Numerical methods | Flow measurement | Drainage basins | Floods | Utah | United States

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