Recurrence of Debris Flows on an Alluvial Fan in Central Utahby Elliott W. Lips, JBR Consultants Group, Salt Lake City, United States,
Gerald F. Wieczorek, JBR Consultants Group, Salt Lake City, United States,
Abstract: In the spring of 1983 a large debris flow occurred in the drainage of Birch Creek, near Fountain Green in central Utah. During the debris-flow activity, a new channel was incised into part of the alluvial fan at the mouth of the canyon. This channel was up to 20 meters deep, approximately one kilometer long, and exposed layers of unconsolidated materials representing distinct depsotional events. Based on morphology and analysis of sedimentological parameters, at least 17 deposits were identified as paleo-debris-flows in the upper part of the alluvial fan. By dating deposits, the average recurrence interval for debris flows to reach this location was determined to be 206 years during the period 4210 to 710 years B.P. At a point lower on the alluvial fan, where eight paleo-debris flows were identified, the average recurrence interval was established to be 296 years during the period 4470 to 2105 years B.P. Exceedance probabilities were calculated for debris flows to reach these two positions on the fan during different intervals of late Holocene time. The techniques used at this site could be applied to other alluvial fans to estimate the hazard from debris flows in probabilitic terms.
Subject Headings: Solids flow | Alluvial channels | Debris | Probability | Occupational safety | Canyons | Rivers and streams | Drainage | Utah | North America | United States
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