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| TITLE: | Normal stresses, longitudinal profiles, and bedrock surface erosion by debris flows: initial findings from a large, vertically rotating drum
| | AUTHOR: | L. Hsu & W.E. Dietrich, L.S. Sklar
| | KEYWORDS: | debris flow, bedrock erosion, laboratory experiments, drum, rotating flume, normal stress
| | ABSTRACT: | Field observations indicate that debris flows can cause erosional wear of bedrock channels and concrete structures. On steep slopes, where debris flows are dominant, this wear may be the primary means of long-term channel incision. To contribute to a process-based theory for bedrock incision by debris flows, we study the erosional processes of granular flows in a vertically rotating drum. Natural, non-scaled materials are studied in a 4-meter diameter, 80-cm wide drum. Slurries composed of grain sizes from clay to large cobble (20 cm) are studied at drum velocities up to 3 m/s tangential speed. A 225-cm2 load plate in the flume bed directly measures normal load on the bed. The longitudinal height profile of the debris slurry is measured with a laser rangefinder. Erosion is obtained by topographic measurement of an embedded synthetic rock sample before and after an experiment. We compare the measured dynamic and predicted static stresses exerted on the bed by the flow. We measure normal stress excursions up to four times higher than the mean stress and over 10 standard deviations from the mean stress, suggesting that bed collisions from large grains may be the important measure of bedrock fracture and removal. We also observe longitudinally- oriented grooves in the synthetic bedrock samples, which record the presence of abrasive sliding wear. These observations emphasize the importance of dynamic point-loading during the process of bedrock erosion by debris flows.
| | COLLECTION: | Dietrich
| | ID: | 180
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