Entrainment of bed sediment by debris flows: results from large-scale experiments

Authors

  • Mark E. Reid United States Geological Survey, Menlo Park, California, USA
  • Richard M. Iverson United States Geological Survey, Cascades Volcano Observatory, Vancouver, USA
  • Matthew Logan United States Geological Survey, Cascades Volcano Observatory, Vancouver, USA
  • Richard G. Lahusen United States Geological Survey, Cascades Volcano Observatory, Vancouver, USA
  • Jonathan W. Godt United States Geological Survey, Denver Federal Center, Denver (CO), USA
  • Julie P. Griswold United States Geological Survey, Cascades Volcano Observatory, Vancouver, USA

DOI:

https://doi.org/10.4408/IJEGE.2011-03.B-042

Keywords:

debris flow, sediment entrainment, scour, large-scale experiment, pore-fluid pressure, soli moisteure

Abstract

When debris flows grow by entraining sediment, they can become especially hazardous owing to increased volume, speed, and runout. To investigate the entrainment process, we conducted eight large-scale experiments in the USGS debris-flow flume. In each experiment, we released a 6 m3 water-saturated debris flow across a 47-m long, ~12-cm thick bed of partially saturated sediment lining the 31o flume. Prior to release, we used low-intensity overhead sprinkling and real-time monitoring to control the bed-sediment wetness. As each debris flow descended the flume, we measured the evolution of flow thickness, basal total normal stress, basal pore-fluid pressure, and sediment scour depth. When debris flows traveled over relatively dry sediment, net scour was minimal, but when debris flows traveled over wetter sediment (volumetric water content > 0.22), debris-flow volume grew rapidly and flow speed and runout were enhanced. Data from scour sensors showed that entrainment occurred by rapid (5-10 cm/s), progressive scour rather than by mass failure at depth. Overriding debris flows rapidly generated high basal pore-fluid pressures when they loaded and deformed bed sediment, and in wetter beds these pressures approached lithostatic levels. Reduction of intergranular friction within the bed sediment thereby enhanced scour effciency, entrainment, and runout.

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Published

2011-11-30

How to Cite

Reid, M. E., Iverson, R. M., Logan, M., Lahusen, R. G., Godt, J. W., & Griswold, J. P. (2011). Entrainment of bed sediment by debris flows: results from large-scale experiments. Italian Journal of Engineering Geology and Environment, 367–374. https://doi.org/10.4408/IJEGE.2011-03.B-042