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

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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 largescale 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 efficiency, entrainment, and runout.

Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Entrainment of bed sediment by debris flows: results from large-scale experiments
DOI 10.4408/IJEGE.2011-03.B-042
Year Published 2011
Language English
Publisher Università La Sapienza
Contributing office(s) Volcano Science Center
Description 8 p.
Larger Work Type Conference Paper
Larger Work Title Debris-flow hazards : mitigation, mechanics, prediction, and assessment : proceedings of 5th international conference : Padua, Italy, 14-17 June 2011
Conference Title 5th International Conference on Debris-Flow Hazards "Mitigation, Mechanics, Prediction and Assessment"
Conference Location Padua, Italy
Conference Date June 14-17, 2011
Online Only (Y/N) N
Additional Online Files (Y/N) N