Driftwood deposition from debris flows at slit-check dams and fans

Abstract

Experience shows that debris flows containing large woody debris (driftwood) can be more damaging than debris flows without driftwood. In this study, the deposition process of debris flows carrying driftwood was investigated using numerical simulations and flume experiments. Debris-flow trapping due to driftwood jamming in a slit-check dam was also investigated. A numerical model was developed with an interacting combination of Eulerian expression of the debris flow and Lagrangian expression of the driftwood, in which the fluctuating coordinates and rotation of the driftwood were treated stochastically. The calculated shapes and thicknesses of a debris-flow fan and the positions and orientations of the deposited driftwood on a debris-flow fan were consistent with experimental flume results. The jamming of driftwood in a slit-check dam was evaluated based on geometry and probability. The simulated results of outflow discharge and the proportion of driftwood passed through the slit-check dam also agreed with the experimental results.

Characterization of wood‐laden flows in rivers

“…Some approaches have been proposed to include the effect of wood on debris-flow simulations (Lancaster et al, 2003;Shimizu et al, 2006;Shrestha et al, 2009Shrestha et al, , 2012). An extension of the Channel-Hillslope Integrated Landscape Development (CHILD) model was presented by Lancaster et al (2003).…”

“…The lack of direct observations of events in which organic material plays a significant role makes it difficult to characterize such flows, analogous to the study of sediment transport in the first half of last century (Braudrick and Grant, 2000). Pioneering observations described wood as an important component in debris flow deposits (Swanson and Lienkaemper, 1978;Nakagawa et al, 1994;May, 2002;Lancaster et al, 2003;Shrestha et al, 2012), but flows in which wood is the main solid fraction (both in terms of mass and volume) have Table S1. Pioneering observations described wood as an important component in debris flow deposits (Swanson and Lienkaemper, 1978;Nakagawa et al, 1994;May, 2002;Lancaster et al, 2003;Shrestha et al, 2012), but flows in which wood is the main solid fraction (both in terms of mass and volume) have Table S1.…”

“…Since then, monitoring techniques and physical and numerical models have contributed greatly to our present knowledge of sediment transport (Kondolf et al, 2005;Gyr and Hoyer, 2006;Rickenmann, 2016Rickenmann, , 2017Tsutsumi and Laronne, 2017), but wood transport has received much less attention. Pioneering observations described wood as an important component in debris flow deposits (Swanson and Lienkaemper, 1978;Nakagawa et al, 1994;May, 2002;Lancaster et al, 2003;Shrestha et al, 2012), but flows in which wood is the main solid fraction (both in terms of mass and volume) have Figure 1. Images of wood-laden flows extracted from the 28 home movies analysed in this work.…”

Experimental and numerical study of slit-check dams

“…The successful application of slit dams for debris flow mitigation has been claimed in several experimental and numerical studies [3,[5][6][7][8][9][10][11]. All those studies concluded that the slit width is the key parameter to decrease the debris flow peak discharge and retain the harmful sediments upstream of the dam.…”

Effect of plan layout on the sediment control efficiency of slit-check dams for stony type debris flows mitigation

“…[1,2,8,[11][12][13][14]). All those studies concluded that free spacings between the piers can be defined in order to decrease the debris flow peak discharge and to allow the non-harmful sediments to pass through freely, while catching the harmful sediments upstream of the dam.…”