Erosion Mechanisms of Debris Flow on the Sediment Bed

Abstract

Debris flows are common geological hazards in mountainous regions worldwide. The scale of debris flows can be significantly enhanced by basal erosion and bank collapse in the transportation process, resulting in an increase in casualties and property losses. However, the mechanisms of this growth are largely unclear. Here, we conduct a series of experiments to investigate the erosion of two different bed sediments (coarse‐grained and widely graded) by released flows with three different densities and two different volumes. The erosion mechanisms of bed sediments are revealed by comparing detailed sensor data for flow level, pore pressure and total normal stress. A flow nose develops on the coarse‐grained bed sediment, resulting in a high flow depth and low velocity, while a tabular flow develops on the widely graded bed sediment, leading to a low flow depth and high velocity. The mean erosion rates of the coarse‐grained bed sediment are generally higher than those of the widely graded bed sediment due to significant pore pressure developed in coarse‐grained bed sediment. The feedback effect of bed sediment on the erosion process strongly influences the flow depth and velocity, which in turn affects the mean erosion rate of bed sediment. The interaction between the overlying flow and sediment bed controls the erosion pattern: coarse‐grained bed sediment is eroded by a layer of mass movement whereas widely graded bed sediment is progressively scoured. The interaction between debris flow and bed sediment during erosion is principally attributed to pore‐pressure transmission.

How debris‐flow composition affects bed erosion quantity and mechanisms: An experimental assessment

“…Our experimental flows clearly show that debris‐flow volume and composition influence erosion magnitude (Figure 7). The increase in erosion with debris flow volume shows that our experiments comply with earlier experimental work (Chen & Zhang, 2015; Zheng et al., 2021) and observations from the field (Schürch et al., 2011). Both in these earlier experiments and in field studies, an increase in debris flow volume correlated with an increase in flow depth, which itself correlated with the magnitude of erosion (Schürch et al., 2011; Zheng et al., 2021).…”

“…The increase in erosion with debris flow volume shows that our experiments comply with earlier experimental work (Chen & Zhang, 2015; Zheng et al., 2021) and observations from the field (Schürch et al., 2011). Both in these earlier experiments and in field studies, an increase in debris flow volume correlated with an increase in flow depth, which itself correlated with the magnitude of erosion (Schürch et al., 2011; Zheng et al., 2021). In our experiments, an increase in flow volume also resulted, next to an increase in flow depth, in an increase in frontal flow velocity, frontal discharge, momentum, shear stress and seismic energy, all correlating with the increase in erosion (Figure 8d,h,l,p,t).…”

Flow and Bed Conditions Jointly Control Debris‐Flow Erosion and Bulking

“…Observations show that erosion volumes may strongly vary between debris‐flow events: some flows increase >50 times their initial volume (Hungr et al., 2005), while others barely increase in size (Santi et al., 2008), and we currently lack the means to explain these contrasting pathways of development. Understanding debris‐flow erosion is notoriously complicated for a number of reasons: (a) debris flows are complex hybrids between a fluid flow and a moving mass of colliding particles that may vary greatly in composition, such that both shear and impact forces may contribute to erosion, but how these forces interact remains partly unclear (De Haas & van Woerkom, 2016; Hsu et al., 2008; Roelofs et al., 2022; Schürch et al., 2011); (b) bed erodibility may strongly vary, as it depends on a combination of grain‐size distribution, moisture content, and hardness (e.g., soft sediment vs. bedrock) (Iverson et al., 2011; Stock & Dietrich, 2003; Zheng et al., 2021); (c) in‐situ flow measurements are cost‐ and time‐demanding because of the destructive and infrequent nature of debris flows and the rough terrain in which they occur.…”

Experimental Investigation on the Breaching Process of Landslide Dams with Differing Materials under Different Inflow Conditions

“…The three above dimensionless numbers set in the experiments fall within the reasonable range of values based on a database of 80 landslide dam cases [ 19 ], verifying that the model dam in this study could simulate real large-scale landslide dams. In addition, there are some other real-world factors that may cause discrepancy for the experiments, such as the measurement method and condition [ 43 ], the irregular or compound channel shape [ 44 ], and the real-world water-worked bed condition [ 45 , 46 ]. This study aims to obtain some preliminary results of the breaching characteristics of landslide dams with different grain compositions.…”