Deriving Debris‐Flow Dynamics From Real‐Time Impact‐Force Measurements. Issue 3 (21st March 2023)

• Record Type: Journal Article
• Authors: Yan, Yan; Tang, Hui; Hu, Kaiheng; Turowski, Jens M.; Wei, Fangqiang
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-21
• Subjects: debris flow -- impact force -- particle impact model -- log‐logistic distribution -- dimensionless parameters; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2022JF006715
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Understanding the impact forces exerted by debris flows is limited by a lack of direct field measurements and validated numerical models. In this study, we use real‐time impact‐force measurements and field observations of debris flows recorded by a sensor network in Jiangjia Ravine, China, to quantify the impact‐force distribution of natural debris flows. We observed one debris flow event during and after a storm on 25 August 2004, including 42 short‐duration surges and seven long‐duration surges, and impact‐force signals were successfully recorded for 38 surges. Our observed debris flows comprise high‐viscosity laminar flows with high sediment concentration and frequent solid‐to‐solid interactions. We identified a large magnitude (up to 1 kN), high‐frequency (greater than 1 Hz) fluctuating component of the impact force that we interpret as solid particle impact on the sensors. The variability of particle impact forces increases with the mean impact force. Our results show that a log‐logistic distribution can describe the probability density distribution of impact forces. Solid‐dominated surges and fluid‐dominated intersurge flows have similar impact‐force distributions, but surges usually have heavy tails. We created a dimensionless number to describe the impact force and correlated it against existing dimensionless parameters. Finally, we develop a simple particle impact model to understand the relationship between flow dynamics and the impact force inside debris flows that could be applied to improve debris‐flow flume experiments and design debris‐flow hazard mitigation measures. Plain Language Summary: Debris flows are fast‐moving mixtures of dirt and water that can cause huge damage to buildings and infrastructures and harm people. For effective hazard protection, we need to understand the impact forces exerted by debris flows. In this study, we measured impact forces at the high temporal resolution of 49 debris‐flow surges during and after a storm on 25 August 2004, recorded by a sensor array in Jiangjia Ravine, southwestern China. We develop statistical descriptions of the mean and the variability of the force and derive a relationship between flow dynamics and the impact force using a simple particle impact model. Our results could be applied to improve the future design of debris‐flow hazard mitigation measures. Key Points: Log‐logistic distribution is a good fit for debris‐flow impact force probability density functions Debris‐flow surges and intersurge flows have similar impact force distribution, but surges usually have heavy tails A simple particle impact model can explain the debris‐flow impact force signal