The Development of a 1-D Integrated Hydro-Mechanical Model Based on Flume Tests to Unravel Different Hydrological Triggering Processes of Debris Flows

Theo Van Asch,Wei Hu,Bin Yu

doi:10.3390/w10070950

Abstract

Many studies which try to analyze conditions for debris flow development ignore the type of initiation. Therefore, this paper deals with the following questions: What type of hydro-mechanical triggering mechanisms for debris flows can we distinguish in upstream channels of debris flow prone gullies? Which are the main parameters controlling the type and temporal sequence of these triggering processes, and what is their influence on the meteorological thresholds for debris flow initiation? A series of laboratory experiments were carried out in a flume 8 m long and with a width of 0.3 m to detect the conditions for different types of triggering mechanisms. The flume experiments show a sequence of hydrological processes triggering debris flows, namely erosion and transport by intensive overland flow and by infiltrating water causing failure of channel bed material. On the basis of these experiments, an integrated hydro-mechanical model was developed, which describes Hortonian and saturation overland flow, maximum sediment transport, through flow and failure of bed material. The model was calibrated and validated using process indicator values measured during the experiments in the flume. Virtual model simulations carried out in a schematic hypothetical source area of a catchment show that slope angle and hydraulic conductivity of the bed material determine the type and sequence of these triggering processes. It was also clearly demonstrated that the type of hydrological triggering process and the influencing geometrical and hydro-mechanical parameters may have a great influence on rainfall intensity-duration threshold curves for the start of debris flows.

Highlights

A debris flow is one of the most dangerous types of mass movement because, depending on the rheology and topography, it can reach a very high speed and large run-out distance
One can make different classifications of initiation mechanisms based on different viewpoints [1]. It was among others [2,3], who stressed the importance of the infiltration capacity of the soil as a key factor for either the development of shallow landslides or surficial erosion and transport of material by overland flow, that might create different types of flow like mass movements
We could distinguish in our flume tests three types of hydro-mechanical processes which may trigger debris flows in channel beds of first order source areas

Summary

Introduction

A debris flow is one of the most dangerous types of mass movement because, depending on the rheology and topography, it can reach a very high speed and large run-out distance. One can make different classifications of initiation mechanisms based on different viewpoints [1] It was among others [2,3], who stressed the importance of the infiltration capacity of the soil as a key factor for either the development of shallow landslides or surficial erosion and transport of material by overland flow, that might create different types of flow like mass movements. Focused more on the slope gradient as a controlling factor for different types of initiation Their flume studies revealed that at gentler slope gradients around 10◦ ± 2◦ , incision and bank failure is dominant, creating channel damming and dam failure, inducing debris flows. What is the influence of hydro-mechanical parameters and related triggering processes on the meteorological thresholds for debris flow initiation?.

Setupp of the Flume Experiments

Design

The Design of a Schematic Source Area at the Field Scale

Discussion

Conclusions