New Numerical Simulation Procedure for Large-scale Debris Flows (Kanako-LS)

Abstract

It is widely recognized that the effects of a phase shift of fine sediment in large-scale debris flows are likely to be large. Therefore, in numerical simulations, it is essential to describe fine sediments in the fluid phase, and not in the solid phase. Recently, the "Kanako" numerical simulator has been widely used for a variety of objectives, particularly because it has a graphical user interface. However, to date, there is no widely available numerical simulation model for large-scale debris flows that includes the effects of phase shifts. Here, we present a modified version of Kanako to describe this phase shift for fine sediment. In the new numerical simulator, which we refer to as Kanako-LS, we assume that sediments can be classified into two groups in terms of sediment diameter (fine and coarse), and define the critical diameter of the sediment (Dc) as the smallest diameter at which sediments behave as a solid phase. Then, we test the applicability of Kanako-LS using an example of debris flows triggered by a deep-seated rapid (catastrophic) landslide in Japan. Our results suggest that Kanako-LS may be useful for a variety of types of large-scale debris flow, particularly if the amount of fine sediment and the magnitude of the interstitial fluid turbulence are sufficient.

Disaster Report of Koslanda Landslide in Sri Lanka on October 29, 2014

“…We considered the Kanako-LS would be applicable to describe debris flow in Koslanda. Details of the program can be found in a previous report [e.g., Uchida et al, 2013].…”

Development of Debris Flow Impact Force Models Based on Flume Experiments for Design Criteria of Soil Erosion Control Dam

“…Moreover, equation 10also considers fine soil particle into the calculation of the impact force of debris flow. Recently, several studies indicated the possibility that fine soil particles can be fluidized caused by phase shift, which can lead to an increase in density and flow regime changes of debris flow accordingly [22,23].…”

“…However, even after such model is improved and verified through additional experiment, it has its own limitations because it is inevitable to assume under which conditions in the field (such as soil moisture content) debris flow will occur. As the suggested models in the current study are expressed in simple empirical formula, they cannot estimate dynamic characteristics of debris flow and its temporal changes of the impact force in detail like numerical models [23,24]. Despite such challenges, equation (10) is meaningful for following reasons: (i) under few practical assumptions, impact force of debris flow can be easily estimated cost effectively in South Korea in a situation in which related design criteria are insufficient and (ii) the model was developed through flume experiments considering soil and topographic characteristics in South Korea while we had inadequate observation equipment for debris flow in field.…”

Survey Report of Sediment Disaster in Aranayake, Sri Lanka, on May, 2016

“…Based on the above, we tried the reproduction of the phenomenon using a one-dimensional debris flow simulation program that could consider the changes of flow condition from debris flow to normal turbulent flow developed by Uchida et al [2013]. Moreover, this program was included the processes of phase-shift of fine sediment.…”