Study on an Evaluation Method of Initiation Probability of Debris Flows During Heavy Rainfall

Abstract

In an extreme climate event named "the Heavy Rain Event of July 2018," prolonged and widespread heavy rainfall in western Japan caused several debris flows, which led the sediment to flow into rivers, causing further damage from sediment-flood inundation. For the existing landslide alert information, it is important to establish prediction methods that account for the amount of rainfall on individual mountain slopes and the topographic and geological information. The estimation of the probability of debris flow initiation and quantitative risk assessment have been challenging issues. In order to solve this problem, in this paper, the rainfall data of XRAIN with high spatial resolution and the features of the slope failure sites were examined during heavy rainfall events. This paper also discussed the reliability of rainfall index ' to the heavy rainfall with strong long-term precipitation in July 2018, which is different from previous disasters due to the heavy rainfall with strong short-term precipitation, such as those in August 2014 and June 1999.

Risk-Level Assessment of Small-Scale Mountain Streams Using a Digital Elevation Model

“…Results of research on debris flow using DEMs have also been reported in the field of railways, and Nunokawa et al 17) proposed a method to evaluate the risk of debris flow using a DEM-based analytical model. 18),19) Hayashi et al 20) evaluated the risk of debris flow through simulations using DEM. In a previous study, 21) the authors used aerial photographs and DEM to estimate increase in soil cohesion due to thickness of the slope surface layer and tree root systems to predict the risk of basin slope collapse during rainfall events.…”

<i>-Editorial-</i> SPECIAL ISSUE ON THE HEAVY RAIN EVENT OF JULY 2018 IN WESTERN JAPAN

“…Kobashi et al 9) examined the rainfall data from the XRAIN network that has excellent spatial resolution, showing the features of each slope in mountainous areas where slope failure occurred during the heavy rain event of July 2018, in which rain fell over a wide area for an extended period, producing numerous debris flows. In contrast to past debris flow disasters in Hiroshima Prefecture in which intense short-term rainfall was predominant, this rain event was characterized by intense long-term rainfall.…”