Variation in rainfall patterns triggering debris flow in the initiation zone of the Ichino-sawa torrent, Ohya landslide, Japan

Abstract. Debris flows usually occur in steep mountain channels and can be extremely hazardous as a result of their destructive power, long travel distance, and high velocity. However, their characteristics in the initiation zones, which could possibly be affected by temporal changes in the accumulation conditions of the storage (i.e., channel gradient and volume of storage) associated with sediment supply from hillslopes and the evacuation of sediment by debris flows, are poorly understood. Thus, we studied the relationship between the flow characteristics and the accumulation conditions of the storage in an initiation zone of debris flow at the Ohya landslide body in Japan using a variety of methods, including a physical analysis, a periodical terrestrial laser scanning (TLS) survey, and field monitoring. Our study clarified that both partly and fully saturated debris flows are important hydrogeomorphic processes in the initiation zones of debris flow because of the steep terrain. The predominant type of flow varied temporally and was affected by the volume of storage and rainfall patterns. Fully saturated flow dominated when the total volume of storage was <  10 000 m3, while partly saturated flow dominated when the total volume of the storage was >  15 000 m3. Debris flows form channel topography which reflects the predominant flow types during debris-flow events. Partly saturated debris flow tended to form steeper channel sections (22.2–37.3°), while fully saturated debris flow tended to form gentler channel sections ( <  22.2°). Such relationship between the flow type and the channel gradient could be explained by a simple analysis of the static force at the bottom of the sediment mass.

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Behaviour of debris flows located in a mountainous torrent on the Ohya landslide, Japan

Canadian Geotechnical Journal ◽

10.1139/t05-019 ◽

2005 ◽

Vol 42 (3) ◽

pp. 919-931 ◽

Cited By ~ 23

Author(s):

Fumitoshi Imaizumi ◽

Satoshi Tsuchiya ◽

Okihiro Ohsaka

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Water Pressure ◽

Pressure Sensors ◽

Ultrasonic Sensors ◽

Erosion And Deposition ◽

Video Cameras ◽

Muddy Water ◽

Initiation Zone ◽

Flow Type

Although information on the behaviour of debris flow in the initiation zone is important for the development of mitigative measures, field data regarding this behaviour are scarce. This research examines the behaviour of debris flow in the initiation zone, based on field observations in the upper Ichinosawa catchment of the Ohya landslide in Japan. In spring 1998, a monitoring system, consisting of video cameras, ultrasonic sensors, capacitive water depth probes, and water pressure sensors (WPS), was installed to assess the behaviour of debris flows in the initiation zone. On the basis of video image analysis, we found that main flow phases during debris-flow events consisted of flow containing largely muddy water and flow containing largely cobbles and boulders. Data obtained from ultrasonic sensors and WPS show that the former flow type (muddy flow) has large amounts of interstitial water throughout its mass, whereas the latter flow type has an unsaturated layer in the upper portion. Results indicate that the concentration of solids in debris flows differs from flow to flow. Debris flows in the upper Ichinosawa catchment cause both erosion and deposition and exhibit changes in their concentration of solids.Key words: debris flow, Ohya landslide, flow behaviour, observation, initiation zone.

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Debris Flow Susceptibility Map for Mount Rainier, Washington Based on Debris Flow Initiation Zone Characteristics from the November, 2006 Climate Event in the Cascade Mountains

10.15760/etd.2650 ◽

2000 ◽

Author(s):

Kassandra Lindsey

Keyword(s):

Debris Flow ◽

Susceptibility Map ◽

Cascade Mountains ◽

Initiation Zone ◽

Mount Rainier ◽

Climate Event ◽

Debris Flow Susceptibility ◽

Debris Flow Initiation

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Temporal changes in the debris flow threshold under the effects of ground freezing and sediment storage on Mt. Fuji

Earth Surface Dynamics ◽

10.5194/esurf-9-1381-2021 ◽

2021 ◽

Vol 9 (6) ◽

pp. 1381-1398

Author(s):

Fumitoshi Imaizumi ◽

Atsushi Ikeda ◽

Kazuki Yamamoto ◽

Okihiro Ohsaka

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Rainfall Threshold ◽

Temporal Changes ◽

Frozen Ground ◽

Sediment Storage ◽

Cold Regions ◽

Initiation Zone ◽

Ground Freezing ◽

Channel Deposits

Abstract. Debris flows are one of the most destructive sediment transport processes in mountainous areas because of their large volume, high velocity, and kinematic energy. Debris flow activity varies over time and is affected by changes in hydrogeomorphic processes in the initiation zone. To clarify temporal changes in debris flow activities in cold regions, the rainfall threshold for the debris flow occurrence was evaluated in Osawa failure at a high elevation on Mt. Fuji, Japan. We conducted field monitoring of the ground temperature near a debris flow initiation zone to estimate the presence or absence of seasonally frozen ground during historical rainfall events. The effects of ground freezing and the accumulation of channel deposits on the rainfall threshold for debris flow occurrence were analyzed using rainfall records and annual changes in the volume of channel deposits since 1969. Statistical analyses showed that the intensity–duration threshold during frozen periods was clearly lower than that during unfrozen periods. A comparison of maximum hourly rainfall intensity and total rainfall also showed that debris flows during frozen periods were triggered by a smaller magnitude of rainfall than during unfrozen periods. Decreases in the infiltration rate due to the formation of frozen ground likely facilitated the generation of overland flow, triggering debris flows. The results suggest that the occurrence of frozen ground and the sediment storage volume need to be monitored and estimated for better debris flow disaster mitigation in cold regions.

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Debris Flow Generation Based on Critical Discharge: A Case Study of Xiongmao Catchment, Southwestern China

10.20944/preprints202001.0012.v1 ◽

2020 ◽

Author(s):

Lingfeng Gong ◽

Chuan Tang ◽

Jiang Xiong ◽

Ning Li

Keyword(s):

Debris Flow ◽

Flow Analysis ◽

Solid Particles ◽

Rainfall Pattern ◽

K Value ◽

Rainfall Frequency ◽

Critical Discharge ◽

Key Factor ◽

Discharge Parameters ◽

Rainfall Patterns

A debris flows generation related to a poorly sorted mixture of soil, catchment topography and rainfall characteristic. Runoff of some depth on valley resulting from intensive rainfall can incur the sediments movement of beds or adjacent banks. The fluid flow in channel affected by rainfall parameters combinations, such as duration, intensity, cumulative rainfall, etc., is the key factor for debris movement. In this paper, the rainfall characteristics and occurrence conditions of debris flow in Xiongmao gully on July, 26th, 2016, have been explored, combined with field survey and indoor simulation experiment on the collected critical discharge parameters of debris movement. Further, debris distribution and the critical discharge characteristics have been analysed, by means of investigation on the catchment topography and occurrence cause of the debris flow, analysis of the critical discharge parameters on which the channel debris began to move, and K value clustering analysis method to characterize the rainfall pattern of the studied area, the discharge calculation of debris flow occurring in different rainfall patterns. The results have shown that, for the debris flow occurrence in Xiongmao gully, the debris initiation on the middle reaches of the gully provide the majority of solid particles for the disaster on July, 26th, 2016, and the upstream confluent provided catchment. Based on the relationship obtained from laboratory test, in which the calculated critical discharge was 43.8m3/s, less than the peak discharge (Qc =66.7m3/s), calculated by morphological method. In addition, it has been indicated that the dominated rainfall patterns of the studied area are first-quartile and second-quartile, that is, the rainfall is primarily at earlier or middle to preliminary stage of this time rainfall event. The critical discharge for the occurrence of debris flow on July, 26th was achieved 20a rainfall frequency, the larger runoff volume generated on shorten heavily rainfall. Based on individuality characteristics, such as distributed hydrological analysis, critical discharge and rainfall pattern of debris flow, the forewarning could be more efficient.

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Temporal changes in the debris flow threshold under the effects of ground freezing and sediment storage on Mt. Fuji

10.5194/esurf-2021-41 ◽

2021 ◽

Author(s):

Fumitoshi Imaizumi ◽

Atsushi Ikeda ◽

Kazuki Yamamoto ◽

Okihiro Osaka

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Rainfall Threshold ◽

Temporal Changes ◽

Frozen Ground ◽

Sediment Storage ◽

Cold Regions ◽

Initiation Zone ◽

Ground Freezing ◽

Channel Deposits

Abstract. Debris flows are one of the most destructive sediment transport processes in mountainous areas because of their large volume, high velocity, and kinematic energy. Debris flow activity varies over time and is affected by changes in hydrogeomorphic processes in the initiation zone. To clarify temporal changes of debris flow activities in cold regions, the rainfall threshold for the debris flow occurrence was evaluated in Osawa failure at a high elevation on Mt. Fuji, Japan. We conducted field monitoring of the ground temperature near a debris flow initiation zone to estimate the presence or absence of seasonally frozen ground during historical rainfall events. The effects of ground freezing and the accumulation of channel deposits on the rainfall threshold for debris flow occurrence were analyzed using rainfall records and annual changes in the volume of channel deposits since 1969. Statistical analyses showed that the intensity-duration threshold during frozen periods was clearly lower than that during unfrozen periods. A comparison of maximum hourly rainfall intensity and total rainfall also showed that debris flows during frozen periods were triggered by a smaller magnitude of rainfall than during unfrozen periods. Decreases in the infiltration rate due to the formation of frozen ground likely facilitated the generation of overland flow, triggering debris flows. During unfrozen periods, the rainfall threshold was higher when the volume of channel deposits was larger. Increases in the water content in channel deposits caused by the infiltration of rainfall is likely important for the debris flow occurrence during unfrozen periods. The results suggest that the occurrence of frozen ground and the sediment storage volume need to be monitored and estimated for better debris flow disaster mitigation in cold regions.

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Hydrogeomorphic processes in a steep debris flow initiation zone

Geophysical Research Letters ◽

10.1029/2006gl026250 ◽

2006 ◽

Vol 33 (10) ◽

pp. n/a-n/a ◽

Cited By ~ 53

Author(s):

Fumitoshi Imaizumi ◽

Roy C. Sidle ◽

Satoshi Tsuchiya ◽

Okihiro Ohsaka

Keyword(s):

Debris Flow ◽

Initiation Zone ◽

Debris Flow Initiation

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Interactions between the accumulation of sediment storage and debris flow characteristics in a debris-flow initiation zone, Ohya landslide body, Japan

10.5194/nhess-2017-20 ◽

2017 ◽

Author(s):

Fumitoshi Imaizumi ◽

Yuichi S. Hayakawa ◽

Norifumi Hotta ◽

Haruka Tsunetaka ◽

Okihiro Ohsaka ◽

...

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Laser Scanning ◽

Flow Characteristics ◽

Sediment Supply ◽

Small Scale ◽

Physical Analysis ◽

Initiation Zone ◽

Landslide Body ◽

Steep Terrain

Abstract. Debris flows often occur in steep mountain channels, and can be extremely hazardous as a result of their destructive power, long travel distance, and high velocity. However, their characteristics in the initiation zones, which could possibly be affected by temporal changes in the channel topography associated with sediment supply from hillslopes and the evacuation of sediment by debris flows, are poorly understood. Thus, we studied the interaction between the flow characteristics and the topography in an initiation zone of debris flow at the Ohya landslide body in Japan using a variety of methods, including a physical analysis, a periodical terrestrial laser scanning (TLS) survey, and field monitoring. Our study clarified that both partly and fully saturated debris flows are important hydrogeomorphic processes in the initiation zones of debris flow because of the steep terrain. The predominant type of flow varied temporally and was affected by the volume of storage and rainfall patterns. The small-scale channel gradient (on the order of meters) formed by debris flows differed between the predominant flow types during debris flow events. The relationship between flow type and the slope gradient could be explained by a simple analysis of the static force at the bottom of the sediment mass.

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