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

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.

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

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.

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

2017 ◽  
Vol 17 (11) ◽  
pp. 1923-1938 ◽  
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 ◽  
Physical Analysis ◽  
Saturated Flow ◽  
Initiation Zone ◽  
Landslide Body ◽  
Steep Terrain

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.

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

2005 ◽  
Vol 42 (3) ◽  
pp. 919-931 ◽  
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.

scholarly journals Estimation of debris flow critical rainfall thresholds by a physically-based model

2012 ◽  
Vol 9 (11) ◽  
pp. 12797-12824 ◽  
Author(s):  
M. N. Papa ◽  
V. Medina ◽  
F. Ciervo ◽  
A. Bateman
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Rainfall Threshold ◽  
Richards Equation ◽  
Reduced Form ◽  
Physically Based Model ◽  
Rainfall Characteristics ◽  
South Italy ◽  
Infinite Slope Stability Model ◽  
Physically Based

Abstract. Real time assessment of debris flow hazard is fundamental for setting up warning systems that can mitigate its risk. A convenient method to assess the possible occurrence of a debris flow is the comparison of measured and forecasted rainfall with rainfall threshold curves (RTC). Empirical derivation of the RTC from the analysis of rainfall characteristics of past events is not possible when the database of observed debris flows is poor or when the environment changes with time. For landslides triggered debris flows, the above limitations may be overcome through the methodology here presented, based on the derivation of RTC from a physically based model. The critical RTC are derived from mathematical and numerical simulations based on the infinite-slope stability model in which land instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled trough a reduced form of the Richards equation. The simulations are performed in a virtual basin, representative of the studied basin, taking into account the uncertainties linked with the definition of the characteristics of the soil. A large number of calculations are performed combining different values of the rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall). For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive RTC curves. The methodology is implemented and tested on a small basin of the Amalfi Coast (South Italy).

Time Since Burning and Rainfall Characteristics Impact Post-Fire Debris-Flow Initiation and Magnitude

2021 ◽  
Vol 27 (1) ◽  
pp. 43-56
Author(s):  
Luke A. McGuire ◽  
Francis K. Rengers ◽  
Nina Oakley ◽  
Jason W. Kean ◽  
Dennis M. Staley ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Debris Flow ◽  
Debris Flows ◽  
Numerical Models ◽  
Ground Cover ◽  
Temporal Changes ◽  
Infiltration Capacity ◽  
Rainfall Characteristics ◽  
San Gabriel Mountains ◽  
Fire Debris

ABSTRACT The extreme heat from wildfire alters soil properties and incinerates vegetation, leading to changes in infiltration capacity, ground cover, soil erodibility, and rainfall interception. These changes promote elevated rates of runoff and sediment transport that increase the likelihood of runoff-generated debris flows. Debris flows are most common in the year immediately following wildfire, but temporal changes in the likelihood and magnitude of debris flows following wildfire are not well constrained. In this study, we combine measurements of soil-hydraulic properties with vegetation survey data and numerical modeling to understand how debris-flow threats are likely to change in steep, burned watersheds during the first 3 years of recovery. We focus on documenting recovery following the 2016 Fish Fire in the San Gabriel Mountains, California, and demonstrate how a numerical model can be used to predict temporal changes in debris-flow properties and initiation thresholds. Numerical modeling suggests that the 15-minute intensity-duration (ID) threshold for debris flows in post-fire year 1 can vary from 15 to 30 mm/hr, depending on how rainfall is temporally distributed within a storm. Simulations further demonstrate that expected debris-flow volumes would be reduced by more than a factor of three following 1 year of recovery and that the 15-minute rainfall ID threshold would increase from 15 to 30 mm/hr to greater than 60 mm/hr by post-fire year 3. These results provide constraints on debris-flow thresholds within the San Gabriel Mountains and highlight the importance of considering local rainfall characteristics when using numerical models to assess debris-flow and flood potential.

scholarly journals Quantitative Analysis of the Effects of an Earthquake on Rainfall Thresholds for Triggering Debris-Flow Events

2021 ◽  
Vol 9 ◽  
Author(s):  
Shuang Liu ◽  
Kaiheng Hu ◽  
Qun Zhang ◽  
Shaojie Zhang ◽  
Xudong Hu ◽  
...  
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Rainfall Intensity ◽  
Focal Depth ◽  
Rainfall Threshold ◽  
Effective Rainfall ◽  
Rainfall Thresholds ◽  
Jiuzhaigou Earthquake ◽  
The Wenchuan Earthquake ◽  
The Moment

The impacts of destructive earthquakes on rainfall thresholds for triggering the debris flows have not yet been well investigated, due to lacks of data. In this study, we have collected the debris-flow records from the Wenchuan, Lushan, and Jiuzhaigou earthquake-affected areas in Sichuan Province, China. By using a meteorological dataset with 3 h and 0.1° resolutions, the dimensionless effective rainfall and rainfall intensity-duration relationships were calculated as the possible thresholds for triggering the debris flows. The pre- and post-seismic thresholds were compared to evaluate the impacts of the various intensities of earthquakes. Our results indicate that the post-quake thresholds are much smaller than the pre-seismic ones. The dimensionless effective rainfall shows the impacts of the Wenchuan, Lushan, and Jiuzhaigou earthquakes to be ca. 26, 27, and 16%, respectively. The Wenchuan earthquake has the most significant effect on lowering the rainfall intensity-duration curve. Rainfall threshold changes related to the moment magnitude and focal depth are discussed as well. Generally, this work may lead to an improved post-quake debris-flow warning strategy especially in sparsely instrumented regions.

scholarly journals Mechanisms of Initiation, Runout, and Rainfall Thresholds of Extreme-Precipitation-Induced Debris Flows

2021 ◽  
Author(s):  
Srikrishnan Siva Subramanian ◽  
Ali. P. Yunus ◽  
Faheed Jasin ◽  
Minu Treesa Abraham ◽  
Neelima Sathyam ◽  
...  
Keyword(s):  
Debris Flow ◽  
Extreme Precipitation ◽  
Debris Flows ◽  
Maximum Velocity ◽  
Rainfall Threshold ◽  
Rainfall Thresholds ◽  
Long Runout ◽  
Loss Of Life ◽  
Extreme Precipitation Events ◽  
Precipitation Events

Abstract The frequency of unprecedented extreme precipitation events is increasing, and consequently, catastrophic debris flows occur in regions worldwide. Rapid velocity and long-runout distances of debris flow induce massive loss of life and damage to infrastructure. Despite extensive research, understanding the initiation mechanisms and defining early warning thresholds for extreme-precipitation-induced debris flows remain a challenge. Due to the nonavailability of extreme events in the past, statistical models cannot determine thresholds from historical datasets. Here, we develop a numerical model to analyze the initiation and runout of extreme-precipitation-induced runoff-generated debris flows and derive the Intensity-Duration (ID) rainfall threshold. We choose the catastrophic debris flow on 6 August 2020 in Pettimudi, Kerala, India, for our analysis. Our model satisfactorily predicts the accumulation thickness (7 m to 8 m) and occurrence time of debris flow compared to the benchmark. Results reveal that the debris flow was rapid, traveling with a maximum velocity of 9 m/s for more than 9 minutes. The ID rainfall threshold defined for the event suggests earlier thresholds are not valid for debris flow triggered by extreme precipitation. The methodology we develop in this study is helpful to derive ID rainfall thresholds for debris flows without historical data.

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

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.

Relationships among three repeated large-scale debris flows at Pubugou Ravine in the Wenchuan earthquake zone

2014 ◽  
Vol 51 (9) ◽  
pp. 951-965 ◽  
Author(s):  
S. Zhang ◽  
L.M. Zhang ◽  
H.X. Chen
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Large Scale ◽  
Solid Materials ◽  
2008 Wenchuan Earthquake ◽  
Hill Slope ◽  
Earthquake Zone ◽  
The Hill ◽  
Channel Deposits

The 12 May 2008 Wenchuan earthquake in China triggered numerous landslides. Loose landslide materials can easily evolve into deadly debris flows during wet seasons. During the period from 2008 to 2011, three separate large-scale debris flows occurred in the Pubugou Ravine near the epicentre of the earthquake that were among the largest repeated debris flows ever reported. Approximately 1.76 × 106 m3 of sediment was deposited during these three events. This paper aims to (i) analyze the movements of solid materials during the repeated debris flows, (ii) discuss the evolution of the initiation mechanisms of these debris flows, and (iii) evaluate the changing depositional morphology of the debris flow fans and examine the particle sizes of the debris flow materials. To achieve the above research objectives, timely field investigations were undertaken in the past 5 years after each of these debris flow events. Satellite images were used to delineate the boundaries of the initiation areas, the transportation channels, and the deposition zones of these debris flows. With the occurrence of the repeated debris flows, the hill slope deposits gradually evolved into channel deposits and the solid materials in the channels moved toward the gully mouth. Hence, channelized flows gradually became dominant. The debris fan materials of the repeated debris flows became coarser and coarser over time. The three debris flows were all characterized by coarse boulder fronts.

Spatial-Temporal Assessment of Debris Flow Risk in the Ms8.0 Wenchuan Earthquake-Disturbed Area

2016 ◽  
Vol 11 (4) ◽  
pp. 720-731 ◽  
Author(s):  
Xin Yao ◽  
◽  
Lingjing Li ◽  
Keyword(s):  
Debris Flow ◽  
Wenchuan Earthquake ◽  
Debris Flows ◽  
Early Warning Systems ◽  
Rainfall Threshold ◽  
Significant Loss ◽  
Seismogenic Fault ◽  
Mountain Area ◽  
Disturbed Area ◽  
Geological Conditions

For 5 years (2009–2013) after the 2008 Ms8.0 Wenchuan earthquake, rainfall led to the transformation of unconsolidated co-seismic deposits into extensive and severe debris flows, causing significant loss of life and property. For debris flows in the earthquake-disturbed area, a few common concerns exist. What is their spatial-temporal distribution? What are the controlling factors? How much is the rainfall threshold for debris flows? What areas are more susceptible? Where suffered the most severe losses of life and property? Using debris flow characteristics, this study analyzes the relationships between seismic geological factors, geomorphologic factors, extreme rainfall, and debris flows in the 5 years following the earthquake, and draws the following conclusions. (1) There are regional differences in the rainfall threshold for generation of debris flows, and the annual maximum 72-hour accumulated rainfall for triggering a debris flow decreases from pre-seismic periods (135–325 mm) to post-seismic periods (75–160 mm) by 44.4–50.8% in study area. (2) Areas with high debris flow susceptibility and hazard are primarily controlled by seismic geological conditions. (3) The long-term risk of debris flows will fall to moderate, and the affected area will shrink to that around the seismogenic fault. The results of this study will help with meteorological early warning systems, deployment of disaster prevention and control projects, and reconstruction site selection in the post-seismic Longmen Mountain area.

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