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.

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.

Flume investigation of cylindrical baffles for dissipation of debris flow energy

2021 ◽  
Author(s):  
Chan-Young Yune ◽  
Beom-Jun Kim
Keyword(s):  
Energy Dissipation ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Flow Characteristics ◽  
Digital Camera ◽  
Major Effect ◽  
Small Scale ◽  
Design Guideline ◽  
Flow Energy

&lt;p&gt;A debris flow with a high speed along valleys has been reported to cause serious damages to urban area or infrastructure. To prevent debris flow disaster, countermeasures for flow-impeding structures are installed on the flow path of debris flows. Recently, an installation of cylindrical baffles which are open-type countermeasures has increased because of a low construction cost, filtering out rocks, and an increased hydraulic continuity. However, a comprehensive design guideline for specification and arrangement on cylindrical baffles has not yet been suggested. Moreover, the design of baffle installation is mainly based on empirical approaches as the influence of baffle array on debris mobility is not well understood. In this study, to investigate the effect of cylindrical baffles on the flow characteristics of debris flow, a series of small-scale flume tests were performed according to the varying baffle height and row numbers of installed baffles. High-speed cameras and digital camera to record the flow interaction with baffles were installed at the top and side of the channel. To reproduce the viscosity of debris flows caused by fine-grained soil in the flume, glycerin was mixed with debris materials (sand and gravel). After the test, the velocity and energy dissipation according to various baffle arrays were estimated. Test results showed that the installation of baffles reduced the frontal velocity of debris flows. Furthermore, taller baffles also increased the effect of the energy dissipation in debris flows, but additional rows of the baffle did not have a major effect on the energy dissipation. Thus, increasing the height of baffle led to an increased efficiency of energy dissipation of debris flows.&lt;/p&gt;

scholarly journals Headwater sediment dynamics in a debris flow catchment constrained by high-resolution topographic surveys

2016 ◽  
Vol 4 (2) ◽  
pp. 489-513 ◽  
Author(s):  
Alexandre Loye ◽  
Michel Jaboyedoff ◽  
Joshua Isaac Theule ◽  
Frédéric Liébault
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Laser Scanning ◽  
Early Spring ◽  
Sediment Dynamics ◽  
Sediment Supply ◽  
Power Law Distribution ◽  
Sediment Reworking ◽  
Sediment Budgets ◽  
Sediment Transfer

Abstract. Debris flows have been recognized to be linked to the amounts of material temporarily stored in torrent channels. Hence, sediment supply and storage changes from low-order channels of the Manival catchment, a small tributary valley with an active torrent system located exclusively in sedimentary rocks of the Chartreuse Massif (French Alps), were surveyed periodically for 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which occurred twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during the winter–early spring season, following a power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge in spring and autumn, which shows effective hillslope–channel coupling. The occurrence of both debris flow events that occurred during the monitoring was linked to recharge from previous debris pulses coming from the hillside and from bedload transfer. Headwater debris sources display an ambiguous behaviour in sediment transfer: low geomorphic activity occurred in the production zone, despite rainstorms inducing debris flows in the torrent; still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting that the stored debris was not exhausted. The seasonal cycle of sediment yield seems to depend not only on debris supply and runoff (flow capacity) but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that monitoring the changes within a torrent's in-channel storage and its debris supply can improve knowledge on recharge thresholds leading to debris flow.

Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply

2021 ◽  
Author(s):  
Marisa C. Palucis ◽  
Thomas P. Ulizio ◽  
Michael P. Lamb
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Sediment Supply ◽  
Moderate Intensity ◽  
Sandy Sediment ◽  
Channel Network ◽  
Sediment Yields ◽  
First Order ◽  
Dry Ravel ◽  
Debris Flow Initiation

Steep, rocky landscapes often produce large sediment yields and debris flows following wildfire. Debris flows can initiate from landsliding or rilling in soil-mantled portions of the landscape, but there have been few direct observations of debris flow initiation in steep, rocky portions of the landscape that lack a thick, continuous soil mantle. We monitored a steep, first-order catchment that burned in the San Gabriel Mountains, California, USA. Following fire, but prior to rainfall, much of the hillslope soil mantle was removed by dry ravel, exposing bedrock and depositing ∼0.5 m of sandy sediment in the channel network. During a one-year recurrence rainstorm, debris flows initiated in the channel network, evacuating the accumulated dry ravel and underlying cobble bed, and scouring the channel to bedrock. The channel abuts a plowed terrace, which allowed a complete sediment budget, confirming that ∼95% of sediment deposited in a debris flow fan matched that evacuated from the channel, with a minor rainfall-driven hillslope contribution. Subsequent larger storms produced debris flows in higher-order channels but not in the first-order channel because of a sediment supply limitation. These observations are consistent with a model for post-fire ravel routing in steep, rocky landscapes where sediment was sourced by incineration of vegetation dams—following ∼30 years of hillslope soil production since the last fire—and transported downslope by dry processes, leading to a hillslope sediment-supply limitation and infilling of low-order channels with relatively fine sediment. Our observations of debris flow initiation are consistent with failure of the channel bed alluvium due to grain size reduction from dry ravel deposits that allowed high Shields numbers and mass failure even for moderate intensity rainstorms.

Research on Risk Level of Debris Flow in an Area

2014 ◽  
Vol 638-640 ◽  
pp. 2015-2018
Author(s):  
Qing Nian Yang ◽  
Shuai Tao Wu ◽  
Zhi Li
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Evaluation Method ◽  
Risk Level ◽  
The Tibetan Plateau ◽  
Adverse Conditions ◽  
Southeastern Margin ◽  
The Sichuan Basin ◽  
Original Vegetation ◽  
Steep Terrain

The research targets at the transition zone from the southeastern margin of the Tibetan Plateau to the Sichuan Basin; it is shown according to field survey: from 2008 to 2010, debris flow occurred twice, resulting in missing of two people, destruction on a lot of farmland and other serious disasters. Such the debris flows were because that the original vegetation was severely damaged after “5.12” earthquake, a lot of loose blocks were scattered in slopes and valleys, and also stimulated by abundant rainfall during rainy season, local steep terrain, as well as narrow valleys. The paper makes qualitative and quantitative evaluation on risk of debris flow within the region by single-valley debris flow risk evaluation method as proposed by Liu Xilin and Tang Chuan et al. it is shown from the results that the risk level H is 0.55, within scope of moderate risk. In case of any adverse conditions, debris flows may occur again.

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 Contribution of Excessive Supply of Solid Material to a Runoff-Generated Debris Flow during Its Routing Along a Gully and Its Impact on the Downstream Village with Blockage Effects

Water ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 169 ◽  
Author(s):  
Ming-liang Chen ◽  
Xing-nian Liu ◽  
Xie-kang Wang ◽  
Tao Zhao ◽  
Jia-wen Zhou
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Large Scale ◽  
Residential Buildings ◽  
Solid Material ◽  
Sediment Supply ◽  
Mitigation Measures ◽  
Dry Land ◽  
Field Investigations ◽  
Abundant Supply

On 8 August 2017, a runoff-generated debris flow occurred in the Puge County, Sichuan Province of southwestern China and caused huge property damage and casualties (25 people died and 5 people were injured). Emergency field investigations found that paddy fields, dry land, residential buildings and roads suffered different degrees of impact from the debris flow. This paper reveals the formation process of the debris flow by analyzing the characteristics of rainfall precipitation and sediment supply conditions in the study area and it approaches the practical application of hazard prevention and mitigation constructions. Doppler weather radar analysis indicates that a very high intensity rainfall occurred in the middle and upper zones of the basin, illustrating the importance of enhancing rainfall monitoring in high-altitude areas. The abundant supply of deposits in gully channels is among the significant causes of a transformation from mountain floods to large-scale debris flows. It was also found that the two culverts played an important role in the movement affecting the processes of debris flows which has substantially aggravated the destructive outcome. The excessive supply of solid material and local blockage with outburst along a gully must receive significant attention for the prediction of future debris flows, hazard prevention and mitigation measures.

The Effects of Particle Segregation on Debris Flow Fluidity Over a Rigid Bed

2020 ◽  
Vol 27 (1) ◽  
pp. 139-149
Author(s):  
Norifumi Hotta ◽  
Tomoyuki Iwata ◽  
Takuro Suzuki ◽  
Yuichi Sakai
Keyword(s):  
Shear Stress ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Particle Diameter ◽  
Flow Characteristics ◽  
Video Camera ◽  
Front Velocity ◽  
Flow Depth ◽  
Particle Segregation

ABSTRACT It is essential to consider the fluidity of a debris flow front when calculating its impact. Here we flume-tested mono-granular and bi-granular debris flows and compared the results to those of numerical simulations. We used sand particles with diameters of 0.29 and 0.14 cm at two mixing ratios of 1:1 and 3:7. Particle segregation was recorded with a high-speed video camera. We evaluated the fronts of debris flows at 0.5-second intervals. Then we numerically simulated one-dimensional debris flows under the same conditions and used the mean particle diameter when simulating mixed-diameter flows. For the mono-granular debris flows, the experimental and simulated results showed good agreement in terms of flow depth, front velocity, and flux. However, for the bi-granular debris flows, the simulated flow depth was less, and both the front velocity and flux were greater than those found experimentally. These differences may be attributable to the fact that the dominant shear stress was caused by the concentration of smaller sediment particles in the lower flow layers; such inverse gradations were detected in the debris flow bodies. Under these conditions, most shear stress is supported by smaller particles in the lower layers; the debris flow characteristics become similar to those of mono-granular flows, in contrast to the numerical simulation, which incorporated particle segregation with gradually decreasing mean diameter from the front to the flow body. Consequently, the calculated front velocities were underestimated; particle segregation at the front of the bi-granular debris flows did not affect fluidity either initially or over time.

Water and Sediment Supply Requirements for Post-Wildfire Debris Flows in the Western United States

2021 ◽  
Vol 27 (1) ◽  
pp. 73-85
Author(s):  
Paul M. Santi ◽  
Blaire Macaulay
Keyword(s):  
Debris Flow ◽  
High Intensity ◽  
Debris Flows ◽  
High Volume ◽  
Sediment Supply ◽  
Time Intervals ◽  
Burned Areas ◽  
Sufficient Intensity ◽  
Water Intensity ◽  
Short Time

ABSTRACT This work explores two hypotheses related to runoff-related post-wildfire debris flows: 1) their initiation is limited by rainstorm intensity rather than cumulative rainfall depths and 2) they are not sediment supply limited. The first hypothesis suggests that it is common to generate more than enough rainfall to account for the volume of water in the debris flow, but to actually produce a debris flow, the water must be delivered with sufficient intensity. This is demonstrated by data from 44 debris flows from eight burned areas in California, Colorado, and Utah. Assuming a debris flow comprises 30 percent water and 70 percent solids, these events were generated during rainstorms that produced an average of 17 times as much water as necessary to develop a debris flow. Even accounting for infiltration, the rainstorms still generated an overabundance of water. Intensity dependence is also shown by numerous cases in which the exact timing of debris flows can be pinpointed and is contemporaneous with high-intensity bursts of rainfall. The hypothesis is also supported by rainfall intensity-duration thresholds where high-volume storms without high-intensity bursts do not generate debris flows. The second hypothesis of sediment-supply independence for the initiation of debris flows is supported by a significant increase in flow volume occurring directly after wildfire, compared to flows in unburned terrain. Also, repeated flows within short time intervals are only possible with an abundance of channel sediment, dry ravel, and bank failure material that can be mobilized. Field observations confirm these sediment sources, even directly after a debris-flow.

Debris flow monitoring in China

2020 ◽  
Author(s):  
Xiaojun Guo
Keyword(s):  
Debris Flow ◽  
Debris Flows ◽  
Flow Characteristics ◽  
Western China ◽  
Flow Density ◽  
Flow Depth ◽  
Jinsha River ◽  
Flow Monitoring ◽  
Jiangjia Gully ◽  
Set Up

&lt;p&gt;&lt;strong&gt;Abstract: &lt;/strong&gt;Debris flow monitoring provides valuable data for scitienfic research and early warning, however, it is of difficulty to sucessfully achive because of the great damage of debris flows and the high cost. This report introduces monitoring systems in two debris flow watersheds in western China, the Jiangjia gully (JJG) in Yunnan Province and the Ergou valley in Sichuan Province. JJG is loacted in the dry-hot valley of Jinsha River, and the derbis flows are frequent due to the semi-arid climate, deep-cut topography and highly weathered slope surface. A long-term mornitoring work has been conducted in JJG and more than 500 debris flows events has been recorded since 1965. The monitoring system consists of 10 rainfall gauges and a measuring section, with instruments to measure the flow depth and velocity; and flow density is measured through sampling the fresh debris flow body. Ergou lies in the Wenchuan earthquake affected area and the monitoring began in 2013 to investigate the characteristics and development tendency of post-earthquake debris flows. Three stations were set up in the mainstream and tributaries, with instruments to measure the flow depth, velocity, and density. Over 10 debris flow events were recorded up to date.&lt;/p&gt;&lt;p&gt;Based on the monitoring output, the rainfall spatial distribution and thresholds for debris flows are proposed. The debris flow dynamics characteristics are analyzed, and the relations between the parameters, e.g. density, velocity, discharge and grain compositions are presented. The debris flow formation modes and the mechanisms in different regions are discriminated and simulation methods are suggested. It is anticipated that the monitoring results will promote understanding of debris flow characteristics in the western China.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; Debris flow, monitoring, rainfall, discharge, formation.&amp;#160;&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document