scholarly journals Debris Flow Characteristics in Flume Experiments Considering Berm Installation

2021 ◽  
Vol 11 (5) ◽  
pp. 2336
Author(s):  
Hyungjoon Chang ◽  
Kukhyun Ryou ◽  
Hojin Lee
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Mobility Ratio ◽  
Mitigation Measures ◽  
Volumetric Concentration ◽  
Flume Experiments ◽  
Flume Tests ◽  
Number Flow ◽  
Channel Slope

This study was conducted to identify the characteristics and mobility of debris flows and analyze the performance of a berm as a debris flow mitigation measure. The debris flow velocity, flow depth, Froude number, flow resistance coefficients, and mobility ratio were accordingly determined using the results of flume tests. To analyze the influence of the berm, the results for a straight channel test without a berm were compared with those for a single-berm channel test. The debris flow velocity was observed to increase with increasing channel slope and decreasing volumetric concentration of sediment, whereas the mobility ratio was observed to increase with increasing channel slope and volumetric concentration of sediment. In addition, it was confirmed that the installation of a berm significantly decreased the debris flow velocity and mobility ratio. This indicates that a berm is an effective method for reducing damage to areas downstream of a debris flow by decreasing its potential mobility. By identifying the effects of berms on debris flow characteristics according to the channel slope and volumetric concentration of sediment, this study supports the development of berms to serve as debris flow damage mitigation measures.

scholarly journals Laboratory Analysis of Debris Flow Characteristics and Berm Performance

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2223
Author(s):  
Kukhyun Ryou ◽  
Hyungjoon Chang ◽  
Hojin Lee
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Flow Depth ◽  
Volumetric Concentration ◽  
Runout Distance ◽  
Deposition Area ◽  
Lateral Width ◽  
Channel Slope ◽  
Study Laboratory

In this study, laboratory tests were used to determine the deposition characteristics (runout distance, lateral width, and deposition area) of debris flow and their relationships with the flow characteristics (flow velocity and flow depth) according to the presence of a berm. An experimental flume 1.3 to 1.9 m long, 0.15 m wide, and 0.3 m high was employed to investigate the effects of channel slope and volumetric concentration of sediment with and without the berm. The runout distance (0.201–1.423 m), lateral width (0.045–0.519 m), and deposition area (0.008–0.519 m2) increased as the channel slope increased and as the volumetric concentration of sediment decreased. These quantities also increased with the flow velocity and flow depth. In addition, the maximum reductions in the runout distance, lateral width, and deposition area were 69.1%, 65.9%, and 93%, respectively, upon berm installation. The results of this study illustrate general debris flow characteristics according to berm installation; the reported relationship magnitudes are specific to the experimental conditions described herein. However, the results of this study contribute to the design of site-specific berms in the future by providing data describing the utility and function of berms in mitigating debris flow.

scholarly journals Debris-flow velocity and volume estimations based on seismic data

2021 ◽  
Author(s):  
Andreas Schimmel ◽  
Velio Coviello ◽  
Francesco Comiti
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Seismic Data ◽  
Debris Flows ◽  
Cross Correlation ◽  
Sampling Rate ◽  
Early Warning Systems ◽  
Velocity Estimation ◽  
Mitigation Measures ◽  
Strong Control

Abstract. The estimation of debris-flow velocity and volume is a fundamental task for the development of early warning systems, the design of control structures and other mitigation measures. Previous analysis of the seismic energy produced by debris flows showed that the peak amplitudes are representative of the kinetic energy of each surge and debris-flow discharge can be therefore estimated based on seismic signals. Also, the debris-flow velocity can be calculated using seismic data recorded at two spatial separated stations located along the channel by the use of cross-correlation. This work provide a first approach for estimating the total volume of debris flows based on the seismic signal detected with simple, low-cost geophones installed along the debris-flow channel. The developed methods was applied to seismic data collected on three different test sites in the Alps: Gadria (IT), Lattenbach (AT), and Cancia (IT). An adaptable cross-correlation time window was used, which can offer a better estimation of the velocity compared to a constant window length. The analyses of the seismic data of 14 debris flows that occurred from 2014 to 2018 shows the strong control of the sampling rate and the sensor-distance on the velocity estimation. A simple approach based on a linear relation between square of the seismic amplitude and the event magnitude is proposed for a first order estimation of the debris-flow magnitude.

scholarly journals The effect of debris-flow sediment grain size distribution on fan forming processes

2021 ◽  
Author(s):  
Haruka Tsunetaka ◽  
Norifumi Hotta ◽  
Yuichi Sakai ◽  
Thad Wasklewicz
Keyword(s):  
Grain Size ◽  
Debris Flow ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Flow Characteristics ◽  
Granular Flows ◽  
Spatial Diversity ◽  
Flume Experiments ◽  
Sediment Grain Size ◽  
Average Grain Size

Abstract. Knowledge of the processes driving debris-flow fan evolution are critical in the support of efforts to mitigate related hazards, reduce risk to populations and infrastructure, and reconstruct the history of sediment dynamics in mountainous areas. Research on debris-flow fan development has focused on topographic controls, debris-flow volume and rheology, and the sequence of occurrence of debris flows. While these items have explained a great deal about fan formation and specifically avulsion and runout mechanisms, there is a need to further investigate other properties as they relate to debris-flow fan formative process. Here, we examined the role of debris-flow grain-size distribution on fan formation. Flume experiments were employed to examine the morphology of debris-flow fans that resulted from flows with mono- or multi-granular sediment composition with the same average grain size. All other flow characteristics were held constant. The mono-granular flows formed a symmetric-like fan morphology because there was little avulsion during the formation process. The multi-granular flows produced fans with an asymmetric morphology. Avulsions occurred on both lateral extents of the fan during the early stages of fan development and caused the runout direction to shift produce the fan asymmetry. Grain-size distribution was closely related to spatial diversity in fan morphology and stratigraphy.

scholarly journals Experimental Study of Flow Characteristics in A Rectangular Gravel Bed Channel

2021 ◽  
Vol 873 (1) ◽  
pp. 012047
Author(s):  
Robby Yussac Tallar ◽  
Dea Teodora Ferninda ◽  
Efferiki ◽  
Prabu Mandvi Hafiz Anjar Suhendar ◽  
Frankie Pandapotan Purba
Keyword(s):  
Experimental Study ◽  
Flow Velocity ◽  
Friction Factor ◽  
Flow Resistance ◽  
Open Channel ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Flume Experiments ◽  
Sediment Bed ◽  
Set Up

Abstract In an open channel flow, the characteristics of flow resistance are greatly affected by the roughness of the base and the walls of the channel. The existence of an object or other material, including gravel, also influenced the resistance of flow, therefore the purpose of this study is to examine the flow characteristics (flow velocity and flow resistance) in gravel open channel by using experimental study. A laboratory study to explore the effect of channel bed in terms of roughness of types of sediment on the hydraulics flow in 8 m length x 40 cm width a rectangular channel is presented. The study consists of an extensive set of rectangular flume experiments for flows with certain slope and sediment bed. The study was using the Before After Control Impact (BACI) method by set up five different scenarios. The results show that the lowest flow velocity (v=0.3041 m/sec) was occurred in the scenario 3 (50%sand and 50% gravel). Based on the Manning’ coefficient (n), it was also found that at the 100% discharge flow condition, the highest value of friction factor (f=0.0780) within 5 scenarios was scenario 3 with the sediment consisted of 50%sand and 50%gravel. Whereas the value of the lowest friction factor(f=0.0652) was scenario 1 with the sediment only gravel within. It concluded that the results gave the lower value of Manning’ coefficient (n) compared to the table of Manning’s coefficient (f= 0.04) for the channel with gravel base condition.

scholarly journals Numerical Simulation of a Debris Flow on the Basis of a Two-Dimensional Continuum Body Model

Geosciences ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 45
Author(s):  
Hiroshi Takebayashi ◽  
Masaharu Fujita
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Flow Characteristics ◽  
Maximum Flow ◽  
Heavy Rain ◽  
Horizontal Distribution ◽  
Residential Area ◽  
Two Dimensional ◽  
Flow Depth ◽  
Maximum Flow Velocity

A two-dimensional debris and mud flow model that considers both laminar and turbulence flow was developed. Subsequently, the model was applied to a debris flow that occurred in Asaminami, Hiroshima, Japan in August 2014. The applicability of the model and the debris flow characteristics are discussed. The calculated horizontal distribution of sediment deposited in the Asaminami residential area was in good agreement with the horizontal distribution of the deposited large rocks and driftwood. This result indicates that the fine material in the downstream area was transported by water flow resulting from heavy rain that occurred after the debris flow. The scale of the initial debris flow was small; however, it increased with time, because eroded bed material and water were entrained to it. Therefore, it is important to reproduce the development process of debris flows to predict the amount of sediment produced, the deepest flow depth, the maximum flow velocity, and the inundation area. The averaged velocity of the simulated debris flow was about 9 m/s, and the velocity at the entrance to the residential area was about 8 m/s. This kind of information can be used to design sediment deposition dams. The travel time of the simulated debris flow from the upstream end of the main channel to the entrance of the residential area was 96 s. This kind of information can be used for making evacuation plans. Valley bed steps can suppress the deepest flow depth which is very important for the design of check dams; therefore, the high-resolution elevation data and fine numerical grids that reproduce step shapes are required to accurately calculate the deepest flow depth and maximum flow velocity.

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

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Song Eu ◽  
Sangjun Im ◽  
Dongyeob Kim
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Impact Force ◽  
Erosion Control ◽  
Velocity Model ◽  
Design Criteria ◽  
Slope Gradient ◽  
Flume Experiments ◽  
Soil Erosion Control ◽  
The Impact

Soil erosion control dams are widely used as part of measures to reduce damage caused by debris flow all over the world. Engineering considerations are needed for proper design of erosion control dams, but in the Republic of Korea, the impact force of debris flow is not fully reflected in the current design criteria of the dam. Against this backdrop, this study was conducted to estimate the impact force of debris flow for the practical purpose of designing erosion control dam. Simulated flume experiments were performed to develop the relationship to estimate the flow velocity as well as the impact force of debris flow. Experimental results showed that increases both in sediment mixture volume and flume slope gradient led to an increase in flow velocity. Especially, it was found that as clay content increased gradually, the flume slope gradient had greater impact on the increase of flow velocity. Also, it was proved that the impact force of debris flow was well fitted to the hydrodynamic model as it showed linear correlation with the flow velocity. Then, the debris-flow velocity model was established based on the factor related to the debris-flow velocity. Finally, the dynamic model to estimate the impact force of debris flow was introduced utilizing correlations between the established debris-flow velocity model and Froude number. Both models which were developed with using statistically significant watershed characteristics succeeded in explaining the experiment results in a more accurate way compared to existing models. Therefore, it is highly expected that these models can be fully utilized to estimate impact force of debris flow which will be required to design erosion control dams in practical use through overcoming their identified limitations.

Debris flow impact on a flexible barrier: laboratory flume experiments and force-based mechanical model validation

2021 ◽  
Vol 106 (1) ◽  
pp. 735-756
Author(s):  
R. Brighenti ◽  
L. Spaggiari ◽  
A. Segalini ◽  
R. Savi ◽  
G. Capparelli
Keyword(s):  
Debris Flow ◽  
Model Validation ◽  
Mechanical Model ◽  
Flume Experiments ◽  
Flexible Barrier ◽  
Laboratory Flume

Application of a combined and automated monitoring and early warning system for debris flows at the Dawinbach

2021 ◽  
Author(s):  
Tobias Schöffl ◽  
Richard Koschuch ◽  
Philipp Jocham ◽  
Johannes Hübl
Keyword(s):  
Debris Flow ◽  
Early Warning ◽  
Pulse Compression ◽  
Mitigation Measures ◽  
Heavy Rainfall Event ◽  
Monitoring Site ◽  
Traffic Lights ◽  
The Road ◽  
Pulse Compression Radar ◽  
Monitoring And Early Warning

<p>After a heavy rainfall event on August 31<sup>st</sup>, 2019, a debris flow at the Dawinbach in the municipality of Strengen (Tyrol, Austria) caused a blockage of the culvert below the provincial road B-316 and deposition in the residential area. The debris deposition raised up to 2 to 3 meters on the road and led to property damage to real estate. The total volume of the debris flow was approximately 15 000 cubic meters.</p><p>In order to control a further debris flow of this magnitude, the Austrian Service of Torrent and Avalanche Control started to construct mitigation measures. They include a channel relocation in order to significantly increase the channel crosssection. Hence the construction company STRABAG is also relocating the provincial road bridge.</p><p>Since the risk for this road section and for the workers on site is particularly high during the construction period, a combined monitoring and early warning concept was developed and implemented by the BOKU, Vienna and the company IBTP Koschuch.</p><p>The monitoring site consisting of a pulse compression radar and a pull rope system was installed 800m upstream from the fan. The combination of the two sensors now results in three major advantages.</p><ul><li>At sensor level, the system operates redundantly.</li> <li>A more reliable differentiation between increased discharge or debris flow is given.</li> <li>In the event of a false alarm, the system provides easier diagnosis and assignment of the fault.</li> </ul><p>Two events of increased runoff occurred during the deployment period. Both were successfully detected by the pulse compression radar. Here, the first event was used for threshold validation of the radar unit. Thus, an alarm could already be sent out automatically for the second one. The road is controlled by an integrated light signal system consisting of three traffic lights. A siren near the construction site can warn workers of an impending event by means of an acoustic signal. The reaction time after the alarm has been triggered is between 75 and 150 seconds, depending on the speed of the debris flow. The responsible authorities are informed by sending an SMS chain, which includes details about the type of process and the type of the activated triggering system.</p>

scholarly journals The Development of a 1-D Integrated Hydro-Mechanical Model Based on Flume Tests to Unravel Different Hydrological Triggering Processes of Debris Flows

Water ◽  
2018 ◽  
Vol 10 (7) ◽  
pp. 950 ◽  
Author(s):  
Theo van Asch ◽  
Bin Yu ◽  
Wei Hu
Keyword(s):  
Debris Flow ◽  
Mechanical Model ◽  
Debris Flows ◽  
Overland Flow ◽  
Slope Angle ◽  
Great Influence ◽  
Flume Experiments ◽  
Triggering Mechanisms ◽  
Bed Material ◽  
Triggering Process

Many studies which try to analyze conditions for debris flow development ignore the type of initiation. Therefore, this paper deals with the following questions: What type of hydro-mechanical triggering mechanisms for debris flows can we distinguish in upstream channels of debris flow prone gullies? Which are the main parameters controlling the type and temporal sequence of these triggering processes, and what is their influence on the meteorological thresholds for debris flow initiation? A series of laboratory experiments were carried out in a flume 8 m long and with a width of 0.3 m to detect the conditions for different types of triggering mechanisms. The flume experiments show a sequence of hydrological processes triggering debris flows, namely erosion and transport by intensive overland flow and by infiltrating water causing failure of channel bed material. On the basis of these experiments, an integrated hydro-mechanical model was developed, which describes Hortonian and saturation overland flow, maximum sediment transport, through flow and failure of bed material. The model was calibrated and validated using process indicator values measured during the experiments in the flume. Virtual model simulations carried out in a schematic hypothetical source area of a catchment show that slope angle and hydraulic conductivity of the bed material determine the type and sequence of these triggering processes. It was also clearly demonstrated that the type of hydrological triggering process and the influencing geometrical and hydro-mechanical parameters may have a great influence on rainfall intensity-duration threshold curves for the start of debris flows.

Sign in / Sign up

Export Citation Format

Share Document