scholarly journals Exploiting LSPIV to assess debris-flow velocities in the field

2018 ◽  
Vol 18 (1) ◽  
pp. 1-13 ◽  
Author(s):  
Joshua I. Theule ◽  
Stefano Crema ◽  
Lorenzo Marchi ◽  
Marco Cavalli ◽  
Francesco Comiti
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Sediment Trap ◽  
Debris Flows ◽  
Large Scale ◽  
Sediment Concentration ◽  
Surface Velocity ◽  
Preliminary Treatment ◽  
Flow Surface ◽  
Scale Particle

Abstract. The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

scholarly journals Exploiting LSPIV to assess debris flow velocities in the field

2017 ◽  
Author(s):  
Joshua I. Theule ◽  
Stefano Crema ◽  
Lorenzo Marchi ◽  
Marco Cavalli ◽  
Francesco Comiti
Keyword(s):  
Debris Flow ◽  
Sediment Trap ◽  
Debris Flows ◽  
Large Scale ◽  
Sediment Concentration ◽  
Surface Velocity ◽  
Preliminary Treatment ◽  
Flow Surface ◽  
Image Velocimetry ◽  
Scale Particle

Abstract. The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes, and for the assessment of related hazards. Large scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris flow events, each of them consisting of several surges featuring different sediment concentration, flow stage and velocity, have been analyzed at the inlet of a sediment trap in a stream of the eastern Italian Alps (Gadria Creek). Free softwares have been employed for preliminary treatment (ortho-rectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements on the ortho-rectified imagery and with front velocity measured from the hydrographs in a channel reach approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross-section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows, and permit to identify the most crucial aspects for improving the accuracy of debris flows velocity measurements.

scholarly journals Debris-flow velocities and superelevation in a curved laboratory channel

2015 ◽  
Vol 52 (3) ◽  
pp. 305-317 ◽  
Author(s):  
Christian Scheidl ◽  
Brian W. McArdell ◽  
Dieter Rickenmann
Keyword(s):  
Debris Flow ◽  
Flow Velocity ◽  
Correction Factor ◽  
Debris Flows ◽  
Laboratory Experiments ◽  
Flow Conditions ◽  
Vortex Equation ◽  
Flow Surface ◽  
Sediment Mixture ◽  
Sediment Mixtures

The vortex equation is often used to estimate the front velocity of debris flows using the lateral slope of the flow surface through a channel bend of a given radius. Here we report on laboratory experiments evaluating the application of the vortex equation to channelized debris flows. Systematic laboratory experiments were conducted in a 8 m long laboratory flume with a roughened bed, semi-circular cross section (top width 17 cm), and two different bend radii (1.0 and 1.5 m) with a common bend angle of 60°, and two channel inclinations (15° and 20°). Four sediment mixtures were used with systematic variations in the amount of fine sediment. In the experiments, 12 kg of water-saturated debris were released in a dam-break fashion, and multiple experiments were conducted to verify the repeatability for a given sediment mixture. Data are available for 69 experimental releases at a channel inclination of 20° and 16 releases at an inclination of 15°. Flow velocity was determined with high-speed video, and flow depth and the lateral inclination of the flow surface (superelevation) were measured using laser sensors. In general, the results from an individual sediment mixture are repeatable. We found that the channel slope as well as centerline radius have a significant influence on the correction factor k used in the vortex equation. Relatively coarse-grained sediment mixtures have larger superelevation angles than finer-grained mixtures. We found a statistically significant relation between the correction factor and Froude number. Correction factors of 1 < k < 5 were found for supercritical flow conditions. However, for subcritical flow conditions the correction factor shows a larger value as a function of the Froude number, which leads to an adaption of the forced vortex formula considering active and passive earth pressures. Finally, based on our experimental results, we present a forced vortex equation for debris-flow velocity estimation without a correction factor.

Reanalysis of Flash Floods and Debris Flows on two continents and their management strategies

2021 ◽  
Author(s):  
Juan Daniel Rios-Arboleda
Keyword(s):  
Risk Management ◽  
Developing Countries ◽  
South America ◽  
Debris Flow ◽  
Debris Flows ◽  
Large Scale ◽  
Management Strategies ◽  
Original Analysis ◽  
Risk Management Strategies ◽  
Latitudinal Patterns

&lt;p&gt;This research expands the original analysis of Baker and Costa (1987) including data from Europe and South America with the objective to understand if there are emerging latitudinal patterns. In addition, the threshold proposed by Zimmermann et al. (1997) it is evaluated with the data from tropical zones finding that this is a good predictor.&lt;/p&gt;&lt;p&gt;Mainly, recent Debris Flow occurred in South America are analyzed with the aim of identifying the best risk management strategies and their replicability for developing countries, particularly, the cases that have occurred in Colombia and Venezuela in the last 30 years are analyzed in order to compare management strategies and understand which are the most vulnerable areas to this phenomenon.&lt;/p&gt;&lt;p&gt;It is concluded that large-scale and multinational projects such as SED ALP are required in South America to better characterize events that have left multiple fatalities (sometimes hundreds of people) and better understand how to manage the risk on densely populated areas.&lt;/p&gt;&lt;p&gt;Finally, the use of amateur videos is proposed to characterize these events in nations with limited budgets for projects such as SED ALP, methodology that will be described extensively in later works.&lt;/p&gt;

Research on Motion Characteristics and Formation Mechanism of Debris Flow

2014 ◽  
Vol 711 ◽  
pp. 388-391
Author(s):  
Ji Wei Xu ◽  
Ming Dong Zhang ◽  
Mao Sheng Zhang
Keyword(s):  
Debris Flow ◽  
Formation Mechanism ◽  
Debris Flows ◽  
Catchment Area ◽  
Large Scale ◽  
Large Range ◽  
Extreme Rainfall ◽  
Small Catchment ◽  
Rainfall Characteristics ◽  
Motion Characteristics

On July 9 2013, debris flows occurred around Longchi town with large scale and wide harm, which was a great threat to people's life and property as well as reconstruction work. Debris flow ditch in the surrounding town was studied. This paper focused on loose materials, topography and rainfall characteristics, and explored the formation mechanism of debris flow in Longchi town. The result shows that: a small catchment area in valleys also have the risk of large range of accumulation of debris flow, the debris flow is caused by a lot of loose materials in mountains after earthquake and extreme rainfall. Research results contribute to a better understanding of trigger condition of debris flow after earthquake.

scholarly journals Risk assessment of debris flow based on group decision making – A case study of Luanchuan County, Henan Province, China

2018 ◽  
Vol 175 ◽  
pp. 04025
Author(s):  
Pengyu Chen ◽  
Ying Kong
Keyword(s):  
Risk Assessment ◽  
Decision Making ◽  
Debris Flow ◽  
Group Decision Making ◽  
Debris Flows ◽  
Large Scale ◽  
Group Decision ◽  
Henan Province ◽  
Comprehensive Assessment ◽  
Material Sources

Luanchuan County, located in the mountains of Western Henan Province, is characterized by poor geological environment and abundant material sources and rainfalls. Debris flows have occurred many times in this county, and in some gully debris flows exhibit a large scale, requiring risk assessment. In the multi-factor comprehensive assessment methods for debris flow risk, it is really important to determine the weight of each factor since this affects the reliability of the assessment results. Given that the subjective weighting method can accurately reflect the importance of each factor, in order to improve the reliability of subjective weighting, the group decision making method is used to determine the weight of each factor. Group decision making is realized using the analytic hierarchy process and the data fusion algorithm. In this method, the expert combination weight is determined; on this basis, a model for comprehensive assessment of debris flow risk is established by the linear weighted sum method, and risk assessment is performed for gullies with medium to large-scale debris flows in the study area. The assessment results show that all debris flow gullies face minor to moderate risks. For gullies with high risk degree, it is suggested to timely clear material sources in channels and construct or reinforce retaining dams in order to prevent re-occurrence of debris flows.

scholarly journals Applications of simulation technique on debris-flow hazard zone delineation: a case study in Hualien County, Taiwan

2010 ◽  
Vol 10 (3) ◽  
pp. 535-545 ◽  
Author(s):  
S. M. Hsu ◽  
L. B. Chiou ◽  
G. F. Lin ◽  
C. H. Chao ◽  
H. Y. Wen ◽  
...  
Keyword(s):  
Debris Flow ◽  
Yield Stress ◽  
Empirical Model ◽  
Water Conservation ◽  
Debris Flows ◽  
Sediment Concentration ◽  
Hazard Zone ◽  
Debris Flow Hazard ◽  
Debris Flow Disaster ◽  
Soil And Water

Abstract. Debris flows pose severe hazards to communities in mountainous areas, often resulting in the loss of life and property. Helping debris-flow-prone communities delineate potential hazard zones provides local authorities with useful information for developing emergency plans and disaster management policies. In 2003, the Soil and Water Conservation Bureau of Taiwan proposed an empirical model to delineate hazard zones for all creeks (1420 in total) with potential of debris flows and utilized the model to help establish a hazard prevention system. However, the model does not fully consider hydrologic and physiographical conditions for a given creek in simulation. The objective of this study is to propose new approaches that can improve hazard zone delineation accuracy and simulate hazard zones in response to different rainfall intensity. In this study, a two-dimensional commercial model FLO-2D, physically based and taking into account the momentum and energy conservation of flow, was used to simulate debris-flow inundated areas. Sensitivity analysis with the model was conducted to determine the main influence parameters which affect debris flow simulation. Results indicate that the roughness coefficient, yield stress and volumetric sediment concentration dominate the computed results. To improve accuracy of the model, the study examined the performance of the rainfall-runoff model of FLO-2D as compared with that of the HSPF (Hydrological Simulation Program Fortran) model, and then the proper values of the significant parameters were evaluated through the calibration process. Results reveal that the HSPF model has a better performance than the FLO-2D model at peak flow and flow recession period, and the volumetric sediment concentration and yield stress can be estimated by the channel slope. The validation of the model for simulating debris-flow hazard zones has been confirmed by a comparison of field evidence from historical debris-flow disaster data. The model can successfully replicate the influence zone of the debris-flow disaster event with an acceptable error and demonstrate a better result than the empirical model adopted by the Soil and Water Conservation Bureau of Taiwan.

Large scale particle image velocimetry measurement of river surface velocity based on images captured by a camera of the mobile phone

2020 ◽  
Author(s):  
Wen-Cheng Liu ◽  
Wei-Che Huang
Keyword(s):  
Particle Image Velocimetry ◽  
Mobile Phone ◽  
Large Scale ◽  
Particle Image ◽  
Digital Camera ◽  
Real Space ◽  
Surface Velocity ◽  
Image Velocimetry ◽  
Scale Particle ◽  
Perspective Center

&lt;p&gt;In this research, we conducted LSPIV (Large Scale Particle Image Velocimetry) measurements to measure river surface velocity based on images recorded by mobile phone. The realization of this research is based on the developments of two products. The first one is the digital camera, which has been combined with the mobile phone after several years of development. The second one is the three-axis accelerometer, which can measure the attitude of the object. A three-axis accelerometer is one of the necessary parts of the mobile phone nowadays, as many functions of the mobile phone, such as step counting, Do Not Disturb mode, games, require the detection of attitude.&lt;/p&gt;&lt;p&gt;In LSPIV, there are nine parameters of the collinear equation. Three of parameters are the coordinates of the perspective center in the image space (focus distance d and image center position (u, v)), which can be determined in advance in the laboratory; the other three parameters are the coordinates (x, y, z) of the perspective center in real space, which can be set to (0, 0, 0); the last three parameters are the attitude of the camera (i.e., the mobile phone), which is determined by the depression angle, the horizontal angle, and the left-right rotation angle and can be measured by three-axis accelerometer. Therefore, river surface velocity could be analyzed by LSPIV with not only continuous images captured by a camera of the mobile phone but also the acceleration values obtained by the three-axis accelerometer when each image was captured.&lt;/p&gt;&lt;p&gt;In the present study, Yufeng gauging station, which is in the upstream catchment of the Shihmen Reservoir in Taiwan, is selected as the study site. Two other measurement methods were used to measure the river surface velocity and the comparison was conducted. One is using a handheld digital flow meter and another is using LSPIV with control points to calculate the parameters for measuring the river surface velocity.&lt;/p&gt;

Comparison of the surface velocity of a debris flow at the Gadria creek using pulse compression radar and digital particle image velocimetry (DPIV).

2020 ◽  
Author(s):  
Tobias Schöffl ◽  
Georg Nagl ◽  
Johannes Hübl
Keyword(s):  
Particle Image Velocimetry ◽  
Debris Flow ◽  
Debris Flows ◽  
Pulse Compression ◽  
Particle Image ◽  
Video Camera ◽  
Digital Particle Image Velocimetry ◽  
Surface Velocity ◽  
Image Velocimetry ◽  
Pulse Compression Radar

&lt;p&gt;&lt;strong&gt;Comparison of the surface velocity of a debris flow at the Gadria creek using pulse compression radar and digital particle image velocimetry (DPIV).&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Tobias Sch&amp;#246;ffl, Georg Nagl, Johannes H&amp;#252;bl&lt;/p&gt;&lt;p&gt;Institute of Mountain Risk Engineering, University of Natural Resources and Life Sciences, Vienna, Austria&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;A central aspect of protection against debris flows is the understanding of the process. The flow velocity is an important parameter which is used, for example, in the dimensioning of protective structures, for technical building protection and for early warning systems. The measurement of the surface velocity which is regarded as the maximum velocity occurring within a debris flow, is therefore an essential link in the chain of fundamental process research and applied protection against natural hazards.&lt;/p&gt;&lt;p&gt;Due to the further development of various technologies such as video technology and high-frequency radar technology, the non-contact measurement of the surface speed of a debris flow has improved significantly in recent years. Radar technology provides a wide aspect of applications in alpine mass movements such as debris flows, avalanches and rockfall and is able to detect such processes up to a range of 2500 meters in distance. An additional beneficial feature is the possibility of non-contact measurement of the surface velocity. In the catchment area of the Gadria basin (South Tyrol, Italy), the measuring station, which has been in operation since 2016, has been extended by a pulse compression radar and a new HD video camera. On July 26, 2019 a debris flow consisting of several surges was recorded with both the radar and the HD video camera. To obtain surface velocity data from the video material, the material was analyzed and evaluated using digital particle image velocimetry by making use of the MATLAB software and its freely accessible ADD-On &quot;PIVlab&quot;.&lt;/p&gt;&lt;p&gt;The results of the compared surface velocity data showed a value of up to 0.74 according to the statistical mean of the coefficient of determination. The results demonstrate the high effectiveness of the pulse compression radar and the DPIV analysis in a wide range of the assessment of surface velocity of natural debris flows. There is great potential in both measuring systems and the chosen comparative analysis provides a blueprint for future recorded debris flows.&lt;/p&gt;

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