Comparing a newly developed DEM-based runout model for hillslope debris flows with full-scale experiments and historical events

The increasing urbanization of mountainous areas increased the risk imposed on residential buildings and infrastructure. In Switzerland, shallow landslides and hillslope debris flows are responsible every year for high infrastructure damage, blocking of important highways, evacuations and deaths. Up till now, the assessment of these processes has been mainly based on the experience of experts, especially in the assessment of their run-out extent and expected damage. In this research we present a new computationally efficient Discrete Element Model (DEM) which has been developed for the aim of simulating the run-out of hillslope debris flows.YADE-DEM open source code has been extended and an elasto-plastic adhesive contact law have been implemented, which partially account for the presence of the fluid composed of water and find material. This is achieved through the adhesive aspect of the contact law, which would indirectly take the presence of such fluid into account, as this fluid would increase the cohesion of the flowing mass. A parametric study has been carried out to define the most sensitive model parameters, which were found to be the microscopic basal friction angle (&#934;b) and the ratio between stiffness parameters (loading and unloading) of the flowing particles <img src="data:image/png;base64,%20iVBORw0KGgoAAAANSUhEUgAAAD0AAAAaCAYAAAAEy1RnAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAHwSURBVFhH7ZVbkYNAEEWxgAYs4AEJaIgFHOAAByhAAQYwgAM8zOawdFVnniTwsVk4VdQu8+i5t7uHZOaC3Kavwm36Khw2XVWVybLszz4+TjH9bRwyPY6jadt2e/sevKaXZTFN05i+77cRPxiepml7ewZ7tlNZltvbKySIrkglqSiK9XwIxZvn2Twej3U+z/NVK6CFca3Jh2OaAxGX2gh2a2NIBGgYJ4EYiJlmDaKFUDzO7bpu/X8YhtW86N2j3zHNoakKA8Hrut7efkEgIkKkKs08HSGk4gmY1vukq0I4pgkg7RUDMZJtgUqyl4c2tZMSM03LskeTigfso8VtzawPVfvFNBkK3UkbqqCDcih7EcGczrwQM824ntsTD4jp60wSZBdFcEzH2kJjr5O7xYNIHzHTVAaDwp54satoJ1HzkWmq4LvPHCIfLB8h0xh8Nx7zoUrCW6btA8g+GdUHhO4z+1lPdfjrW+MT4qtYLB7jOknosePubm/gAP1RICCC9EeGLCNCYL3eR0URLe9SLdbwMK9/YvgQaVLx0CKx5EGnZveHDOyqCgSRatiteARicuaZpK6pY5ps6koIiGOc+TNFUsFQRT4hpF/jmAY20sK6ZRijDeXjcgYIw/RZEI+CpJLoNf3fuU1fhdv0VbigaWN+AIO900eKtwXkAAAAAElFTkSuQmCC" alt="">. Data of full-scale experiments of hillslope debris flows were used to compare the flow kinematics with the model&#8217;s prediction. A good agreement between the model and experiments was observed concerning the mean front velocity (average margin of error of 8%) and the maximum applied pressure (average margin of error of 5%), with less agreement of the flow height (average margin of error of 13%). Detailed comparisons of pressure evolution between different selected experiments and simulations revealed the model&#8217;s capability of reproducing observed pressure curves, especially during the primary loading phase, leading to maximum pressure.In order to test the model&#8217;s prediction of run-out distance of hillslope debris flow, hundreds of past hillslope debris flow events in the Swiss Alps were analyzed and 30 cases were selected representing different situations (i.e. different release volumes, slopes and forest cover). Due to the discrete nature of results in YADE, a GIS algorithm was developed in order to create envelopes representing the temporal evolution of the simulated propagating processes, which were compared to the those of the historical events. Results of the comparison revealed that, with the calibration of the two sensitive parameters in YADE, a fair to very good agreement was observed between the envelopes of the model and those of historical events for 87% of the tested cases. Difficulties in reproducing the envelopes of the rest of the cases are linked to the uncertainties in the mapping of the envelopes of past events, the role of the forest which is not taken into account in the model, and the lack of direct representation of fluid in the model.

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The importance of entrainment and bulking on debris flow runout modeling: examples from the Swiss Alps

Natural Hazards and Earth System Science ◽

10.5194/nhess-15-2569-2015 ◽

2015 ◽

Vol 15 (11) ◽

pp. 2569-2583 ◽

Cited By ~ 37

Author(s):

F. Frank ◽

B. W. McArdell ◽

C. Huggel ◽

A. Vieli

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Field Data ◽

Average Rate ◽

Hazard Analysis ◽

Maximum Shear Stress ◽

Empirical Relationship ◽

Swiss Alps ◽

Field Site ◽

Practical Applications

Abstract. This study describes an investigation of channel-bed entrainment of sediment by debris flows. An entrainment model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the entrainment model, an empirical relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally, the average rate of erosion, measured at the same field site, is used to constrain the erosion rate. The model predicts plausible erosion values in comparison with field data from highly erosive debris flow events at the Spreitgraben torrent channel, Switzerland in 2010, without any adjustment to the coefficients in the entrainment model. We find that by including bulking due to entrainment (e.g., by channel erosion) in runout models a more realistic flow pattern is produced than in simulations where entrainment is not included. In detail, simulations without entrainment show more lateral outflow from the channel where it has not been observed in the field. Therefore the entrainment model may be especially useful for practical applications such as hazard analysis and mapping, as well as scientific case studies of erosive debris flows.

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Uncertainty in debris flow rainfall thresholds

10.5194/egusphere-egu21-15175 ◽

2021 ◽

Author(s):

Matteo Berti ◽

Alessandro Simoni

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Measurement Errors ◽

Critical Conditions ◽

Model Parameters ◽

Average Intensity ◽

Rainfall Thresholds ◽

Sources Of Uncertainty ◽

Time Space ◽

Physically Based

Rainfall is the most significant factor for debris flows triggering. Water is needed to saturate the soil, initiate the sediment motion (regardless of the mobilization mechanism) and transform the solid debris into a fluid mass that can move rapidly downslope. This water is commonly provided by rainfall or rainfall and snowmelt. Consequently, most warning systems rely on the use of rainfall thresholds to predict debris flow occurrence. Debris flows thresholds are usually empirically-derived from the rainfall records that caused past debris flows in a certain area, using a combination of selected precipitation measurements (such as event rainfall P, duration D, or average intensity I) that describe critical rainfall conditions. Recent years have also seen a growing interest in the use of coupled hydrological and slope stability models to derive physically-based thresholds for shallow landslide initiation.In both cases, rainfall thresholds are affected by significant uncertainty. Sources of uncertainty include: measurement errors; spatial variability of the rainfall field; incomplete or uncertain debris flow inventory; subjective definition of the &#8220;rainfall event&#8221;; use of subjective criteria to define the critical conditions; uncertainty in model parameters (for physically-based approaches). Rainfall measurement is widely recognized as a main source of uncertainty due to the extreme time-space variability that characterize intense rainfall events in mountain areas. However, significant errors can also arise by inaccurate information reported in landslide inventories on the timing of debris flows, or by the criterion used to define triggering intensities.This study analyzes the common sources of uncertainty associated to rainfall thresholds for debris flow occurrence and discusses different methods to quantify them. First, we give an overview of the various approaches used in the literature to measure the uncertainty caused by random errors or procedural defects. These approaches are then applied to debris flows using real data collected in the Dolomites (Northen Alps, Itay), in order to estimate the variabilty of each single factor (precipitation, triggering timing, triggering intensity..). Individual uncertainties are then combined to obtain the overall uncertain of the rainfall threshold, which can be calculated using the classical method of &#8220;summation in quadrature&#8221; or a more effective approach based on Monte Carlo simulations. The uncertainty budget allows to identify the biggest contributors to the final variability and it is also useful to understand if this variability can be reduced to make our thresholds more precise.&#160;

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2D Runout Modelling of Hillslope Debris Flows, Based on Well-Documented Events in Switzerland

Geosciences ◽

10.3390/geosciences10020070 ◽

2020 ◽

Vol 10 (2) ◽

pp. 70 ◽

Cited By ~ 2

Author(s):

Florian Zimmermann ◽

Brian W. McArdell ◽

Christian Rickli ◽

Christian Scheidl

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Mass Movement ◽

Clay Content ◽

Systematic Evaluation ◽

Mountain Areas ◽

Flow Processes ◽

Friction Parameters ◽

Cohesive Interaction ◽

Hillslope Debris Flow

In mountain areas, mass movements, such as hillslope debris flows, pose a serious threat to people and infrastructure, although size and runout distances are often smaller than those of debris avalanches or in-channel-based processes like debris floods or debris flows. Hillslope debris-flow events can be regarded as a unique process that generally can be observed at steep slopes. The delimitation of endangered areas and the implementation of protective measures are therefore an important instrument within the framework of a risk analysis, especially in the densely populated area of the alpine region. Here, two-dimensional runout prediction methods are helpful tools in estimating possible travel lengths and affected areas. However, not many studies focus on 2D runout estimations specifically for hillslope debris-flow processes. Based on data from 19 well-documented hillslope debris-flow events in Switzerland, we performed a systematic evaluation of runout simulations conducted with the software Rapid Mass Movement Simulation: Debris Flow (RAMMS DF)—a program originally developed for runout estimation of debris flows and snow avalanches. RAMMS offers the possibility to use a conventional Voellmy-type shear stress approach to describe the flow resistance as well as to consider cohesive interaction as it occurs in the core of dense flows with low shear rates, like we also expect for hillslope debris-flow processes. The results of our study show a correlation between the back-calculated dry Coulomb friction parameters and the percentage of clay content of the mobilised soils. Considering cohesive interaction, the performance of all simulations was improved in terms of reducing the overestimation of the observed deposition areas. However, the results also indicate that the parameter which accounts for cohesive interaction can neither be related to soil physical properties nor to different saturation conditions.

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Atmospheric Forcing of Debris Flows in the Southern Swiss Alps

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-13-077.1 ◽

2013 ◽

Vol 52 (7) ◽

pp. 1554-1560 ◽

Cited By ~ 14

Author(s):

Andrea Toreti ◽

Michelle Schneuwly-Bollschweiler ◽

Markus Stoffel ◽

Jürg Luterbacher

Keyword(s):

Time Series ◽

Debris Flow ◽

Debris Flows ◽

Large Scale ◽

Reanalysis Data ◽

Swiss Alps ◽

Classification Algorithms ◽

Precipitation Series ◽

Large Scale Circulation

AbstractThis article addresses the role of large-scale circulation and thermodynamical features in the release of past debris flows in the Swiss Alps by using classification algorithms, potential instability, and convective time scale. The study is based on a uniquely dense dendrogeomorphic time series of debris flows covering the period 1872–2008, reanalysis data, instrumental time series, and gridded hourly precipitation series (1992–2006) over the area. Results highlight the crucial role of synoptic and mesoscale forcing as well as of convective equilibrium on triggering rainfalls. Two midtropospheric synoptic patterns favor anomalous southwesterly flow toward the area and high potential instability. These findings imply a certain degree of predictability of debris-flow events and can therefore be used to improve existing alert systems.

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The importance of erosion for debris flow runout modelling from applications to the Swiss Alps

Natural Hazards and Earth System Sciences Discussions ◽

10.5194/nhessd-3-2379-2015 ◽

2015 ◽

Vol 3 (4) ◽

pp. 2379-2417 ◽

Cited By ~ 3

Author(s):

F. Frank ◽

B. W. McArdell ◽

C. Huggel ◽

A. Vieli

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Field Data ◽

Hazard Analysis ◽

Maximum Shear Stress ◽

Swiss Alps ◽

Erosion Model ◽

Practical Applications ◽

Bed Erosion ◽

The Relationship

Abstract. This study describes an investigation of channel-bed erosion of sediment by debris flows. An erosion model, developed using field data from debris flows at the Illgraben catchment, Switzerland, was incorporated into the existing RAMMS debris-flow model, which solves the 2-D shallow-water equations for granular flows. In the erosion model, the relationship between maximum shear stress and measured erosion is used to determine the maximum potential erosion depth. Additionally, the maximum rate of erosion, measured at the same field site, is used to constrain the erosion rate. The model predicts plausible erosion values in comparison with field data from highly erosive debris flow events at the Spreitgraben torrent channel, Switzerland in 2010, without any adjustment to the coefficients in the erosion model. We find that by including channel erosion in runout models a more realistic flow pattern is produced than in simulations where entrainment is not included. In detail, simulations without channel bed erosion show more lateral outflow from the channel where it has not been observed in the field. Therefore the erosion model may be especially useful for practical applications such as hazard analysis and mapping, as well as scientific case studies of erosive debris flows.

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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 ◽

10.3390/w11010169 ◽

2019 ◽

Vol 11 (1) ◽

pp. 169 ◽

Cited By ~ 10

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.

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Effects of Y-type spillway lateral contraction ratios on debris flow patterns and scour features behind a check dam

10.5194/nhess-2016-189 ◽

2016 ◽

Author(s):

Huayong Chen ◽

Jinfeng Liu ◽

Wanyu Zhao

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Flow Patterns ◽

Check Dam ◽

Mountainous Areas ◽

Dimensionless Analysis ◽

Lateral Contraction ◽

Contraction Ratio ◽

New Type ◽

Good Agreement

Abstract. Debris flows often cause devastating damage to property and can injure or kill residents in mountainous areas. The construction of check dams in debris flow valleys is considered a useful strategy for mitigating the damages downstream. In this paper, a new type of spillway structure with lateral contraction was proposed to distribute debris flows after the check dam storage filled up. Four different lateral contraction ratios of the spillway were considered in experiments that investigated debris flow patterns, scour characteristics, and energy dissipation rates when debris flows passed through the spillway. The results indicated that lateral contraction considerably influenced the extension of debris flow nappes. The drop length of the nappe at η = 0.7 (η means lateral contraction ratio) was approximately 1.4 times larger than at η = 0.4. The collision, friction, and mixing forces between the debris flow nappes and debris flows in downstream plunge pools dissipated much of the debris flow kinetic energy, ranging from 42.03 % to 78.08 % at different contraction ratios. Additionally, based on a dimensionless analysis, an empirical model was proposed to predict the maximum scour depth behind the check dam. It indicated that the results calculated by the model exhibited good agreement with the experimental results.

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Simplified simulation of rock avalanches and subsequent debris flows with a single thin-layer model. Application to the Prêcheur river (Martinique, Lesser Antilles)

10.5194/egusphere-egu21-2752 ◽

2021 ◽

Author(s):

Marc Peruzzetto ◽

Clara Levy ◽

Yannick Thiery ◽

Gilles Grandjean ◽

Anne Mangeney ◽

...

Keyword(s):

Debris Flow ◽

Thin Layer ◽

Debris Flows ◽

Initial Conditions ◽

Rock Avalanche ◽

Numerical Code ◽

Lesser Antilles ◽

Rheological Parameters ◽

Model Parameters ◽

High Discharge

This work focuses on the use of thin-layer models for simulating fast gravitational flows for hazard assessment. Such simulations are sometimes difficult to carry out because of the uncertainty on initial conditions and on simulation parameters. In this study, we aggregate various field data to constrain realistic initial conditions and to calibrate the model parameters. By using the SHALTOP numerical code, we choose a simple and empirical rheology to model the flow (no more than two parameters), but we model more finely the geometrical interactions between the flow and the topography. We can thus model both a rock avalanche, and the subsequent remobilization of the deposits as a high discharge debris flow.Using the Pr&#234;cheur river catchment (Martinique, Lesser Antilles) as a case study, we focus on extreme events with a high potential to impact populations and infrastructures. We use geological and geomorphological data, topographic surveys, seismic recordings and granulometric analysis to define realistic simulation scenarios and determine the main characteristics of documented events. The latter are then reproduced to calibrate rheological parameters. With a single rheological parameter and the Coulomb rheology, we thus model the emplacement and main dynamic characteristics of a recent rock avalanche, as well as the travel duration and flooded area of a documented high discharge debris flow. Then, in a forward prediction simulation, we model a possible 1.9x106 m3 rock avalanche, and the instantaneous remobilization of the resulting deposits as a high-discharge debris flow. We show that successive collapses allow to better reproduce the dynamics of the rock avalanche, but do not change the geometry of the final deposits, and thus do not influence the initial conditions of the subsequent debris flow simulation. A progressive remobilization of the materials slows down the debris flow and limits overflow, in comparison to instantaneous release. However, we show that high discharge debris flows, such as the one considered for model calibration, are better reproduced with an instantaneous initiation. The range of travel times measured for other significant debris flows in the Pr\^echeur river is consistent with our simulation results, with various rheological parameters and the Coulomb or Voellmy rheology.

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Impact of a Random Sequence of Debris Flows on Torrential Fan Formation

Geosciences ◽

10.3390/geosciences9020064 ◽

2019 ◽

Vol 9 (2) ◽

pp. 64 ◽

Cited By ~ 4

Author(s):

Nejc Bezak ◽

Jošt Sodnik ◽

Matjaž Mikoš

Keyword(s):

Debris Flow ◽

Numerical Simulations ◽

Rheological Properties ◽

Debris Flows ◽

Random Sequence ◽

Rheological Parameters ◽

Model Parameters ◽

Maximum Height ◽

Wide Range ◽

The Impact

Debris flows with different magnitudes can have a large impact on debris fan characteristics such as height or slope. Moreover, knowledge about the impact of random sequences of debris flows of different magnitudes on debris fan properties is sparse in the literature and can be improved using numerical simulations of debris fan formation. Therefore, in this paper we present the results of numerical simulations wherein we investigated the impact of a random sequence of debris flows on torrential fan formation, where the total volume of transported debris was kept constant, but different rheological properties were used. Overall, 62 debris flow events with different magnitudes from 100 m3 to 20,000 m3 were selected, and the total volume was approximately 225,000 m3. The sequence of these debris flows was randomly generated, and selected debris fan characteristics after the 62 events were compared. For modeling purposes, we applied the Rapid Mass Movement Simulations (RAMMS) software and its debris flow module (RAMMS-DF). The modeling was carried out using (a) real fan topography from an alpine environment (i.e., an actual debris fan in north-west (NW) Slovenia formed by the Suhelj torrent) and (b) an artificial surface with a constant slope. Several RAMMS model parameters were tested. The simulation results confirm that the random sequence of debris flow events has only some minor effects on the fan formation (e.g., slope, maximum height), even when changing debris flow rheological properties in a wide range. After the 62 events, independent of the selected sequence of debris flows, the final fan characteristics were not significantly different from each other. Mann–Whitney (MW) tests and t-tests were used for this purpose, and the selected significance level was 0.05. Moreover, this conclusion applies for artificial and real terrain and for a wide range of tested RAMMS model rheological parameters. Further testing of the RAMMS-DF model in real situations is proposed in order to better understand its applicability and limitations under real conditions for debris flow hazard assessment or the planning of mitigation measures.

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Debris Flow Modelling Using RAMMS Model in the Alpine Environment With Focus on the Model Parameters and Main Characteristics

Frontiers in Earth Science ◽

10.3389/feart.2020.605061 ◽

2021 ◽

Vol 8 ◽

Author(s):

Matjaž Mikoš ◽

Nejc Bezak

Keyword(s):

Debris Flow ◽

Debris Flows ◽

Mass Movement ◽

Friction Model ◽

Economic Damage ◽

Model Parameters ◽

Comprehensive Overview ◽

Alpine Environment ◽

Flow Modelling ◽

Parameter Ranges

Debris flows are among the natural hazards that can occur in mountainous areas and endanger people’s lives and cause large economic damage. Debris flow modelling is needed in multiple applications such as design of protection measures or preparation of debris flow risk maps. Many models are available that can be used for debris flow modelling. The Rapid Mass Movement Simulation (RAMMS) model with its debris flow module, (i.e. RAMMS-DF) is one of the most commonly used ones. This review provides a comprehensive overview of past debris flow modelling applications in an alpine environment with their main characteristics, including study location, debris flow magnitude, simulation resolution, and Voellmy-fluid friction model parameter ranges, (i.e. μ and ξ). A short overview of each study is provided. Based on the review conducted, it is clear that RAMMS parameter ranges are relatively wide. Furthermore, model calibration using debris-flow post-event survey field data is the essential step that should be done before applying the model. However, an overview of the parameters can help to limit the parameter ranges. Particularly when considering the similarity between relevant case studies conducted in similar environments. This is especially relevant should the model be applied for estimating debris-flow hazard for potential future events. This model has been used mostly in Europe, (i.e. Alpine region) for modelling small and extremely large debris flows.

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