Runout Length Research Articles

Investigation of the 2010 rock avalanche onto the regenerated glacier Brenndalsbreen, Norway

Rock avalanches onto glaciers are rare in Norway. Here, we examine a rock avalanche that spread onto the regenerated Brenndalsbreen, an outlet glacier from Jostedalsbreen ice cap. The rock avalanche is intriguing in that limited information exists with respect to the exact time of failure, location of detachment area, and preparatory and triggering processes. Based on an analysis of ice stratigraphy and photographic documentation, we assess that the event happened between mid-March and June 4, 2010. A potential triggering factor could have been heavy snow and rainfall combined with above freezing air temperatures on March 18–19, 2010. We use digital terrain models to determine that the detachment area is at an almost vertical rock slope in a narrow gorge above Lower Brenndalsbreen. The deposit volume is estimated to 0.130 ± 0.065 Mm3, and the H/L ratio and fahrböschung are 0.45 and 24°, respectively. We apply a Voellmy flow model to confirm the detachment location and volume estimate by producing realistic runout lengths. Although glacial debuttressing may have been a likely preparatory process, the detachment area was exposed for 45–70 years before the rock avalanche occurred. The supraglacial rock avalanche debris was separated into two branches with a distinct melt-out line across the glacier. The debris reached the glacier front in 2019 and 2020, where it started being deposited proglacially while Lower Brenndalsbreen kept receding. The 2010 Brenndalsbreen rock avalanche may not be a unique event, as deposits constituting evidence of an old rock avalanche are currently melting out at the glacier front.

Scaling between volume and runout of rock avalanches explained by a modified Voellmy rheology

Abstract. Rock avalanches reach considerably greater runout lengths than predicted by Coulomb friction. While it has been known for a long time that runout length increases with volume, explaining the increase qualitatively is still a challenge. In this study, the widely used Voellmy rheology is reinterpreted and modified. Instead of adding a Coulomb friction term and a velocity-dependent term, the modified rheology assigns the two terms to different regimes of velocity. While assuming a transition between Coulomb friction and flow at a given velocity is the simplest approach, a reinterpretation of an existing model for the kinetic energy of random particle motion predicts a dependence of the crossover velocity on the thickness of the rock avalanche. Analytical solutions for a lumped mass on a simple 1D topography reveal the existence of a slope-dominated and a height-dominated regime within the regime of flow. In the slope-dominated regime, the kinetic energy at the foot of the slope depends mainly on the slope angle, while the absolute height relative to the valley floor has little effect, and vice versa. Both regimes can be distinguished by the ratio of a length scale derived from the rheology and the length scale of the topography. Long runout occurs in the height-dominated regime. In combination with empirical relations between volume, thickness, and height, the approach based on the random kinetic energy model reproduces the scaling of runout length with volume observed in nature very well.

A machine learning model of liquid bridge force and its application in discrete element method

Developing an accurate and efficient contact model for discrete element method (DEM) simulation that can describe the microscopic dynamics of low moisture content wet granular systems continues to be a major challenge. In this study, a improved energetic approach based on the traditional linear unit discretization method is introduced to solve liquid bridge problems. This improved approach significantly ameliorates the efficiency of constructing the databases while ensuring high data accuracy. Using this method, we generated databases consisting of 163,440,000 and 2043,000 data points for the sphere-sphere and sphere-wall systems, respectively. Machine learning capillary force models (ML-Capillary) are trained using the Catboost algorithm. These models demonstrate excellent performance in predicting capillary force between particles as well as between particles and walls, considering different particle sizes, moisture levels, and contact angles, while neglecting the influence of gravity. The corresponding relative errors are below 1.5% and 2%, respectively, which are lower than existing simulation models. We incorporated the obtained models into the discrete element method and calculated capillary force between particle pairs and simulated wet granular column collapse tests. The simulation results show good agreement with experimental results in terms of parameters such as inter-particle capillary forces and particle column collapse run-out length. This study will provide an accurate and efficient numerical model for simulating low saturation wet granular systems using the discrete element method.

Grain-size variability in debris flows of different runout lengths, Wenchuan, China

Debris-flow grain-size distributions (GSDs) control runout length and mobility. Wide, bimodal GSDs and those containing a higher proportion of silt and clay have been shown experimentally to increase runout length. However, the relationship between grain size and mobility has not been well established in field conditions. Here, we compared the grain-size characteristics of two debris flows with considerably different runout lengths (1.5 km vs. 8 km) to understand the role of grain size in governing runout. The two debris flows were triggered in the same rainfall event from coseismic landslide debris generated in the 2008 Wenchuan earthquake in catchments with similar lithology and topography. We compared the deposited GSDs and their spatial patterns using our rare, three-dimensional GSD datasets. Surprisingly, the proportions of each size fraction deposited by the two flows were statistically indistinguishable. The spatial pattern of grain size differed between the two flows, with evidence of inverse grading only preserved in the smaller deposit. From these observations, we can infer that the GSDs of both flows were determined by the coseismic landslide source material, and that there was little difference in the GSDs of material entrained as the flows bulked. The contrasting spatial distributions of grains indicated that different internal processes were dominant within the two flows. These findings demonstrate that where GSDs are dominated by coarse grains and are governed by similar source conditions, grain size plays a lesser role relative to sediment supply and hydrology in controlling the runout length of large catastrophic post-earthquake debris flows.

A data-driven method for the estimation of shallow landslide runout

Rainfall-induced shallow landslides cause damages and casualties. Estimating the development of the runout is essential, however, the methods which are traditionally employed to predict the runout distance are either reliable but complex and applicable at a local scale or applicable at a larger scale but highly simplified.The present work aims to develop a method based on data-driven algorithms for predicting the runout of shallow landslides at a large scale, taking into account geological, geomorphological, and land use heterogeneities.The model, which was tested in the Oltrepò Pavese (Italy), a hilly area of over 1000 km2, requires as inputs a set of predictors collected from geological maps, land use maps and freely available satellite images. Different algorithms were tested, identifying the Random Forest algorithm as the best performing, with a Coefficient of Determination of 0.94 and Mean Absolute Error of 4–5.8 m. The size of the source area strongly influences runout estimation, as do land use, lithology, and slope angle. The model provides a probable runout length, which can be estimated, based on past observations in the test area, to propagate along the line of the greatest slope.The main novelties of this work include: a) the development of a methodology to study the previously overlooked runout dynamics, b) the exploitation of remotely-derived, freely available input data, c) the application at a large scale in a heterogenous area, d) the adaptability of the model different study areas and e) the dependency of the model on land use, which allows for land use change scenarios to be made. If coupled with a susceptibility assessment tool to identify where a landslide might develop, it could be used to give a fast yet accurate assessment of the probable runout length and to identify which targets could potentially be affected by the landslide.

Grain size variability in debris flows of different runout lengths, Wenchuan, China

Grain size variability in debris flows of different runout lengths, Wenchuan, China

Effect of flocculation on turbidity currents

Flocculation between inorganic sediment, salt ions and microscopic organic matter present in the marine environment might play an important role in the dynamics of turbidity currents. The ability to predict, understand, and potentially leverage the effect of flocculation on turbidity currents will help to minimize the impact of human interventions such as dredging, trenching, and deep-sea mining. To better characterize the effect of flocculation on the benthic turbidity currents generated by these activities, a series of laboratory experiments were performed. Turbidity currents were created by means of lock exchange experiments. The present work focuses on the flocculation of clays that are representative for abyssal regions where deep-sea mining is performed, but most of the conclusions of this work are generic and can be applied to other types of benthic flows, occuring in harbours and channels. The effect of salt and organic material as flocculant agent was investigated. Various concentrations of clay and organic flocculant were tested. Video analysis was used to determine the head velocity of the plume. Samples at different run-out lengths were collected at the end of the lock exchange experiments for particle size and settling velocity measurements. The velocities of the turbidity currents in fresh and saline water (when no organic matter was present) were found to be similar, which was expected considering the timescales of salt-induced flocculation (about 30 min or more compared to the duration of lock exchange experiment <60 s). It was however demonstrated that, in presence of organic matter, flocculation occurred during the short time (30–60 s) of the experiment, leading to a reduced current propagation and a significant change in floc sizes (from 20 to 1,000 µm) and settling velocities (from 1 to 60 mm s−1). Salt ions contributed to flocculation in the sense that flocculation with organic matter was improved in the presence of salt.

The impact of terrain model source and resolution on snow avalanche modeling

Abstract. Natural hazard models need accurate digital elevation models (DEMs) to simulate mass movements on real-world terrain. A variety of platforms (terrestrial, drones, aerial, satellite) and sensor technologies (photogrammetry, lidar, interferometric synthetic aperture radar) are used to generate DEMs at a range of spatial resolutions with varying accuracy. As the availability of high-resolution DEMs continues to increase and the cost to produce DEMs continues to fall, hazard modelers must often choose which DEM to use for their modeling. We use satellite photogrammetry and topographic lidar to generate high-resolution DEMs and test the sensitivity of the Rapid Mass Movement Simulation (RAMMS) software to the DEM source and spatial resolution when simulating a large and complex snow avalanche along Milford Road in Aotearoa/New Zealand. Holding the RAMMS parameters constant while adjusting the source and spatial resolution of the DEM reveals how differences in terrain representation between the satellite photogrammetry and topographic lidar DEMs (2 m spatial resolution) affect the reliability of the simulation estimates (e.g., maximum core velocity, powder pressure, runout length, final debris pattern). At the same time, coarser representations of the terrain (5 and 15 m spatial resolution) simulate avalanches that run too far and produce a powder cloud that is too large, though with lower maximum impact pressures, compared to the actual event. The complex nature of the alpine terrain in the avalanche path (steep, rough, rock faces, treeless) makes it a suitable location to specifically test the model sensitivity to digital surface models (DSMs) where both ground and above-ground features on the topography are included in the elevation model. Considering the nature of the snowpack in the path (warm, deep with a steep elevation gradient) lying on a bedrock surface and plunging over a cliff, RAMMS performed well in the challenging conditions when using the high-resolution 2 m lidar DSM, with 99 % of the simulated debris volume located in the documented debris area.

기후변화를 고려한 토석류 재해취약지역 레질리언스 강화를 위한 연구

Recently, climate change has caused serious natural disasters at the vulnerable areas with many mountainous regions. This study analyzes the behavior of debris flow with respect to time elapse by applying various precipitation, mountain slope change, and the categories of vegetation loosened in mountainous areas. The behavior of debris flow is debris flow discharge and water depth. In addition, the runout length of debris flow passed through the channel and reached the downstream according to the change of the water supply and slope was measured. The larger the supply flow, the higher the debris flow discharge, and the second peak value became faster as the supply flow increased, and the slope became steeper. In the category where the multiplier of vegetation for debris flow is large, the fluctuation period was made long, and the amplitude of the fluctuation was also made large. As for the debris flow runout length, the supply flow was large and it was spread in a considerable range on steep slopes. This study will provide various information such as establishing measures for debris flow occurring in vulnerable areas to natural disasters due to climate change, or establishing a plan for strengthening resilience.

The Namaras rock avalanche: Evidence of mid-to-late Holocene paraglacial activity in the Central Taurus Mountains, SW Turkey

The Namaras rock avalanche (NRA) deposit originated from the northern flank of the glaciokarstic Geyikdağ Mountain in the Central Taurus Range, SW Turkey. The deposit has an area of ~0.430 km2 and an estimated average thickness of 10 m, corresponding to 4.3 million m3 volume. The fan-shaped deposit area consists of house-sized Jurassic-Cretaceous neritic limestone boulders that overlie lateral and hummocky moraines down into the valley. We used geomorphological mapping and 36Cl surface exposure dating to obtain six boulder ages which unravelled the NRA age, the number of events and their geometric features. Our results indicate that the NRA consists of two successive mid-to-late Holocene events; the first high magnitude main event with a weighted average age of 4.59 ± 0.25 ka followed by a second low magnitude event with a weighted average age of 3.77 ± 0.20 ka. 36Cl exposure dating of the lateral moraine covered by the rock avalanche deposit yielded approximately an age of ~12.30 ± 1.20 ka. The older event with a maximum runout distance of 1550 m and 600 m elevation loss yielded in a travel angle of 21°. Similarly, the younger event with 1720 m maximum runout length and 640 m vertical elevation loss resulted in a travel angle of 20°. The bedded limestone with cross-joints in the glacial cirque preconditioned the NRA slope failure. The significant lag time between deglaciation and the rock avalanche indicates that the glacial erosion and debuttressing acted as preparatory factors. Based on the low seismic activity in the Central Taurus Range and the synchronicity of the rock avalanche with mid-to-late Holocene climatic transitions, we propose that climatic factors may have triggered the NRA failure. The age of the older main event coincides with the warm drought period of the mid-Holocene associated with torrential rainfalls in the Taurus Mountains, while the age of the younger event correlates with the long wet period in the late Holocene. Thus, the main NRA event may have been triggered by the influence of warm temperatures and intense rainfall, while the second event may have been triggered by prolonged period of high precipitation. The two events of the NRA are coeval with the enhanced rock slope failures dating back to 5–3 ka in the Alps.

Corridor-Based Procedure for Determining Longitudinal Barrier Length of Need

Determining the optimal length of need (LON) to prevent vehicles from striking roadside hazards is an important part of roadside design. Although barriers can provide significant safety benefits by preventing run-off-road (ROR) crashes, the barrier itself presents a small but nonzero risk of serious injury or fatality. The purpose of this study is to present a method for quantifying the protection of barrier LON using departure corridors developed with NCHRP 17-43 data. Based on real-world ROR crash trajectories from the NCHRP 17-43 database, departure corridors were constructed. This study focused on a subset of 171 crashes on roads with a speed limit between 60 and 80 km/h with a reconstructed impact speed. In these crashes, the vehicle trajectory was interrupted by either a collision or a rollover. Our approach was to extrapolate the trajectory that could have been followed by the vehicle had the collision not occurred. The original trajectory data were retained before impact and extrapolated after impact using a linear fit. These corridors incorporated the effects of hazard location, departure side, and barrier location on the runout length. Left-side departures required a longer LON to intercept the same proportion of crashes. The runout length needed for objects close to the road based on the corridor method was much smaller than the length recommended by the 2011 Roadside Design Guide. The benefit of this corridor-based approach to barrier placement is that each agency can balance barrier length and the proportion of encroachments intercepted depending on their priorities.

Bottom Current Modification of Turbidite Lobe Complexes

Submarine lobes form at the distal end of sediment gravity flow systems and are globally important sinks for sediment, anthropogenic pollutants and organic carbon, as well as forming hydrocarbon and CO2 reservoirs. Deep-marine, near bed or bottom currents can modify gravity flow pathways and sediment distribution by directly interacting with the flow or by modifying seafloor morphology. Deciphering the nature of gravity- and bottom currents interaction, particularly in ancient systems, remains a challenge due to the lack of integrated datasets and the necessary oceanographic framework. Here we analyse high-resolution 3D seismic reflection and core data from the Upper Cretaceous interval offshore Tanzania to reveal the interaction of turbidite lobes with fine-grained sediment waves and contourite drift deposits. Contourite drift morphology governs the large-scale confinement style and shape of lobes that range from frontally confined and crescent shaped, to laterally confined and elongated, to semi-confined lobes. Core data reveals massive to cross-laminated high density turbidites in the lobe axis position that show no direct interaction between gravity flows and contour currents. Lobe off-axis and fringe deposits consist of parallel- and ripple-laminated, low density turbidites, which are inter-bedded with bioturbated, muddy siltstones that represent the toes of contourite drifts. Starved ripples, and streaks of up to fine-grained sandstone above individual turbidite beds indicate reworking by bottom currents. This facies distribution reflects the temporal interaction of quasi-steady bottom currents and turbidity currents that interact with the topography and build lobes over short periods of time. Frontally confined turbidity currents form lobes in a fill-and-spill fashion, in which the confinement of turbidity currents causes rapid deposition and obscures any bottom current signal. Lateral confinement causes increased turbidity current runout length, and promotes the development of lobe fringes with a high proportion of bottom current reworked sands. During times when sediment gravity flows are subordinate, contourites accumulate on top of the lobe, confining the next flow and thus modifying the overall stacking pattern of the lobe complex. Although sediment volumes of these bottom current modified lobe complexes are comparable to other deep-marine systems, bottom currents considerably influence facies distribution and deposit architecture.

The impact of vent geometry on the growth of lava domes

SUMMARY Thick lava flows that are a feature of many volcanic fields on the Earth and Venus vary from sheet-like to nearly perfect axisymmetric domes. Here, we investigate how these geometrical characteristics depend on the shape of the feeder vent. We study the gravitational spreading of viscous lava erupting from elliptical vents onto a flat surface using 3-D numerical models. The aspect ratio of the vent, defined to be the major to minor axes ratio, varies between 1 and 25. In the limit of an aspect ratio of one, the vent is circular and spreading is axisymmetric. In the limit where the ratio is large, the vent behaves as a fissure. The numerical models rely on an isoviscous lava rheology and a constant volumetric eruption rate. In all cases, the initial phase of the dome’s evolution is in a lava-discharge dominated regime such that spreading is insignificant and the height of the dome increases at a constant rate over the vent area. For vent aspect ratios greater than five, three successive regimes of spreading are identified: 2-D spreading in the direction perpendicular to the major axis of the vent, a transient phase such that the dome shape evolves towards that of a circular dome and a late axisymmetric spreading phase that does not depend on the vent shape. These regimes are delimited by the times required for the flow thickness above the vent to reach a given height and for the flow to spread axisymmetrically up to a length equal to the semi-major axis of the vent. Numerical results for the flow height and runout length tend towards the similarity solutions in the 2-D and axisymmetric regimes. Two main implications for highly viscous (rhyolitic) fissure eruptions can be drawn. First, the fissure length determines the flow regimes. The longer the vent fissure length, the longer the early lava discharge regime and 2-D spreading perpendicular to the length of the fissure. Second, the aspect ratio of fissure-fed lava flows can be used as an indicator of the fissure length and the duration of lava discharge. The ellipticity of some terrestrial fissure-fed flows provides evidence for viscous gravity-driven spreading terminated before the onset of the axisymmetric regime. On the other hand, the circular domes on Venus appear to be the result of fissure-fed eruptions sustained enough for the spreading to reach the axisymmetric regime. We propose relationships providing estimates of the fissure length and the duration of lava discharge based on fossil dome dimensions.

Geomorphic analyses of two recent debris flows in Brazil

Debris flows are one of the main geomorphic processes resulting in economic and social losses in Brazil. Due to the recurrence of these events and the damage they can cause, it is necessary to better characterize the process to mitigate new occurrences and prevent casualties. On March 11, 2011, extreme rainfall contributed to triggering debris flows and shallow landslides in the Tingidor watershed (TW), causing three deaths, destroying houses, and partially destroying the main road to the state capital. Similarly, on January 13, 2014, rainfall-induced shallow landslides triggered debris flows in the Guarda-mão watershed (GW), causing 25 deaths and destroying infrastructure. Both areas are located in the Serra do Mar, a mountain range that extends for 1500 km along the south and southeast coasts of Brazil. The main goal of this work was to investigate and compare the main triggering factors and geomorphic characteristics of these two recent events. To achieve this goal, a landslide inventory was compiled, and the main debris-flow features were mapped in detail. Flow discharges, velocities and volumes were also estimated. Despite having an initial source volume more than 30 times smaller, the GW event had a total volume of approximately 237,700 m³, compared with 196,800 m³ in the TW event. Along with differences related to runout length and topography in both areas, the results demonstrate that entrainment is an important characteristic of debris flows in the two recent occurrences evaluated in Brazil.

Modelling the impact of seismic triggered landslide location on basin sediment yield, dynamics and connectivity

As evidenced by recent earthquakes in Chi-Chi, Wenchuan and Gorkha, seismic triggered landslides can have a major impact on river basins and landscape evolution. The location of landslides with respect to river channels plays an important role in post-earthquake sediment dynamics. As well as direct impacts such as damming rivers, the connectivity of landslides to the fluvial network can alter how quickly sediment is moved and stored within river basins. Such “landslide-landscape relationships” are dominated by factors including geology, hydrological and geomorphic characteristics of the landscape, the location of landslides, and the geometric properties (e.g., size and runout length) of landslides. These factors will therefore control the magnitude and retention of associated sediment transportation. But key characteristics of this relationship and how it controls sediment dynamics are poorly understood. In this research, we probed the impact of landslide location on sediment dynamics and the response of sediment yields through numerical modelling. We modified the landscape evolution model, CAESAR-Lisflood (CL) to enable sediment from landslides to be tracked throughout the basin, and to include spatial changes in landslide failure angle. The model was then used to investigate impact of the different landslide location scenarios on basin morphology and sediment yields. Using a study area in the Hongxi river basin, four different regions (upstream-high, upstream-low, downstream-high, and downstream-low) were determined in terms of the distance to main stream for an upstream and downstream basin - and in each region landslides were generated for twenty times at random locations. The model results indicate that the location of landslides could alter the fluvial sediment yields and spatial pattern of the sediment dynamics, with low location landslides being more likely to link or connect to the drainage system (higher connectivity) thus leading to greater sediment yields at basin outlet. Whereas material generated by high location landslides tended to accumulate on hillslopes, which could lead to a lag sediment evacuation from the basin. Simulations also show a big latency of sediment yield between upstream and downstream scenarios, which is largely due to the differences of the flow length from landslides source to the basin outlet. These findings are of great importance to understand the characteristics especially the location of landslides and measures for landslide risk prevention and mitigation.

Study of the Dilatancy/Contraction Mechanism of Landslide Fluidization Behavior Using an Initially Saturated Granular Column Collapse Simulation

AbstractFluidlike and integral sliding behaviors can be partly attributed to the dilatancy/contraction behavior of granular materials. A three‐dimensional two‐phase model and smoothed particle hydrodynamics method are applied to study the fluidization behavior by simulating the collapse of an initially fully saturated granular column. The dimensionless numbers (the initial aspect ratio, initial solid volume fraction, and Stokes number associated with the grain size) are varied to examine the collapse process and deposition characteristics. The profiles and front location during collapse highlight that the mechanism changes with the Stokes number and initial solid volume. The granular migration and pore pressure evolution characteristics are presented to clarify the differences in the collapse procedures and mechanisms pertaining to the simulation cases. The dimensionless final runout length and deposition height present monotonically increase and decrease following power laws with increasing initial aspect ratio, respectively; the dimensionless final runout length and deposition height also have monotonically decreasing and increasing relationships with increasing initial solid volume fraction and strongly increasing and decreasing characteristics during the transfer from the viscous flow regime to the inertial flow regime with increasing Stokes number, respectively. The simulation results indicate that the dynamic mechanism of the fluidization transformation is controlled by the Stokes number and initial solid volume fraction. Moreover, the coupling effect of the Stokes number, initial solid volume fraction and initial aspect ratio controls the collapse process of the initially saturated granular column.

Influence of erodible layer on granular column collapse using discrete element analysis

ABSTRACT Landslides, debris flows and avalanches are geophysical hazards, which require sophisticated multi-scale analysis to understand the nature of the flow behaviour. This article discusses numerical investigation of the behaviour of granular flows through granular column collapse model. The column is allowed to collapse on an erodible bed of granular particles to understand the mechanism of entrainment. Discrete Element Method (DEM) is used to model the column collapse to investigate the run-out length and velocity of flow. Simulations were performed at the particulate level in this method. Particle–particle interaction in DEM helps in better understanding of the entrainment phenomenon. Run-out lengths increase with the increase in the initial column aspect ratio of the granular column with rigid bed. In this study, substantial variations were observed in the final run-out lengths in the presence of erodible bed in the model. The force of impact induces frontal ploughing giving rise to the entrainment of particles into the flowing mass and increased mean flow velocity. Column collapse over erodible bed resulted in thicker final deposits, which is evident from the increased coordination number.

Stability of rigid body motion through an extended intermediate axis theorem: application to rockfall simulation

The stability properties of a freely rotating rigid body are governed by the intermediate axis theorem, i.e., rotation around the major and minor principal axes is stable whereas rotation around the intermediate axis is unstable. The stability of the principal axes is of importance for the prediction of rockfall. Current numerical schemes for 3D rockfall simulation, however, are not able to correctly represent these stability properties. In this paper an extended intermediate axis theorem is presented, which not only involves the angular momentum equations but also the orientation of the body, and we prove the theorem using Lyapunov’s direct method. Based on the stability proof, we present a novel scheme which respects the stability properties of a freely rotating body and which can be incorporated in numerical schemes for the simulation of rigid bodies with frictional unilateral constraints. In particular, we show how this scheme is incorporated in an existing 3D rockfall simulation code. Simulations results reveal that the stability properties of rotating rocks play an essential role in the run-out length and lateral spreading of rocks.

Runout modelling and hazard assessment of Tangni debris flow in Garhwal Himalayas, India

Debris flows are frequently occurring natural processes in geologically complex terrains of the Indian Himalayas. Debris flow runout modelling leading to hazard assessment is essential for planning, designing, and execution of mitigation measures. In the present context, debris flow hazard assessment has been carried out for the Tangni debris flow in Garhwal Himalayas, India. Runout modelling was carried out using a Voellmy model-based 3D numerical simulation for estimation of flow intensity parameters such as runout distance, flow velocity, height and pressure along the propagation path. For calibration of the model inputs, back analysis of Tangni debris flow event that occurred in 2013, with its known runout length and deposition volume as the criteria, has been conducted. The best calibrated values of frictional parameters are obtained at μ = 0.10 and ξ = 400 m/s2. Using the best calibrated values of frictional parameters, hazard assessment was carried out for two potential release areas separately, with different initial volumes, and in combination to derive the probable runout distance along with other flow intensity parameters for different scenarios that may happen in the future. It has been observed that this debris flow scenario including the combination of two potential release areas will block the Alaknanda River, forming a landslide dam with a probable height of 6 m. Debris flow runout modelling-based hazard assessment will be helpful in determining quantitative information on flow intensity parameters, where complete data on past events are generally not available or were not possible to capture for the Indian Himalayan region.

Enhanced weakly-compressible MPS method for immersed granular flows

We develop and validate a three-dimensional particle method based on an Enhanced Weakly-Compressible MPS approach for modeling immersed dense granular flows. For this purpose, we adopt a generalized rheological model, using a regularized visco-inertial rheology, for all regimes of multiphase granular flow. Moreover, we propose a new consistent formulation to estimate the effective pressure of the solid skeleton based on the continuity equation of the pore-water. To improve the accuracy of the multiphase particle methods, especially near boundaries and interfaces, we introduce a modified high-order diffusive term by employing the convergent form of the Laplacian operator. The effectiveness of the new diffusive term is particularly demonstrated by modeling the hydrostatic pressure of two fluid phases. Further, coupling the generalized rheology model with the flow equations, we investigate the gravity-driven granular flows in the immersed granular collapse and slide in three dimensions. As a part of this study, we represent the experiment on the immersed granular collapse to validate the model. The evolution and runout length of the granular bulk are compared with those from experiments confirming good compatibility. Overall, the qualitative and quantitative results justify the proposed developments shown to be essential for predicting different states of the immersed granular flows.