Debris-flow Volume Research Articles

A hybrid machine-learning model to estimate potential debris-flow volumes

Empirical-statistical models of debris-flow are challenging to implement in environments where sedimentary and hydrologic triggering processes change through time, such as after a large earthquake. The flexible and adaptive statistical methods provided by machine learning algorithms may improve the quality of debris flow predictions where triggering conditions and the nature of sediment that can bulk flows varies with time. We developed a hybrid machine-learning model of future debris-flow volumes using a dataset of measured debris-flow volumes from 60 catchments that generated post-Wenchuan Earthquake (Mw 7.9) debris flows. We input topographic variables (catchment area, topographic relief, channel length, distance from seismic fault, and average channel gradient) and the total volume of co-seismic landslide debris into the PSO-ELM_AdaBoost machine-learning model, created by combining Extreme learning machine (ELM), particle swarm optimization (PSO) and adaptive boosting machine learning algorithm (AdaBoost). The model was trained and tested using post-2008 Mw 7.9 Wenchuan Earthquake debris flows, then applied to understand potential volumes of post-earthquake debris flows associated with other regional earthquakes (2013 Mw 6.6 Lushan Earthquake, 2010 Mw 6.9 Yushu Earthquake). We compared the PSO-ELM_Adaboost method with different machine learning methods, including back-propagation neural network (BPNN), support vector machine (SVM), ELM, PSO-ELM. The Comparative analysis demonstrated that the PSO-ELM_Adaboost method has a higher statistical validity and prediction accuracy with a mean absolute percentage error (MAPE) less than 0.10. The prediction accuracy of debris-flow volumes trigged by other earthquakes decreases to 0.11–0.16 (absolute percentage error), suggesting that once calibrated for a region this method can be applied to other regional earthquakes. This model may be useful for engineering design to mitigate the risk of large post-earthquake debris flows.

How does co-registration affect geomorphic change estimates in multi-temporal surveys?

ABSTRACT High-Resolution Topography (HRT) data sets are becoming increasingly available, improving our ability and opportunities to monitor geomorphic changes through multi-temporal Digital Terrain Models (DTMs). The use of repeated topographic surveys enables inferring the sediment dynamics of hazardous geomorphic processes such as floods, debris flows, and landslides, and allows us to derive important information on the risks often associated with these processes. The topographic surveying platforms, georeferencing systems, and processing tools have seen important developments in the last two decades, in particular Light Detection And Ranging (LiDAR) technology used in Airborne Laser Scanning (ALS) and Terrestrial Laser Scanning (TLS). Moreover, HRT data, produced through these techniques, changed a lot in terms of point cloud density, accuracy and precision over time. Therefore, old “legacy” data sets and recent surveys can often show comparison problems, especially when multi-temporal data are not homogeneous in terms of quality and uncertainties. In this context, data co-registration should be used to guarantee the coherence among multi-temporal surveys, minimizing, on stable areas, the distance between corresponding points acquired at different epochs. Although several studies highlight that this process is fundamental to properly compare multi-temporal DTMs, it is often not addressed in LiDAR post-processing workflows. In this paper we focus on the alignment of multi-temporal surveys in a topographically complex and rugged environment as the Moscardo debris-flow catchment (Eastern Italian Alps), testing various co-registration methods to align multi-temporal ALS point clouds (i.e. years 2003, 2009 and 2013) and the derived DTMs. In particular, we tested the pairwise registration with manual correspondences, the Iterative Closest Point (ICP) algorithm and a mathematical model that allows aligning simultaneously a generic number of point clouds, the so-called Generalized Procrustes Analysis (GPA), also in its GPA-ICP variant. Then, to correct the possible small inaccuracies generated from the gridding interpolation process, a custom-developed DTM co-registration tool (GRD-CoReg) was used to align gridded data. Both alignment phases (i.e. at point cloud and DTM level) proved to be fundamental and allowed us to obtain proper and reliable DTMs of Difference (DoDs), useful to quantify the debris mobilized and to detect the spatial and temporal patterns of catchment-scale erosion and deposition. The consistency of DoDs data was verified through the comparison between the erosion estimate of DoDs and the volumes of debris-flow events measured by the monitoring station close to the Moscardo torrent catchment outlet. The GPA-ICP algorithm followed by the GRD-CoReg tool proved to be the most effective solution for improving DoDs results with a decrease of systematic trend due to vertical and horizontal uncertainties between surveys, especially at steep slopes. The net volume difference (i.e. the sediment output from the catchment) of the 2003–2013 period changed from 3,237,896 m3 to 135,902 m3 in DoDs obtained from not co-registered and co-registered DTMs. The volume of debris flows measured at the catchment outlet during the same time interval amounts to 169,660 m3. The comparison with debris-flow volume measures at the monitoring station shows, therefore, that the DTMs obtained from the co-registration processes generate more reliable DoDs than those obtained from the raw DTMs (without the alignment).

Sensitivity analysis of influencing parameters on slit-type barrier performance against debris flow using 3D-based numerical approach

Extreme rainfall-induced debris flow can be catastrophic to an urban area, and installation of slit-type barriers can prevent such damage while minimizing negative impact on environments. However, the performance of slit-type barriers against debris flows remains poorly identified partly due to the innate complexity in interactions between debris flow and solid structure. This paper investigated the flow behaviors of debris affected by slit-type barriers using the computational fluid dynamics (CFD) method, in which the numerical model based on the volume of fluid method was verified using the physical modeling results. The sensitivity analysis was performed by building metamodels to determine the primary parameters influencing the barrier performance against debris flows among various variables, in which the effect of input properties and design parameters, particularly the soil concentration in fluidized debris, initial velocity and volume of debris, the barrier height, and the opening ratio, was evaluated from the perspectives of the flow energy reduction and debris trapping. The initial velocity and volume of debris were found to play a significant role in determining the debris flow characteristics. A decrease in the opening ratio in the channel primarily facilitated the energy reduction and trapping due to the reduced opening size. However, the barrier height exhibited a limited effect when the height was sufficiently high to block the debris flow volume. In addition, it was observed that the double barrier system effectively increased the energy reduction while keeping the benefit of open-type barrier. The developed simulation method and obtained results provide an effective tool and an insight that can contribute to an optimum design of the debris-flow barrier.

Debris flow enlargement from entrainment: A case study for comparison of three entrainment models

Material entrainment can significantly magnify debris flow volume and increase its destructive power. Despite great research efforts, entrainment is still not well understood. To meet the needs for debris flow simulation and hazard analysis, it is of practical significance to understand and evaluate existing entrainment models. In this study, we evaluate three entrainment models on an integrated single-phase continuum debris flow simulation platform. The well-documented Tsing Shan debris flow in 1990 in Hong Kong, with an initial landslide volume of 2500 m3 and a final deposit volume of 20,400 m3, is used as a benchmark to compare the three models. The characteristics and performance of each model and its model parameters are discussed. Although numerical results achieve reasonable agreement with detailed field investigations, some parameters are still determined empirically and subjectively. Despite of the imperfection, these models can be used for debris flow hazard analysis in the Hong Kong region with similar conditions. More physically-based entrainment models considering two-phase flow need to be adopted and further developed in the future.

Glacial Lake Inventory and Lake Outburst Flood/Debris Flow Hazard Assessment after the Gorkha Earthquake in the Bhote Koshi Basin

Glacial lake outburst floods (GLOF) evolve into debris flows by erosion and sediment entrainment while propagating down a valley, which highly increases peak discharge and volume and causes destructive damage downstream. This study focuses on GLOF hazard assessment in the Bhote Koshi Basin (BKB), where was highly developed glacial lakes and was intensely affected by the Gorkha earthquake. A new 2016 glacial lake inventory was established, and six unreported GLOF events were identified with geomorphic outburst evidence from GaoFen-1 satellite images and Google Earth. A new method was proposed to assess GLOF hazard, in which large numbers of landslides triggered by earthquake were considered to enter into outburst floods enlarge the discharge and volume of debris flow in the downstream. Four GLOF hazard classes were derived according to glacial lake outburst potential and a flow magnitude assessment matrix, in which 11 glacial lakes were identified to have very high hazard and 24 to have high hazard. The GLOF hazard in BKB increased after the earthquake due to landslide deposits, which increased by 216.03 × 106 m3, and provides abundant deposits for outburst floods to evolve into debris flows. We suggest that in regional GLOF hazard assessment, small glacial lakes should not be overlooked for landslide deposit entrainment along a flood route that would increase the peak discharge, especially in earthquake-affected areas where large numbers of landslides were triggered.

Experimental and numerical study on the load and deformation mechanism of a flexible net barrier under debris flow impact

High-strength flexible net barriers have achieved a certain effect in mountainous debris flow prevention, but research on the mechanism of structural stress and deformation is still developing. This study first presents an analytical model based on the quasi-static mechanical equilibrium to evaluate the geometric nonlinearity and the load performance of the structure and then conducts a flume experiment to reveal the load mechanism of the structure. Then, a full-scale simulation is performed to investigate the deformation and failure of the flexible net barrier impacted by the debris flow via PFC3D software. The results show that the deformation of the flexible net barrier occurs not only in the direction of flow but also in other directions to make the structure force balanced under debris flow impact. The load impacting on the barrier is far less than the total impact force exerted by debris flow. The flexible barrier has an obvious effect to block a coarse debris flow, and the blocking capacity is related to the volume of debris flow and the slope gradient of the flume. The displacement patterns of loaded cable in the experiment and the simulation are different, but the cable under non-debris flow impact is only dragged by the mesh rope showing a regular parabolic shape, and the tension inside the flexible mesh is far less than that of the transverse cable. In addition, the model shows the failure characteristics of flexible barrier under large-scale debris flow, which plays a guiding role in practical engineering design of the structure.

Debris-flow generated tsunamis and their dependence on debris-flow dynamics

Debris-flow generated tsunamis can be extremely dangerous for lakeside settlements and infrastructure. Debris-flow composition strongly affects debris-flow thickness and velocity, and therefore also the generated tsunami. This interaction is, however, poorly understood. We investigate the effects of debris-flow volume, composition (gravel, sand, clay, water) and subaerial outflow slope on wave celerity and amplitude in a small-scale physical model consisting of an inclined outflow channel which transits into a three-dimensional water reservoir.We find that upon debouching, a debris flow pushes the water forward until wave celerity exceeds subaqueous debris-flow velocity (i.e. Froude number <1). The wave then detaches from the debris flow and travels into the far-field. Pushing of the debris-flow oversteepens and accelerates the generated wave beyond the celerity predicted by linear wave theory for shallow waves. It also increases its non-linearity but does not result in wave breaking.Wave celerity has the strongest relation with debris-flow velocity. Debris-flow velocity increases with increasing water and clay content (up to 22%), which both lubricate the flow. Far-field leading wave amplitude has the strongest relation with debris-flow momentum (velocity times effective mass), which is mostly a function of debris-flow thickness, water and clay content.We test the applicability of published (semi-empirical) equations for predicting tsunami amplitude generated by dry landslides, and show that they are to some extent also applicable to debris flow. Potential scale effects, especially considering the smallest waves and water depths, could influence the applicability of these predictors and translation of the results to the field scale. Our results demonstrate the importance of debris-flow composition on tsunami generation and evolution, and thus the necessity of including flow composition in predictive simulation models.

MASS FORMATION OF DEBRIS-FLOWS IN THE LOW MOUNTAINS OF SAKHALIN ISLAND: CONDITIONS AND REPEATABILITY

In the debris-flows basins of the Southern and Middle part of Sakhalin island are formed debris-flows, mudflows, slushflow and suspended stream. Average volumes of debris-flows: 500 - 10 000 m3, maximum-more than 500 000 m3. In July-October, periods of mass formation of debris-flows and mudflows are repeated from 1 time in 3-5 years to 1 time in 10-12 years. These periods last from 1 to 3-5 days. These periods occur during deep cyclones (when more than 50 mm of precipitation falls per day). During these periods some hundreds of debris-flows and mudflows form in most mud basins. For example, during the passage of typhoons Ojin and Phyllis on August 3-5, 1981 on the South-Western coast of Sakhalin Island, 154 debris-flows and mudflows with a volume of up to 12 thousand m3 descended on a section 55 km long. At the same time, 55 debris-flows and mudflows with a volume of up to 35 thousand m3 descended on the South-Eastern coast of Sakhalin Island (on a section 30 km long). Periods of mass formation of debris-flows and mudflows on Southern Sakhalin were noted in 1947, 1951, 1964, 1965, 1970, 1972, 1978, 1981, 1992, 1993, 2000, 2002, 2003, 2009, 2010, 2011, 2013, 2016, 2018. The high intensity of the manifestation of debris-flows and mudflows processes on Sakhalin Island is due to the following factors: a large depth of relief (500 – 1000 m), large slopes of debris-flows and mudflows channels (35°-50°), strong precipitation (daily maximum precipitation – 230 mm, hourly – more than 50 mm), as well as the geological structure of debris-flows and mudflows basins: young rocks, weakly cemented, easily eroded and soaked (siltstones, mudstones, sandstones) saturating the debris-flows with clay fractions; strong Intrusive, volcanogenic and metamorphic rocks (diorite porphyrites, andesites, diorites, dacites, Greenstone shales, serpentinites), form a boulder-block fraction of mudflows.

A combined method for modeling the triggering and propagation of debris flows

This study describes a combined method for rainfall-induced debris flow initiations (landslides) and propagations including a series of numerical analyses. In this study, the debris is assumed as a mixture of soils and water which is physically non-Newtonian fluid. The emphasis is placed on applying the effect of the combination of rainfall-induced landslides and debris flows to the numerical analysis. An analysis of rainfall-induced landslides is conducted to identify the thickness and location of the initial volume of debris flow. The movement of debris flow is subsequently simulated considering entrainments affected by the initial wetting condition (wetting front) estimated from the rainfall-infiltration analysis. The proposed method can simulate a sequential process from the initiation of the debris flows to the deposition based on the prediction of slope failure by rainfall, fluid dynamics based on Navier–Stokes equation, and the analysis of entrainments by considering the effect of the weight of debris and the wetting condition of soil beds. Based on the numerical results of this study, the proposed method could be applied to the analysis of regional-scale landslides and debris flows.

Early identification of river blocking induced by tributary debris flow based on dimensionless volume index

River-blocking events induced by tributary debris flows occur frequently in mountainous areas. If a dam formed by a river-blocking debris flow were damaged, a massive outburst flood could induce downstream hazards. Therefore, early identification of areas potentially at risk of river blocking is essential for hazard mitigation, particularly in extensive mountainous areas. This study proposed a dimensionless volume index (DVI) to evaluate river-blocking formation by considering the relationship between the deposition volume of a tributary debris flow in a river and the minimum river-blocking volume. The values of both parameters can be established based on the theory of debris flow run-out distance, deposition width, and deposition thickness with consideration of the effects of drag force, hydrostatic force, and buoyancy. The efficacy of the proposed method was demonstrated through two case studies of mainstream blocking/nonblocking by tributary debris flow events in Taiwan during Typhoon Morakot. The results indicated that early identification of river blocking could be achieved using the DVI based on a pre-established database of potential debris flow hazard areas, including local site information, rainfall intensities at potential debris flow hazard areas under varying recurrence periods, and mainstream discharge at varying recurrence periods.

Empirical relationships for the estimation of debris flow runout distances on depositional fans in the Wenchuan earthquake zone

The Wenchuan area has become highly susceptible to landslides and debris flows since the earthquake occurred on 2008. A detailed debris flow hazard assessment is necessary to provide information for future risk management. Debris flow runout on a depositional fan is an important factor for assessing debris flow hazard, and its estimate becomes essential for the planning of the mitigation works that must be built. We therefore developed two simple empirical relationships based both on univariate and multivariate approaches, which provide the runout distance using the data for 134 channelized debris flow events in 134 catchments in the Wenchuan earthquake zone. We generated a correlation matrix of the debris flow runout distances and the relevant variables. Because of the high correlations, the independent variable debris flow volume (VD) was selected for the univariate approach. Using a multicollinearity analysis and a stepwise regression technique, the catchment (basin) internal relief (H), and VD were used to develop a multivariate runout relationship. The coefficients of the variables were obtained using 80% of the dataset (training dataset); the remaining 20% was used for test of estimated performance by comparing the computed runout distances with observed values. The validation demonstrated that the proposed relationships are suitable for estimating the runout distances of debris flows on depositional fans in the Wenchuan earthquake zone. The univariate runout relationship has the advantage of being simple, whereas the multivariate runout relationship provides higher accuracy. Additionally we rearranged and reformulated existing relationships using the same training dataset and compared the results with those from the relationships here proposed. The estimations provided by our relationships were the closest to the observed values. The presented approaches may be applied to estimate debris flow runout distances in other areas after they are retrained using local datasets.

Debris Flow Activity in Trans-Ili Alatau in the 20th — Early 21st Centuries

We examine the debris flow activity in Trans-Ili Alatau since 1900 till the present. Characteristics of the debris flow formation conditions and data on the largest debris flows are presented. A study is made of the interannual and intra-annual variability of debris flow activity. The debris flow activity was characterized by the number of debris flows in a year, and by the total volume of debris transported. For the period from 1900 to 2017 we recorded 481 debris flows. It was found that the genetic types of debris flows are dominated by rain-induced and glacial flows (87 % of the total number of debris flows). The other genetic types (snow-caused, seismogenic and anthropogenic) account for 13%. Most of the debris flows have a rain genesis (71% of the total number of rain-induced and glacial debris flows). Glacial debris flows account for 79% of the volume of debris transported. The volumes of the largest debris flows, both glacial and rain-induced, exceed one million cubic meters. They make up 3% of the total number of debris flows but they transported 70 % of debris. Small debris flows with a volume of less than 10 thousand cubic meters, in terms of their number, constitute 74%; however, they account for a mere 3% of the volume of debris flow deposits. Observations indicate that the earliest debris flows occurred in the second ten-day period of March, and the latest occurred in the first ten-day period of September. The distribution of the number of debris flows according to the dates of their occurrence clearly shows two maxima: one maximum in the second ten-day period of June, and the other maximum in the second ten-day period of July. The June maximum is due to rain precipitation, and the July maximum is associated with glacial debris flows. From 1950 to 2017 there were only 5 (7%) years without any debris flows. Four of them corresponded to the 2010s. The number of years with rain-induced and glacial debris flows was 55 (81%) and 39 (57%), respectively.

Debris-flow volume quantile prediction from catchment morphometry

Abstract Estimation of the volumes of potential future debris flows is a key factor in hazard assessment and mitigation. Worldwide, however, there are few catchments for which detailed volume-frequency information is available. We (1) reconstructed volume-frequency curves for 10 debris-flow catchments in Saline Valley, California (USA), from a large number of well-preserved, unmodified surficial flow deposits, and (2) assessed the correlations between lobe-volume quantiles and a set of morphometric catchment characteristics. We found statistically significant correlations between lobe-volume quantiles, including median and maximum, and catchment relief, length (planimetric distance from the fan apex to the most distant point along the watershed boundary), perimeter, and Melton ratio (relief divided by the square root of catchment area). These findings show that it may be possible to roughly estimate debris-flow lobe-volume quantiles from basic catchment characteristics that can be obtained from globally available elevation data. This may assist in design-volume estimation for debris-flow catchments where past flow volumes are otherwise unknown.

Insights into the catastrophic Xinmo rock avalanche in Maoxian county, China: Combined effects of historical earthquakes and landslide amplification

A large and catastrophic rock avalanche occurred at the Xinmo village in the Maoxian county of the Sichuan province of China on June 24, 2017. The avalanche destroyed 64 houses and killed 10 people, and 73 people were reported to be missing. In this study, we focused on the contributions of six historical earthquakes to the collapse of rocks in the source area and the landslide amplification caused by the entrainment of pre-existing deposits on the landslide path. The historical earthquakes in this area contributed different levels of damage on the source rocks; particularly, the 1933 Diexi earthquake induced a few initial cracks in rocks at the crest of the steep hillslope. Under the combined time-effects of long-term weathering and gravity, the rock blocks in the source area were detached from the crest along the intersecting cracks and over-dip soft layer (namely, the sliding surface). The avalanche was amplified by the entrainment of colluvium on its path. The influence of the colluvium on the movement process of the Xinmo landslide was modelled by the GPU-based parallel discontinuous deformation analysis (DDA) method, and the effect of the impact and entrainment in the debris flow was rigorously analysed. The results indicate that the impact and entrainment can continuously increase the volume of debris flow, and the thickness of the colluvium was established to be in the range of 25.9–33.9 m based on the analysis of the deposit pattern and movement duration of the avalanche. There were numerous unstable rocks induced by historical earthquakes, at the crests of steep hill slopes in the earthquake-stricken area. With long-term damage caused by environmental factors and gravity, the failure of unstable rocks with high potential energy is likely to cause severe disasters. The excess pore water pressure likely to be present in the colluvium or deposits during impact and entrainment can considerably reduce the effective stress and degrade friction resistance along the runout path. As a result, the landslide can be intensively amplified owing to the effect of impact and entrainment under a lower friction resistance

Identifying post-earthquake debris flow hazard using Massflow

Catastrophic debris flows are common after large earthquakes and pose a significant risk for recovering communities. The depositional volume of these large debris flows is often much greater than the initiation volume, suggesting that bulking of the flow plays an important role in determining their volume, speed, and runout distance. Observations from recent earthquakes have driven progress in understanding the relationship between triggering rainfall events and the timing of post-earthquake debris flows. However, we lack an adequate mechanism for quantifying bulking and applying it within a hazard context. Here we apply a 2D dynamic debris flow model (Massflow) that incorporates a process-based expression of basal entrainment to understand how debris flow bulking may occur within post-earthquake catchments and develop hazard maps. Focussing on catchments in the epicentral area of the 2008 Mw 7.9 Wenchuan Earthquake, we first parameterised the model based on a large debris flow that occurred within the Hongchun catchment, before applying the calibrated model to adjoining catchments. A model sensitivity analysis identified three main controls on debris flow bulking; the saturation level of entrainable material along the flow pathway, and the size and position of initial mass failures. The model demonstrates that the difference between small and very large debris flows occur across a narrow range of pore-water ratios (λ). Below λ = 0.65 flows falter at the base of hillslopes and come to rest in the valley bottom, above λ = 0.70 they build sufficient mass and momentum to sustain channelised flow and transport large volumes of material beyond the valley confines. Finally, we applied the model across different catchments to develop hazard maps that demonstrate the utility of Massflow in post-earthquake planning within the Wenchuan epicentral region.

Geomorphic effectiveness of check dams in a debris-flow catchment using multi-temporal topographic surveys

Torrent control works, such as grade control dams and sediment retention dams, are structural measures for controlling debris flows and debris floods. In spite of the widespread presence of such hydraulic structures in steep mountain streams worldwide, there are still few studies monitoring the effects of check dams on sediment dynamics.The use of repeated topographic surveys allows us to characterize debris-flow activity at multiple temporal and spatial scales and its interaction with torrent control works. Structure from Motion (SfM) technique paired with Multi-View Stereo (MVS) algorithms represents a low-cost opportunity to conduct such multi-temporal surveys. This enables us to better study the effects of individual debris flows, track geomorphic changes and evaluate the effectiveness of torrent control works (e.g. check dams).The effect of check dams on sediment dynamics is investigated by means of multi-temporal topographic surveys before and after debris-flow events in the Moscardo torrent (eastern Italian Alps) where two check dams have recently been built. Multi-temporal SfM based on images taken from the ground in combination with imagery taken by an Unmanned Aerial Vehicle (UAV) is used to obtain DEMs and to study topographic changes through the comparison of repeat DEMs (DEM of Difference, i.e. DoD).The results show that the new check dams considerably modified sediment dynamics in the studied channel but their performance cannot be considered satisfactory. The sediment flowed around the upstream check dam on the right wing, while deep erosion observed downstream of the check dam threatened to undermine the foundation's stability. Moreover, debris-flow lobes deposited upstream of the check dams could act as sources of sediment further increasing downstream debris-flow volume. The analysis proposed in this work could help improve design strategies and permitting the identification of a proper site for check dam building.

Real-time observation of an active debris flow watershed in the Wenchuan Earthquake area

Debris flows occur frequently and cause considerable damage in the Wenchuan Earthquake area; however, there has been no systematic real-time monitoring of such events. This study used a monitoring system to consider the spatial variation of meteorological and flow processes in a 39.4 km2 watershed. The system comprised three rainfall gauges at different locations, and three hydrological monitoring stations, located on the mainstream and tributaries, with instruments to measure the velocity, height, and density of debris flows. Based on the monitoring data, the debris flow events were categorized and the general runoff velocity, discharge, and density were analysed. We proposed empirical methods for estimating the velocity and the total volume of debris flows based on other easily obtainable parameters, e.g., maximum flow depth and duration. Comparison of the results derived using the monitoring data and empirical formulas with those obtained in other small watersheds worldwide revealed the debris flow characteristics in this relatively large watershed. Rainfall threshold for the debris flows was proposed, which is higher than those proposed for the same region for periods shortly after the Wenchuan Earthquake (2008–2013), and the temporal evolution of the rainfall conditions necessary for debris flows was addressed.

EDDA 2.0: integrated simulation of debris flow initiation and dynamics considering two initiation mechanisms

Abstract. Climate change is resulting in more frequent rainstorms and more rain-induced debris flows in mountainous areas. The prediction of likely hazard zones is important for debris flow risk assessment and management. Existing numerical methods for debris flow analysis often require the input of hydrographs at prescribed initiation locations, ignoring the initiation process and leading to large uncertainties in debris flow initiation locations, times, and volumes when applied to regional debris flow analysis. The evolution of the flowing mixture in time and space is also barely addressed. This paper presents a new integrated numerical model, EDDA 2.0, to simulate the whole process of debris flow initiation, motion, entrainment, deposition, and property changes. Two physical initiation mechanisms are modelled: transformation from slope failures and surface erosion. Three numerical tests and field application to a catastrophic debris flow event are conducted to verify the model components and evaluate the model performance. The results indicate that the integrated model is capable of simulating the initiation and subsequent flowing process of rain-induced debris flows, as well as the physical evolution of the flowing mixture. The integrated model provides a powerful tool for analysing multi-hazard processes, hazard interactions, and regional debris flow risk assessment in the future.

Automatic Identification of Alpine Mass Movements by a Combination of Seismic and Infrasound Sensors.

The automatic detection and identification of alpine mass movements such as debris flows, debris floods, or landslides have been of increasing importance for devising mitigation measures in densely populated and intensively used alpine regions. Since these mass movements emit characteristic seismic and acoustic waves in the low-frequency range (<30 Hz), several approaches have already been developed for detection and warning systems based on these signals. However, a combination of the two methods, for improving detection probability and reducing false alarms, is still applied rarely. This paper presents an update and extension of a previously published approach for a detection and identification system based on a combination of seismic and infrasound sensors. Furthermore, this work evaluates the possible early warning times at several test sites and aims to analyze the seismic and infrasound spectral signature produced by different sediment-related mass movements to identify the process type and estimate the magnitude of the event. Thus, this study presents an initial method for estimating the peak discharge and total volume of debris flows based on infrasound data. Tests on several catchments show that this system can detect and identify mass movements in real time directly at the sensor site with high accuracy and a low false alarm ratio.

Relation between basin morphometric features and dynamic characteristics of debris flows – a case study in Siberia, Russia

Extreme and prolonged rainfall in the Tunka Ridge caused several debris flows in the vicinity of the Arshan village (Siberia, Russia) on June 28, 2014. These debris flows, in spite of similar geological conditions, had different velocity, peak discharge and alluvial fan volume values. The flow velocity was from 3.5 m/s to 19.6 m/s, the peak discharge ranged from 63 m3/s to 13566 m3/s, and the alluvial fan volume varied from 4.13×103 to 8.45×105 m3. Such a great range of values is due to the morphometric parameters of the debris flow basins. The article deals with the influence of morphometric parameters of debris flow basins, such as the basin area, the average slope, Melton ratio, relief ratio on the debris flow velocity, peak discharge and volume of alluvial fans. In this debris flow event the average values of slope angle and total basin relief of the debris flow basins did not affect the values of debris flow velocity, peak discharge and alluvial fan volume. The highest correlations were observed with the debris flow basin area that was connected with the water inflow volume into the debris flow basins during the rainfall. The unequal water distribution among debris flow basins also had an impact on the debris flow velocity, peak discharge and volume of alluvial fans.