Large Debris Flows Research Articles

Synergistic analysis of satellite, unmanned aerial vehicle, terrestrial laser scanner data and process-based modelling for understanding the dynamics and morphological changes around the snout of Gangotri Glacier, India

The glaciated areas of the Himalaya often experience mass movement, glacial lake outburst flood and other associated hazards, posing threat to the communities and infrastructure in the downstream areas. A large debris flow occurred during July 16–19, 2017 near the present snout of the Gangotri Glacier in the Garhwal Himalaya, India resulting in significant geomorphological changes in the vicinity. The present study assesses the applicability of multi-source remote sensing data from satellites, unmanned aerial vehicle (UAV) and terrestrial laser scanner (TLS) along with process-based modelling to understand and quantify glacier snout dynamics and morphological changes around Gangotri Glacier in the Garhwal Himalaya of India. We show that retreat rates of Gangotri Glacier snout along the lateral flowlines are (left flowline 29.6 m year−1; right flowline 60.5 m year−1) are significantly higher compared to the central flowline (18.2 m year−1) during 2010–2020 leading to total loss in glacial ice area of 0.11 ± 0.015 km2. The snout dynamics and evolution of the new channel from the terminus of the adjoining Meru Glacier, connecting the moraine-dammed glacial lake and the Bhagirathi River, suggest that retreat of the Gangotri Glacier, intense precipitation and excessive seepage from the glacial lake were the important drivers of the debris flow in July 2017. The accumulated debris occupied an area of ~0.25 km2 near the snout of the Gangotri Glacier and shifted Bhagirathi River by 36–200 ± 9.35 m towards northeast. The synergistic analysis of pre- and post-event satellite, UAV and TLS-based digital elevation models (DEMs) and satellite images indicate that about −8 ± 0.066 × 106 m3 of sediments were generated by the debris flow. The results from remote sensing data suggest that a significant portion (~60%) of the deposited debris has been transported to the downstream areas between July 16–19, 2017 and October 2, 2017. Regular monitoring of the area is recommended, especially in light of climate change using earth observation data and ground measurements. The multi-source integrated framework implemented in this study is generic and can be applied for any debris flow or landslide studies in glaciated terrain.

Intense rainfall and debris flows in the Lomond Hills, Fife, 11–12 August 2020

ABSTRACT Over the night of 11–12th August 2020, unusually intense convective rainfall triggered several debris flows along the Lomond Hills escarpment. Rainfall intensities locally exceeded an estimated 0.33% annual exceedance probability. Each debris flow had a different magnitude and physical character depending on the availability of water and sediment and the effectiveness of the vegetation buffer, such that similar-looking micro-catchments responded in different ways. The largest debris flow far exceeded the others in magnitude, extending over 1 km with a descent of 246 m and an estimated volume of c. 1500–3000 m3, causing damage to a forestry road. Debris was entrained from a gullied relict talus, including fallen trees and incision of Lateglacial glaciofluvial sand. Deposit sedimentology and morphology demonstrate an initial debris-flow surge probably happened early in the storm coinciding with the greatest runoff generation, followed by later fluvial incision and sediment reworking. This appears to be the largest such event in the Lomond Hills for more than 90 years and may be characteristic of the landscape response to projected increases in convective rainfall intensities in twenty-first century summers.

Coupled SPH–FEM Modeling of Tsunami-Borne Large Debris Flow and Impact on Coastal Structures

Field surveys in recent tsunami events document the catastrophic effects of large waterborne debris on coastal infrastructure. Despite the availability of experimental studies, numerical studies investigating these effects are very limited due to the need to simulate different domains (fluid, solid), complex turbulent flows and multi-physics interactions. This study presents a coupled SPH–FEM modeling approach that simulates the fluid with particles, and the flume, the debris and the structure with mesh-based finite elements. The interaction between the fluid and solid bodies is captured via node-to-solid contacts, while the interaction of the debris with the flume and the structure is defined via a two-way segment-based contact. The modeling approach is validated using available large-scale experiments in the literature, in which a restrained shipping container is transported by a tsunami bore inland until it impacts a vertical column. Comparison of the experimental data with the two-dimensional numerical simulations reveals that the SPH–FEM models can predict (i) the non-linear transformation of the tsunami wave as it propagates towards the coast, (ii) the debris–fluid interaction and (iii) the impact on a coastal structure, with reasonable accuracy. Following the validation of the models, a limited investigation was conducted, which demonstrated the generation of significant debris pitching that led to a non-normal impact on the column with a reduced contact area and impact force. While the exact level of debris pitching is highly dependent on the tsunami characteristics and the initial water depth, it could potentially result in a non-linear force–velocity trend that has not been considered to date, highlighting the need for further investigation preferably with three-dimensional models.

Earthquake-induced debris flows at Popocatépetl Volcano, Mexico

Abstract. The 2017 Mw 7.1 Puebla–Morelos intraslab earthquake (depth: 57 km) severely hit Popocatépetl Volcano, located ∼ 70 km north of the epicenter. The seismic shaking triggered shallow landslides on the volcanic edifice, mobilizing slope material saturated by the 3 d antecedent rainfall. We produced a landslide map based on a semi-automatic classification of a 50 cm resolution optical image acquired 2 months after the earthquake. We identified hundreds of soil slips and three large debris flows for a total affected area of 3.8 km2. Landslide distribution appears controlled by the joint effect of slope material properties and topographic amplification. In most cases, the sliding surfaces correspond with discontinuities between pumice-fall and massive ash-fall deposits from late Holocene eruptions. The largest landslides occurred on the slopes of aligned ENE–WSW-trending ravines, on opposite sides of the volcano, roughly parallel to the regional maximum horizontal stress and to volcano-tectonic structural features. This suggests transient reactivation of local faults and extensional fractures as one of the mechanisms that weakened the volcanic edifice and promoted the largest slope failures. The material involved in the larger landslides transformed into three large debris flows due to liquefaction. These debris flows mobilized a total volume of about 106 m3 of material also including large wood, were highly viscous, and propagated up to 7.7 km from the initiation areas. We reconstructed this mass wasting cascade by means of field evidence, samples from both landslide scarps and deposits, and analysis of remotely sensed and rainfall data. Although subduction-related earthquakes are known to produce a smaller number of landslides than shallow crustal earthquakes, the processes described here show how an unusual intraslab earthquake can produce an exceptional impact on an active volcano. This scenario, not related to the magmatic activity of the volcano, should be considered in multi-hazard risk assessment at Popocatépetl and other active volcanoes located along volcanic arcs.

A Pilot Experiment on Infrasonic Lahar Detection at Mount Adams, Cascades: Ambient Infrasound and Wind-Noise Characterization at a Quiescent Stratovolcano

AbstractErosion, hydrothermal activity, and magmatism at volcanoes can cause large and unexpected mass wasting events. Large fluidized debris flows have occurred within the past 6000 yr at Mount Adams, Washington, and present a hazard to communities downstream. In August 2017, we began a pilot experiment to investigate the potential of infrasound arrays for detecting and tracking debris flows at Mount Adams. We deployed a telemetered four-element infrasound array (BEAR, 85 m aperture), ~11 km from a geologically unstable area where mass wasting has repeatedly originated. We present a preliminary analysis of BEAR data, representing a survey of the ambient infrasound and noise environment at this quiescent stratovolcano. Array processing reveals near continuous and persistent infrasound signals arriving from the direction of Mount Adams, which we hypothesize are fluvial sounds from the steep drainages on the southwest flank. We interpret observed fluctuations in the detectability of these signals as resulting from a combination of (1) wind-noise variations at the array, (2) changes in local infrasound propagation conditions associated with atmospheric boundary layer variability, and (3) changing water flow speeds and volumes in the channels due to freezing, thawing, and precipitation events. Suspected mass movement events during the study period are small (volumes <105 m3 and durations <2 min), with one of five visually confirmed events detected infrasonically at BEAR. We locate this small event, which satellite imagery suggests was a glacial avalanche, using three additional temporary arrays operating for five days in August 2018. Events large enough to threaten downstream communities would likely produce stronger infrasonic signals detectable at BEAR. In complement to recent literature demonstrating the potential for infrasonic detection of volcano mass movements (Allstadt et al., 2018), this study highlights the practical and computational challenges involved in identifying signals of interest in the expected noisy background environment of volcanic topography and drainages.

Debris flow initiation from ravel-filled channel bed failure following wildfire in a bedrock landscape with limited sediment supply

AbstractSteep, rocky landscapes often produce large sediment yields and debris flows following wildfire. Debris flows can initiate from landsliding or rilling in soil-mantled portions of the landscape, but there have been few direct observations of debris flow initiation in steep, rocky portions of the landscape that lacdk a thick, continuous soil mantle. We monitored a steep, first-order catchment that burned in the San Gabriel Mountains, California, USA. Following fire, but prior to rainfall, much of the hillslope soil mantle was removed by dry ravel, exposing bedrock and depositing ∼0.5 m of sandy sediment in the channel network. During a one-year recurrence rainstorm, debris flows initiated in the channel network, evacuating the accumulated dry ravel and underlying cobble bed, and scouring the channel to bedrock. The channel abuts a plowed terrace, which allowed a complete sediment budget, confirming that ∼95% of sediment deposited in a debris flow fan matched that evacuated from the channel, with a minor rainfall-driven hillslope contribution. Subsequent larger storms produced debris flows in higher-order channels but not in the first-order channel because of a sediment supply limitation. These observations are consistent with a model for post-fire ravel routing in steep, rocky landscapes where sediment was sourced by incineration of vegetation dams—following ∼30 years of hillslope soil production since the last fire—and transported downslope by dry processes, leading to a hillslope sediment-supply limitation and infilling of low-order channels with relatively fine sediment. Our observations of debris flow initiation are consistent with failure of the channel bed alluvium due to grain size reduction from dry ravel deposits that allowed high Shields numbers and mass failure even for moderate intensity rainstorms.

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

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.

The twin catastrophic flows occurred in 2014 at Ambato Range (28°09′–28°20′S), Catamarca Province, Northwest Argentina

Two destructive and almost simultaneous flows occurred in January 2014 in Catamarca Province, Northwest Argentina. They took place in the Ambato and Siján river watersheds where the villages El Rodeo and Siján are located respectively. As a result, 15 people lost their lives, almost 100 houses and buildings were destroyed and bridges collapsed. In this paper, a comprehensive assessment of the flow events is done by the study of triggering conditions, basin morphometric parameters, flow deposits description and runout characteristics. To achieve this goal, field data, satellite image analysis, digital elevation model information and empirical equations are used. The data analysis suggests that two distinct process types acted in the Ambato and Siján watersheds. The flow event of the Ambato river basin was a debris flood characterized by an extremely high velocity (5.6 m/s) with a peak flow of 581 m3/s. The debris flood was generated by abundant sediment influx coming from landslides generated by the storm in different sub-basins and by the break of a small landslide-dam. In the case of the Siján river basin the event was a debris flow characterized by a velocity that ranged between 2 m/s to 4 m/s with a peak flow of 472 m3/s. The event was generated by an important input of sediments from hillslopes debris flows and translational slides generated during the storm that coalesced downstream forming one large debris flow. Morphometric differences between the two basins under study influenced the type and mechanism of the flows registered. The catastrophic consequences of the events highlight the necessity of an early warning system based on rainfall thresholds and hydrogeomorphic response of the basins.

Tree growth in the aftermath of A flood: A tree-ring based reconstruction of the impacts of the 1996-Biescas catastrophe

Catastrophic floods and large debris flows are natural hazards common in mountain areas. They cause injuries and impact the radial growth of trees growing in the affected basins. Reconstructing how these catastrophic events impact trees by using dendrochronology improves our understanding of natural hazards. The 1996-Biescas (Central Spanish Pyrenees) flood was a catastrophic event causing the loss of many lives in a campsite located on an active alluvial fan. We investigated using tree rings how this catastrophic flood impacted planted trees (poplars, cedars) located in the campsite. Conspicuous scars in the stem were more abundant in cedar trees (75 %) than in poplar (36 %) trees. Scarred cedar trees formed traumatic resin ducts after the flood. In cedar tree perimeter influenced the size of the wound formed after the flood, but this was not observed in poplar. On average, 63 % of trees showing scars formed them in the side of the stem (N-NW) where the impact of the flood was assumed to be strongest. We also detected sharp reductions of tree-ring width after the flood (–56 % and –16 % in poplar and cedar, respectively). However, this was not found when using basal area increment, which suggests there was an age effect on the post-flood growth changes. The two species mean chronologies were also more coupled after the flood in agreement with an increased responsiveness to climate, particularly a higher dependence of growth on June precipitation. To adequately reconstruct responses to flood and to assess the actual vulnerability of forests to debris flow impacts tree features such as species, age, growth rate and responsiveness to climate must be considered.

Risk assessment of Sichuan–Tibet Highway susceptible to debris flows at Suotong Basin, southeastern Tibet

The planned Sichuan–Tibet Highway will pass through many debris flow-prone areas. Suotong catchment with a drainage area of 38.03 km2, a tributary of Parlung Zangbo River in the Bomi County of Tibet, has not experienced large-scale debris flows since 1991. Field survey and image interpretation show that glacial till in the catchment has volume of approximately 160 mm3 and is the primary source of loose materials for debris-flow reoccurrence. Once large glacial debris flows occur, they will cause harm to the highway. A comprehensive method including engineering geology, hydraulics, and computational mathematics is developed to quantitatively assess the debris-flow risk to the highway. The magnitude and peak discharge of glacial debris flows of a 100 year return period are calculated using empirical relationships in this region. The peak velocity at the outlet can reach 6.75 m/s, and the peak discharge is 6238 m3/s for such a return period. The Saint–Venant equations governing debris-flow movements are numerically solved by finite difference method. The simulated results are close to those by empirical methods. The hazard value at the alluvial fan is as high as 24.7 according to the numerical simulation. Two routing schemes (one goes through the tunnel and other pass the bridge) are compared with each other. Although the bridge scheme is cheaper than the tunnel scheme, the bridge’s section cannot fully discharge debris flows within the 100-year return period. Therefore, the tunnel scheme is safer and more strongly recommended than the bridge scheme.

The seismic microzonation study of Pescara del Tronto (Central Italy) during and after the Central Italy earthquake sequence.

Site effects in consequence of the 2016–2018 Central Italy seismic sequence “marked the fate” of many villages located close to the epicenters along the Apennine chain. Pescara del Tronto, a small settlement located on a mountain slope in the municipality of Arquata del Tronto, (AP) is very representative of such territories since, early after the onset of the seismic sequence, suffered very impressive site effects, including a large seismically-induced debris flow and a high number of small volume landslides. This paper describes the main results of the scientific activities carried out by the authors in this locality in the framework of the unprecedented large-scale Seismic Microzonation project funded by Italian Government in Central Italy for 138 territories. Through an intense field activity, the geological and geomorphologic setting of the study area were revised and updated, including a landslide susceptibility assessment that helped the Italian Department of Civil Protection in the emergency management for temporary housing and, later on, was included in the 3rd Level Seismic Microzonation study implemented by authors while the seismic sequence was still ongoing. A very detailed and reliable subsoil model for this municipality was defined, despite difficulties faced in performing direct and indirect investigations due to the safety restrictions for many areas. The Local Seismic Site response was finally assessed for this locality and the results discussed. A key role in the occurrence of strong site effects into Pescara del Tronto has been played by quaternary deposits having an unexpected heterogeneity under the old village.

Evaluations and proposals for the debris flow hazard mapping method of the GIDES Project

On March 11 and 12, 2011, a large rainfall event caused floods and thousands of gravitational mass movements on the coast of the state of Parana, Brazil. This paper focuses on the large debris flows that reached the Jacarei river basin and uses them to test the new hazard mapping method proposed by the GIDES Project, a technology transfer partnership between Brazil and Japan. The method’s purpose is to be simple and fast, and, so, applicable in a developing country of continental dimension. Comparison of the maps generated by the GIDES methodology and the actual events that happened in the study area showed many discrepancies, that is, in its original form the methodology could not predict accurately the events. However, after adaptations to the studied case, major improvements were obtained. The adaptations aimed at testing morphometric parameters as the original technique to reach the best fit possible between the generated maps and the occurrence area of the studied event. For the debris flow transportation area, the parameters that produced better maps closer to the studied actual event was made with the relation between the maximum height reached by the debris flow and the maximum channel slope. No satisfactory morphometric relationship was found for the boulders’ deposition region. For the area of fine or less dense materials’ deposit, the most significant change was the incorporation of slopes from 0° to 2° in the mapping procedure. Finally, we found values and equations that could be used initially in the analysis of other sub-basins with some similarity with the studied area to map the debris flow hazard, although validation in other places is still needed. These different techniques adapted to the local reality can be used separately or together to create faster, simpler, cheaper, and reliable maps using relatively easy to find morphometric input data.

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.

Laboratory study on the characteristics of large wood and debris flow processes at slit-check dams

Large wood (LW) in debris flows during flooding can cause significant damage to check dams, bridges, and other major infrastructure in its flow path. When LW accumulates and forms logjams, large volumes of sediment can be deposited, resulting in increased backwater. The logjams can then suddenly collapse, with the deposited sediment and accumulated water increasing the magnitude of debris-flow peak discharge. To better understand the characteristics of debris flow discharge caused by LW accumulation and collapsed logjams, as well as the associated magnitude amplification effects, a series of experiments was carried out in a laboratory experimental channel. The main purpose of this study was to analyze the process of LW accumulation and collapse and to determine the magnitude amplification ratio of the debris flow peak discharge with LW. The results revealed three types of debris flow movement with LW: flow with no clogging or breakage, flow with clogging but without breakage, and flow with both clogging and breakage. The results indicated a significant effect on the magnitude amplification ratio caused by LW clogging and breakage. The maximum magnitude amplification ratio was 1.60 in the experiments, with a relative LW length and volume of 0.875 and 0.75, respectively, during the clogging and breakage process.

Cannibalism of contourites by gravity flows: explanation of the facies distribution of the Ordovician Pingliang Formation along the southern margin of the Ordos Basin, China

The Late Ordovician Pingliang Formation accumulated along the southern margin of the Ordos Basin in China. The convergence of the Yangtze Plate and Sino-Korean Plate led to a trench–arc–basin system during the Middle Ordovician, with a platform- and slope-dominated setting in the east where a graben complicated the overall simple paleogeographical picture, relatively parallel zones of a platform and a slope setting in the middle, and a change from platform to slope to deep marine to a trench setting in the west. This configuration resulted in various types of gravity flow deposits and contourites with different compositions and pathways. The present study focuses on the typical characteristics of contourites in the geological record and the relationships between contour currents and gravity flows. The Pingliang Formation contains eleven lithofacies grouped into five facies associations. These facies associations represent deep sea autochthonous deposits, several types of debrites, turbidites, and contourites, as well as turbidites within which the fine-grained top portion was reworked by a contour current. The various lithofacies are concentrated in different parts of the study area: micritic contourites and debrites are concentrated in the eastern part; debrites, and sandstone and siltstone turbidites are concentrated in the middle part; and calcarenitic turbidites, contourites, and reworked turbidites occur in the western part. The main contour current ran parallel to the contour lines from east to west. Although most of the contour current continually moved westward in the eastern part of the study area, a minor part split off and followed a semicircular pathway through the Fuping Graben; its velocity became reduced here so that micritic contourites were deposited. The velocity of the contour current was increased locally when it entered a confined trough in the western part of the study area. The relatively high energy of the contour current here resulted in calcarenitic contourites. The velocity of the contour current was low where it ran through an open environment, resulting in fine-grained, thin contourites in the middle part of the study area. Large turbidity currents and debris flows occurred here, and their high energy destroyed almost all earlier deposited contourites. This explains why traces of contour currents in the middle part of the study are very scarce, although the east–west-running contour current must have passed through this area.

Aquatic and riparian ecosystem recovery from debris flows in two western Washington streams, USA.

An exceptionally powerful storm struck southwestern Washington in December 2007 causing large debris flows in two adjacent streams. The two affected streams had been studied prior to the storm, providing a rare opportunity to examine ecosystem recovery. We monitored the streams and their riparian zones for six years after the disturbances to determine whether recovery rates of biota, physical habitat, and water temperature differed, and if so, what factors affected resilience. Along both streams, the debris flows removed wide swaths of soil, rock, and coniferous riparian forests, widening the active channel and increasing solar exposure and summer water temperatures. Initially depauperate of vegetation, after four years red alder trees dominated the riparian plant communities. The warmer water, greater solar radiation, and unstable substrates likely contributed to variable benthic insect and tailed frog tadpole densities over time, although benthic insect communities became more similar after three years. The debris flows also decreased channel slopes and removed channel step barriers such that cutthroat trout were able to rapidly occupy habitats far upstream, but sculpins were slower to recolonize and both fish species exhibited some differences in recovery between the two streams. Crayfish were severely impacted by the debris flows; this may be due to attributes of their life history and the timing of the flows. Overall, we found that recolonizing aquatic species exhibited varying levels of resilience and recovery after the disturbances being related to the influence of physical habitat conditions, species dispersal ability, and the presence of nearby source populations.

Large debris flows in Chosica, Lima, Peru: the application of hydraulic infrastructure for erosion control and disaster prevention

Large debris flows in steep-sloped ravines debouching to the Rimac River, in metropolitan Lima (Peruvian capital), have resulted in considerable loss of life and property adversely impacting communities in the region. Temporal, spatial and volumetric features of debris flows are difficult to predict, and it is of utmost importance that achievable management solutions are found to reduce the impact of these catastrophic events. The emotional and economic toll of these debris flows on this increasingly densely populated capital city in South America is devastating where communities must live in such inadequate and dangerous conditions. To address this problem, the application of advanced Japanese technology, Sustainable Actions Basin Orientation (SABO), has been investigated using a geomorphological modelling to develop an implementation plan. Rayos de Sol stream basin in Chosica, was selected as a pilot to develop the proposal, as it is considered high risk due to the presence of ancient debris flows and recent flows in 2012, 2015 and 2017. The recurrence of debris flows in this location has resulted in numerous deaths and catastrophic property losses. This study combines geologic and geomorphic mapping and hydraulic and landform evolution numerical modelling. The implementation of a SABO Master Plan based on the multidisciplinary assessment hazard scenarios, will allow the implementation of feasible mitigation actions. The SABO technology has been applied successfully in Japan and other countries in areas with steep short slopes, similar to the conditions surrounding the Peruvian capital. Results from this study will be presented to the Peruvian Government as part of an action plan to manage debris-flow impact.KEY POINTSHigh-risk mass slope failure is linked to poor urban planning in urban developing regions of Lima the capital of Peru.A multidisciplinary study including geotechnical and hydrological analysis, engineering design, and socio-economic research is required to implement a SABO Master Plan, and this basin is pilot study basin.At the present time, a maintenance programme for existing hydraulic structures should be implemented, and a flood risk management plan developed may propose the relocation of some communities and infrastructure.

Investigating the slope failures at the Lou rock glacier front, French Alps

AbstractOn August 14 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three‐week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast‐moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization.

An effectiveness evaluation method for debris flow control engineering for cascading hydropower stations along the Jinsha River, China

Four large hydropower stations are located along the Jinsha River, in an area that has the highest frequency of large damaging debris flows in China. The total power generation capacity of the dams is >42 million kilowatts. Through field investigation, laboratory analysis, model calculation, and statistical analysis, we studied the debris flows occurring in the gullies near the Baihetan hydropower station to determine the characteristics of their dynamic parameters and the effectiveness of existing debris flow control measures. The dynamic parameters of debris flows vary significantly because of the different characteristics of the fluvial basins and their longitudinal slope gradients. Evaluation results showed that the existing debris flow control measures in the Aizi and Dazhai gullies should be able to withstand events with 100-year recurrence period. The debris flow risk in these gullies is therefore low in the present situation. It is important to note that these control measures would also be adequate for events with 500-year recurrence period; therefore, the debris flow risk would remain low in the theoretical future situations. We propose an evaluation method of the effectiveness of debris flow engineering control based on an analysis of the engineering measurements' effectiveness. The research results can be implemented to improve the design of the Baihetan hydropower station. More importantly, the results can be applied for the development of evaluation methods of the effectiveness of other similar and significant projects in China and elsewhere.

Topographical and geological factors on gully-type debris flow in Malai River catchment, Siwaliks, Nepal

The Siwalik hill of Nepal lies in between the two major thrusts; Main boundary Thrust and Main Frontal Thrust. Thrusting and continuous erosion of material from surface causes several landslides and debris flow problem in the Siwalik region. Debris flow commonly occurs after landslide during heavy rainfall in the steep slope. This paper described about the topographical and geological controls on debris flow occurring in gullies in the Siwaliks of the Malai River catchment of mid-Western Nepal. The length of gully, length of debris channel, area of debris channel, area of catchment of debris flow, area of gully without debris flow were found using Google earth pro, a free version online database. Similarly, a form factor (F), average gradient of stream, slope area ratio and a topographical factor (T) were calculated. Lithology and geological structure were studied in the field. The relation between each factor was identified.
 Gully having larger debris flow event had T value greater than 0.01 and that having small debris flow event had T value less than 0.01. Gully without debris flow had T value less than 0.001. Gully having debris flow had F more than 0.1 and that free from debris flow had F less than 0.1. Both topographic and form factors were found greater than 0.1 at the hanging wall of the Malai Thrust, where large size debris flows were encountered. The T and F values obtained from the Middle and Upper Siwaliks were greater than 0.1.The number of debris flow events and large debris flows were found high the in the Middle and the Upper Siwaliks, and hanging wall of the Malai Thrust.