Recent developments in debris flow research in Italy

During the initiation and movement of debris flow, low frequency infrasound is generated and emitted with characteristics such as strong penetration, low attenuation, and a high propagation speed that is faster than the debris flow. Monitoring infrasound has been used in debris flow detection and early warning systems; however, although the current infrasound-based warning system of debris flow can provide an alarm when debris flow occurs, it cannot locate and track the movement of debris flow in real time, and cannot determine the arrival time of debris flow to its potential victims. Thus, the potential applications of low frequency infrasound in debris flow disaster prevention and reduction have not yet been fully explored. In this study, we constructed an optimal triangular monitoring array based on factors such as the terrain of the monitoring area and characteristics of infrasound propagation. Combined with the time-delay estimation method, we determined and established an acoustic source localization model based on the time difference of arrival. Furthermore, with the help of a GIS platform, a visualized localization and tracking system for debris flow movement was developed to achieve real-time monitoring of debris flow. The performance of the system on acoustic source localization was validated using a simulation test and long-term field monitoring of debris flow at Jiangjia gully in Dongchuan, Yunnan province, China. Both the simulation and field test results showed that the system has high localization accuracy and strong real-time response. The results of the monitoring system could provide more accurate warning information of debris flow to local government and residents, allowing them to take appropriate mitigation measures well in advance to reduce the loss of life and property caused by debris flows.

Debris flow seismic monitoring and warning

In order to document the on-site debris flow events, the Soil and Water Conservation Bureau (SWCB), Council of Agriculture, Taiwan, has de- voted to develop the debris flow monitoring system since 2002. This paper introduces the technology of 17 on-site and 3 mobile debris flow monitoring sta- tions established by SWCB in Taiwan. In each on-site monitoring station, several observation instruments including rain gauges, CCD cameras, wire sensors, geophones, and water level meters were installed to collect the dynamic debris flow information that can be used as the references for countermeasures of de- bris flow disaster mitigation. Besides, several mete - orological sensors are also adopted recently in order to record the long-term climate change effects on the slopeland of Taiwan. The framework of the debris flow monitoring system consists of monitoring sen- sors, instrumental cabin (vehicle platform for mobile station), transmission system and web-based display system. During the typhoon Mindulle period in 2004, a debris flow event in Aiyuzih creek was observed by the Shenmu debris flow monitoring station on July 2, Nantou County, central Taiwan. On-site observation data including the rainfall patterns, video images, wire sensor ruptures and ground vibrations caused by de- birs flows are analyzed in detail.

In view of the problem that the debris flow monitoring equipment is easy to be destroyed and can not be used again in the field environment, a recyclable debris flow monitoring and early warning micro buoy is proposed. This technology combines the position information of the monitoring node with the auxiliary information provided by the beacon node, and can obtain the centimeter level position settlement accuracy. The monitoring node floats on the debris flow when the debris flow occurs, and floats downstream with the debris flow. The status information of the debris flow is inversely displayed through the position solution. The test results show that 1) the micro buoy has good stability with a deep draft ratio of 2.3. 2) The communication rate between the buoy and the reference station is 1.14kBps, which meets the rate requirements of RTK data interaction. 3) The final latitude deviation is 0.09cm, longitude deviation is 0.11cm and altitude deviation is 0.28cm, which is far less than the change order of mud water level when debris flow occurs. Therefore, the micro buoy can effectively monitor the change of mud water level caused by debris flow.

A physically-based multi-hazard risk assessment platform for regional rainfall-induced slope failures and debris flows

<p>Debris flows are among the most widespread natural hazards in mountain areas. They play an important role in sediment transfer from low order channel networks to downstream areas and, thus, they can pose a serious threat to infrastructure. For debris flows to be released, in addition to a considerable amount of rainfall, sediment availability and a peculiar morphological setting (e.g. inclined terrain) are required. However, areas prone to trigger debris flows are not always structurally connected to the main channel, and thus do not necessarily provide sediments to the draining channel network. Despite the relatively high number of published research in the fields of debris flow susceptibility mapping and sediment connectivity analyses, to our knowledge, no attempts have yet been made to combine these two aspects, explicitly by means of data-driven procedures.</p><p>This work builds upon a novel data-driven approach developed by Steger et al. (under review), which allows to categorize areas based on both aspects, debris flow release susceptibility and structural connectivity. The original method was tested within three mountain catchments in the South Tyrolean Alps (max area 140 km²). This study aims at upscaling this approach at the regional scale and to this end, the whole South Tyrolean Dolomites (1,120 km²) has been selected as study area. In summary, the methodical framework comprised (i) modelling of debris flow release susceptibility using an interpretable machine learning algorithm (generalized additive model) and derivation of a quantitative threshold (susceptible vs. not-susceptible areas), (ii) training a logistic regression model to calculate the probability of an area being structurally connected in terms of debris flow release and subsequent thresholding (connected vs. disconnected areas), and (iii) combination of both previously generated and validated binary maps to create a joint susceptibility-connectivity map.</p><p>The results are represented via a variety of maps and associated statistics. It is shown that only 1.7% of the Dolomites were determined to be both susceptible to debris flow initiation and structurally connected to a target channel system, whereas areas that are susceptible but disconnected cover 8.2% of the whole study area. 16.5% of the area represents hillslopes that are potentially connected to the river network but result not susceptible in terms of debris flow release.</p><p>The straightforward implementation of this approach allows it to be an effective tool to assist hazard mapping and management. This study shows that the presented method provides spatial information useful to preliminary identify areas of interest for connected debris flows at the regional scale, but at the same time, it also highlights the need for further ground truth data to validate the results quantitatively beyond single catchment analyses.</p><p>Stefan Steger, Vittoria Scorpio, Francesco Comiti, Marco Cavalli. <em>Data-driven modelling of joint debris flow release susceptibility and connectivity</em>. Earth Surface Processes and Landforms. Under review.</p>

Debris flows represent one of the most prevalent and impactful natural hazards in mountainous areas, posing significant risks to both human life and infrastructure. Alpe di Succiso (2017 m a.s.l.) located in Northern Apennines, Italy, is an area where numerous occurrences of debris flows have been identified in this area encompassed by a National Park, thus densely traversed by touristic routes and infrastructures. Understanding the spatial and temporal patterns of these debris flows is critical for assessing the hazard and managing the associated safety risks for mountaineers, hikers, tourists, and, more generally, for the communities and infrastructure in the area.This research integrates field observations of debris flows, dendrochronological analysis, geomorphological mapping (Rashid et al., 2024), and satellite imagery to reconstruct the history of debris flow events and is partially comprised in the DECC project (2023). A key focus is the 1987 debris flow, triggered by an intense rainfall event on August 25, which recorded 179 mm of rainfall in a single day, including 133 mm within a 6-hour period.This study investigates the dynamics of debris flows, through channel-specific analysis, GIS-based zonation, and statistical evaluation. Slope angle and elevation data were analyzed to delineate source, transport, and deposition zones across four channels of debris flows. Channel 1 was identified as a debris flood channel, while Channels 2, 3, and 4 exhibited typical debris flow characteristics.To account for the wide variation in grain sizes in the study area (0.0005 mm to 5 meters), four techniques were employed. Sieve analysis was used for grains between 2 mm and 32 mm, while laser granulometry measured finer particles below 2 mm. Direct field measurement was applied to intermediate grains (32 mm to 1000 mm), and particle counting was used for large particles above 1 meter. This multi-method approach ensured accurate representation of sedimentary material across the broad grain size spectrum.Geomorphological analysis indicates that rockfalls and rock weathering significantly contribute to the material on the slopes. During debris flow events, these deposits are triggered at the first stage like debris/rock slide and then as flow creating channels and deposits. A geological survey of rock outcrops feeding these debris flow channels revealed that the Rock Quality Designation (RQD) ranges from 44 to 65 (poor to fair quality), while the Rock Mass Rating (RMR) falls between 45 and 56 (fair quality).Using the RAMMS Debris Flow software (RAMMS, 2017), a scenario-based modeling approach was employed to better understand the interactions between debris flow and material constituting the slope deposits. Simulation results are currently being compared with the geometry of levees and lobes to refine the model and ensure accuracy. This comprehensive approach aims to improve the understanding of debris flow dynamics and the influence of rockfalls, thereby aiding hazard assessment and management.

Gravitational mass movements, such as debris and mud flows, are among the most destructive natural hazards, leading to substantial fatalities and extensive economic damage worldwide. Improving our understanding and modeling of these processes is essential for developing effective risk management and early warning strategies. When debris and mud flows pass through a curved channel, centrifugal forces may cause a difference in flow height between the inner and outer banks of the channel. This height difference, known as superelevation, can be described using analytical models that establish a relationship between the superelevation height and the flow velocity.Analytical models often employ a forced vortex approach, incorporating parameters such as the cross-sectional slope of the flow surface, flow width, and bend radius. These models, however, rely on assumptions such as a linear flow surface between mud deposits on the banks, a rectangular cross-section, and neglect both complex rheological behaviors and solid-fluid interactions. As a result, an empirically determined correction factor is required within the formula. The absence of a clear mechanical rationale for this correction factor presents challenges, as it is currently derived only through field investigations and laboratory experiments.This study presents an enhancement to the existing forced vortex approach by incorporating insights from numerical modeling. A coupled SPH-DEM numerical model is employed, where DEM particles represent coarse solid particles, and SPH accounts for the fluid phase, comprising fines and water. The SPH-DEM coupling is based on the no-slip interaction model, with simulations performed using a GPU-based solver to ensure enhanced computational efficiency. To validate the approach, a parametric test is conducted, initially back-calculating laboratory-scale experiments. The study further involves varying the water content in debris and mud flows to examine its impact on flow behavior and superelevation. Larger water contents lead to an increased superelevation angle. Results from the parametric test reveal a clear correlation between water content and the flow surface shape in curved channels. Specifically, mud flows are characterized by convex upward surface shapes, whereas more granular debris flows typically exhibit concave downward shapes.The distribution of material within the cross-section of the flow is governed by the equilibrium between boundary forces and centrifugal forces acting on the flow, which directly influences the superelevation. Numerical investigations are conducted to determine a correction factor and assess the extent to which inertial effects contribute to this correction factor for different material mixtures. Furthermore, we demonstrate that the effect of the flow surface shape is significant and is currently only accounted for by the empirical correction factor. This study offers new physical insights for the back-calculation of debris flow velocities in curved sections marked by mud deposits. Large-scale SPH-DEM simulations of a real debris flow event at Illgraben (Switzerland) are performed, showing good agreement with field data and its potential for further real-scale modeling.

As a natural hazard in mountainous terrain, debris flows cause considerable disruptions, human casualties and economic damage in many regions world-wide. However, the spatially localized nature of debris flows together with the lack of data at sufficient temporal and spatial resolutions make the triggering processes difficult to describe. As a result, debris flows are problematic to predict. Effective regional and local early warning systems, built on both process-based or statistical models, have therefore so far remained elusive. Even more, common statistical models, such as  precipitation-intensity threshold models, rely on precipitation. As debris flows are essentially in-channel processes, precipitation is an indirect predictor and proxy for in-channel processes. As such it is not surprising that precipitation has limited predictive power. In spite of recent progress, general and detailed descriptions of in-channel processes that control debris flow triggering only start to emerge. Most generally, sediment supply and channel flow magnitudes can be considered major direct controls on debris flow occurence. As both are difficult to observe, they have so far not been systematically exploited and quantitatively described for their role as debris flow triggers.  Based on 20-year records of hydro-climatic data, several dozens of well documented debris flow events in three contrasting head-water catchments in the Central Alps and a semi-distributed, process-based hydrological model, the objectives of our analysis are to (1) quantify the critical channel runoff magnitudes that have triggered past debris flows and to establish whether characteristic magnitudes can be found as a function of topography, soils, geology and other factors, (2) identify the relevance of snow melt vs. rainfall for the generation of debris flow triggering critical channel runoff, and (3) to test whether modelled critical channel runoff has higher power to predict debris flows than standard precipitation-intensity models.Overall, we have found that indeed, relatively well-defined minimum critical channel flows as lower limits above which debris flows occur feature each of the three study catchments. It was also found that the general magnitudes are highly site specific. In spite of that, no obvious relation between the average critical flow magnitudes and landscape characteristics, such as local terrain or channel slopes, vegetation cover, soil type or geology at the three sites could be identified. In general, it was found that flow peaks, generated by short-duration, high-intensity rainfall events, mostly during summer, dominated the debris flow trigger dynamics at the study sites. In addition, several instances when debris flows were triggered by flow peaks of similar magnitudes but generated by high-intensity snow melt in combination with rain-on-snow were observed, highlighting the importance of quantifying liquid water input dynamics instead of bulk precipitation as system input that causally leads to the occurrence of debris flows. Intrinsically accounting not only for this distinction but also additional effects by evaporation, modelled channel flow magnitudes were found to be better predictors of debris flows, with respect to both, higher rates of true positives (correctly predicted debris flows) and lower rates of false positives (predicted but not occurred in reality), than traditional precipitation thresholds. 

Recent advances in vulnerability assessment for the built environment exposed to torrential hazards: Challenges and the way forward

Volcanic eruptions may produce large amounts of pyroclastic material. Such material will then be transported down a volcano’s rivers due to slope instability or rainfall, and then settle in alluvial fan areas. Further migration of this deposited sediment along the river may occur through both natural mechanisms (hydraulic phenomena) as well as anthropogenic processes (human interference). This paper presents the application of monitoring and early warning systems to mitigate the impact of debris flows, using adaptive, low-cost, and collaborative-based technology. A long-running and sustainable system for monitoring and early warning of debris flows in the rivers of Mt. Merapi volcano in Indonesia will be used as case study for the implementation of this model. The 2010 Mt. Merapi eruption produced approximately 140 million m3 of pyroclastic deposits, of which more than 10 million m3 deposits have a potential to move downstream through Boyong/Code River towards Yogyakarta City and cause damage to the settlement areas. A real-time monitoring and warning system has been developed by considering community wishes in determining the types and placement of monitoring equipment, and maintaining it sustainably. The equipment consists of an automatic rainfall recorder, automatic water level recorder, debris sensor, and interval camera. The information flow for the proposed early warning system has been set up. The central station receives both the results of the real-time monitoring, and information through radio communication from key persons. Afterward, a warning alert is sent to key persons and the debris flow monitoring radio. This newly built system is expected to be integrated with the monitoring system of rivers, not only at Mt. Merapi but also on other volcanoes in Indonesia.

The 2010 Mt. Merapi eruption has produced approximately 140 million m3 of pyroclastic deposit, in which more than 10 million m3 deposits are potential to move downstream through Boyong/Code River towards Yogyakarta City. The flow behavior of Code River may be affected by the presence of accumulated sediment at the upstream of the river (namely Boyong River). By rainfall trigger, this potential source can cause debris flow disaster that may contribute damage to the settlement areas in Yogyakarta City. This paper presents the application of monitoring and early warning system to mitigate the impact of debris flow disaster along Boyong/Code River as revealed by most adaptive, low cost, and collaborative-based technology. The real-time monitoring equipment consists of automatic rainfall recorder, automatic water level recorder, debris sensor, and interval camera. The system was developed by considering the community aspiration in determining the types and placement of monitoring equipment, and maintaining its sustainability. The information flow of the proposed early warning system has been introduced accordingly. The central station receives the results of the real-time monitoring and the information through radio communication from the focal points located along Boyong/Code River. Afterward, the warning alert is sent to focal points and the debris flow monitoring radio. This newly built system is expected to be integrated with the monitoring system of other volcanic rivers at Merapi Volcano.KeywordsVolcanic debris flowReal-time monitoringEarly warning systemCommunity preparedness

<p>Debris flow is one of the most hazardous events that occur in all mountain regions.  Direct debris flow damage includes loss of human life, destruction of houses and facilities, damage to roads, rail lines and pipelines, vehicle accidents, and many other losses that are difficult to quantify. In July 2015, in the valley of the Barsemdara River (Gorno-Badakhshan Autonomous Region, Tajikistan), plenty of debris flows were observed. As a result, residential areas, social facilities, and infrastructure in Barsem village and neighboring settlements were destroyed and flooded. Besides, debris flow deposits blocked the Gunt River with the subsequent formation of a dammed lake with a maximum volume of 4.0 million m<sup>3</sup>. <br>The aim of this study was to obtain hydrographs of debris flow waves in the source and detailed zoning of the Barsemdara river valley. For the debris flow source, we applied transport-shift model. Equations of this model were developed by Yu.B. Vinogradov basing on Chemolgan experiments of artificial debris flows descending. Previously, the model characteristics were compared with the observational data of the Chemolgan experiments, and the results were found to be satisfactory [Vinogradova, Vinogradov, 2017]. Based on the equations, a computer program was created in the programming language Python. Besides, we improved the model by adding flow velocity calculations, and eventually it became possible to obtain hydrographs. To investigate quantitative characteristics of the debris flow in the river valley we implied a two-dimensional (2D) model called FLO-2D PRO. It is based on the numerical methods for solving the system of Saint-Venant equations. Besides, in this model, it is assumed that debris flows move like a Bingham fluid (viscoplastic fluid) [O'Brien et al., 1993]. The input information for modeling was digital elevation model (DEM) and previously obtained hydrographs. The output information included flow depth, velocity distribution and hazard level of the territory. The results of the study will be reported.</p><p>1.    Vinogradova T.A., Vinogradov A.Y. The Experimental Debris Flows in the Chemolgan River Basin // Natural Hazards. – 2017. – V. 88. – P. 189-198.<br>2.    O'Brien J. S., Julien P.Y., Fullerton W.T. Two-dimensional water flood and mudflow simulation //Journal of hydraulic engineering. – 1993. – V. 119, No 2. – P. 244-261.</p>

Debris flow is a common natural hazard in the mountain areas of Western China due to favorable natural conditions, and also exacerbated by mountainous exploitation activities. This paper concentrated on the characteristics, causes and mitigation of a catastrophic mine debris flow hazard at Longda Watershed in Songpan County, Sichuan Province, on 21 July 2011. This debris flow deposited in the front of the No.1 dam, silted the drainage channel for flood and then rushed into tailing sediment reservoir in the main channel and made the No.2 dam breached. The outburst debris flow blocked Fu River, formed dammed lake and generated outburst flood, which delivered heavy metals into the lower reaches of Fu River, polluted the drink water source of the population of over 1 million. The debris flow was characterized with a density of 1.87∼2.15 t/m3 and a clay content of less than 1.63%. The peak velocity and flux at Longda Gully was over 10.0∼10.9 m/s and 429.0∼446.0 m3/s, respectively, and the flux was about 700 m3/s in main channel, equaling to the flux of the probability of 1%. About 330,000m3 solid materials was transported by debris flow and deposited in the drainage tunnel (120,000∼130,000 m3), the front of No.1 dam (100,000 m3) and the mouth of the watershed (100,000∼110,000 m3), respectively. When the peak flux and magnitude of debris flow was more than 462 m3/s and 7,423 m3, respectively, it would block Fu River and produce a hazard chain which was composed of debris flow, dammed lake and outburst flood. Furthermore, the 21 July large-scale debris flow was triggered by rainstorm with an intensity of 21.2 mm/0.5 h and the solid materials of debris flow were provided by landslides, slope deposits, mining wastes and tailing sediments. The property losses were mainly originated from the silting of the drainage tunnel for flash flood but not for debris flow and the irrational location of tailing sediment reservoir. Therefore, the mitigation measures for mine debris flows were presented: (1) The disastrous debris flow watershed should be identified in planning period and prohibited from being taken as the site of mining factories; (2) The mining facilities are constructed at the safe areas or watersheds; (3) Scoria plots, concentrator factory and tailing sediment reservoir are constructed in safe areas where the protection measures be easily made against debris flows; (4) The appropriate system and plan of debris flow mitigation including monitoring, remote monitoring and early-warning and emergency plan is established; (5) The stability of waste dump and tailing sediment reservoir are monitored continuously to prevent mining debris flows.

This paper describes how debris flows are natural hazards that look like a combination of flood, land and rock slide. The phenomenon is also called mud or debris avalanche because similar flow behavior is compared with snow avalanches. Debris flows regularly cause severe damages in mountainous areas like the Alps. Like rock fall, the debris flows loads act mainly on a protection barrier. But in contrast to falling rocks, debris flows are not punctual impacts but a distributed load on the protection system. A further difference between the two hazards is the fact that rockfalls are single events while debris flows mostly occur in surges. Experiences from North America, Japan and Europe prove that flexible protection systems like the Geobrugg VX/UX Systems have an ideal bearing behavior to stop dynamic loads such as debris flows because of their large deformation capacity