NH3.1 | Debris flows: advances on mechanics, monitoring, modelling and risk management
EDI
Debris flows: advances on mechanics, monitoring, modelling and risk management
Convener: Marcel Hürlimann | Co-conveners: Velio Coviello (deceased), Xiaojun Guo, Sara Savi, Jacob HirschbergECSECS
Orals
| Fri, 28 Apr, 14:00–15:30 (CEST), 16:15–17:45 (CEST)
 
Room C
Posters on site
| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)
 
Hall X4
Posters virtual
| Attendance Fri, 28 Apr, 10:45–12:30 (CEST)
 
vHall NH
Orals |
Fri, 14:00
Fri, 10:45
Fri, 10:45
Debris flows are among the most dangerous natural hazards that threaten people and infrastructures in both mountainous and volcanic areas. The study of the initiation and dynamics of debris flows, along with the characterization of the associated erosion/deposition processes, is of paramount importance for hazard assessment, land-use planning and design of mitigation measures, including early warning systems. In addition, the impacts of climate change on debris-flow activity must be considered and carefully analyzed, as the number of mountain areas prone to these events may increase in future.
A growing number of scientists with diverse backgrounds are studying debris flows and lahars. The difficulties in measuring parameters related to their initiation and propagation have progressively prompted research into a wide variety of laboratory experiments and monitoring studies. However, there is a need of improving the quality of instrumental observations that would provide knowledge for more accurate hazards maps and modeling. Nowadays, the combination of distributed sensor networks and remote sensing techniques represents a unique opportunity to gather direct observations of debris flows to better constrain their physical properties.
Scientists working in the field of debris flows are invited to present their recent advancements. In addition, contributions from practitioners and decision makers are also welcome. Topics of the session include: field studies and documentation, mechanics of debris-flow initiation and propagation, laboratory experiments, modeling, monitoring, impacts of climate change on debris-flow activity, hazard and risk assessment and mapping, early warning, and alarm systems.

Orals: Fri, 28 Apr | Room C

Chairpersons: Velio Coviello (deceased), Sara Savi, Xiaojun Guo
Observations
14:00–14:10
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EGU23-4021
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NH3.1
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On-site presentation
Mark Reid and Hirotaka Ochiai

Debris-flow mobilization from shallow landsliding is widespread, can be deadly, and is the focus of warning systems worldwide. One challenge of forecasting is that some shallow landslides transform into rapid debris flows, whereas others do not. Although early warning systems can depend on forecasting this poorly understood transition, high-resolution hydrologic and deformation data from debris-flow mobilization events are rare. As part of the APERIF project (Ochiai et al., Landslides, 2004), we performed a field-scale artificial rainfall (sprinkling) experiment on a planar 33º natural hillslope near Mt. Kaba-san, Japan. Using 100-Hz sampling, we recorded synchronous subsurface pore-pressure response and ground-surface motion throughout the transition from slide (~1 m thick) to flow, including slow precursory deformation, abrupt rapid failure, and subsequent debris-flow motion down a small channel. The experiment began with ~6 hours of high-intensity sprinkling (at 78 mm/hr), which triggered motion of the slide in response to rising positive pore-water pressures. Continued sprinkling led to persistent slow motion of the slide for ~1 hour, until acceleration and abrupt failure. Our data revealed that during the several seconds of rapid failure, pore pressures dropped (indicative of soil dilation) then oscillated greatly in response to deformation, thereby enhancing liquefaction and flow.

 

An abrupt transition from slow to fast motion in dilative soils can present a mechanical conundrum. Although loose, contractive soils may collapse and liquefy, many hillslope soils are dense and dilate in shear, thereby impeding motion. We explored slide behavior using a 1D model (Iverson, 2005) that fully couples slide motion and pore pressure with evolving shear-zone dilatancy, and utilized measured and estimated parameters from our hillslope experiment. Simulations demonstrated that dilative soils impede motion, as observed initially in our experiment. However, dilatant systems can evolve dynamically through persistent landslide motion driven by prolonged rainfall. When motion-inhibiting dilatant effects are exhausted, our analysis showed rapid acceleration during a swift drop and subsequent increase in pore pressures (within a few sec), as was also observed in the field experiment. This behavior provides a mechanism to mobilize debris flows from shallow landsides in dense hillslope soils. Our results suggest that although high-resolution monitoring might detect precursory motion, forecasting liquefaction and debris-flow genesis is still dependent on soil properties and transient hydrologic conditions.

How to cite: Reid, M. and Ochiai, H.: Abrupt debris-flow mobilization in a hillslope experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4021, https://doi.org/10.5194/egusphere-egu23-4021, 2023.

14:10–14:20
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EGU23-11999
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NH3.1
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ECS
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On-site presentation
Amanda Fawley, Alexander Taylor-Noonan, Lisa Tauskela, Erica Treflik-Body, and W. Andrew Take

Laboratory landslide flume tests provide valuable insights into the mechanics of multi-phase granular flows within highly controlled settings. Past studies have revealed the complex fluid-particle interactions associated with saturated granular flows result in greater mobility than their dry counterparts, being notably faster, further reaching, and experiencing enhanced spreading. The ability to reliably measure the pore pressures at the base of these flows in the laboratory is critical for developing, evaluating, and validating constitutive relationships linking the effects of pore pressure to the mechanisms causing increased mobility. Unfortunately, experience has shown that two identical sensors installed in the base of a landslide flume can yield wildly different responses to the same multi-phase landslide. In this session, we explore an answer to the question “Why is it so difficult to reliably measure the pore pressure at the base of a fast landslide in a laboratory flume test?” using evidence accumulated from ten years of flume testing using the Queen’s University Landslide Flume. In particular, we explore the hypothesis that surface roughness around pore pressure sensor filter elements can influence sensor readings. A unique experimental strategy of simplifying the flow into a single fluid phase is used to validate sensor readings, prior to application in multi-phase flows. Dam-break releases of 600 kg of water at the top of the inclined flume slope are used as a parametric study to provide evidence to support the hypothesis that surface roughness significantly impacts the pore pressure recorded in high velocity flows. These results are then contrasted to observations of releases of multi-phase flows to derive best practices for the reliable measurement of pore pressure in landslide flume tests.

How to cite: Fawley, A., Taylor-Noonan, A., Tauskela, L., Treflik-Body, E., and Take, W. A.: Why is it so difficult to reliably measure the pore pressure at the base of a fast landslide in a laboratory flume test?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11999, https://doi.org/10.5194/egusphere-egu23-11999, 2023.

14:20–14:30
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EGU23-10744
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NH3.1
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Highlight
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On-site presentation
Qiang Zou, Bin Zhou, Siyu Chen, Wentao Zhou, Hu Jiang, and Hongkun Yao

Global warming has led to environmental changes in the alpine Himalayan mountains, with significant glacier retreat, an increase in the area and number of glacial lakes, and an increase in the frequency and scale of glacial lake outburst debris flows, causing significant damage to people and facilities in downstream. In this study, we analyzed the spatial heterogeneity and variations of disaster-forming environments on the north and south areas of the Himalayan, identified the distribution patterns of glacial lake outburst debris flows, and predicted debris flows’ changing trends in the Himalayas. The results demonstrate that the distribution and variations of glaciers and glacial lakes in the Himalayan region have apparent spatial heterogeneity. The Central and South Himalayas are where glaciers and glacial lakes undergo the most dramatic changes. Glacial lakes are widely distributed in the Central Himalayas and southern slopes, with an increase in area and number from 1990-2015. New glacial lakes at higher elevations and alterations in moraine lakes dominate glacial lake variations across the region. Since the 20th century, there have been 249 outbursts of 113 glacial lakes in the Himalayan, Karakorum, and Southeast Tibetan regions, with the majority of outbreaks occurring in the Central and Eastern Himalayas along steep sections of main rivers. In the period 1901-2019, the inflection point for glacial lake outburst hazard is 1966+37/-31 years (median and 95% HDI), and the frequency of glacial lake outbursts proliferates before the inflection point and slowly increases after the break-point; the annual mean temperature changes have opposite trends before and after the inflection point, reflecting the lag effect of glacial lake outbursts on temperature changes. In addition, the measured data were calibrated and down-scaled the future simulated climate prediction data to reveal the spatial and temporal trends of glacial lake outburst debris flow disaster risk under the influence of future climate-causing factors. The annual mean temperature and precipitation in the Himalayas generally exhibited an upward trend in the 21st century, with higher increment speeds of warming and humidification on the northern slopes; Increasing very high and high glacial lake outburst debris flow hazard zones are a consequence of climate change, with a more concentrated distribution in the centre and northwest of the Himalayan Mountains.

How to cite: Zou, Q., Zhou, B., Chen, S., Zhou, W., Jiang, H., and Yao, H.: Glacial lake outburst debris flows in the Himalayas in response to climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10744, https://doi.org/10.5194/egusphere-egu23-10744, 2023.

14:30–14:40
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EGU23-10888
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NH3.1
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On-site presentation
Jiao Wang and Guotao Zhang

On the southeastern Tibetan Plateau, which is an area widely covered by alpine glaciers, two types of debris flow generally occur: glacier-related debris flows (GDFs) and rainfall-related debris flows (RDFs). It is widely accepted that topographic conditions influence debris flow activities; however, few studies have examined the differences between such influence on GDFs and RDFs. This study investigated the GDFs and RDFs in the periglacial area of the Parlung Tsangpo Basin, and calculated 12 geomorphic indexes to reveal the topographic features associated with these two types of debris flow. It was found that lower values in the drainage area, main channel length, and relative elevation occurred in RDFs compared to the GDFs, whereas higher values in the channel gradient, relief ratio, and effective basin area appeared in RDFs. The discrepancy is mainly related to the different topographic and geomorphic shaping of modern glaciers. According to its geomorphological characteristics, the Parlung Tsangpo Basin can be divided into three sections: the upper V-shaped canyon section, middle wide valley section, and lower steep canyon section. The scale and frequency of debris flows in the upstream canyon region are substantially lower than those of debris flows in the downstream canyon region. Moreover, the frequency and scale of RDFs are substantially different to those of GDFs, primarily because of the different geomorphic evolutionary stages of debris flows gullies in different regions.

How to cite: Wang, J. and Zhang, G.: Study on the influence of  the geomorphic  on debris flow activity in the paraglacial zone of the Southeast Tibetan Plateau, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10888, https://doi.org/10.5194/egusphere-egu23-10888, 2023.

14:40–14:50
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EGU23-568
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NH3.1
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ECS
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Highlight
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On-site presentation
Elena Ioriatti, Velio Coviello, Francesco Comiti, Pierpaolo Macconi, Mauro Reguzzoni, and Matteo Berti

In mountain regions, debris flows are responsible for major damage to infrastructure and many casualties every year. Early Warning Systems (EWSs) based on sensor networks installed along the debris-flow channel have been implemented in some catchments around the world, including the Alps. Detecting the early phase of debris flows would allow expanding the lead time of an EWS compared to the monitoring of channelized flows upstream a vulnerable site. In this study, monitoring data gathered from 2019 to 2022 in the headwaters of the Gadria catchment, eastern Italian Alps, are analyzed. One active channel located at 2200 m a.s.l. was instrumented with a time-lapse video camera, a tipping-bucket rain gauge, and a 4.5-Hz vertical geophone. The dataset includes 5 debris-flow events that propagated from the monitored channel to the basin outlet and a large number of signals produced by other seismic sources (e.g., rockfalls, earthquakes, animals, wind). The peak amplitude, the duration and the frequency content of the seismic signals were analyzed with the support of video images to identify the different seismic sources. Results show that different seismic sources produce signals with different characteristics and that it is possible to discriminate the most intense channel processes by analyzing seismic data only. Adopting an approach similar to the rainfall thresholds, debris-flow and runoff events have been bounded by means of a power relationship between peak amplitude and signal duration. The next step of the research would be the development of an algorithm able to automatically classify the seismic sources and identify intense channel processes that can generate debris flows. A similar approach will be applied to the Blé catchment (Val Camonica, central Italian Alps) to study the triggering mechanisms and dynamics of debris flows and analyse whether the proposed approach is valid in other locations. The analysis of seismic data will be combined with the identification of triggering rainfall thresholds and the analysis of infrasound signals to develop reliable EWSs for debris flows.

How to cite: Ioriatti, E., Coviello, V., Comiti, F., Macconi, P., Reguzzoni, M., and Berti, M.: Detection of debris-flow initiation with seismic techniques for early-warning purposes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-568, https://doi.org/10.5194/egusphere-egu23-568, 2023.

14:50–15:00
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EGU23-17212
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NH3.1
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ECS
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On-site presentation
Tobias Schöffl, Jordan Aaron, Roland Kaitna, and Johannes Hübl

The surface velocity of debris flows is constantly subject to strong temporal and spatial fluctuations. These are amplified by the pulse-like occurrence of surges throughout the event and by the high variance of the solids fraction. However, continuous information on velocities of multiple consecutive surges within a single debris-flow event with high temporal resolution is rare. In this study, we test a pulse-Doppler (PD) radar over a total torrent length of 180 m. The PD radar utilizes pulsed transmission and provides spatially resolved cells, called range gates, that extend over a width of 20 meters. Doppler velocity spectra composed of velocity classes and echo intensities are obtained at 4 Hz for each range gate. From these, we derived continuous velocity-time data sets. We present PD radar data for three debris flows that occurred on 05.06, 30.06, and 08.09.2022 at the Illgraben creek, Switzerland. The radar data were validated at the first event with a velocity data set obtained from a LiDAR scanner installed at the same location. This novel method collects high-resolution 3D point clouds at 10 Hz. This data was used to derive a high-resolution velocity vector field for one of the events. We isolate a ~ 2x2 m box in the middle of the channel and compare the LiDAR derived velocities at this location to those measured by the PD radar. Our comparison shows a strong correlation between the two data sets, with a coefficient of determination of 0.85. In addition, we note a minor consistent offset in the two velocity data sets of 0.5 m/s. We attribute this to the nature of the different measurement methods and conclude that the two methods may be sensitive to different features of the surface of the flow. However, our results show the high effectiveness and reliability of both methods in debris-flow monitoring. We anticipate that further analysis of the data sets will provide new insights into the geophysical principles of debris flows.

How to cite: Schöffl, T., Aaron, J., Kaitna, R., and Hübl, J.: Application of pulse-Doppler radar and 3D LiDAR for high-resolution velocity measurements of three debris flows at Illgraben (Switzerland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17212, https://doi.org/10.5194/egusphere-egu23-17212, 2023.

15:00–15:10
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EGU23-12134
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NH3.1
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ECS
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On-site presentation
Amanda Åberg, Jordan Aaron, Jacob Hirschberg, Tjalling de Haas, Brian McArdell, and James Kirchner

Debris flows are a highly hazardous landslide type, and their impact forces, peak discharges and runout distances are dependent on the flow velocity. Knowledge of flow velocities is therefore often required for hazard planning and mitigation, as well as for validating numerical models. One commonly used method for post-hoc estimation of debris flow velocities uses the mudlines left behind by a passing flow as it travels through a bend. The surface inclination derived from these mudlines can be used to estimate velocity based on the forced vortex equation, originally developed for clear water flows and later adapted to debris flows using a correction factor k to back-calculate the flow velocity1,2:

where Rc is the radius of curvature of the bend, g* is the bed-normal component of acceleration due to gravity, B is the flow width, and Δh is the difference in elevation of the flow surface between the inner and outer bend.

This approach involves some uncertainties, however, such as how best to define the radius of curvature, the influence of roll waves and splashing on the post-event mudlines used to measure the surface inclination, as well as the meaning and appropriate value of the correction factor k. In this study, we first derive a database of superelevation velocity estimates based on pre- and post event UAV data for seven events from the years 2019 to 2021 in the monitored Illgraben torrent in Switzerland. Analysis of this database firstly indicates that the placement of cross-sections for surface inclination measurements is more important than how the radius of curvature is defined due to the large influence of local topography on mudlines. Secondly, the data indicates that the correction factor k increases nonlinearly with decreasing Froude numbers, as has been previously suggested2,3. The correction factors were back-calculated using eq. 1 and reference velocities from geophone detections of the front arrival, and seemed to range between approximately 1 and 7. We next present a first comparison of these data to surface inclination and radius of curvature values derived from high-resolution 3D LiDAR scanners for one event in the summer of 2022. We use this unique dataset to directly derive the radius of curvature (based on surface velocity vectors) and surface inclination of the flow, as well as the appropriate correction factor.  We compare these values to those derived by the above-mentioned commonly used method based on bend topography and post-event mudlines to assess the efficacy of these methods. This preliminary study thus provides a validation of the superelevation approach and will provide a basis for more in-depth research on this topic.

 

1 Hungr, O., Morgan, G.C. and Kellerhals, R., 1984. Quantitative analysis of debris torrent hazards for design of remedial measures. Canadian Geotechnical Journal21(4), pp.663-677.

2 Scheidl, C., McArdell, B., Nagl, G. and Rickenmann, D., 2019. Debris flow behavior in super-and subcritical conditions. Association of Environmental and Engineering Geologists; special publication 28.

3 Scheidl, C., McArdell, B.W. and Rickenmann, D., 2015. Debris-flow velocities and superelevation in a curved laboratory channel. Canadian Geotechnical Journal52(3), pp.305-317.

How to cite: Åberg, A., Aaron, J., Hirschberg, J., de Haas, T., McArdell, B., and Kirchner, J.: LiDAR-based investigation of debris flow superelevation and velocity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12134, https://doi.org/10.5194/egusphere-egu23-12134, 2023.

15:10–15:20
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EGU23-1454
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NH3.1
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ECS
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On-site presentation
Tjalling de Haas, Brian McArdell, Wiebe Nijland, Amanda Åberg, Jacob Hirschberg, and Pierre Huguenin

Debris flows are water-laden masses of soil and rock, which are common geological hazards in mountainous regions worldwide. They can grow greatly in size and hazardous potential by eroding bed and bank materials. However, erosion mechanisms are poorly understood because debris flows are complex hybrids between a fluid flow and a moving mass of colliding particles, bed erodibility varies between events, and field measurements are hard to obtain. Here, we combine detailed flow measurements, rainfall data, and high-resolution UAV measurements of channel-bed erosion and deposition for 13 debris flows in the Illgraben (CH), to identify the key controls on debris-flow erosion and deposition. We show that flow conditions and bed wetness jointly control debris-flow erosion. Flow conditions that describe the cumulative forces exerted at the bed over the full event (flow volume, cumulative shear stress, and seismic energy) have the strongest correlations with measured erosion and deposition. However, we also find statistically significant correlations between erosion and deposition and frontal flow properties, including frontal velocity, flow depth, shear stress, and peak discharge. Antecedent rainfall over a period of 2-3 hours prior to the debris-flow events strongly correlates to erosion and deposition, while the correlation decreases in strength and diminishes towards shorter and longer time periods of antecedent moisture. Shear forces and particle-impact forces are strongly correlated and act in conjunction in the erosion process. A shear-stress approach accounting for bed erodibility may therefore be applicable for modelling and predicting debris-flow erosion.

How to cite: de Haas, T., McArdell, B., Nijland, W., Åberg, A., Hirschberg, J., and Huguenin, P.: Flow and Bed Conditions jointly control Debris-Flow Erosion and Bulking, Illgraben (CH), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1454, https://doi.org/10.5194/egusphere-egu23-1454, 2023.

15:20–15:30
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EGU23-6251
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NH3.1
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ECS
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On-site presentation
Jakob Rom, Florian Haas, Florentin Hofmeister, Tobias Heckmann, Moritz Altmann, Fabian Fleischer, Madlene Pfeiffer, and Michael Becht

In order to calibrate and validate debris flow models, high precision in situ measurements are essential. However, it is quite difficult to acquire detailed information about debris flows, as they only rarely occur during exceptional high precipitation intensities. In July 2022, a series of such high-intensity short-duration precipitation events triggered several debris flows within the area of the Stubai Alps/Austria, which caused severe damage. On the 20th and 23rd of July 2022, two of these convective events initiated multiple debris flows on the slopes of the Horlachtal, a side valley of the Oetztal.

These events have been registered by measurements of three different meteorological stations and four different discharge gauges distributed over the study area. In addition, INCA (Integrated Nowcasting through Comprehensive Analysis) rainfall data provided by ZAMG (Austrian Central Institute for Meteorology and Geodynamics) allow insights in the spatial and temporal characteristics of the rainfall patterns. Furthermore, two airborne LiDAR (Light Detection and Ranging) campaigns of the Chair of Physical Geography at the University of Eichstätt-Ingolstadt covering the whole Horlachtal (about 55 km²) provide detailed pre and post event topographical data.

A combined evaluation of the different data sets allows us to characterise the debris flow events in the study area in great detail. Topographical analyses show that a total number of 156 debris flows were triggered with accumulation volumes up to 40.000 m³. These volumes can be related to the individual catchment areas in combination with precipitation intensities. Furthermore, the spatial distribution of the triggered debris flows show a concentration to a certain region within the study area, which relates to the spatial patterns of the precipitation events.

How to cite: Rom, J., Haas, F., Hofmeister, F., Heckmann, T., Altmann, M., Fleischer, F., Pfeiffer, M., and Becht, M.: Quantitative evaluation of the debris flow events in July 2022 in Horlachtal/Austria by combining different data sets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6251, https://doi.org/10.5194/egusphere-egu23-6251, 2023.

Coffee break
Chairpersons: Marcel Hürlimann, Velio Coviello (deceased), Jacob Hirschberg
16:15–16:25
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EGU23-8751
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NH3.1
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On-site presentation
Roland Kaitna, Philipp Aigner, Tazio Bernardi, Philipp Wagner, Erik Kuschel, Christian Zangerl, Markus Hrachowitz, and Leonard Sklar

Debris flows initiate by a critical combination of abundant sediment, steep inclination, and water. The latter is mostly provided by rainfall that can lead to landslides at the hillslope or along the channel and/or erosion and bulking of sediment due to increased runoff. Location of sediment sources and channel recharge are related to short- and long-term geomorphological processes within the watershed. Up to now, there are only a few studies investigating sediment dynamics in high alpine watersheds that are regularly affected by debris flows. In this contribution we report of our ongoing efforts to monitor sediment dynamics and debris-flow activity in three very different watersheds in the Austrian Alps. We use a combination of remote sensing and in-channel monitoring techniques including UAV, air-borne and terrestrial laser scanning before and after debris-flow events. We find that debris-flows frequency and volumes are strongly related to movement rates of landslides present in the watershed. At high movement rates, most of the channel refill occurs within the time scale of hours. In the absence of active landslides, debris-flow activity is limited by rainfall-triggered embankment failures along the channel and continuous transfer of hillslope sediment into the channel. In the steepest and smallest monitored watershed, active landslides and continuous surface erosion from landslide scars leads to a high frequency of debris flows of all magnitudes, even in the absence of rainfall. Our study shall provide the basis for a more complete modeling framework for a better prediction of debris flows now and in a future climate. 

How to cite: Kaitna, R., Aigner, P., Bernardi, T., Wagner, P., Kuschel, E., Zangerl, C., Hrachowitz, M., and Sklar, L.: Sediment dynamics related to the triggering of debris flows in different alpine watersheds, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8751, https://doi.org/10.5194/egusphere-egu23-8751, 2023.

16:25–16:35
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EGU23-6690
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NH3.1
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ECS
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Highlight
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On-site presentation
Saverio Romeo, Mauro Bonasera, Vittorio Chiessi, Danilo D'Angiò, Alessandro Fraccica, Luca Olivetta, Michele Perrotti, Mauro Roma, Alessandro Trigila, Valerio Vitale, and Marco Amanti

Active volcanic environments, due to their rapid processes of growth and deformation, can be considered a typical setting for the formation of both subaerial and subaqueous gravitational instabilities. Occasionally, such conditions - coupled with heavy rainfalls or earthquakes - can trigger sudden and rapid mass movements such as mud-debris flows and/or debris avalanches, representing serious hazards for human settlements.

The active volcanic island of Ischia is localized within the Gulf of Naples and its complex volcanism began prior to 350ka and continued, with centuries to millennia of quiescence, until the last eruption occurred in the historical period (AD 1302). 56ka a caldera-forming eruption occurred, followed by a resurgence process that has affected the caldera floor and generated a net uplift of about 900m since 33ka. Thus, the main morphostructural feature is the Mt. Epomeo resurgent block.

From a geological point of view, the island is composed of volcanic rocks, epiclastic deposits, and terrigenous sediments, demonstrating an alternation of constructive and destructive phases. In this context, the continuous occurrence of landslides on the island, even causing death to humans, is historically documented. In the last decades, the risk has been greatly exacerbated by the high level of human exposure due to not properly planned urban development.

On November 26, 2022, as a consequence of heavy rainfall, diffuse landslide events occurred along the island, the main of which affected a small catchment basin in the vicinity of an urban settlement within the Casamicciola Municipality. The area affected by the landslide events is located along the northern slope of Mt. Epomeo. On the summit, Mt. Epomeo is characterized by the strongly weathered Green Tuff Formation. The generated debris flow affected about 30 buildings causing 12 casualties, 5 injured, 230 people displaced, and severe damages to roads and properties. It should be pointed out that the maximum occurred rainfall - recorded by the local weather station - for durations from 1 to 24 hours are all higher than the corresponding maximum values recorded in the years 2007÷2021.

The present work shows the first outcomes, in terms of landslide types, volumes, extent, etc., from a preliminary multidisciplinary investigation carried out immediately following the event by using desk research, on-field survey, geomorphological mapping, remote sensing, and numerical modeling.

How to cite: Romeo, S., Bonasera, M., Chiessi, V., D'Angiò, D., Fraccica, A., Olivetta, L., Perrotti, M., Roma, M., Trigila, A., Vitale, V., and Amanti, M.: Investigation and preliminary assessment of the Casamicciola landslide in the island of Ischia (Italy) on November 26, 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6690, https://doi.org/10.5194/egusphere-egu23-6690, 2023.

Modeling
16:35–16:45
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EGU23-5869
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NH3.1
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ECS
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On-site presentation
Xilin Xia, Kristine Jarsve, Tom Dijkstra, Qiuhua Liang, and Xingmin Meng

Climate change is forecasted to result in more frequent and intense storms, which in turn are likely to cause more flash floods and other hazardous processes in steep hilly and mountainous catchments. These flash floods are driven by complex and rapid overland flow responses to intense rainfall across these catchments. Where loose slope or valley-based deposits are available, flood water may mobilise these materials and transform into dynamic high-velocity, high-density debris flows that can pose significant threats to people, property, and infrastructure considerable distances away from the areas where these deposits are mobilised, exacerbating the already devastating situation caused by flooding. Hydro-dynamic models solving the full shallow water equations (SWEs) have shown great potential to reliably simulate the dynamics of overland flows and flash floods at catchment scales. However, simulating the transition from flash flood into debris flow is still technically challenging because of the difficulty of simulating erosion and deposition processes robustly. A reason is that the commonly used method for calculating erosion and deposition rate may suffer from singularity in the presence of vanishing velocity, which poses a major challenge for practical applications. In this work, we have developed a novel integrated hydrodynamic model for simulating flash floods and debris flows. Overland flows, change of debris concentration and bed elevation change are simulated simultaneously to model the transition between flash flood and debris flow. The overland flow processes are simulated by solving the full SWEs using a Godunov-type finite volume method. A novel method for calculating erosion and deposition rates is incorporated into the SWEs-based model to simulate the change of debris concentration and bed elevation change. The new method can maintain numerical stability and accuracy even in the presence of vanishing velocity. Therefore, the new model can effectively simulate the full process of rainfall-runoff-flooding turning into debris flows. Satisfactory simulation results have been obtained for both laboratory-scale and real-world test cases. The new model has the potential to be applied for flash flood/debris flow risk assessment and early warning.

How to cite: Xia, X., Jarsve, K., Dijkstra, T., Liang, Q., and Meng, X.: An integrated hydrodynamic model for flash flood and debris flow simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5869, https://doi.org/10.5194/egusphere-egu23-5869, 2023.

16:45–16:55
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EGU23-2407
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NH3.1
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ECS
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Virtual presentation
Nadia Mubarak and Ritesh Kumar

Climate change-induced geohazards pose significant threat to the sustainability and serviceability of built environment. Among such disasters debris flows are prominent in hilly areas and pose threat to life and property all over the world. Debris flows are coupled geo-hydro-mechanical phenomena with high flow velocity and long runout distance, resulting in a large impact force on the associated built environment. For effective hazard mitigation it is crucial to investigate the dynamic impact of debris flows on structures. It has been established that barriers in the way of debris flow helped to reduce the energy of the flow, leading to a lesser impact on the downstream end. As such many studies have focused on installing barriers at varied locations and of various sizes. However, there is still need for innovative research on how to increase the performance of these barriers. In this study an investigation to evaluate the impact on a structure on downstream due to debris flows is carried out. Besides, the implications of introducing a barrier structure with passages on upstream end is also studied. Smoothed Particle Hydrodynamics (SPH), a mesh-free Lagrangian method, is employed to capture the motion of debris flow and its impact on a rigid structure. For this study the authors have considered the Rishiganga river valley of Uttarakhand state in India, where a recent event of debris flow on February 07, 2021, caused large destruction to important facilities including the hydroelectric power plant. Located in the southern part of the Himalayas, this region is geo-morphologically sensitive and seismically active, making it susceptible to frequent events of landslides, debris flows and other mass movements. Three dimensional (3D) analyses are carried out for three different cases: case1, with no barrier structure on the upstream, case 2, where a barrier structure with one large passage has been placed and case 3, where a barrier structure with two passages has been placed on the upstream. Based on the outcomes, it is inferred that the presence of a rigid structure at the upstream end reduces the impact on the downstream structure considerably. The impact is found to be highest for case 1, followed by cases 2 and 3, with impact values which are only 35% and 30% of case 1, respectively. Similar trend is found in the velocity gradient at a location between the barrier and the main structure. After the introduction of barrier structure, there is a decrease of approximately 10% in maximum velocity for case 2 and a drastic decrease of approximately 90% for case 3 as compared to case 1, showing consistency with the impact values. It is established, that the introduction of passages decreases the impact considerably owing to the decrease in velocity as well as the volume of debris reaching the main structure, because of some accumulation behind the barrier. Moreover, increasing the number of passages, while keeping the passage area constant, causes the flow to become more streamlined, hence making the flow more uniform, which leads to a further reduction in impact forces.

  

How to cite: Mubarak, N. and Kumar, R.: Mitigating the Impact of Debris Flows on the Built Environment: A Case Study of Southern Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2407, https://doi.org/10.5194/egusphere-egu23-2407, 2023.

16:55–17:05
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EGU23-8143
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NH3.1
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ECS
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On-site presentation
Yuhan Wang, Wuwei Mao, and Elías Rafn Heimisson

Vibrating boundaries are widely encountered, for example, between soil and bedrock during earthquake shaking. We understand that vibration of such boundaries can lead to instabilities in granular media with many applications to geological hazards, such as liquefaction and landslides, and during geological engineering applications. Although numerous studies have been dedicated to revealing the behavior of granular flows under various flowing regimes, the significance of vibrating boundaries remains an open problem. To fill this gap, we introduce a vibrating base boundary into the collapse of a granular column with a numerical scheme. To understand the role of fluids, we contrast the behavior of granular flows under dry and fluid-saturated conditions. From the simulations, the development of anisotropy in spatial inter-grain contact force distribution is studied. The fluid-saturated condition is achieved via a two-way coupled CFD-DEM method. From these simulations, a scaling law of granular flow is derived for vibrating boundaries. We illustrate for the first time the energy evolution of the granular system with vibrating boundaries. This work demonstrates the role of vibration in increasing the runout distance and the maximum kinetic energy of granular flows, this suggests a link between the mesoscale inter-grain responses and macro-scale dynamics of granular geological hazards triggered by earthquakes. Additionally, the spatial distribution of inter-grain contact forces is presented under dry and fluid-saturated conditions to indicate the anisotropic development inside the granular assembly.

How to cite: Wang, Y., Mao, W., and Rafn Heimisson, E.: On the effect of vibration on dry/fluid-saturated granular flows: Implications for geological hazards induced by earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8143, https://doi.org/10.5194/egusphere-egu23-8143, 2023.

17:05–17:15
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EGU23-8083
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NH3.1
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ECS
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On-site presentation
Rosanna Salone, Marianna Pirone, Claudio De Paola, Giovanni Forte, Antonio Santo, Gianfranco Urciuoli, and Rosa Di Maio

Flowslides, which occur mainly in shallow granular soils resting on bedrock, are among the most dangerous natural hazards to humans and utilities in both mountainous and volcanic areas. These phenomena are strongly controlled by the stratigraphic and topographic characteristics of the slope and the groundwater regime, which are commonly recognized as predisposing factors for the occurrence of flow-like landslides. Therefore, the study of the spatial variability of the local geological setting and hydrogeological conditions in partially saturated slopes is of fundamental importance for the prediction of flowslide events. In this framework, we propose a procedure based on 3D time-lapse electrical resistivity tomography imaging of the slope, integrated with geotechnical numerical modelling of hydraulic phenomena affecting the land cover, to analyse the effects of the stratigraphic variability in terms of geometry, continuity, and thickness of the soil horizons on the groundwater regime over time. The goal of the proposed approach is to set up an effective tool for predicting debris-flow landslides occurrence at the slope scale, thereby increasing the predictive capacity of early warning systems. The proposed multidisciplinary study was applied to the test site on Mt. Faito, in the northernmost part of the Lattari Mountains (Naples, Southern Italy), where loose pyroclastic deposits from the explosive eruptions of the nearby Somma-Vesuvius volcano cover a karst-fractured carbonate bedrock with a natural slope more than 30° steep. Specifically, seasonally repeated 3D electrical resistivity tomography surveys, suitably complemented with geological and geotechnical investigations, were carried out to determine the electro-stratigraphic and geological setting of the pyroclastic cover, the local morphology and physical conditions of the underlying carbonate bedrock, and the saturation degree distribution on a seasonal time scale. The latter was estimated through the resistivity vs. water content characteristic curves of the different soil horizons, which were obtained from laboratory measurements on specimens sampled in the survey area. The maps of the water content distribution within the pyroclastic cover, determined by the repeated field resistivity surveys, were validated by comparison with those obtained from 2D geotechnical numerical modelling aimed at simulating hydraulic phenomena affecting the soil cover. As main findings, the integrated approach showed that i)  the buried bedrock morphology heavily influences the pore water distribution in the soil cover and ii) ashy material fills the upper karst portion of the bedrock, providing a hydraulic connection of the water flow infiltrating from the topsoil downward.

How to cite: Salone, R., Pirone, M., De Paola, C., Forte, G., Santo, A., Urciuoli, G., and Di Maio, R.: Integration of geophysical and geotechnical modelling to define hydrogeological conditions for unsaturated soils prone to shallow flowslides, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8083, https://doi.org/10.5194/egusphere-egu23-8083, 2023.

17:15–17:25
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EGU23-16507
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NH3.1
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On-site presentation
Vicente Medina, Marcel Hürlimann, and Laura Molano

FLATModel (Medina et al. 2008) was developed as a modeling tool for debris flow (DF) events. It includes several specific DF features, among them, a simple erosion mechanism was proposed and implemented. The previous validation of this model capability was based on event volume comparison. Now, a more detailed analysis has been performed, and several constraints in its applicability emerge. Model results for erosion present an important dependence on numerical parameters configuration, hence, not only the physical parameters calibration is required. Accuracy in erosion modeling requires proper numeric setup resulting in high computational effort, compromising the model performance. New specific algorithm or erosion computation approach is required.
A part from these numerical aspects, we present some results obtained in the Rebaixader torrent (Central Pyrenees), where a debris-flow monitoring system is installed and annual UAV-surveys are performed.


Medina, V., Hürlimann, M., Bateman, A. (2008) FLATModel: 2D finite volume code for debris-flow modelling. Application to different events occurred in the Northeastern part of the Iberian Peninsula. Landslides, 5, 127-142. https://doi.org/10.1007/s10346-007-0102-3

How to cite: Medina, V., Hürlimann, M., and Molano, L.: Drawbacks in modeling debris flow erosion using the shallow water equations and the finite volume method. Examples from FLATModel and the Rebaixader torrent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16507, https://doi.org/10.5194/egusphere-egu23-16507, 2023.

17:25–17:35
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EGU23-5870
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NH3.1
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ECS
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On-site presentation
Hui Tang

Extreme climate events (e.g., extreme rainfall and glacier melting) in alpine areas can result in significant runoff or mass movements (e.g., flash floods and debris flows) that pose substantial threats to human life and infrastructure downstream. However, due to sparse measurements, understanding the sediment transport mechanisms that control these processes still needs to be completed. Scaling laws and dimensionless numbers provide valuable insights into complex physical systems and processes. Several dimensionless numbers (e.g., Einstein number and Savage number) have been proposed to investigate the relative importance of different sediment transport-related stresses for different systems or processes. In this study, we propose a new data-driven approach that embeds the principle of dimensional analysis in an unsupervised machine learning scheme to discover the best combination of dimensionless numbers that can describe sediment transport mechanisms in torrent processes. We reduce high-dimensional parameter spaces (12 dimensions) to descriptions involving only a few (about 3-4) physically interpretable dimensionless numbers. Using a unique field dataset, we demonstrate this idea to investigate the transition in different transport mechanisms. The result is generally applicable criteria that can improve existing classification models and aid in developing appropriate hazard assessments in mountainous regions based on scarce hydrologic measurements. 

How to cite: Tang, H.: Data-driven discovery of dimensionless numbers for extreme flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5870, https://doi.org/10.5194/egusphere-egu23-5870, 2023.

17:35–17:45
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EGU23-5593
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NH3.1
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ECS
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On-site presentation
Tengfei Wang, Kunlong Yin, Yuanyao Li, Juan Du, Lei Gui, and Zizheng Guo

Typhoon debris flows are recurrent phenomena with a high capacity to cause significant economic and life loss in the coastal areas. Accurately predicting the movement process and determining the potential zones and risk assessment are crucial to design mitigation strategies and to reduce societal and economic losses. In this study, the Wangzhuangwu (WZW) gully was chosen as the study object, which once broke out a debris flow induced by the Typhoon Likima on 10 August 2019. First, a detailed field investigation and interpretation of remote sensing imagery were carried out to study the trigger mechanism and quantify the characteristics of the debris flow. Second, the movement and deposition process of the 2019 WZW debris flow were reconstructed based on the Soil Conservation Service-curve number (SCS-CN) approach and a two-dimensional finite model (FLO-2D PRO model). The debris flow inundation and evolutionary trajectory were shown to be reasonably comparable with historical debris flows. Then, the potential hazard zones of debris flows with different recurrence intervals were determined based on the validated rheological parameters. Here we established a two-factors model that couples maximum flow depth with momentum to classify the hazard zones. Finally, we calculated the vulnerability distribution and economic risk of the buildings with different recurrence intervals based on a quantitative risk formula. This study provides a complete and efficient mean to determine the values of debris flow parameters and to implement a hazard and risk assessment based on numerical simulation. This proposed approach efficiently generated a debris flow risk distribution map that can be used for effective disaster prevention in the debris flow-prone areas.

How to cite: Wang, T., Yin, K., Li, Y., Du, J., Gui, L., and Guo, Z.: Reconstruction and risk predication of a typhoon-triggered debris flow via numerical simulation: A case study of Zhejiang Province, SE China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5593, https://doi.org/10.5194/egusphere-egu23-5593, 2023.

Posters on site: Fri, 28 Apr, 10:45–12:30 | Hall X4

Chairpersons: Sara Savi, Velio Coviello (deceased), Xiaojun Guo
X4.13
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EGU23-1052
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NH3.1
Vivian Cristina Dias, Helen Cristina Dias, and Carlos Henrique Grohmann

Among the hydrogeomorphologic processes, debris flows, debris floods, and floods stand out as the most destructive due to their potential to transport a variety of materials over long distances and the damage caused to urban infrastructures. The watershed dynamic and morphometry stand out as one of the paramount factors related to triggering the processes. The Serra do Mar, on the southeast coast of Brazil, is a mountain range with about 1,500 km where landslides are frequent, causing a high number of casualties and economic losses, especially when related to debris flows/floods.  Thus, studies focusing on the evaluation of the susceptibility of the areas are needed, aiming for mitigation and planning actions. In this way, the aim of this research was the characterization of watersheds for the occurrence of hydrogeomorphologic processes using morphometry on the North shore of Serra do Mar in São Paulo State. To reach this goal, the following methodological steps were carried out: (a) delimitation of the watersheds considering the proximity of the scarp of the Serra do Mar, altimetric range, angle, confinement of the channel, and evidence of past events; b) mapping of morphometrics parameters (Area, Length, Basin relief, Relief ratio, and Melton ratio) using a TanDEM-X Digital Elevation Model with 12 meters spatial resolution; and c) identification of watersheds prone to debris flows, debris floods, and floods according to the morphometry results. A total of 355 watersheds were mapped in three cities (Ubatuba, Caraguatatuba, and São Sebastião). The results show that according to the Melton ratio, 67% of the watersheds are prone to debris flows, with values > 0,60, followed by 30% prone to debris floods and floods, and only 3% prone to fluvial processes. Values vary from 0,16 to 1,70, with a mean of 0,68. Values for Area were between 0,07 to 8,02 km² (mean 0,70 km²), in the range for areas prone to debris flows, according to the literature (up to 10 km²). For the Length, the values vary from 0,47 to 6,73 (mean 1,30 km), with most of the watersheds (94%) with values up to 2,7 km (the threshold indicated for debris flow prone areas). Basin relief and Relief ratio presented values varying between 0,26 to 1,27 km (mean 0,57 km), and 0,09 to 0,79 (mean 0,44), respectively. The next step of the research is the investigation of past events using aerial photos and satellite images. The results of this research can contribute to government response and the reduction of the damage caused by natural hazards in Brazil.  

How to cite: Dias, V. C., Dias, H. C., and Grohmann, C. H.: Distinction between watersheds prone to debris flow, debris flood, and flood using morphometry in Serra do Mar, Brazil (São Paulo State North shore)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1052, https://doi.org/10.5194/egusphere-egu23-1052, 2023.

X4.14
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EGU23-3752
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NH3.1
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Highlight
SoungDoug Kim, Hojin Lee, and Hyungjoon Chang

The purpose of this present study is to investigate and analyze the extension and the effect of debris flow generated in mountainous terrain due to climate change on the coastal and ocean downstream areas. As the target area of this study, the coast of Fiji in the South Pacific region affected by super hurricanes every year was selected. The category 5 Hurricane Winston in 2016 produced 42,700 tons of debris flow and caused massive damage to the entire Fiji. For debris flow analysis, mass conservation and momentum conservation equations were used as governing equations, and the finite difference method was applied to the numerical model. As a result of the analysis, the increase in the discharge of debris flow generated in the upstream mountainous area and the increase of the flow water depth extend along the downstream river to the Pacific coast, and a lot of soil run out. To check how far the debris flow moves along the river, the diffusion length of the debris flow was calculated, and the debris flow spreads over a considerable range during heavy rain. Corresponding author: Hojin Lee(hojin@chungbuk.ac.kr)

How to cite: Kim, S., Lee, H., and Chang, H.: Discharge and extension of debris flow and its application to ocean environments in South Pacific Area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3752, https://doi.org/10.5194/egusphere-egu23-3752, 2023.

X4.15
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EGU23-5132
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NH3.1
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ECS
Seungjun Lee, Hyunuk An, and Minseok Kim

The check dam is one of the most effective countermeasures to reduce the damage caused by debris flows. While several previous studies have tried to find the priority factor of check dam construction, there are still limitations in terms of quantitive analysis for figuring out the factor of check dam influencing debris flow damages. This study analyzed the most influential factor to assess the best location for the mitigation effect through numerical simulations, which are on the Raemian apartment at Mt. Umyeon in Seoul and Gallam-ri in Gangwon-do, the Republic of Korea, in 2011 and 2019, respectively. The simulation results were quantitatively analyzed by Spearman's rank correlation method. As a result, it was found that the topographical components are more reasonable than flow characteristics in the construction of the check dam. In particular, the check dam constructed at the point which could store more debris revealed the best performance in mitigation effect.

How to cite: Lee, S., An, H., and Kim, M.: Analysis of factors influencing the construction of a check dam to reduce damage caused by debris flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5132, https://doi.org/10.5194/egusphere-egu23-5132, 2023.

X4.16
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EGU23-6460
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NH3.1
Jacob Hirschberg, Yoann Sadowski, Adrien Michel, Brian W. McArdell, and Peter Molnar

Debris flows are surging mixtures of water and sediments and can threaten humans and infrastructure. In alpine catchments, debris flows are often triggered by runoff events as a response to intense rainfall, snowmelt, or a combination thereof. Therefore, debris-flow triggering is expected to be sensitive to future changes in temperature and precipitation. Quantifying these changes is, however, challenging. While changes in temperature are relatively certain, future precipitation characteristics have lower signal-to-noise ratios (e.g., Hirschberg et al., 2021). Furthermore, how such changes influence the seasonal snowpack is not trivial. For example, snowmelt is predicted to start earlier in the year, but at lower rates (Musselman et al., 2017). Quantifying climate change impacts on debris-flow triggering runoff events in high-alpine catchments, therefore, requires studying the complex interactions of changes in precipitation, temperature and the snowpack.

Our study focuses on the Grabengufer rock glacier and the gully below, which is located above the municipality of Randa in the canton of Valais, Switzerland. The rock glacier front regularly delivers mobile sediments to the gully (1900 m a.s.l.), where debris flows are frequently triggered after rain and/or snowmelt. We use ALPINE3D, which is a spatially distributed version of the multi-layer snowmodel SNOWPACK (Lehning et al., 2002), to simulate the snowpack evolution and runoff in the Grabengufer basin. Due to the small size and the steepness of the basin, the discharge can be simplified as the snowmelt and liquid precipitation in each pixel and in each timestep. A debris-flow record consisting of 34 events between 1985 and 2016 allowed for calibrating a debris-flow triggering discharge threshold. Ultimately, we plan to use the AWE-GEN stochastic weather generator (Fatichi et al., 2011) and the CH2018 climate scenarios to study changes in debris-flow triggering discharge at hourly resolution. Preliminary results show clear relations between snowmelt, rainfall and debris-flow triggering for the calibration period and provide a proof of concept. Although we cannot address the full complexity of such geomorphic systems leading to debris-flow triggering (e.g., rock-glacier dynamics), we study changes in extreme discharge, which is a key variable for future debris-flow hazards. Furthermore, the studied basin is representative of high-alpine debris-flow torrents and the outcome will be useful for researchers and authorities interested in climate change impacts on alpine mass movements.

REFERENCES

CH2018 Project Team 2018: CH2018 - Climate Scenarios for Switzerland. National Centre for Climate Services.

Fatichi, S., Ivanov, V. Y., & Caporali, E. 2011: Simulation of future climate scenarios with a weather generator. Advances in Water Resources, 34(4), 448-467.

Hirschberg, J., Fatichi, S., Bennett, G.L., McArdell, B.W., Peleg, N., Lane, S.N., Schlunegger, F., Molnar, P. 2021: Climate Change Impacts on Sediment Yield and Debris-Flow Activity in an Alpine Catchment. J. Geophys. Res. Earth Surf. 126.

Lehning, M., Bartelt, P., Brown, B., and Fierz, C. 2002: A physical SNOWPACK model for the Swiss avalanche warning: Part III: meteorological forcing, thin layer formation and evaluation, Cold Reg. Sci. Technol., 35, 169–184.

Musselman, K. N., Clark, M. P., Liu, C., Ikeda, K., & Rasmussen, R. 2017: Slower snowmelt in a warmer world. Nature Climate Change, 7(3), 214-219.

How to cite: Hirschberg, J., Sadowski, Y., Michel, A., McArdell, B. W., and Molnar, P.: Climate change impacts on rainfall- and snowmelt-triggered debris flows in an Alpine catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6460, https://doi.org/10.5194/egusphere-egu23-6460, 2023.

X4.17
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EGU23-8783
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NH3.1
Tien-Chien Chen and Yang Hung

The micro geomorphology characteristics of 47 hillslope debris flow (HDF) and 16 channelized debris flow (CDF) events were studied to explore the difference between HDF and CDF. In Taiwan, debris flow torrents are classified into CDF and HDF two types. CDF watershed consists of tributaries and gullies, in which one or multi tributaries might occur the debris flow then inducing the CDF. HDF is located upstream of the watershed and caused by a landslide on the slope and transforming into HDF. The result shows that the factors of CDF are larger than those of HDF including the watershed area, initiation region, length of the transport segment, and elevation differences of the transport segment. The gradient of the riverbank slope is similar between CDF and HDF. However, the channel gradient of the transport segment of HDF is higher than that of CDF. The gradient ratio between the channel gradient and the average gradient of the riverbank slope on the transport segment of CDF is smaller than the gradient ratio of HDF, revealing that CDF valley erosion is higher than HDF valley. This study attempts to establish the criteria for the interpretation of CDF and HDF and explores the differences between the two in the topographic characteristics.

How to cite: Chen, T.-C. and Hung, Y.: Mirco-Geomorphology Differences Between Channelized Debris Flow with Hillslope Debris Flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8783, https://doi.org/10.5194/egusphere-egu23-8783, 2023.

X4.18
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EGU23-9654
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NH3.1
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ECS
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Highlight
Francisco J. Vasconez, Pablo Samaniego, Jeremy Phillips, S. Daniel Andrade, Edwin Simbaña, Valeria Nogales, José Luis Román Carrión, Anais Vásconez Müller, and María Antonieta Vásquez

In Ecuador, a country with numerous potentially active volcanoes, recurrent large earthquakes, and regular climate-related events, it is surmised that phenomena such as debris flows have affected pre-Hispanic populations since their settlement in ~5000 cal BC. Here, using a multidisciplinary approach, we studied the most recent debris flow events that affected the Cayambe city area, located 15 km west of the active glacier-clad Cayambe volcano. Based on detailed characterization of the deposits, including sedimentological, archaeological, and paleontological analyses, as well as radiocarbon dating. We found that two debris flow (i.e., Río Blanco I and II) destroyed Caranqui settlements in 665–775 cal AD and 774–892 cal AD, respectively, while another event impacted a Spanish colonial farm in 1590 –1620 cal AD (Río Blanco III). The grain size distribution of these deposits indicates a gravel-rich flow for Río Blanco I and clay-rich flow for Río Blanco II and III, whilst componentry suggests low juvenile volcanic content for all three deposits. Juvenile components include pumice and lustrous dense dacites, while accidental clasts are dull dense dacites, oxidized and hydrothermally-altered material, as well as archaeological artifacts. These results, in addition to radiocarbon ages, suggest that the debris flows could either be post-eruptive or not related to volcanic eruptions. Potential non-volcanic trigger mechanisms for these events include rainfall and/or earthquakes, which implies that they can occur at any time and without forecast. Currently, the city of Cayambe is rapidly expanding and, consequently, our findings are relevant for creating impact scenarios for future debris flows forming in the Rio Blanco headwaters and descending to the city.

How to cite: Vasconez, F. J., Samaniego, P., Phillips, J., Andrade, S. D., Simbaña, E., Nogales, V., Román Carrión, J. L., Vásconez Müller, A., and Vásquez, M. A.: Evidence of destructive debris flows at (pre-) Hispanic Cayambe settlements, Ecuador, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9654, https://doi.org/10.5194/egusphere-egu23-9654, 2023.

X4.19
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EGU23-2525
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NH3.1
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ECS
Seulgi Lee and Sungsu Lee

Concerns about landslides or dam failures are increasing due to torrential rains, sudden heavy rains, and typhoons caused by global warming. In the 21st century, more than 200 dam and reservoir failures have occurred worldwide, causing enormous damage of human life and property. When a dam or reservoir collapses, a large amount of water and various sizes of earth and rocks are mixed and a debris flow occurs. Debris flows are dangerous because they move quickly and destroy objects in their path. In order to predict the damage caused by these dam and reservoir failures, 3D multiphase flow numerical analysis can be used. This study proposes a downstream risk assessment technique in the event of dam and reservoir failure that predicts downstream damage using a three-dimensional multi-phase flow numerical analysis and evaluates quantitative losses using a building's vulnerability curve against debris flows. This research was supported by Research Program to Solve Urgent Safety Issues of the National Research Foundation of Korea(NRF) funded by the Korean government (Ministry of Science and ICT(MSIT)) (Grant Number : 2021M3E9A1103506)

How to cite: Lee, S. and Lee, S.: Risk Assessment of Downstream Areas in Case of Earth Dam Failure Using 3D Simulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2525, https://doi.org/10.5194/egusphere-egu23-2525, 2023.

X4.20
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EGU23-8803
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NH3.1
Matteo Mantovani, Stefano Crema, Giulia Bossi, Federica Ceccotto, Gianluca Marcato, and Alessandro Pasuto

The ability to detect and map landslides triggered by intense rainfall in quasi-real time is essential to mitigate their impact and for effective crisis management. The manipulation of space-borne synthetic aperture radar (SAR) images has proven to be one of the most valuable and inalienable asset for this type of investigation. In mountainous areas, morphological variations, related to surface processes and activated by forceful meteorological events, can be usually detected by applying three type of approaches: amplitude-based methods, phase-coherence-based methods and polarimetric techniques. This study present a rapid, effective and straightforward coherence-based methodology which, using just three SAR images, can detect the activation of debris flows with a latency solely related to the repeat cycle of the SAR mission. The technique has been tested in the Italian Dolomites using the dataset of European Space Agency’s mission Sentinel-1, showing promising results. This research is carried out in the framework of Project VAILAND, a joint research agreement funded by the Veneto Region (Italy).

How to cite: Mantovani, M., Crema, S., Bossi, G., Ceccotto, F., Marcato, G., and Pasuto, A.: Rapid Detection Of Debris Flows Using Synthetic Aperture Radar: A Coherence-Based Methodology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8803, https://doi.org/10.5194/egusphere-egu23-8803, 2023.

X4.21
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EGU23-10319
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NH3.1
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ECS
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Esme Hirsch, Joshua Woods, Ryan Mulligan, and Andy Take

Landslide barrier structures constructed on high-risk slopes are a useful strategy to halt and retain debris to protect vulnerable downslope infrastructure and inhabitations. To appropriately design these systems, an estimate of the likely volume, thickness, and velocity of the flow is required immediately prior to interaction with the barrier. These characteristics of the flow, when combined with an analytical model or numerical simulation of the impact, define the structural demand on the barrier. In this study, we use the large Queen’s University Landslide Flume to explore the relative contributions of the fluid and solid phases of a multi-phase flow on the structural demand on a barrier. Impact forces following dam break experiments of up to 1 m3 of material, released from the top of a 6.5 m long slope inclined at 30 degrees are explored for releases of pure water, dry granular particles, and fully-saturated granular water-grain mixtures. Impacting the barrier at approximately 4-5 m/s, temporal impact behaviour captured using ultrahigh speed imaging is correlated with the time series of impact load. Quantitative comparisons are then made between the observations of impact force by each class of flow to predictive equations published in the literature, highlighting the degree of match, hypotheses for observed discrepancies, and the relative contributions of the fluid and solid phases.

How to cite: Hirsch, E., Woods, J., Mulligan, R., and Take, A.: Exploring the relative contributions of fluid and solid phases in debris flow barrier impact, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10319, https://doi.org/10.5194/egusphere-egu23-10319, 2023.

X4.22
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EGU23-10895
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NH3.1
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ECS
Kaiyan Hu, Peng Han, Chunyu Mo, Yihua Zhang, Shuangshuang Li, Jianwei Sun, and Qinghua Huang

Based on the electrokinetic effect, the pore-water flows can produce electrical streaming currents. The electrokinetic mechanism makes electrical voltage differences on the ground or underground be observed, which can be called as Self-Potential (SP). SP as a passive geophysical method could be used to understand water flow, which has a potential application in monitoring rainfall-induced landslides. In this study, we implemented a laboratory experiment by imposing rainfall to measure SP data variations due to soil imbibition and water flows. SP, pore-water pressure inside the slope and surface displacement are synchronously measured by a data acquisition system from National Instruments (NI Compact DAQ). The observed results indicate that (1) SP sensitively responds to the pore-water pressure variations, and (2) the significant increase of surface displacement lagging behind changes in SP. The experimental results show the potential that SP can be used to quantitatively interpret the changes in the water flowing pattern inside the slope.

How to cite: Hu, K., Han, P., Mo, C., Zhang, Y., Li, S., Sun, J., and Huang, Q.: Self-Potential signatures on monitoring a rainfall-induced landslide based on a laboratory experiment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10895, https://doi.org/10.5194/egusphere-egu23-10895, 2023.

X4.23
|
EGU23-12196
|
NH3.1
Zhen-Yu Wu, Wei-An Chao, and Chi-Yao Hung

In the steep mountain catchment, measuring the budget change of soil and sediment has always been a great challenge. Results of recent research have shown that the seismic station nearby river channels can capture seismic signals cause by different mechanisms such as water flow, sediment transport, and debris flow. Among them, river sediment transport and the debris flow have a more serious impact on the sediment mass distribution of river bed. This study site selected the Putanpunuas River in southern Taiwan where landslide occurred frequently, which could provide a stable source of sediment materials for this river. The temporals changes of erosion and deposition in the downstream alluvial fan can represent the income and expenditure of soil and sediment in the catchment area. Therefore, two broadband stations and one Geophone station were installed at downstream of the Putanpunuas River, and a broadband station was installed at the confluence of the Putanpunuas River and the Laonong River, which was named the Putanpunuas seismic array (PSA). By using a multi-temporal digital elevation model (DEM) of downstream alluvial fan, water level information captured by time-lapse images, time-frequency analysis of seismic signals, and the seismic physical models for different mechanisms (turbulent flow, bed saltation, debris flow), out study not only effectively monitor sediment transport but also provide better understanding on sediment budget in the catchment area. Temporal changes in erosion and deposition volume of the downstream alluvial fan was used to validate above seismology-based results.

How to cite: Wu, Z.-Y., Chao, W.-A., and Hung, C.-Y.: Seismic constraints on sediment budget for a mountainous catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12196, https://doi.org/10.5194/egusphere-egu23-12196, 2023.

X4.24
|
EGU23-13421
|
NH3.1
Ruoshen Lin and Gang Mei

Glacier is sensitive to climate warming, and changes in mountainous areas can lead to serious hazards to human society. Glacial debris flow is a type of geological hazards characterized by suddenness and high mobility in high-mountain regions due to deglaciation. The study of susceptibility analysis for glacial debris flow can effectively reduce its potential negative effects. However, when evaluating susceptibility of glacial mudflow, most research work takes the existing glacier area into consideration and ignores the effect of glacier ablation volume. The improved glacial geomorphological information entropy theory based on glacial correction coefficients can be used to evaluate the susceptibility. The correction coefficients can be calculated by investigating the changes in glacier ablation and distribution based on remote sensing applications. In addition, a deep learning-based approach for extracting glacier boundaries is proposed. We present a case study evaluating the susceptibility of along the Duku Highway in Tien Shan area. The results show that the improved method based on glacier ablation can effectively increase the accuracy of the susceptibility analysis. Based on the theory of glaciology and geomorphology, the changes of glacier can be used in the susceptibility of glacial debris flow. In the future, we will explore a new prediction method of geo-hazards based on glacier dynamics.

How to cite: Lin, R. and Mei, G.: Susceptibility of Glacier Debris Flow Based on Remote Sensing: Case Study in the Tien Shan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13421, https://doi.org/10.5194/egusphere-egu23-13421, 2023.

X4.25
|
EGU23-17359
|
NH3.1
Chih-Ming Tseng, Yie-Ruey Chen, and Jen-Yen Tseng

Upstream of notches in mountainous rivers reveal backwater effect and velocity decreasing characteristics. The sediment transport in the upstream of reach with notches is therefore affected by the plane morphological characteristics. The upstream reach could possibly play a role of sediment control section for temporary sediment trapping and mitigation similar like check dam. In this study, we used the DTM of difference (DoD) method to perform four multi-temporal high-resolution DTMs during 2009 to 2021 to obtain the quantitative terrain elevation variance of river channels in five notch regions. The research results show that during Typhoon Morakot, the sediment control in notch area no. 1 can reach more than 20%. From 2012 to 2018, the control effect of sediment in notch regions no. 1, 2 and 4 is more than 14%. Overall, the notches no. 1 and 2 are the main sediment control areas, and the area of notch number 3 is limited in the amount of sediment due to the small contraction ratio of notch; the area of the notch number 4 and 5 is the secondary sediment control area, because the notch area 5 both the area and the contraction degree of the notch are smaller than those in area 4, and the control effect of sediment is more significant in area 4. Therefore, if we can make good implementation of the natural morphological features combined with the engineering structures to improve the effect of sediment regulation and control, it can be used as a reference for formulating watershed management strategies.

How to cite: Tseng, C.-M., Chen, Y.-R., and Tseng, J.-Y.: Evaluation of sediment control due to notches of mountainous river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17359, https://doi.org/10.5194/egusphere-egu23-17359, 2023.

Posters virtual: Fri, 28 Apr, 10:45–12:30 | vHall NH

Chairpersons: Marcel Hürlimann, Xiaojun Guo, Jacob Hirschberg
vNH.2
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EGU23-4721
|
NH3.1
|
ECS
Leilei Chen, Gordon G.D. Zhou, Yingguang Fang, Yunxu Xie, and Kahlil F. E. Cui

A large number of glacial tills are distributed in the high and cold mountainous areas of the Qinghai-Tibet Plateau. Recently, climate change compounded by many other factors, promote the instability of glacial tills resulting in more frequent mountain disasters. Although the physical properties of glacial tills have been extensively studied in previous works, there are relatively few works that have focused on their shear behavior and critical state for different water contents. To understand the failure mechanisms, it is necessary to study the effects of water content on the shear behavior and critical state characteristics of glacial tills. This work discusses and studies the significance of compression, shear, and dilatancy of glacial tills in landslide prediction. The experimental results in this study are aimed to provide a basic understanding of the underlying failure mechanisms of glacial tills. Reconstituted specimens are studied through an oedometer, isotropic compression, and consolidated undrained shear tests. We compared the compressibility and shear behavior of glacial tills with three other types of weathered soils in Hong Kong: Lateritic soil (LAT), completely decomposed granite (CDG), and volcanic soils (CDV). Test results reveal similarities and differences between the tested soils. Through one-dimensional consolidation and triaxial compression tests, we find that the compressibility of glacial till is the lowest. Secondly, the stress-strain relationship exhibited by the glacial till is inconsistent with those of the other tested soils. Our test results showed that upon increasing the applied stress, glacial tills first softened and then hardened. Stress path analysis further showed that glacial tills first dilated and then shear contracted indicating a phase transition. In comparison, the other weathered soils consistently all shrink and eventually reach a critical state. The processes between soils are more complex. The slope and friction angle of the critical state line of glacial tills is significantly higher than that of CDG and CDV, but lower than that of LAT. This might be due higher large particle content of glacial tills and the difference in mineral composition.

How to cite: Chen, L., Zhou, G. G. D., Fang, Y., Xie, Y., and Cui, K. F. E.: The critical state behavior of saturated glacial till, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4721, https://doi.org/10.5194/egusphere-egu23-4721, 2023.

vNH.3
|
EGU23-4724
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NH3.1
|
ECS
Yunxu Xie, Gordon G.D. Zhou, Leilei Chen, Kahlil F. E. Cui, and Xueqiang Lu

Geohazards chain in watershed contains a landslide, which contributes to the propagation on the slope, intruding into river channels forming a landslide dam, a subsequent dam breach, and outburst flooding. Since the sub-process belonging to one chain are all coupled, one or several sub-processes can be the triggering factors of the subsequent one. They can generally own a larger space and time scale than that of a single disaster resulting in greater destructive power and amount of impact area. In this study, the most recent geohazard chain event that happened in the 2018-Baige landslide in Sichuan province, China is adopted for a numerical case study. This event can be divided into several sub-processes according to the coupling order within the chain process. The first landslide generates a landslide dam followed by another landslide and landslide dam sharing the same location. The second landslide overlapped with the first one forming a higher landslide dam. A larger-scale dam breach and resulting outflow occurred eventually. For solving this, a series of validated depth-averaged containing models for geohazards chain is adopted to simulate the whole coupling sub-processes, as well as, the standard LxF central differencing scheme is adopted for retaining high resolution and avoiding Riemann characteristic decomposition. The numerical study simulates the landslide propagation process using a viscos-inertial friction law. The numerical prediction is verified by values from field measurement in the literatures, indicating the feasibility of the (K) viscos-inertial rheology in simulating the large-scale landslide and the landslide dam formation. The overtopping failure process of the two overlapping landslide dams and the outburst flooding is numerically modeled by the proposed model. The results of maximum discharge illustrate the proposed model for landslide dam failure can simulate the interaction process of dam breach and outburst flood. The numerical results, validated by the literature provide reliable assessment and emergency relief support of the actual event. This proposed modeling framework is expected to improve mitigation strategies for geo-hazard chain hazards.

How to cite: Xie, Y., Zhou, G. G. D., Chen, L., Cui, K. F. E., and Lu, X.: Numerical study of  2018 Baige landslides induced geohazards chain and dynamic proesses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4724, https://doi.org/10.5194/egusphere-egu23-4724, 2023.

vNH.4
|
EGU23-10822
|
NH3.1
|
ECS
Non-uniform Breach Evolution of Landslide Dams during Overtopping Failure
(withdrawn)
Xueqiang Lu, Gordon G.D. Zhou, Yunxu Xie, Kahlil F.E. Cui, and Hui Tang
vNH.5
|
EGU23-3665
|
NH3.1
|
ECS
Carlos Millan, Waldo Lavado-Casimiro, and Oscar Felipe-Obando

The objective of this work is to estimate regional rainfall thresholds obtained from a combination of high-resolution gridded rainfall data and debris flow events. The debris flow events were associated with rainfall data, determining triggering and non-triggering rainfall events. The method for determining the thresholds is based on an empirical–statistical approach, and the predictive performance of the thresholds is evaluated whit “true skill statistics”. The validation of the thresholds was carried out by selecting one year of the debris flow dataset to focus on the operability evaluation of thresholds in early warning systems in Peru. In addition, another validation method based on a random selection of the events was used to compare the validation procedure. The thresholds were determined for 11 rainfall regions in Peru. The best predictive performance is the mean daily intensity-duration I-D threshold curve, followed by accumulated rainfall E. This study is highly important to Peru because is one of the first approximations of rainfall thresholds at a regional scale in Peru.

How to cite: Millan, C., Lavado-Casimiro, W., and Felipe-Obando, O.: Rainfall thresholds estimation for debris flow occurrence in Peru, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3665, https://doi.org/10.5194/egusphere-egu23-3665, 2023.

vNH.6
|
EGU23-13031
|
NH3.1
Manish Dewrari and Srikrishnan Siva Subramanian

Debris flows are rapid mass movements with great potential energy to move and are among the most dangerous natural hazards due to their high velocities and longer runout distances. For hazard assessment, early warning systems, and to construct structural mitigation measures in mountainous catchments, it is crucial to study the origin, initiation, and dynamics of debris flows as well as the characterisation of the associated erosion and deposition processes. Debris flow deposit grain-size distributions (GSD) reflect the source properties and the transport and deposition mechanisms and control the sediment transport rates in fluvial systems. In this study, we characterise deposits of ~120 debris flows that occurred in Kedarnath, Mandakini valley, India, during the 2013 North India Floods and find the relation between GSDs and runout distances. Here, we use an approach that combines two methods of measuring GSDs, i.e., volumetric sieving and pebble count. Volumetric sieving can measure grain size only up to 80 mm and takes much fieldwork, while the pebble count method can only measure surface grain sizes but can measure all three axes of grains which is useful in the case of non-spherical grains. We measure surface and subsurface grain sizes and large boulders using this approach. After obtaining the GSDs for the number of debris flows, we do a statistical study on the relationship between GSDs, transport mechanism and runout length. Debris material characterisation is crucial, and the approach has large potential applications in understanding the initiation, failure, and transport mechanisms of extreme-precipitation induced sediment disasters.

How to cite: Dewrari, M. and Subramanian, S. S.: Correlating grain-size distributions, transport mechanism, and runout distance of debris flow deposits in the Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13031, https://doi.org/10.5194/egusphere-egu23-13031, 2023.

vNH.7
|
EGU23-4741
|
NH3.1
|
ECS
Songtang He, Xiaoqing Chen, Daojie Wang, Yuchao Qi, Yong Li, Zengli Pei, and Peng Zhao

With the growing development of nature-based solutions (NBS) for debris flow hazard mitigation, the eco-geotechnical coupled technical system has drawn public concern. While the scheme of debris flow prevention and control are constantly improved, the current collaborative patterns, mechanism, and effects on debris flow interception are not clear. In this study, a new synergistic mitigation methodology of reducing debris flow impact risk coupling tree-shrub mixed vegetation filter stripes (T-SMVFS) in S-shape flow paths and dams was proposed. Four efforts were achieved stepwise: 1) the optimal row and stem spacing of T-SMVFS were determined by the overspread T-SMVFS type; 2) set “S-shape” flow path parameters: width ratio (30%, 45%, 60%, 75%); 3) Comprehensively compared the effects of synergistic measures and single measures (ecological or geotechnical measure) on debris flow reduction; 4) Calculation equation of flow reduction considering the influence of topographic features (channel width, roughness), vegetation planting pattern (stem spacing and row spacing), physical properties of debris flow (capacity, mass) was constructed. The results showed that the overspread T-SMVFS with the row spacing of 10cm and stem spacing of 6cm, respectively presented the best reduction effects with energy regulation reaching 43%, flow regulation reaching 46%, and flow rate being close to 40%, respectively. As the flow path widths of the S-shape vegetation filter strips increased (0%-75%), the flow reduction rate (≈45-8%), flow reduction rate (≈58-13%), and sediment interception rate (≈78-5%) decreased sequentially, but the transport capacity increased. Synergistic measures achieved 60% energy reduction, which was better than pure geotechnical (8.9-23.6%) and pure biological (11.56-52.72%) measures, and 70% sediment interception, and were also much higher than single measures. In the comparison of multiple synergistic approaches, the coupled s-shape vegetated filter strip with a 45% proportion of flow path and beam dam is more effective in synergistic hazard reduction. The synergistic eco-geotechnical mitigation measures proposed in this study are a pattern and an attempt to mitigate disasters based on the concept of NBS and provide a reference for subsequent more optimal mitigation solutions.

How to cite: He, S., Chen, X., Wang, D., Qi, Y., Li, Y., Pei, Z., and Zhao, P.: Experiment on the benefits of natural-based solutions for debris flow mitigation using synergistic eco-geotechnical measures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4741, https://doi.org/10.5194/egusphere-egu23-4741, 2023.

vNH.8
|
EGU23-16411
|
NH3.1
Evaluation of open check dams within modelling chains
(withdrawn)
Gabriele Bertoldi, Federico Bridi, Valentina Cavedon, Tamara Michelini, and Ruggero Valentinotti