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Volume 38, Issue 3 (2023)
GeoRes 2023, 38(3): 373-380 |
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Received: 2023/08/8 | Accepted: 2023/09/20 | Published: 2023/10/2
Received: 2023/08/8 | Accepted: 2023/09/20 | Published: 2023/10/2
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Galoie M, Motamedi A. Evaluation of the Vertical Piers Impact on Debris Flow Hazard Mitigation Using a Numerical Model. GeoRes 2023; 38 (3) :373-380
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1- Civil Engineering Department, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran
2- Civil Engineering Department, Buein Zahra Technical University, Qazvin, Iran
2- Civil Engineering Department, Buein Zahra Technical University, Qazvin, Iran
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Introduction
A debris flow is one of the most destructive natural and environmental phenomena, in which a massive volume of water, rocks, soil, and vegetation moves downslope under the force of gravity and typically comes to rest at the base of the slope [King, 2018]. The initiation of such movement usually requires a triggering force, most commonly flash floods caused by intense rainfall or rapid snowmelt, and in some cases earthquakes or anthropogenic factors such as deforestation and alteration of natural slopes [Takahashi, 2007]. In this process, the momentum and pressure generated by the motion of fine particles and water are sufficient to mobilize coarse rock fragments and large boulders due to the instability of soil and substrate. Moreover, the intense friction with the soil surface exacerbates erosion along the flow path [Takahashi & Das, 2014]. Therefore, the analysis of debris flows and the estimation of associated parameters such as total travel distance from the initiation point to the deposition zone, the extent of affected area, maximum flow depth, and others are not feasible without adequate knowledge of both the basal friction coefficients and the internal resistance of the debris mass [Armanini & Michiue, 1997].
In Iran, landslides and debris flows occur frequently, particularly during springtime heavy rainfall. In the most recent case, on June 9, 2023, an estimated 1.6 million cubic meters of mud and rock inundated a large section of northern transport routes. In some locations, deposit depths exceeded six meters. Part of this debris entered the Karaj Dam reservoir, leading to water supply disruptions in several districts of Tehran, where pressure drops and turbidity lasted for six days. The magnitude of damage and deposited material was so severe that clearance operations in some corridors extended for more than a month (Etemad Online, 2022).
To mitigate the hazards associated with debris flows, researchers have proposed various structural approaches depending on regional topography, material composition, event magnitude, recurrence intervals, and other factors [Jakob & Hungr, 2005]. Some of the most widely applied methods include check dams, grid or slit dams, wire mesh structures, slope stabilization techniques, or combinations thereof, which aim to decelerate or entirely block the flow.
Each method presents distinct advantages and drawbacks, and studies have shown that some interventions may be ineffective or even hazardous. For instance, on August 8, 2010, a debris flow check dam in Sanyanyu Valley, Zhouqu, China, failed under flow pressure, leading to the destruction of over 200 buildings and causing 1,756 fatalities [Wang, 2013]. Similarly, wire mesh systems can deteriorate or collapse due to aging, inadequate design, or base instability [Gong et al., 2020]. In addition, several researchers have investigated approaches to mitigate secondary hazards such as floods triggered by dam failure, demonstrating significant reductions in wave depth and velocity [Fan et al., 2020; Fan et al., 2021].
The proper design and performance evaluation of such structural measures requires a comprehensive understanding of debris flow forces, velocities, depths, and other related parameters [Xiong et al., 2016]. Given that debris flows are multiphase, heterogeneous, and characterized by highly complex motion dynamics that vary across different events, the governing equations are extremely intricate and their analytical solutions are nearly impossible. Consequently, researchers often employ laboratory experiments, empirical models based on statistical data, or numerical simulations.
However, experimental studies are limited by small-scale setups and the inability to replicate real-world conditions such as topography, slope gradients, channel bends, and geologic variability. Hence, their outcomes lack universal applicability [Cui et al., 2015; Zhao et al., 2018; Termini et al., 2020]. Similarly, empirical equations derived from limited experimental or observational data tend to be weak and prone to significant error [Zhou et al., 2019; Ji et al., 2020; Di Perna et al., 2022]. With advances in computing and numerical methods, it has become feasible to simplify and solve the complex governing equations, enabling debris flow simulations across diverse topographic conditions.
The Rapid Mass Movement Simulation (RAMMS) software is one such numerical model developed by the WSL Institute for Snow and Avalanche Research (SLF) in Switzerland. In recent years, RAMMS has gained wide attention, particularly in Europe, due to its user-friendly interface, relatively low data requirements, and strong graphical visualization capabilities. To initiate debris flow simulations, the model requires a digital elevation model (DEM) of the study area, specification of Voellmy-type friction coefficients, and an inflow hydrograph [RAMMS, 2022]. Studies have shown that RAMMS is highly sensitive to input parameters, which can lead to significant variability in outcomes [De Finis et al., 2018; Bezak et al., 2019; Krušić et al., 2019; Zimmermann et al., 2020; Frank et al., 2017]. Nevertheless, its use provides valuable insights into flow parameters and enables simulations over near-real topographic conditions.
The present study aims to evaluate the effectiveness of vertical concrete barriers in controlling debris flows using the RAMMS numerical model. Vertical obstacles along the flow path play a significant role in altering flow parameters, and their number, configuration, and placement can cause substantial variations in debris flow behavior.
Methodology
The present research employed an experimental–computational approach and was conducted during the first half of 2023. The study area was a section of Soolaqan village, located in the northwest of Tehran. Due to its position at the lower slope of a mountain with a relatively steep gradient (29.5°), the area is frequently affected by severe floods accompanied by significant amounts of mud during heavy rainfall events. Figure 4 shows the DEM map of the study area alongside its Google Earth representation.
Governing Equations of Debris Flow in RAMMS
The governing equations implemented in RAMMS are depth-averaged two-dimensional equations, formulated as the conservation of mass and momentum in the x and y directions, expressed as follows (Equations 1–5) [Hussin et al., 2012]:
Equation (1)
Equation (2)
Equation (3)
Equation (4)
Equation (5)
Here, μ denotes the dry Coulomb friction coefficient, and ξ is the turbulent-viscous friction parameter of the Voellmy rheology. Although these coefficients exhibit wide variability, calibration studies in RAMMS based on observed debris flow data indicate that μ typically ranges from 0.1 to 0.5, while ξ varies between 200 and 800 [RAMMS, 2022].
Initial Conditions
RAMMS enables debris flow modeling either by defining an inflow hydrograph or by specifying an erosion depth for the computational domain. In this study, the hydrograph method was adopted. The inflow hydrograph was defined using a three-point input curve, commonly applied in debris flow modeling, based on numerous observational datasets [RAMMS, 2022].
The total flow volume for the catchment was estimated at 20,000 m³. Based on this input, RAMMS automatically generated a three-point hydrograph:
Simulation of Vertical Concrete Barriers
To evaluate the effect of vertical concrete barriers on debris flow parameters, various barrier configurations were considered, and the debris flow was simulated around them. The different layouts are shown in Figure 5.
Since the primary function of these barriers is to reduce the momentum of large particles, particularly coarse clasts and boulders located at the flow front—their dimensions and spacing significantly affect their collective performance. In this study, the barriers were designed with a diameter of 1 m and a height of 2 m. To maximize energy dissipation and particle trapping efficiency, barrier spacing was varied between 2 m and 5 m.
Findings
Debris flow was simulated in the study area using RAMMS under conditions without any control structures along the flow path. For this purpose, a DEM with a cell size of 5 m was applied, which provides relatively satisfactory accuracy for simulating this phenomenon. The simulation results, represented as the total affected area, are shown in Figure 1 using the Google Earth environment to identify the hazardous zones. Although the simulation duration was set at 1500 seconds, the debris flow completely ceased at approximately 940 seconds, as the flow momentum reached zero.
A comparison between Figure 1 reveals that the debris flow significantly affected a considerable number of buildings located near the mountain slope. Therefore, flow-control structures are required in the upstream region to mitigate damage from such events.
Figure 1. Total affected area of the debris flow in Google Earth under conditions without control structures
To estimate the efficiency of vertical barriers as a flow-control structure, debris flow simulations were repeated for the study area with different barrier configurations. In order to compare the results of these configurations with the no-barrier condition and to evaluate their influence on flow parameters, the percentage-change relation (Equation 6) was applied [Fan et al., 2021; Galoie & Motamedi, 2021]:
Equation 6
where R is the percentage change, and P0 and Pn are the values of the same parameter in the no-barrier and barrier conditions, respectively.
Following simulations of each configuration, percentage changes were calculated for two critical parameters of total affected area and total travel distance both of which play a vital role in assessing vulnerable regions. It should be noted that configuration “E” represents barriers installed on the steep upstream slope near the initiation point of the flow, while all other configurations were placed on the gentler downstream slope.
Installing barriers on the steep upstream slope (configuration E) did not significantly improve flow control compared to other layouts. Although the barriers absorbed some kinetic energy upon impact, the flow quickly regained velocity due to the steep gradient, diminishing the effectiveness of the barriers. In this case, the affected area decreased by only 12.3%, and the travel distance by 6.8%, relative to the no-barrier scenario.
By contrast, installing barriers on the gentler downstream slope substantially reduced kinetic energy as particles collided with the barriers, and the lower gradient prevented flow re-acceleration, resulting in quicker flow stoppage. Configurations with irregular, staggered barriers were more effective, as repeated particle collisions enhanced energy dissipation and trapping efficiency. Configuration C, however, showed limited impact since the barriers were aligned in regular rows, leaving free-flowing gaps where particles could pass through without significant interaction. In this case, the affected area decreased by 16.8% and the travel distance by 11.4%.
In configuration B, where barriers were arranged in an upstream-pointing triangular layout, the flow was diverted laterally after colliding with the first row of barriers. This diversion reduced interactions with subsequent rows, thereby diminishing overall effectiveness. Here, the affected area decreased by only 13.1%, and the travel distance by 12.2%.
Among all tested configurations, configurations A and D proved most effective in controlling debris flow and reducing both affected area and travel distance. Given that their results were nearly identical, configuration A, featuring fewer barriers arranged in a downstream-pointing triangular layout was identified as the optimal solution. In this case, the affected area was reduced by 25.1% and the travel distance by 20.8%, which represents a significant improvement. Moreover, further reductions could be achieved by adjusting the number or spacing of barriers.
Figure 2. Simulated debris-flow impact area displayed in Google Earth for the case where the pile group is arranged in a triangular configuration on the lower slope
Figure 2 shows the debris flow simulated with the triangular barrier arrangement. Compared to Figure 1, there is a marked reduction in both affected area and travel distance, such that nearly all buildings located downslope are no longer exposed to risk.
Figure 2. Simulated total affected area in Google Earth with triangular (configuration A, Figure 5) barrier arrangement at the downslope area
Unlike other methods, the use of vertical barriers demonstrated multiple advantages. In this approach, the failure of one or even several barriers only reduces system efficiency without causing total system collapse, whereas wire mesh structures or check dams may fail catastrophically due to dam breaches or mesh ruptures. Additionally, barrier construction is considerably simpler and more cost-effective compared to other methods. Therefore, based on the above findings and numerical modeling results, the vertical barrier method can be regarded as one of the effective and practical approaches for debris flow control.
Discussion
The main driving force of debris flows is the momentum generated by soil and water particles, which are capable of mobilizing very coarse rock fragments. Structural control measures must therefore be able to dissipate the flow’s kinetic energy and prevent its propagation. Conventional methods are generally based on constructing check dams or steel net frameworks; however, such structures may fail under severe debris flows and consequently cause downstream destruction.
The use of vertical piles for dissipating the kinetic energy of debris flows has not previously been applied or evaluated. Nevertheless, the modeling results of this study demonstrated that debris flows can be effectively controlled by such piles. The pile groups have the capacity to significantly reduce the flow momentum and kinetic energy through successive impacts, thereby trapping coarse particles within the inter-pile spaces. In this regard, the number of piles, their arrangement, and the spacing between them play a critical role in determining debris-flow parameters. Although the present research employed uniform pile spacing in all scenarios to facilitate comparison of different configurations, pile performance can be further improved by optimizing inter-pile distances.
Using piles to control debris flows offers several advantages over conventional methods such as check dams. Pile construction is faster and more cost-effective than check dams, and even if some piles fail during flooding, the overall system performance is not compromised, as the remaining piles continue to dissipate flow momentum. Moreover, post-flood clearance and restoration are far simpler compared to the removal of sediments deposited behind check dams.
Since numerical models often rely on assumptions and simplifications in discretizing complex governing equations, potentially introducing numerical errors and deviations from reality, it is recommended that the results of this numerical model be validated using a physical model to further assess pile performance in debris-flow mitigation. It should be noted, however, that the RAMMS model has been extensively applied by numerous researchers worldwide, and its accuracy has been validated, particularly in Europe [RAMMS, 2022]. Despite this, no numerical or laboratory studies specifically addressing the present research topic have been conducted to date, preventing direct comparison of the results with other investigations. Related studies, however, can be found where vertical piles have been applied to influence various sediment-laden flows, dam-break waves, and similar processes. A comprehensive numerical analysis in this context demonstrated that vertical piles play a significant role in reducing flow momentum and wave depth following dam-break events [Fan et al., 2020]. That study revealed how successive interactions of dam-break waves with piles resulted in substantial dissipation of kinetic energy and momentum. Hence, the effectiveness of pile groups in reducing flow momentum and energy can be equally exploited for debris-flow mitigation
Conclusion
The application of vertical pile groups was examined as a practical method for debris-flow mitigation. Among the tested configurations, the triangular arrangement of cylindrical concrete piles with a diameter of 1 m and a height of 2 m, positioned on the lower slopes of mountainous areas, was identified as the most effective strategy compared with other layouts.
Acknowledgments: This research is based on a study project on debris-flow modeling and hazard mitigation conducted at the Institute of Mountain Hazards and Environment Research in China. For the purpose of comparative analysis, part of the project was also implemented in one of the catchments in Iran. The authors sincerely acknowledge the efforts, guidance, and support of the research team, particularly Professor Fan, as well as the Institute’s Computer Center for providing the software license.
Ethical Approval: This article has not been published in any domestic or international journal to date.
Conflict of Interest: The authors declare no conflict of interest with any institutions or individuals. The sole purpose of this paper is to present practical methods in the field of Geographic Information Systems (GIS) and their effective application in water resources management and protection.
Authors’ Contributions: Galoie M (first author), principal Researcher/Methodologist (50%); Motamedi A (second author), Statistical Analyst/Discussion Writer (50%).
Funding: This article is derived from a joint research collaboration between Iran and China. All research-related expenses and software usage fees were funded by the Ministry of Science of China.
A debris flow is one of the most destructive natural and environmental phenomena, in which a massive volume of water, rocks, soil, and vegetation moves downslope under the force of gravity and typically comes to rest at the base of the slope [King, 2018]. The initiation of such movement usually requires a triggering force, most commonly flash floods caused by intense rainfall or rapid snowmelt, and in some cases earthquakes or anthropogenic factors such as deforestation and alteration of natural slopes [Takahashi, 2007]. In this process, the momentum and pressure generated by the motion of fine particles and water are sufficient to mobilize coarse rock fragments and large boulders due to the instability of soil and substrate. Moreover, the intense friction with the soil surface exacerbates erosion along the flow path [Takahashi & Das, 2014]. Therefore, the analysis of debris flows and the estimation of associated parameters such as total travel distance from the initiation point to the deposition zone, the extent of affected area, maximum flow depth, and others are not feasible without adequate knowledge of both the basal friction coefficients and the internal resistance of the debris mass [Armanini & Michiue, 1997].
In Iran, landslides and debris flows occur frequently, particularly during springtime heavy rainfall. In the most recent case, on June 9, 2023, an estimated 1.6 million cubic meters of mud and rock inundated a large section of northern transport routes. In some locations, deposit depths exceeded six meters. Part of this debris entered the Karaj Dam reservoir, leading to water supply disruptions in several districts of Tehran, where pressure drops and turbidity lasted for six days. The magnitude of damage and deposited material was so severe that clearance operations in some corridors extended for more than a month (Etemad Online, 2022).
To mitigate the hazards associated with debris flows, researchers have proposed various structural approaches depending on regional topography, material composition, event magnitude, recurrence intervals, and other factors [Jakob & Hungr, 2005]. Some of the most widely applied methods include check dams, grid or slit dams, wire mesh structures, slope stabilization techniques, or combinations thereof, which aim to decelerate or entirely block the flow.
Each method presents distinct advantages and drawbacks, and studies have shown that some interventions may be ineffective or even hazardous. For instance, on August 8, 2010, a debris flow check dam in Sanyanyu Valley, Zhouqu, China, failed under flow pressure, leading to the destruction of over 200 buildings and causing 1,756 fatalities [Wang, 2013]. Similarly, wire mesh systems can deteriorate or collapse due to aging, inadequate design, or base instability [Gong et al., 2020]. In addition, several researchers have investigated approaches to mitigate secondary hazards such as floods triggered by dam failure, demonstrating significant reductions in wave depth and velocity [Fan et al., 2020; Fan et al., 2021].
The proper design and performance evaluation of such structural measures requires a comprehensive understanding of debris flow forces, velocities, depths, and other related parameters [Xiong et al., 2016]. Given that debris flows are multiphase, heterogeneous, and characterized by highly complex motion dynamics that vary across different events, the governing equations are extremely intricate and their analytical solutions are nearly impossible. Consequently, researchers often employ laboratory experiments, empirical models based on statistical data, or numerical simulations.
However, experimental studies are limited by small-scale setups and the inability to replicate real-world conditions such as topography, slope gradients, channel bends, and geologic variability. Hence, their outcomes lack universal applicability [Cui et al., 2015; Zhao et al., 2018; Termini et al., 2020]. Similarly, empirical equations derived from limited experimental or observational data tend to be weak and prone to significant error [Zhou et al., 2019; Ji et al., 2020; Di Perna et al., 2022]. With advances in computing and numerical methods, it has become feasible to simplify and solve the complex governing equations, enabling debris flow simulations across diverse topographic conditions.
The Rapid Mass Movement Simulation (RAMMS) software is one such numerical model developed by the WSL Institute for Snow and Avalanche Research (SLF) in Switzerland. In recent years, RAMMS has gained wide attention, particularly in Europe, due to its user-friendly interface, relatively low data requirements, and strong graphical visualization capabilities. To initiate debris flow simulations, the model requires a digital elevation model (DEM) of the study area, specification of Voellmy-type friction coefficients, and an inflow hydrograph [RAMMS, 2022]. Studies have shown that RAMMS is highly sensitive to input parameters, which can lead to significant variability in outcomes [De Finis et al., 2018; Bezak et al., 2019; Krušić et al., 2019; Zimmermann et al., 2020; Frank et al., 2017]. Nevertheless, its use provides valuable insights into flow parameters and enables simulations over near-real topographic conditions.
The present study aims to evaluate the effectiveness of vertical concrete barriers in controlling debris flows using the RAMMS numerical model. Vertical obstacles along the flow path play a significant role in altering flow parameters, and their number, configuration, and placement can cause substantial variations in debris flow behavior.
Methodology
The present research employed an experimental–computational approach and was conducted during the first half of 2023. The study area was a section of Soolaqan village, located in the northwest of Tehran. Due to its position at the lower slope of a mountain with a relatively steep gradient (29.5°), the area is frequently affected by severe floods accompanied by significant amounts of mud during heavy rainfall events. Figure 4 shows the DEM map of the study area alongside its Google Earth representation.
Governing Equations of Debris Flow in RAMMS
The governing equations implemented in RAMMS are depth-averaged two-dimensional equations, formulated as the conservation of mass and momentum in the x and y directions, expressed as follows (Equations 1–5) [Hussin et al., 2012]:
Equation (1)
Equation (2)
Equation (3)
Equation (4)
Equation (5)
Here, μ denotes the dry Coulomb friction coefficient, and ξ is the turbulent-viscous friction parameter of the Voellmy rheology. Although these coefficients exhibit wide variability, calibration studies in RAMMS based on observed debris flow data indicate that μ typically ranges from 0.1 to 0.5, while ξ varies between 200 and 800 [RAMMS, 2022].
Initial Conditions
RAMMS enables debris flow modeling either by defining an inflow hydrograph or by specifying an erosion depth for the computational domain. In this study, the hydrograph method was adopted. The inflow hydrograph was defined using a three-point input curve, commonly applied in debris flow modeling, based on numerous observational datasets [RAMMS, 2022].
The total flow volume for the catchment was estimated at 20,000 m³. Based on this input, RAMMS automatically generated a three-point hydrograph:
- Point 1 (time = 0 s): discharge = 0 m³/s, velocity = 2 m/s,
- Peak (time = 5 s): discharge = 382 m³/s, velocity = 5 m/s,
- Point 3 (time = 104 s): discharge = 0 m³/s, velocity = 1 m/s.
- Simulation duration = 1500 s,
- Bulk density = 2000 kg/m³,
- Dry Coulomb friction coefficient (μmuμ) = 0.2,
- Turbulent-viscous friction coefficient (ξxiξ) = 200 m²/s.
Simulation of Vertical Concrete Barriers
To evaluate the effect of vertical concrete barriers on debris flow parameters, various barrier configurations were considered, and the debris flow was simulated around them. The different layouts are shown in Figure 5.
Since the primary function of these barriers is to reduce the momentum of large particles, particularly coarse clasts and boulders located at the flow front—their dimensions and spacing significantly affect their collective performance. In this study, the barriers were designed with a diameter of 1 m and a height of 2 m. To maximize energy dissipation and particle trapping efficiency, barrier spacing was varied between 2 m and 5 m.
Findings
Debris flow was simulated in the study area using RAMMS under conditions without any control structures along the flow path. For this purpose, a DEM with a cell size of 5 m was applied, which provides relatively satisfactory accuracy for simulating this phenomenon. The simulation results, represented as the total affected area, are shown in Figure 1 using the Google Earth environment to identify the hazardous zones. Although the simulation duration was set at 1500 seconds, the debris flow completely ceased at approximately 940 seconds, as the flow momentum reached zero.
A comparison between Figure 1 reveals that the debris flow significantly affected a considerable number of buildings located near the mountain slope. Therefore, flow-control structures are required in the upstream region to mitigate damage from such events.
Figure 1. Total affected area of the debris flow in Google Earth under conditions without control structures
To estimate the efficiency of vertical barriers as a flow-control structure, debris flow simulations were repeated for the study area with different barrier configurations. In order to compare the results of these configurations with the no-barrier condition and to evaluate their influence on flow parameters, the percentage-change relation (Equation 6) was applied [Fan et al., 2021; Galoie & Motamedi, 2021]:
Equation 6
where R is the percentage change, and P0 and Pn are the values of the same parameter in the no-barrier and barrier conditions, respectively.
Following simulations of each configuration, percentage changes were calculated for two critical parameters of total affected area and total travel distance both of which play a vital role in assessing vulnerable regions. It should be noted that configuration “E” represents barriers installed on the steep upstream slope near the initiation point of the flow, while all other configurations were placed on the gentler downstream slope.
Installing barriers on the steep upstream slope (configuration E) did not significantly improve flow control compared to other layouts. Although the barriers absorbed some kinetic energy upon impact, the flow quickly regained velocity due to the steep gradient, diminishing the effectiveness of the barriers. In this case, the affected area decreased by only 12.3%, and the travel distance by 6.8%, relative to the no-barrier scenario.
By contrast, installing barriers on the gentler downstream slope substantially reduced kinetic energy as particles collided with the barriers, and the lower gradient prevented flow re-acceleration, resulting in quicker flow stoppage. Configurations with irregular, staggered barriers were more effective, as repeated particle collisions enhanced energy dissipation and trapping efficiency. Configuration C, however, showed limited impact since the barriers were aligned in regular rows, leaving free-flowing gaps where particles could pass through without significant interaction. In this case, the affected area decreased by 16.8% and the travel distance by 11.4%.
In configuration B, where barriers were arranged in an upstream-pointing triangular layout, the flow was diverted laterally after colliding with the first row of barriers. This diversion reduced interactions with subsequent rows, thereby diminishing overall effectiveness. Here, the affected area decreased by only 13.1%, and the travel distance by 12.2%.
Among all tested configurations, configurations A and D proved most effective in controlling debris flow and reducing both affected area and travel distance. Given that their results were nearly identical, configuration A, featuring fewer barriers arranged in a downstream-pointing triangular layout was identified as the optimal solution. In this case, the affected area was reduced by 25.1% and the travel distance by 20.8%, which represents a significant improvement. Moreover, further reductions could be achieved by adjusting the number or spacing of barriers.
Figure 2. Simulated debris-flow impact area displayed in Google Earth for the case where the pile group is arranged in a triangular configuration on the lower slope
Figure 2 shows the debris flow simulated with the triangular barrier arrangement. Compared to Figure 1, there is a marked reduction in both affected area and travel distance, such that nearly all buildings located downslope are no longer exposed to risk.
Figure 2. Simulated total affected area in Google Earth with triangular (configuration A, Figure 5) barrier arrangement at the downslope area
Unlike other methods, the use of vertical barriers demonstrated multiple advantages. In this approach, the failure of one or even several barriers only reduces system efficiency without causing total system collapse, whereas wire mesh structures or check dams may fail catastrophically due to dam breaches or mesh ruptures. Additionally, barrier construction is considerably simpler and more cost-effective compared to other methods. Therefore, based on the above findings and numerical modeling results, the vertical barrier method can be regarded as one of the effective and practical approaches for debris flow control.
Discussion
The main driving force of debris flows is the momentum generated by soil and water particles, which are capable of mobilizing very coarse rock fragments. Structural control measures must therefore be able to dissipate the flow’s kinetic energy and prevent its propagation. Conventional methods are generally based on constructing check dams or steel net frameworks; however, such structures may fail under severe debris flows and consequently cause downstream destruction.
The use of vertical piles for dissipating the kinetic energy of debris flows has not previously been applied or evaluated. Nevertheless, the modeling results of this study demonstrated that debris flows can be effectively controlled by such piles. The pile groups have the capacity to significantly reduce the flow momentum and kinetic energy through successive impacts, thereby trapping coarse particles within the inter-pile spaces. In this regard, the number of piles, their arrangement, and the spacing between them play a critical role in determining debris-flow parameters. Although the present research employed uniform pile spacing in all scenarios to facilitate comparison of different configurations, pile performance can be further improved by optimizing inter-pile distances.
Using piles to control debris flows offers several advantages over conventional methods such as check dams. Pile construction is faster and more cost-effective than check dams, and even if some piles fail during flooding, the overall system performance is not compromised, as the remaining piles continue to dissipate flow momentum. Moreover, post-flood clearance and restoration are far simpler compared to the removal of sediments deposited behind check dams.
Since numerical models often rely on assumptions and simplifications in discretizing complex governing equations, potentially introducing numerical errors and deviations from reality, it is recommended that the results of this numerical model be validated using a physical model to further assess pile performance in debris-flow mitigation. It should be noted, however, that the RAMMS model has been extensively applied by numerous researchers worldwide, and its accuracy has been validated, particularly in Europe [RAMMS, 2022]. Despite this, no numerical or laboratory studies specifically addressing the present research topic have been conducted to date, preventing direct comparison of the results with other investigations. Related studies, however, can be found where vertical piles have been applied to influence various sediment-laden flows, dam-break waves, and similar processes. A comprehensive numerical analysis in this context demonstrated that vertical piles play a significant role in reducing flow momentum and wave depth following dam-break events [Fan et al., 2020]. That study revealed how successive interactions of dam-break waves with piles resulted in substantial dissipation of kinetic energy and momentum. Hence, the effectiveness of pile groups in reducing flow momentum and energy can be equally exploited for debris-flow mitigation
Conclusion
The application of vertical pile groups was examined as a practical method for debris-flow mitigation. Among the tested configurations, the triangular arrangement of cylindrical concrete piles with a diameter of 1 m and a height of 2 m, positioned on the lower slopes of mountainous areas, was identified as the most effective strategy compared with other layouts.
Acknowledgments: This research is based on a study project on debris-flow modeling and hazard mitigation conducted at the Institute of Mountain Hazards and Environment Research in China. For the purpose of comparative analysis, part of the project was also implemented in one of the catchments in Iran. The authors sincerely acknowledge the efforts, guidance, and support of the research team, particularly Professor Fan, as well as the Institute’s Computer Center for providing the software license.
Ethical Approval: This article has not been published in any domestic or international journal to date.
Conflict of Interest: The authors declare no conflict of interest with any institutions or individuals. The sole purpose of this paper is to present practical methods in the field of Geographic Information Systems (GIS) and their effective application in water resources management and protection.
Authors’ Contributions: Galoie M (first author), principal Researcher/Methodologist (50%); Motamedi A (second author), Statistical Analyst/Discussion Writer (50%).
Funding: This article is derived from a joint research collaboration between Iran and China. All research-related expenses and software usage fees were funded by the Ministry of Science of China.
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