Sabo Dam Research Articles

Analysis of The Effectiveness of Sediment Control Structures and River Improvement on The Omu River Post-Earthquake in Sigi Regency

This study aims to analyze the effectiveness of sediment control structures, such as sabo and consolidation dams, and river normalization on sediment control in the Omu River after the earthquake in Sigi Regency on September 28, 2018. The analysis was conducted using the Universal Soil Loss Equation (USLE) method based on average rainfall data over 20 years. Erosion and sedimentation volumes before and after the earthquake were analyzed to understand the changes. The results showed that in 2020, the erosion volume reached 120,700.27 m³/year, and sedimentation was 17,030.81 m³/year, an increase from 2017, which recorded an erosion volume of 91,282.60 m³/year and sedimentation of 12,879.97 m³/year. Sediment transport simulation with daily discharge over 12 years indicated that in Scenario-1, sediment could be reduced by 10.81%, and in Scenario-3 by 23.18%. Meanwhile, simulation with Q100 flood discharge in Scenario-2 showed sediment reduction by 47.18%, and in Scenario-4 by 62.96%. The general conclusion of this study is that sediment control structures and river normalization are effective in reducing sediment volumes. Specifically, the construction of sediment control structures has proven to significantly reduce erosion and sedimentation. This research highlights the importance of structural improvements in mitigating post-disaster erosion impacts. The results of this study can serve as a reference for planning and implementing sediment control in disaster-prone areas. Keywords: sediment control, sabo dam, consolidation dam, river normalization, Omu river

Estimation of bed load sediment rate at sabo dam 2 bangga river

Estimation of bed load sediment rate at sabo dam 2 bangga river

Evaluation of Sabo Infrastructure Using UAV/Drone Technology for Monitoring and Inspection Data (Case Study: Sabo Dam Bakalan, Cangkringan District, Sleman)

The sabo dam serves as a structure positioned along a river branch, intended to manage and contain sediment for either a temporary or permanent duration, functioning as a system to combat potential disasters caused by erosion and sedimentation. Given the significance of sabo infrastructure in mitigating sediment- related calamities, it is essential to uphold and advance these structures through continuous monitoring, necessitating timely access to detection data. However, the inspection and monitoring of sabo buildings present considerable challenges, including the extensive coverage area of the river and the difficulty in accessing various building locations.To address these challenges, alternative approaches are being employed for the inspection and monitoring of sabo buildings. One such approach involves the utilization of drone-based asset survey technology. This technology enables the recording of precise object geometries and the generation of structural information that can be validated on-site, particularly in the context of infrastructure conditions related to sabo dams. By integrating drone technology, it is anticipated that the process of inspecting and monitoring buildings and land areas surrounding sabo dams can be expedited, with increased precision and enhanced safety measures.

Influence of approach shape of debris flow on impact load to open Sabo dam in experiment

Recently, the magnitude of landslide caused by torrential rain and typhoons is increasing in Japan. This high intensity rainfall disaster induces some structural failure of steel pipe open Sabo dams. Thus, current static design loads and impact loads are being considered. To prevent some structural failure of the dam, a new design concept is necessary at the severe load that is exceeding the present design load. However, the influence of debris flow impact load on steel pipe open Sabo dam is not clear to make a design load. The study experimentally approaches a vertical load distribution shape and its time history based on a comparison with a wedge approach shape and a front boulder concentrated shape. The load and moment action of a front boulder concentrated shape debris flow is greater than that of a wedge approach shape. Mechanism making the difference is made clear by observation of vertical detail measurement of impact load.

Factors, variables, and aspects Sabo Dam modelling capacity based on the Purwantoro Sabo Dam index model

Volcanic disaster risk mitigation cannot be perceived as a separating part of disaster management. Sabo Dam technology applied as lahar controller infrastructure that is part of management disaster and widely used in Indonesia. Purwantoro Sabo Dam Performance Index Model estimates the general functionality of a sabo dam in one index number. The simple calculation steps had been made which is conveniently usable and answer further practical demand such as operation and maintenance necessity, rehabilitation – newly construction prioritization decision support system, or emergency inspection aspect. Purwantoro Formula composed variables and factors that can be developed into more practical usage in the outcome approach. Capacity estimation over the Purwantoro Index is used as a disaster management approach to create capacity functions. Reviews of the actual capacity of compatibility of the three hierarchical factors, variables, and aspects are needed. It is carried out using a structural equation model with the partial least square method. The compatibility among the structures and outcome of capacity generates twenty-five grouped by nine components that are under three aspects (physical, regulative, and social) that suit the sabo dam’s potential capacity. The three hierarchical structures of aspect, component, and indicator are valid and appropriate to fulfill the t-test.

SWE Modelling of Debris-flow body-sedimentation and Tail-flow Remobilization in a Check-dam Controlled Gully (Unzen Volcano, Japan) using UAV LiDAR, SfM-MVS

On 13th August 2021 at Unzen Volcano (Japan), an 81 mm.hr-1 peak-rainfall (1486 mm in 2 weeks) triggered series of erosion and deposition features in the Tansandani and the Gokurakudani gullies, all adding up to 57,800 m3 of erosion and 39,600 m3 of deposition. Upstream of the Sabo dam located at the exit of the Tansandani Gully, a large deposit has been visually identified as a potential debris-flow front candidate. However, the absence of direct observation leaves some uncertainty on the process that deposited the material and the magnitude of the flow. In the present contribution, the authors are investigating (1) the role of the debris-flow body in constructing the deposit and (2) the role of the tail of the debris-flow in eroding the fresh deposit. To reach this objective, the authors have combined a field investigation with direct observation, UAV (Unmanned Aerial Vehicle) LiDAR (Light Detection And Ranging) and Photogrammetry, and GIS (Geographic Information System) analysis of the field data. From this data, a 2D hydrodynamic simulation and sediment transport models were applied. The results show that the debris-flow ran beyond the first Sabo dam, with part of the material trapped on both sides of the gully. Afterwards, a central channel connected to sub-channels conveyed the diluted flow, most probably < 25 cm with maximum velocities between 4 to 5 m.s-1 at peak flow. Only the debris-flow phase went over the internal shoulders of the Sabo dam. A lobe occupies the top half of the study area and its deposition has been discussed to be related to the sudden widening of the gully, while the lower half is connected to the base-level created by the check dam.

Large wood remobilization in Asakura (North Kyushu, Japan): Adapting strategies to climate change and rural population depletion

In the aftermath of the heavy rainfall events of 2017 in North Kyushu, Asakura (Japan), driftwood-related disaster risk has proven to be as real as it was in 1933, when wood-laden debris-flow invaded the city centre of Kobe City near Sannomiya station. Despite a temporary truce obtained thanks to extensive Sabo dam constructions, climate change, the return of forest on agricultural land due to rural exodus and an ageing population are once again increasing driftwood hazard and disaster risk. In the face of these novel challenges, new management strategies may need to be considered, and the present contribution aims to propose a new approach to driftwood hazards and disaster risk. For this purpose, the present contribution is analysing the 2D hydrodynamic of scenario-based floods on driftwood deposited after the 2017 heavy-rainfall event in Asakura. The boundary conditions for the simulation were generated using UAV photogrammetry calibrated against existing DEM data to generate a DEM at 25 cm horizontal resolution and an orthophotographs at 5 cm resolution. The results show that with the new river configuration (post-2017), an instantaneous peak flow of 90 m3/s is necessary to flood the areas where the driftwood has stopped with a water depth of >40 cm. This is 9 times the mode discharge calculated from the inlet geometry. The majority of the driftwood is thus not an immediate hazard, and leaving the wood instead of removing it should be considered as a management strategy whenever it is feasible. Recent research in Western Europe and Northern America has already shown the importance of driftwood for biodiversity and wildlife, and combining both environmental and hazards and disaster risk objectives may be a solution. For this purpose, the authors propose that medium-size ditch and artificial “abandoned channels” could be created in order to trap the wood in the floodplain, so that the cost from removing the wood can be alleviated, horizontal trapping could complement vertical trapping at slit dams, and the local wildlife could benefit from the wood decomposition in the floodplain.

The Prediction of Debris Flow Based on Eruption and Rainfall Event for River Infrastructure Mitigation: Study Case Opak River, Sleman Regency

Mount Merapi is a volcano active in Indonesia. The eruption that occurred in 2010 was a major eruption with a return period of 100 years. Dominant debris to the Opak – Gendol Watershed; the biggest debris flood occurred in 2010 – 2011. One of the disaster mitigations on the Opak River is the Sabo Dam infrastructure. Currently, in the upper reaches of the Opak River, there are 5 Sabo Dams. In 2022, 2 additional Sabo Dams were built, namely OP RRC4 and OP RRC3a. This study will be used modelling 2D HEC-RAS Non-Newtonian before the construction of 2 Sabo Dams and after the construction of 2 Sabo Dams with river geometry measured in 2020 and flood discharge as measured from rainfall triggering debris flow on 03 January 2011, from this rainfall a 6-hour rain distribution was carried out using the PSA coefficient to be input in the HEC-HMS, the hydrological parameters used on 03 January 2011, were used to calculate the Q100 flood discharge. The results of modelling at the observation point using the Q100 showed that the elevation of the debris flow after the presence of the new Sabo Dam series could be reduced by up to 47.21 %, Sabo Dam effectively reduces the rate of debris flow to reduce the potential debris flood.

Comparison of River Stability using 2D HEC-RAS Newtonian and Non-Newtonian Flow Modelling (Case Study: Design of Sabo Dam in the Namo River Basin, Sigi Regency, Indonesia)

River stability is a crucial factor in assessing and managing risks associated with natural disasters, such as debris flows. This study compares river stability using two-dimensional (2D) HEC-RAS modeling with both Newtonian and Non-Newtonian flow approaches. Typically, non-Newtonian flow models are used for modeling debris flows. However, this study examines how the differences in modeling using Newtonian and non-Newtonian flows affect the potential for debris and the stability of the river system. The study focuses on the Namo River located in Sigi Regency, Indonesia, which is prone to debris flow events. In order to mitigate debris flows in the Namo River, three Sabo Dams and one Consolidation Dam have been built. The conditions before and after the construction of the Sabo Dam and the Consolidation Dam will also be modeled in this study. By comparing the results obtained from these modeling techniques, the study aims to provide a comprehensive understanding of river stability and improve the accuracy of debris flow prediction. The findings from this study have significant implications for the management and planning of the Namo River and similar river systems, enabling effective measures to minimize the potential risks associated with debris flow events.

Modeling of 2D Hec-Ras Simulation on Debris Flow Analysis on Morphological Changes of the Omu River, Sigi Regency, Central Sulawesi

Landslide is a natural disaster that shows if the soil structure in the area is unstable, where landslides occurred was in the upper part of the Omu River. When there is heavy rain, landslide material in the form of debris is carried into the river flow increasing the concentration of sediment in the river which causes debris flow. Debris flow has a destructive power that can cause damage to buildings, utilities and can threaten the lives of people in the area. This study aims to NonNewtonian method analysis models in the HEC-RAS (2D) 6.4 software. The findings reveal that debris flow has a significant impact on the morphological stability of the Omu River, stability of the riverbed and bank erosion, which can disrupt the overall river system stability. One effective strategy for mitigating the potential risks of debris flow is the construction of the Sabo Dam on the Omu River. This dam is designed to capture and retain debris sediment, preventing it from being carried downstream. By doing so, it helps to maintain the morphological stability of the Omu River, riverbed, and reduce the impact of destructive debris flow forces.

Proposed Countermeasures against Woody Debris Damage Considering Runoff Characteristics

In recent years, a combination of forestry decline and global climate change has led to heavy rains and landslides in Japan that have caused extensive forest damage through woody debris outflow. The current configuration of impermeable sabo dams has insufficient capacity to capture woody debris under these conditions; therefore, improvements to permeable sabo dams, which have a high woody debris capture capacity, are underway; these sometimes involve the addition of steel fittings. In this study, we examined the effectiveness of such measures in consideration of the factors affecting woody debris flow. After reviewing a woody debris outflow that occurred during a heavy rain disaster in northern Kyushu, Japan, we propose woody debris countermeasures that consider basin and runoff characteristics. Our results indicate that woody debris flow occurs later than sediment flow. Therefore, we performed experiments to test the effectiveness of various methods to slow water flow using the terrain conditions at the nearest valley outflow point. Finally, we propose woody debris countermeasure policies considering basin characteristics, to promote the future preservation of river basins.

Continuous debris flow monitoring using DFLP and LVP on Sakura-jima Island

Since 2010, numerous debris flows have occurred on Sakura-jima Island due to rainfall events that occurred after extensive ash deposition associated with volcanic activity. The study area included the Nojiri and Arimura rivers in the southwestern and southeastern parts of Sakura-jima, respectively. Debris flow monitoring systems consisting of loadcell and pressure sensor (DFLP) were installed to evaluate characteristics of moving weight and so on during debris flows. The systems were installed at the Arimura River No. 3 sabo dam in June in 2012 and at the Nojiri River No. 1 sabo dam in 2014. In addition, LVP (Load, Vibration and Pressure) sensors consisting of loadcells and accelerometers for measuring vibration and pressure were installed on the riverbed for debris flow detection. Modified LVP systems were installed at the Nojiri River No. 7 sabo dam in February in 2015, and at the Arimura River No. 3 sabo dam in October in 2016. Interesting characteristics of debris flows were obtained by the DFLP and LVP systems. The findings showed that the sediment concentrations of both the coarse and the suspended and liquid phases could be estimated by the DFLP systems, and several patterns of debris flows were observed by the LVP systems.

Sediment control and logs capturing in sand pocket with combination of sabo dam with large conduit and iron bars

In the Otoishi River, a tributary on right side of the Akatani River in the Chikugo River basin, a large amount of sediment and woody debris were deposited on riverbed due to the sediment disaster caused by the heavy rainfall in northern part of Kyushu Region on 5th to 6th July in 2017. As one of countermeasures to control the outflow of sediment and woody debris to the Akatani River, a sand pocket is planned with the sabo dam with large conduit parts and the log broom works. In this study, hydraulic model test and flume test were carried out to obtain knowledges for design of the sand pocket. Iron bars are installed vertically at the upstream front of the large conduit parts for capturing sediment and logs, and those intervals are desirable to be set in consideration of sediment diameter and sediment movement without the dam. Besides, it is necessary to consider capturing function and flow characteristics such as shockwave when the log broom works is planned in setting of layout and dimensions.

A simplified numerical model for evaluating sediment control by open-type sabo dams in the Joganji River basin

The present study proposes a method to estimate sediment runoff by introducing a dam function of the relationship between inflow sediment and sediment runoff through a slit dam. The model can process rainfall runoff, sediment yield and runoff of a mountainous basin, and the model is applied to the upper reaches of the Joganji River basin, which is known for its huge amount of sediment runoff and intense bed variation because of the sediment yield caused by the earthquake in 1858. The performance of the calculations of sediment control of the slit dam is evaluated by the model. The result indicates that sediment deposition is significantly changed by sediment runoff. The proposed method can be expected to evaluate sediment transport with sabo dams on a basin scale.

Propose of Design Method on Level II load of open Sabo dam

This study presents a load model of the Level II design for a steel pipe open Sabo dam. The Level II design is associated with a lower occurrence frequency than the conventional design concept, to the performance of debris flow trapping efficacy against higher discharge caused by heavy precipitation in recent years. A dynamic load model reveals experimental observations, and static models similar to the conventional design load models are evaluated from the viewpoint of a rational load. Dynamic and elastoplastic analyses are conducted for one structure, and three types of basin area models utilized Level II load models using a dynamic load. The safety evaluation results confirm that the design load models are composed of each other.

Influence of approach shape of debris flow on impact load subjected to open Sabo dam under an overturning experiment of open Sabo dam

Recently high intensity rainfall disaster induces some structural failure of steel pipe open Sabo dam. To prevent such failure of the dam, a new design concept is necessary at the severe load exceeding the present design load. However, influence of debris flow impact load on steel pipe open Sabo dam is not clear to make a design load. The study experimentally approaches a vertical load distribution shape and its time history based on comparison with a wedge approach shape or a front boulder concentrated shape. The load and moment action of a front boulder concentrated shape debris flow is greater than that of a wedge approach shape. Mechanism making the difference is made clear by observation of vertical detail measurement of impact load.

Hydraulic model test on channel shifting and yielding woody debris on the fan after sediment disaster in the past

The re-movement of sediment and woody debris in torrents after huge sediment transport in the past could cause new flood and sediment disasters due to heavy rainfall events. However, it is not clear how re-movement of logs effects on bed variations such as bars and river channel divergence. In present study, hydraulic model tests were carried out referring to the magnitude of floods, that was over the plan size, in Tottabetsu River basin in August in 2016. These tests include different magnitudes of flood, suppling logs from bed/side bank erosion, and existence of sabo facilities. The key results were as follows: The presence of logs by bed/side bank erosions influences on the patterns of flows and sediment transport, because deposition of logs affects formation of bars. Difference of the magnitudes of the floods affects the activeness of the interaction between logs and sediment transport. In additions, the locations and slits of the sabo dam need to consider hydraulic conditions and characteristics of woody debris for appropriate control of sediment and woody debris.

Numerical modeling of debris flows using basic equations in generalized curvilinear coordinate system and its application to debris flows in Kinryu River Basin in Saga City, Japan

Each year, structures installed in rivers and valleys (e.g., bank protections, bridges, and sabo dams) are damaged by debris flows; therefore, it is necessary to predict the flow characteristics of debris flows accurately to design river and valley structures that are robust against such debris flows. In recent years, several two-dimensional models have been developed to simulate debris flow. However, the basic equations in the numerical simulation models are in the Cartesian coordinate system, and the shape of each numerical analysis grid is square or rectangular. It is impossible to use numerical grids that match the horizontal shape of the river or valley structures, such as bank protections and sabo dams, when employing square or rectangular grids. This makes it difficult to calculate the fluid forces acting on river or valley structures. In this study, the basic equations of debris flow are provided in the generalized curvilinear coordinate system and a numerical simulation model of debris flow designed using an orthogonal curved grid along the horizontal shape of rivers and valleys is developed. Numerical simulations of a periodical meandering valley are conducted using the basic equations in the generalized curvilinear and Cartesian coordinate systems; the difference between the two results is discussed. Further, numerical simulations of the debris flow that occurred in the Kinryu River Basin in Saga City, Japan, in 2019 are performed using the basic equations in the generalized curvilinear and Cartesian coordinate systems, and the difference between the two simulation results is discussed. The numerical simulation results of debris flow in a periodical meandering channel suggest a slow propagation of debris flow when equations in the Cartesian coordinate system are used; this is attributed to the rough boundaries of debris flow when a square grid is used, which causes numerical energy dissipation that does not exist physically. The inundation areas and land surface deformation of debris flow in Kinryu River Basin were reproduced well by the developed numerical analysis model; the basic equations were written in the generalized curvilinear coordinate system. The development and decrescence of debris flows were reproduced using the developed model; the first debris flow in Kinryu River Basin was stopped in the upstream mild slope area, while the second flowed into the residential area. Reproducing the flow depth, velocity, and discharge could be improved by the model using basic equations in the generalized curvilinear coordinate system, as compared with those reproduced using basic equations in the Cartesian coordinate system. When the Cartesian coordinate system was used, the volume of the debris flow was evaluated to be small and the travel distance of the debris flow was evaluated to be short; thus, the debris flow does not arrive at the residential area and the risk of debris flows is underestimated.

Effect of dent deformation of a joint of steel pipe on global failure of steel pipe open sabo dam

Effect of dent deformation of a joint of steel pipe on global failure of steel pipe open sabo dam

Load measurement experiment of a hangover-type driftwood catchment on an existing Sabo dam

Load measurement experiment of a hangover-type driftwood catchment on an existing Sabo dam