Presentation Information
[O12-P104]Design of high-capture-capacity Sabo dams ~Based on comparison between impermeable type and permeable type~
*Sudo Shintaro1 (1. Meikei High School)
Keywords:
sediment trapping,debris flow,flood control
In recent years, the number of sediment disaster occurrences has been on the rise. Against this backdrop, erosion control dams (sabo dams) constructed during the period of high economic growth are approaching the end of their service lives, making renovation and repair an urgent priority. To contribute to the critical challenge of sustainable sediment disaster countermeasures, this study aimed to evaluate the performance of permeable and impermeable sabo dams using experimental flumes, and to propose a sabo dam design with high sediment trapping efficiency and reduced maintenance frequency.
Drawings were created using Fusion 360, and four types of dam models — impermeable, permeable, Type A, and Type B — were produced using a 3D printer. Each model was installed at a point 100 cm from the upstream end of a flume measuring 13 cm in width and 6 cm in height, with the flume tilted at 15 degrees and set on an experimental table. In each trial, 1 kg of river sand and 10 chopstick pieces cut to 5 cm in length were released down the flume, and the weight of untrapped sediment and the number of untrapped chopstick pieces were measured. This procedure was repeated four times. The river sand and chopstick pieces trapped by the dam were not removed between trials; instead, after each trial, 0.2 kg of sediment was released while water was flowing for one minute.
In the flume experiment using the impermeable sabo dam model, 0.75 kg of river sand was trapped in the first trial. The amount of trapped sand subsequently decreased with each trial: 0.45 kg, 0.31 kg, and 0 kg. The number of chopstick pieces trapped was approximately 1–2 per trial. In contrast, the permeable sabo dam model trapped 0.45 kg of river sand in the first trial, and 0.6–0.75 kg in the second trial onward. The number of chopstick pieces trapped was 8–10 per trial. Thus, compared to the impermeable type, the permeable sabo dam has been found to have a higher wood capture capacity, while also maintaining a sustained sediment retention effect.
In the flume experiment using the self-designed Type A sabo dam, based on the results of the existing experiments, the amount of trapped river sand was 0.4 kg in the first trial and 0.6 kg in the second through fourth trials, and all 10 chopstick pieces were trapped in all four trials. In the experiment using the Type B sabo dam, the amount of trapped river sand was 0.3 kg in the first trial and 0.6–0.8 kg from the second trial onward, with 8–10 chopstick pieces trapped per trial. Neither Type A nor Type B showed the sharp decline in performance observed in the impermeable type.
The impermeable sabo dam exhibits high trapping capacity against a single debris flow, but its sediment trapping performance deteriorates markedly as the number of events increases. This is thought to be due to the diminishing elevation difference between the top of the dam and the riverbed, leading to overflow. Therefore, regular dredging is essential to maintain its effectiveness. The permeable sabo dam, on the other hand, is able to maintain stable trapping performance even after approximately four debris flow events. This is attributed to the formation of a pseudo-wall as wooden pieces become lodged in the lattice structure of the dam.
Type A, designed to incorporate the advantages of both the impermeable and permeable types, demonstrated high trapping performance for both river sand and chopstick pieces, suggesting it may also perform well against actual debris flows. However, concerns remain regarding structural strength and vulnerability to erosion due to its streamlined form. Type B, compared to Type A, features a less pointed tip and a structure designed to deflect water flow, offering greater structural stability and higher potential for practical implementation in terms of ease of maintenance and durability. Furthermore, since both Type A and Type B adopt the slit structure of the permeable type, they do not block the movement pathways of aquatic organisms, and are therefore expected to minimize impacts on river ecosystems.
Going forward, it will be necessary to conduct larger-scale experiments using the Type B sabo dam to verify its sediment and driftwood trapping effectiveness, and to examine the costs associated with installation and maintenance.
Drawings were created using Fusion 360, and four types of dam models — impermeable, permeable, Type A, and Type B — were produced using a 3D printer. Each model was installed at a point 100 cm from the upstream end of a flume measuring 13 cm in width and 6 cm in height, with the flume tilted at 15 degrees and set on an experimental table. In each trial, 1 kg of river sand and 10 chopstick pieces cut to 5 cm in length were released down the flume, and the weight of untrapped sediment and the number of untrapped chopstick pieces were measured. This procedure was repeated four times. The river sand and chopstick pieces trapped by the dam were not removed between trials; instead, after each trial, 0.2 kg of sediment was released while water was flowing for one minute.
In the flume experiment using the impermeable sabo dam model, 0.75 kg of river sand was trapped in the first trial. The amount of trapped sand subsequently decreased with each trial: 0.45 kg, 0.31 kg, and 0 kg. The number of chopstick pieces trapped was approximately 1–2 per trial. In contrast, the permeable sabo dam model trapped 0.45 kg of river sand in the first trial, and 0.6–0.75 kg in the second trial onward. The number of chopstick pieces trapped was 8–10 per trial. Thus, compared to the impermeable type, the permeable sabo dam has been found to have a higher wood capture capacity, while also maintaining a sustained sediment retention effect.
In the flume experiment using the self-designed Type A sabo dam, based on the results of the existing experiments, the amount of trapped river sand was 0.4 kg in the first trial and 0.6 kg in the second through fourth trials, and all 10 chopstick pieces were trapped in all four trials. In the experiment using the Type B sabo dam, the amount of trapped river sand was 0.3 kg in the first trial and 0.6–0.8 kg from the second trial onward, with 8–10 chopstick pieces trapped per trial. Neither Type A nor Type B showed the sharp decline in performance observed in the impermeable type.
The impermeable sabo dam exhibits high trapping capacity against a single debris flow, but its sediment trapping performance deteriorates markedly as the number of events increases. This is thought to be due to the diminishing elevation difference between the top of the dam and the riverbed, leading to overflow. Therefore, regular dredging is essential to maintain its effectiveness. The permeable sabo dam, on the other hand, is able to maintain stable trapping performance even after approximately four debris flow events. This is attributed to the formation of a pseudo-wall as wooden pieces become lodged in the lattice structure of the dam.
Type A, designed to incorporate the advantages of both the impermeable and permeable types, demonstrated high trapping performance for both river sand and chopstick pieces, suggesting it may also perform well against actual debris flows. However, concerns remain regarding structural strength and vulnerability to erosion due to its streamlined form. Type B, compared to Type A, features a less pointed tip and a structure designed to deflect water flow, offering greater structural stability and higher potential for practical implementation in terms of ease of maintenance and durability. Furthermore, since both Type A and Type B adopt the slit structure of the permeable type, they do not block the movement pathways of aquatic organisms, and are therefore expected to minimize impacts on river ecosystems.
Going forward, it will be necessary to conduct larger-scale experiments using the Type B sabo dam to verify its sediment and driftwood trapping effectiveness, and to examine the costs associated with installation and maintenance.