210 / 2024-02-27 22:11:59

Effect of driftwood jamming on characteristics of bed deformation around traditional river structure “seigyu”

driftwood,traditional river work,scour,deposition,permeability

Due to global warming, climate change is exacerbating water-related disasters, making them more severe and frequent. In the past several years, water-related disasters caused huge damages in terms of human lives, properties and social activities in Japan. Consequently, Japan has reevaluated its river management standards, emphasizing collaboration with multiple stakeholders and the adoption of various technologies in river basins. Traditional river structures constructed by local residents using natural materials such as wood and stone, offer a lot of advantages. These structures are environment-friendly, cost-effective and allow residents to actively participate in their construction. Seigyu, a kind of crib spur dyke, is a traditional river structure consisting of wooden frames and gabions. It alters flow velocities and directions, and has been installed to prevent river bank from erosion, to enhance the diversity of river environment and so on. There is a high potential to use it for river management as a kind of green infrastructure technology after revitalization.

In actual rivers, the jamming of driftwood at Seigyu is a common phenomenon during floods, which may affect the original hydraulic function of the structure. In this study, laboratory experiments were carried out to investigate the effect of driftwood jamming on the bed deformation characteristics around a Seigyu. The change of the permeability of the front surface of the Seigyu and the location of jammed driftwood were considered as two key factors. In the experiments, various permeabilities were tested for the former factor. While for the latter one, 4 kinds of scenarios were considered, i.e. driftwoods were arranged evenly in the vertical direction (Pattern A), evenly in the horizontal direction (Pattern B), as an impermeable part at the top (Pattern C), and as an impermeable part at the bottom (Pattern D). Through the experiments, the shapes and volumes of scour-deposition, local bed slopes and the amount of Seigyu’s movement were analyzed. The findings revealed that despite differences in permeability and jamming location, the presence of driftwood jams led to increased bed deformations. Interestingly, Pattern C exhibited the most significant deformations, while Patterns A and B generally displayed similar trends with the same permeability.