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HYDRAULIC ANALYSIS OF SEDIMENT TRANSPORTATION IN YAMADA WEIR LOCATED IN CHIKUGO RIVER, JAPAN

The Yamada Weir, located in the middle region of the Chikugo River and known as the rivers of rampage, is a fixed weir that was constructed over 200 years ago. The Yamada Weir has unique structure in that the weir body is installed obliquely to the flow direction of the river, and it is structured to guide water to the intake gate while reducing the water force by overflowing the weir body in case of flooding. In addition, the weir requires no electric power for water intake and is easy to maintain and manage. Owing to these structural considerations and durability, a weir modeled on the Yamada Weir was built in Afghanistan. This weir greatly contributed to the irrigation project in Afghanistan. Therefore, the Yamada Weir has received great attention, and its application to developing countries is now required. However, the weir constructed in Afghanistan has been suffering from sediment inflow to the canal; it was difficult to reproduce its hydraulic phenomena simply by mimicking the structure of Yamada Weir. Moreover, although it is necessary to understand the hydraulic characteristics of Yamada Weir for the application, hydraulic studies were not conducted previously. Therefore, in this research, a hydraulic analysis of sediment transport was conducted using a two-dimensional depth-averaged model in the Yamada Weir to understand its characteristics of flow and sediment discharge. Wet and dry schemes were utilized to reproduce the overflowing water on the weir body. After calculating the flow field, the riverbed variation was analyzed to evaluate the function of sediment flushing. The results showed that three waterways have the function of sediment flushing. In addition, not only these structures but also the construction site contributed to avoiding sediment discharge to the water intake. These results contribute to the application of Yamada Weir in developing countries in the future.