Experimental Study of Morphological Changes and Flow Structure around the Vegetated Groyne

There are many steep rivers in Japan, one of them is Shigenobu river, and the water pressure at the time of flooding is severe. This study focuses on clarifying the vegetated groyne not only to prevent scouring and sedimentation problems but also to optimize for ecosystems and landscapes, which cuts the upper half of the existing groyne constructed and installs a permeable part at the top of it. In this research, investigation of the more efficient vegetated groyne was carried out. The vegetation has been represented as the wooden bar with setting various sizes (diameter of the wooden), changing the density of the vegetation part to be installed, with setting different conditions. The flow visualization and bed changes are the two components which analysed. The measurements in the laboratory flume were characterized by observation of flow structures with particle image velocimetry. The results show that the effect becomes vegetated groyne, the flow rate difference with the inner side of the river has been stabilized. Sediment accumulation and local scouring are reduced, and clearly, there is an effect of suppressing excessive scouring and sedimentation as compared with the existing groyne. With paying attention to the area ratio of the wood rod in the upper part of the groyne, the effect of suppressing riverbed fluctuation was more demonstrated when 1/5 than 1/10. Moreover, for the diameter of the wood stick, it was revealed that the vegetated groyne with the diameter of 8 mm and 5 mm exerts more effect than 10 mm