Vol.8 (2018) No. 1 ISSN: 2088-5334 Experimental Study of Morphological Changes and Flow Structure around the Vegetated Groyne Pratiwi Aziz # , Akihiro Kadota * # Graduate School of Science and Engineering, Ehime University, 3, Bunkyo-cho, Matsuyama, 790-8577, Japan E-mail: pratiwi_aziz@yahoo.com *Department of Civil and Environmental Engineering, Ehime University, 3, Bunkyo-cho, Matsuyama, 790-8577, Japan E-mail: akado@cee.ehime-u.ac.jp Abstract— 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. Keywords— Flow visualization; morphological changes; vegetated groyne; Shigenobu river. I. INTRODUCTION Rivers are something related to the interests of many people and have been regarded as social goods from long ago. Various river maintenance managements have been carried out until now, to keep it in accordance with its function. The sedimentary content and the quality of water were influencing the condition of the river. There are three processes, erosion, transport and deposition that are interacting along the river from the upstream to downstream of the river. The velocity of water an important role in the erosion activity and sediment production, the velocity depends on the intensity of rainfall [1], [2]. The distribution of rainfall, the river discharge, flow rate and amount sediment production were interdependencies between each other. The river discharge rate was vital in the aspect of flood controls, stabilization or development of the river [1]. There are many steep rivers in Japan, one of them is Shigenobu river flowing through Matsuyama, Ehime. It makes the water pressure at the time of flooding to be severe. So, the groyne has been established as one of river construction methods against this severity. The characterized rivers in Japan are considerably steep gradients due to the narrow and mountainous topography of the country. Groyne is a river structure installed in a form protruding from the riverbank to reduce the flow velocity in the vicinity to the river and change the flow direction. On one side, the groynes enhance the velocity in the main channel. On the other hand, a slow flow zone during submerged flow conditions, or either dead zones in the region between the groynes during emerged conditions. This velocity difference leads to the formation of a mixing layer, exchange of mass and momentum between the groyne fields (slow), and the main channel (fast) takes place [3]. The flow velocity and turbulence structure in the rivers can be altered with vegetation [4]. Therefore, it can influence the bed morphology and the sediment transport [5]. The effect of vegetation typically depends on the flow characteristics, vegetation flexibility, and density [6], [7], [8]. This study focuses to be 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. By lowering the height of 99