Research on dynamic state of river-mouth bar under flood condition in the Yura River

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Takaharu Ochi, Keiichi Kanda, Hiroshi Miwa, Huminori Nakamura

Tuesday 30 june 2015

17:36 - 17:39h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics, Poster pitches

Parallel session: Poster pitches: 7B. Sediment - River

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The Yura River is located at the north of Kyoto Prefecture in Japan, topographic changes of river-mouth bar is continuously activated by sediment transport due to river flow and sea wave. On October 2004, a large part of the river-mouth bar was eroded by the flood flow. After that, the river-mouth bar has developed along the right bank only. This situation may cause some problems such as bank erosion, washout of bank protection works and harmful effects on other coastal structures. In order to avoid these problems and risk, it is important to understand the characteristics of the topographic change of the river-mouth bar and its cause, and to propose a control method of the bar geometry. In this study, the effects of the river water discharge and the sea wave height on the geometrical properties of the bar were investigated. As for the bar control, the effectiveness of a spur dike, which can change the flow direction, for erosion of the bar was evaluated by means of flume experiments. The two-dimensional numerical model was also applied to further investigate the effects of spur dike on the bar control. The simulation results were verified against the experimental results. The results are summarized as follows: 1) Although the bar area and volume of the river-mouth bar showed the short-term fluctuations due to flood, they also showed the increase tendency on a long-term basis. The flush condition of the river-mouth bar sediments due to flood does not depend on the width of river-mouth channel. 2) In the experiment without spur dikes, the scour depth of the river-mouth channel became large because the flow converges into the channel. On the other hand, in the experiments with the spur dikes, the erosion of the river-mouth bar became active and the scour depth of the river- mouth channel became small because the spur dikes redirected the flow toward the river-mouth bar. 3) The simulation results showed that the mechanisms of flow which takes a long way around the spur dikes and river bed variation process were clarified by the reproduction calculation of the experiments.