NUMERICAL ANALYSIS ON THE BEHAVIOR OF DRIFTWOOD IN DRIFTWOOD CAPTURING FACILITY

In recent years, river disasters associated with extreme heavy rainfall have frequently occurred, and driftwood that has flowed out from landslides and bank erosion has been captured in the bridge piers, which is one factor that increases flood damages. In Omoto River, Iwate Prefecture, the development plan of the driftwood capturing facility using a channel curving section in a mountainous area was set up for mitigating of driftwood damages in urban area taking advantage of driftwood damages by the typhoon No. 10 heavy rain in August 2016. At present, a structural specifications of the capturing facility that is able to capture the driftwood efficiently by grasping the behavior of the three-dimensional driftwood by hydraulic flume experiments are set. Therefore, in order to analyze the behavior of three-dimensional driftwood obtained by hydraulic flume experiment, the numerical analysis was carried out by applying a numerical calculation model incorporating a driftwood model using the discrete element method to a calculation model of quasi three-dimensional flow. Results suggest that the driftwood in the depth average entered into the catchment reservoir, and there are two types of driftwood such as the driftwood flowing to the slit and the driftwood deposited in the inner band of capturing facility on the bottom flow velocity.