EXPERIMENTAL STUDY ON ACCUMULATION OF CEDAR AT THE BRIDGE

Abstract

 This paper presents an experimental approach to investigate the accumulation process of cedar at the bridge. Recently, it is frequently confirmed damage resulting from driftwoods in Japan. For example, Typhoon No. 10 in August 2016 caused flooding of Omoto River. It was a possibility of similar disaster in Akita Prefecture which has a lot of cedars. The hydraulic model experiments were carried out using a bridge model at Omoto River. The scale was 1/180. It based on the width of Omoto River and the water channel. The cedar rod was used for driftwood model. In the experiment, we focused on the number of driftwood accumulation at the bridge and changed in the water level on the upstream and downstream sides of the bridge. At that time, several patterns were prepared regarding the length of the driftwood, the average length of the mixed driftwood, and the flow rate as comparison objects. In conclusion, the experiment shows that the longer the driftwood length the larger the amount accumulation at bridge. This tendency was also observed in the mixed driftwood experiment. However the length of driftwood were different, water level was not changed. And the time which was taken to stop the rise of water level did not change due to the difference of driftwood length. In the experiment of the flow late, the ratio of driftwood accumulation was increased with the increase of the flow rate. In addition, it was suggested that flow velocity related to driftwood accumulation.