| Typhoon Etau (Japanese code name: Typhoon No. 10) struck the Pacific side of Hokkaido Island、 JAPAN on August 9、 2003、 especially in Iburi and Hidaka sub prefectures. Flood generated by the typhoon caused landslide and driftwood to wash out in large amounts from mountainous parts of the Saru River basin. The driftwood accumulated in the river channel、 at bridge piers、 and elsewhere. This resulted in some bridges on the Nukabira River、 a tributary of the Saru River、 being washed out and others tilting in the downstream direction. In addition、 there was erosion to many bridge approach roads.[*]Accumulation of driftwood at a bridge causes bridge damage and overflow to outside of river channel、 and the overflow causes human damage、 resident’s property (house、 household effects、 car、 etc.) damage and erosion to bridge approach roads. As this is a major issue in the river disaster prevention、 we researched the relationship between bridge parameters and driftwood accumulation during this flood. In addition、 the cause of bridge damage was considered.[*]As a result、 we can infer about the mechanism of Flood damage to bridges in this case as follows.[*]1) It is difficult to relate length of the shortest span in that bridge to bridge damage. [*]2) There are no differences at the level of damage between bridge located in the upstream and bridge located in the downstream.[*]3) The influence of driftwood accumulation on bridge grows as number of bridge piers increases. |
