2006年11月フィリピン共和国マヨン火山で発生した泥流による山麓部の深掘現象

抄録

The area around Mt. Mayon in Albay Province Philippines was affected seriously by large mudflow caused by heavy rainfall of the typhoon 21 in Nov. 2006. The loss of human lives amounted to 1,300 deaths and many houses, infrastructures were damaged. After the disaster, an urgent survey conducted by a research team dispatched by Ministry of Land Infrastructure and Transportation Japan revealed that all of the riverbeds in the mountain foot area where mudflow passed were scoured deeply and widely in spite of the gentle slope, which was around 3-4 degree. Maximum depth of the scouring reached to 10 m, and maximum width reached to 30-50 m. It was remarkable that the gradient of the sections where we found the deep scouring was too gentle to result in such a deep scouring. We tried to clarify this mechanism of the deep scouring by a numerical riverbed fluctuation model to refer to further counter measures. Due to lack of data in detail such as rainfall data in upper stream and the latest map to know the condition of catchment area, it was impossible to know an exact peak discharge and a hydrograph, so it didn't allow us to say anything quantitative. However, our result infers that the very low sediment concentration in the subsequent flow and the fine and loose material of the sediment in riverbed might cause the deep scouring.