著者

田村 俊和 加藤 仁美 松林 武 古田 智弘 チャタリジ デボスリ 李 穎

出版者

日本地形学連合

雑誌

地形 (ISSN:03891755)

巻号頁・発行日

vol.23, no.4, pp.675-694, 2002-10-25

参考文献数

17

被引用文献数

4

---

This paper presents the results of observations at different hilly watersheds in Sendai area in different periods with the aim at contributing to the study of pipe-flow initiation, pipe-outlet shift and surface-slide occurrence on valley-head slopes with increase in rainfall. The critical rainfall for the initiation of pipe-flow at channel-heads is variable with rainfall characteristics including antecedent precipitation, and with micro-topographic, pedologic and geologic conditions of the valley-head. Soil pipes at more upstream position begin to operate when total rainfall increases, for instance, in a 2 or 3 hour storm with the intensity of more than 5-10 mm/h without antecedent precipitation. This is considered the results of stepwise expansion of contributing areas and contributing soil-mass. Sediment discharge and opening of new pipes as results of intra-pipe erosion and small-scale failures occur in the case of an almost yearly storm, i.e., several tens of millimeter of total rainfall with over 10 mm/h of maximum intensity After a storm, pipe-flow continues longer on the hilislopes where deep weathering crust of andesite is distributed than on the hilislopes composed of semi-consolidated siltstone or sandstone. It is considered to be due to water-supply from saprolite to soil pipes. Surface slides are triggered with an intense rain of about 30 mm/h following to a 10 to 15 hour storm with the intensity over 10 mm/h on lower hillslope segments, particularly immediately below the convex break of slope at the lower margin of head hollows. Stronger storm, for instance, a 80 mm/h rain following to a 3 hour storm reaching to 170 mm, induces surface slides on upper hillslope segments, particularly headmost walls. Pipe outlets are observed on any slide scar. These phenomena suggest that working pipe network is switched several times with the increase of both total rainfall and rainfall intensity.