Successive Landslides and Debris Movement in Forested Drainage Basin

1990

S. 299-320

12 Abb., 4 Tab., 4 Lit. Ang.

Unselbständiges Werk

200037159

The interpretation of time-sequential sets ofaerophtos and field investigations were undertaken to clarify the history of successive landslides, hillslope erosion and sediment movement in stream channels. Major climatic events were mostly responsible for large landslides and were the main process of fluvial sediment transport. At least 12 large landslides occurred over the 20-year period from 1961-1981 with a recurrence interval between a year and six years in the study site. Most of the subsequent landslides occurred at the site of former landslide scars. Total debris production for these successive landslides was about 60,000 cubic meters of which less than 50 percent entered the main channel. In the Saru River area, voluminous sediment could be produced by deep-seated landslides and transported during major climatic events. On the other hand, shallow debris and creep were mostly delivered fromthe upslope sites to the main channel in a persistent process. In the Jyurokusen Creek Basin, sediment discharged from landslides could abruptly accumulate in an adjacent downstream channel forming a flood plain during debris torrents. The response of the channels to landslide debris varied in accordance with the rate of sediment production by landslides and the capability of the river flows to transport landslide debris.