Journal of the Japan Society of Erosion Control Engineering, Vol.62,No.2,2009

Estimation of debris flow induced by a deep]seated landslide at the Funaishi river basin, Kagoshima prefecture in Japan

Nagazumi TAKEZAWA, Taro UCHIDA, Ryuji SUZUKI and Keiji TAMURA


Abstract

Debris flow was induced by a deep]seated landslide on July, 2007 in the Funaishi River basin, Kagoshima Prefecture in Japan. We made field surveys at this site and estimated flow velocity and flow depth of the debris flow based on field observation, the stability analysis of steel cell of right wing section, marks of steel pipe generated by collision of gravel, and marks of superelevation of debris flow. It can be estimated that the flow depth was 3.3`5.0m and the flow velocity is around 6`8 m/s in Sabo dam site and 2.1`14.3 m/s in flow down section. The flow depth equal to approximately half of slope failure depth. The peak discharge of debris flow was estimated at the Sabo dam site and flow down section.
We also compiled the flow depth and flow velocity by using the investigational data of debris flow induced by a deep]seated landslide and observational data of the mountain stream where the debris flow occur frequently. It was found that the flow velocity and flow depth of debris flow induced by a deep]seated landslide is larger than that of observed debris flow induced by removal of unstable sediment on stream bed. However, flow velocity of debris flow in the Funaishi River basin was an exception. Peak discharge of debris flow induced by a deep]seated landslide is about from 10 to 100 times as large as that of peak discharge of debris flow induced by removal of unstable sediment on stream bed.

Key wordsFdeep]seated landslide, debris flow, funaishi river, steel cell


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