Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 17, 1923-1938, 2017
https://doi.org/10.5194/nhess-17-1923-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
14 Nov 2017
Relationship between the accumulation of sediment storage and debris-flow characteristics in a debris-flow initiation zone, Ohya landslide body, Japan
Fumitoshi Imaizumi1, Yuichi S. Hayakawa2, Norifumi Hotta3, Haruka Tsunetaka4, Okihiro Ohsaka1, and Satoshi Tsuchiya1 1Faculty of Agriculture, Shizuoka University, Shizuoka, 422-8529, Japan
2Center for Spatial Information Science, The University of Tokyo, Kashiwa, 277-0871, Japan
3Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-8657, Japan
4Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, 305-8572, Japan
Abstract. Debris flows usually occur in steep mountain channels and can be extremely hazardous as a result of their destructive power, long travel distance, and high velocity. However, their characteristics in the initiation zones, which could possibly be affected by temporal changes in the accumulation conditions of the storage (i.e., channel gradient and volume of storage) associated with sediment supply from hillslopes and the evacuation of sediment by debris flows, are poorly understood. Thus, we studied the relationship between the flow characteristics and the accumulation conditions of the storage in an initiation zone of debris flow at the Ohya landslide body in Japan using a variety of methods, including a physical analysis, a periodical terrestrial laser scanning (TLS) survey, and field monitoring. Our study clarified that both partly and fully saturated debris flows are important hydrogeomorphic processes in the initiation zones of debris flow because of the steep terrain. The predominant type of flow varied temporally and was affected by the volume of storage and rainfall patterns. Fully saturated flow dominated when the total volume of storage was  <  10 000 m3, while partly saturated flow dominated when the total volume of the storage was  >  15 000 m3. Debris flows form channel topography which reflects the predominant flow types during debris-flow events. Partly saturated debris flow tended to form steeper channel sections (22.2–37.3°), while fully saturated debris flow tended to form gentler channel sections ( <  22.2°). Such relationship between the flow type and the channel gradient could be explained by a simple analysis of the static force at the bottom of the sediment mass.

Citation: Imaizumi, F., Hayakawa, Y. S., Hotta, N., Tsunetaka, H., Ohsaka, O., and Tsuchiya, S.: Relationship between the accumulation of sediment storage and debris-flow characteristics in a debris-flow initiation zone, Ohya landslide body, Japan, Nat. Hazards Earth Syst. Sci., 17, 1923-1938, https://doi.org/10.5194/nhess-17-1923-2017, 2017.
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Short summary
Debris flow characteristics in the initiation zones are poorly understood because of the difficulty in monitoring. We studied the relationship between the flow characteristics and the accumulation conditions of the storage in an initiation zone of debris flow. Our study clarified that both partly and fully saturated flows are important processes in the initiation zones of debris flow. The predominant type of flow varied temporally and was affected by the volume of storage and rainfall patterns.
Debris flow characteristics in the initiation zones are poorly understood because of the...
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