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Water 2019, 11(1), 17; https://doi.org/10.3390/w11010017

Evaluating Factors for Controlling Sediment Connectivity of Landslide Materials: A Flume Experiment

1
Institute of Global Innovation Research, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8538, Japan
2
Toa Grout Kogyo Co. Ltd., Yotsuya, Shinjuku-ku, Tokyo 160-0004, Japan
3
Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
4
Sustainability Research Centre, University of the Sunshine Coast, Sippy Downs, QLD 4556, Australia
5
Mountain Societies Research Institute, University of Central Asia, Bishkek 720001, Kyrgyzstan
*
Author to whom correspondence should be addressed.
Received: 6 November 2018 / Revised: 17 December 2018 / Accepted: 19 December 2018 / Published: 21 December 2018
(This article belongs to the Special Issue Landslide Hydrology)
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Abstract

Connectivity of landslide sediment to and within fluvial systems is a key factor affecting the extent of mobilization of hillslope material. In particular, the formation of landslide dams and the transformation into landslide-induced debris flows represent “end members” of landslide sediment mobility. To quantify sediment connectivity, we developed a two-segment flume representing tributary inflow and the main channel. Mobility of sediment was examined by combinations of various topographic factors, such as tributary inflow angle (0 to 90° in 30° increments) and main channel gradient (10° and 15°), as well as water content of sediment (0 to 100% in 20% increments). We also examined differences of mobility among sediments derived from various lithologies (sand and shale, pyroclastic sediment, weathered granite, and weathered sedimentary rock). Mobility of sediment differed, depending on the water content of sediment, particularly less than saturation or greater than saturation. When all types of unsaturated landslide sediments entered the channel at inflow angles of 60° and 90°, substantial deposition occurred, suggesting the formation of landslide dams. At low inflow angles (0° and 30°) in a steep channel (15°), >50% of landslide sediment was transported downstream, indicating the occurrence of a debris flow. The amount of sediment deposited at the junction angle was greater for pyroclastic sediment followed by weathered granite, weathered sedimentary rock, and finally, sand and shale. Our connectivity index suggests that a threshold exists between landslide dam formation and debris flow occurrence associated with topographic conditions, water content, and types of sediment. View Full-Text
Keywords: debris flow; landslide dam; flume experiment; hydrogeomorphic conditions; connectivity debris flow; landslide dam; flume experiment; hydrogeomorphic conditions; connectivity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Kharismalatri, H.S.; Ishikawa, Y.; Gomi, T.; Sidle, R.C.; Shiraki, K. Evaluating Factors for Controlling Sediment Connectivity of Landslide Materials: A Flume Experiment. Water 2019, 11, 17.

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