Sediment storage by woody debris on a stream bed of a mountainous river channel
1994
Kasai, M. (Kyushu Univ., Fukuoka (Japan). Faculty of Agriculture) | Marutani, T.
Sediment storage is often caused by woody debris on stream beds of mountainous river channels. Woody debris is produced by land slips of mountain slopes that build up a wall structures on stream beds (called a "wall" here). The volume of sediment storage seems to relate to the strength of a wall which consists of many logs. The purpose of this paper is to clarify the relationship between the volume of sediment storage and the strength of a wall according to the wall structure changes along the distance from the log source. Strength of a wall, S, was calculated as the product of cross-point numbers of logs per unit width and the sum of standard deviations (S.D.) in vertical angles and S.D. in horizontal angles of logs included in the wall. The strength of a wall increases to 2.0 x 10(4) at a maximum according to the distance from the log source; then the volume of sediment storage attains 550 cubic meter. The process of building up a wall structure with the debris flow was studied. the wall structure (deposit area and number of logs) and the volume of sediment rocks were measured, as well as the changing diameter distribution and sediment concentration of the debris flow. Strength of the wall and the volume of sediment rocks tended to increase along the distance from the log source. Strength of a wall became greater according to the increment of the velocity of the debris flow with decrements of the volume of sediment rocks in the debris flow
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