抄録
There are many experimental approaches, field investigations and numerical calculations for movements of woods in a clear water and debris flow. However, treatments and evaluations for accumulated logs and interactions between a main flow and logs are not fully developed. In mountainous torrents, the logs yielding from slopes and stream beds depend on the condition of previous and present forest stands. Mitigations for woods need to be conducted taking into account tree species such as conifer and broad-leaf trees and shapes such as root swells and crown. In the present study, we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width. Conifer and broad-leaf tree are considered as floating and submerged solid phase, respectively. Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate flow characteristics of clear and debris flow with woods. Debris flow is specified as flow with clear water and sediment mixture layers on a rigid bed, whose slope is 0.045. Preliminary experimental data, which suggest that influences of specific weight on logs movements are significant, has been obtained to evaluate those experimental results such as movements of floating and submerged woods and multi-layer consisted of woods and debris flow. However, detail considerations and collections of flume data are needed based on flow characteristics such as spatial eddies structures in depth-scale, diffusion/dispersion of woods, momentum transfer induced interactions between logs and mixture flow and bed conditions.
