| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2005: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2004: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
As recent channel characteristics of gravel-bed river, bed degradation, immobilization of the low-water course, local scour near river bank, extension of relative elevation, and overgrowth of vegetation are mentioned. Especially, the occurrence of riparian trees in the course of gravel-bed rivers has been very much increasing, which produces source of driftwoods in rivers. First in this study, recent characteristics of gravel-bed river and factors that cause the forestation of the river channel were investigated by analysis of the changes in both the channel cross-section and the woodland in the gravel segment of the River Watarase, a tributary of the River Tone. Here we focused on the excessive growth of Robinia pseudo-acacia, the representative species in river forestation.
These channel characteristics in gravel-bed river are produced as results of the morphological change under the medium-size floods in the low-water course affected by alternate bars. We also discuss the low-water channel formation where recent river channel characteristics of the gravel-bed river are reflected, and the process of morphological change was examined from numerical calculation. First, a channel with alternate bar was made, afterwards, the flow discharge was lowered and the meandering low-water channel, which brings about the bank erosion and local scour, was formed. These processes were investigated from the results of present numerical calculation.
Finally, a numerical simulation method has been developed for describing the behavior of driftwoods motion and their accumulation process. The present model has been composed of Eulerian analysis of fluid motion given by depth-averaged flow analysis and of Lagragian analysis of driftwoods motion by using the extended Distinct Element Method (DEM), which can simulate the motion of driftwood as the rigid body.
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