樹林化した河道の流況観測と樹林内外の流況・樹木抗力の解析

抄録

Vegetation overgrowth in river channels has become a serious engineering problem for river management in Japan. It is not a feasible solution to cut off all the trees on flood plains in the channel maintenance program for river flood protection, ecological conservation, and economic administration. In order to manage the river channels in a lower cost system, it is necessary to make a suitable channel design in which vegetation on flood plains could be flushed out by natural flood flows with certain frequency. As an engineering tool for designing the suitable channel, a two-layer river flow model was developed in this paper, which could simulate the flows in both main channels and flood plains with tree vegetation. A significant feature of the present model is the capability of estimating the bed shear stress and the drag force acting on the vegetation. Field measurements of flood flows and vegetation structures confirmed the model capability. The analysis was in good agreement with the observation both on the flood flow fields and the damaged areas of vegetation in August 2009 flood event in the Kako River. It is expected that the findings from the study would contribute to construction of river management strategy.