支川合流の影響を受ける大堰湛水区間における河川地形の経年変化解析

抄録

The topic in this study is river morphological changes in the last two and half decades after a barrage construction. The major impacts imposed on morpho- and hydrodynamics in this reach are formation of the reservoir by the barrage and confluence of a major tributary, which have caused significant regime shits such as formation of an island in front of the tributary confluence, main channel migration from the left to right bank around the confluence, vegetation overgrowth on emergent sandbars, erosion of the main channel and deposition on the floodplain, loss of spawning habitat for sweetfish, water depth decrease in the area of regatta course and other issues, etc. In order to examine the mechanism of the historical changes in river morphology, a numerical analysis on hydrodynamic and sedimentation processes was carried out by using an open source software, the "iRIC". Characteristic geomorphological features such as formation of an island at the tributary confluence and an emerged sandbar development at the left bank side are well reproduced by the present analysis. Influence of the two major impacts, i.e. reservoir formation and tributary confluence, was discussed by performing a response analysis under two scenarios that are in the absence of the reservoir and tributary.