ABSTRACT
The lower Shinanogawa River is known as a typical low-lying river in Japan. This river system is comprised of several tributaries, a branched river and a no embankment area. In the recordbreaking flood observed in 2011 , backward flows around confluences and large inundation from the no embankment area were caused due to large inflows from main tributaries. Flood flows and bed variations in such a complex river system have not been studied so far. In this study, we developed a numerical model applying the Bottom Velocity Computation (BVC) method and 2D bed-variation analysis using observed water surface profiles in the lower Shinanogawa River. Finally the mechanisms of the complex flows around river confluences and functions of the flood flow storage in the complex river system were clarified by using the numerical model developed.
