Abstract
As one of flood control measures, installation of a fixed weir is scheduled at the bifurcation point between the Asahi River and its distributary, the Hyakken River. Forestation has recently been of concern in these rivers, because it might cause a change of diverging discharge at the weir. Therefore, it is necessary to clarify the effect of vegetation on distributary for river management. This study describes flow simulations for two floods of different scales in these rivers, and demonstrates the relation between vegetation conditions, longitudinal variation of water levels and diverging discharges. Results showed that vegetation growth contributes little to increase of water levels because these rivers were mostly covered by trees whose heights were taller than water levels during these floods. Additionally, simulated water levels are approximately consistent with observations, except for situations when the Asahi River discharges were recorded at less than 2000 m3/s. Such discrepancy is supposedly attributable to low accuracy of the rating curve.
