Alternate bars are formed in the main channel of the Kurobe River on the alluvial fan. Patterns of the alternate bars are controlled by the Aimoto ground sill which is directed slightly toward the right bank at the apex of the alluvial fan. At flow attacking points, longitudinal dikes have been installed for bank protection. However, the extension of revetments at the downstream of the ground sill brought bed scouring along the new revetments, resulting in changes in the pattern and the flow attacking points. Therefore, the longitudinal dikes are not able to work effectively against flood flows. In this study, we propose river improvement works for restoring pattern of alternate bars and maintaining functions of the existing longitudinal dikes by using sandbars with boulders and improving main channel. Stability of the proposed channel was investigated by applying the two-dimensional flood flow and bed variation analysis.