When the torrent conservation works were carried out on the alluvial fan and at the bottom of ravine plains, it was a general procedure to shape the channel rectangle by simply fixing its bank with concrete revetment. Recently, however, such works strongly require harmonization with the surrounding environment, therefore, it is considered important to diversify the section of the channel. One method, we believe, will be useful in securing the long wings of groundsels without fixating the low water channel, which then forms a desirable cross-sectional shape. And to be sure of the effectiveness of the riparian trees on the rectification of flood water, we carried out a hydraulic model experiment. We later found that the bank erosion was strongly affected by the growth of the alternating bars at the center part of the channel. Therefore, the roughness effect of the riparian trees to centralize the main current should be utilized after arranging the channel work structure in order to reduce the effects of the alternating bars. Moreover, a numerical simulation model was tested to calculate the width etc. of the maximum bank erosion and the effect of the riparian trees. In the case where the sediment provided from the bank corresponded to the hydrodynamic force and the resistance against the wave force, the two-dimensional sheet flow model which transport the sediment as bed load could, to a certain extent, reappear in the erosion process.
