In Japan, most of rivers on alluvial fans are bounded by the artificial levees, which may affect or change fluvial processes of the rivers. In order to properly analyze the present stages in the development of alluvial fans, it is necessary to know differences of fluvial characteristics before and after building artificial levees.<br> Assuming that a present river bed shows the present fluvial characteristics and the other part of the fan surfaces shows the former fluvial characteristics before building artificial levees, low-water channel patterns were investigated using airphotos and the maximum grain sizes of fan deposits were measured in the field on Oi, Tetori, Kurobe, and Joganji alluvial fans in the central Japan.<br> Low-water channels on the present river beds show a braided pattern, and have directions of the flows along the artificial levees. The former low-water channels before the build of artificial levees, shown on the fan surfaces, also have a braided pattern and their main directions of the flows are radial from the fan apex (Fig. 1). Comparing the present low-water channels with the older, the former has a larger sinuosity than the latter. Intersect-ing angles of the low-water channels show the same tendency (Table 1).<br> At the same distances from the fan apexes, the maximum grain sizes on the present river beds are larger than those on the other part of the fan surfaces or the former river beds (Fig. 2).<br> These differences might come from the changes of river conditions or fluvial processes. In this study, examined are the three possible causes, that is, basin transitions by forest cuttings or landslides, artificial reformations of the river beds, and boundings of rivers by artificial levees.<br> After due considerations, the author concluded that the main cause of changing the flu-vial characteristics was the builds of artificial levees or fixing of river channels. Because the artificial levees bound the course of flows, the river can not completely adjust their morphologies or fluvial characteristics under given conditions. Especially under a flood with a given volume, flood flows may be concentrated in the present river bed by artificial levees and the velocity of the flood or the tractive force may be much higher than that in the river bed without artificial levees.<br> This study indicates that effects of artificial levees can not be neglected in order to analyze processes of alluvial fan formation or histories of alluvial fan development in Japan with considering the present river processes.