比良山系大谷川流域における降雨流出特性と地形変化プロセスの関連について

Abstract

A preliminary consideration of the hydrogeoinorphological interactions in the River Otanibasin is described. Systematic observation of the hydrogeoinorphological processes in this basinwas started in 1989 by the authors. Discharge of two major tributaries (Nakatani and Oiwa-dani) was analyzed by the tank model to see how the ground surface conditions and the struc-ture of the weathered zone affect the runoff. Although no difference was suggested in the hy-draulic properties of the soil horizons, it was revealed that a difference in the infiltration propertiescaused a greater percentage of direct runoff in the Nakatani basin. This difference is attri-butable to the extensive distribution of bare lands (recently replanted) in the Nakatani basin.The bare lands in the River Otani basin seem to have been caused by the accelerated erosionin and around landslide sites. The distribution of the bare lands is limited in the part downslopethe erosion front, which is recognized as falls and the break of slope angle chained along thecontour line. A catena of different mass movements is suggested in the part upslope the erosionfront by a preliminary investigation of microtopography and the penetration test. Location ofsoil creep, surficial slump, piping and landslide is closely related to the geomorphic conditionswhich should be affected by the hydrological conditions in their turn. Detailed observation ofhydrogeomorphological processes is planned in a zero-order valley (unchannelized hollow) toexamine the interactions between the surficial slump and the subsurface runoff.