Abstract
Originally, vast gravel bars spread in fluvial fan. Gravel mining, however, caused a great change of this spatial distribution of habitats and had resulted in the reduction of gravel area and the increase of wood area In this study, inundation frequency was focused to realize the factor for the change of habitats, and analyzed the relationship between each habitat type and their inundation frequency. Shizukuishi River was chosen for the study river, whichad taken a great change of habitats indicated above. Aerial photograph was used for the grasp of the habitat changes and the river morphology during past five decades, and historical daily discharge data was analyzed to estimate inundation frequency. Based on this study, the morphological change caused by gravel mining had caused the alteration of inundation frequency, and this alteration would be a key element for the reduction of the gravel area and the increase of the wood area in the rivers. Especially, a specific inundation frequency, l-5days/year could be an important threshold for the evaluation what kind of habitat will be.
