DENTIFICATION OF RIVER CHANNEL TOPOGRAPHY THAT INFLUENCES THE PROCESS OF INVASION AND SPREAD OF NON-NATIVE TREE SPECIES, AND VERIFYING THE CONDITIONS FOR CALCULATING RIVER-BED VARIATIONS TO REPRODUCE THE RIVER CHANNEL TOPOGRAPHY

Abstract

 In the Tedorigawa river, we conducted analysis on relationships between invasion and spread process of alien species such as black locust (Robinia pseudoacacia), tree of heaven (Ailanthus altissima) and river channel morphology using from the past vegetation map National Census of River Environment (NCRE). Then we identified river channel morphology influencing spread of the alien wood were. After the analysis and identification, calculation condition of riverbed movable simulation and its times that could reproduce the river morphology were evaluated. In the results, we clarified that invasion and spread of alien species were caused not only along main river channel during normal water level but also secondary channel during in flood. To reproduce river morphology of the secondary channel, numerical simulation condition that is riverbed material was mixed substrate type, upper flow discharge condition was hourly discharge, spatial distribution of roughness using the vegetation map of NCRE were effective.