CHANGES IN RIVER GEOMORPHOLOGY OF THE KUMA RIVER AND TRIBUTARIES DUE TO THE ARASE DAM REMOVAL PROJECT

Abstract

The Arase Dam is the Japan's first full-scale dam removal project. This paper considers changes in river geomorphology etc., based on the results of the environmental monitoring conducted in the project. Image analysis using a river monitoring camera with a surveying function revealed that the water level at the Arase Dam site dropped by about 4m. The change in the river geomorphology of the Kuma River mainstream took place only in the sections located about 4 km above and below the dam site, and there were no significant changes in the other sections. Kudaraki River, joining just upstream of the dam, has changed in two stages, affected by the water level at the time of floods in the mainstream. Riverbed sediment had a higher sand content at the weir downstream of the dam whereas no silt was deposited.