SEDIMENT EROSION AND DEPOSITION IN THE FORMER ARASE DAM RESERVOIR UNDER THE DAM REMOVAL PROJECT

Abstract

 The Arase Dam on the Kumagawa River in Kumamoto Pref., Japan, has been subsumed under removal project as the first high-dam removal in Japan. In March 2015, the dam crest on the right side has been removed with the first flushing and continuity of flow and sediment has been restored. In this study, we conducted elevation measurement with RTK-GNSS and SfM analysis using UAV aerial photo set. As a result of our investigation, we found significant scouring in the upper stream of the dam site caused by several times of floods (Q_max=2000-3000 m³/sec). According to our estimation, 1.5 * 10⁵ m³ of the sediment on former reservoir (26% of total) are washed to the downstream and 1.8 * 10⁵ m³ was found on the immediate downstream of the dam site and it created new sand bar.