Development for Sediment Runoff Monitoring in the Joganji River Basin

The Joganji River basin in Toyama Prefecture, Japan, has experienced numerous sediment-related disasters due to the considerable sediment yield of approximately 0.1 billion m3 attributed to mountain collapse following the Hietsu Earthquake of 1858. Over the past 100 years, the sabo facilities that have been constructed in the basin have reduced the sediment runoff from the surrounding mountainous region. However, it is becoming increasingly important to balance appropriate sediment runoff for bed variation with countermeasures against the large volumes of sediment in runoff from upstream reaches. Monitoring of bedload and debris flow has been conducted since the 1960 s in this basin, and a comprehensive monitoring network has been established to evaluate sediment movement using data collected by a variety of sensors. A sabo dam with a movable shutter and a slit dam was installed in the middle reaches of the Joganji River to control sediment runoff from the catchment. An effective control of sediment runoff tries to be found by operations during a flood and be evaluated measured data using sensors. This approach allows both the capture of transported sediment at the beginning of a flood and the release of deposited sediment from the storage area of the dam as the flood recedes. Pilot operations have been conducted in successive floods since July 2016, following several operational rules. The present study introduces the sediment runoff data that have been collected by sensors, such as the Japanese pipe-hydrophone, and provides several examples of applied sediment control using the movable shutter.