粒度組成を考慮したダム排砂時の微細土砂流下に伴う河川環境影響評価に関する検討

抄録

In the Kurobe River, coordinated sediment flushing and sluicing of Dashidaira and Unazuki dams have been executed since 2001. From the view point of the comprehensive sediment management in the sediment routing system and the environmental assessment of these operations, it is very important to monitor quantity and quality of sediment transport, and water quality changes during these events in rivers and reservoirs.

This paper discusses the results of suspended sediment concentration (SS) measurement during sediment flushing and sluicing operation of Unazuki dam from 2001 through 2005. These data show gradual increase of SS-peaks and duration of high concentration based on the progress of sedimentation of Unazuki reservoir. These impacts on aquatic species can be measured by the ‘stress-index’ that was proposed by Newcomb and Macdonald, and finer suspended sediment concentrations (FSS) that are equal to multiplying the SS by the composition rates of grain size up to 10, 30 and 75 µm respectively are also important to measure these impacts more accurately considering biological characteristics of fish species.