牧尾ダムによる王滝川の水質変化と用水への影響

Abstract

The water quality of the Ohtakigawa River has been influenced by volcanic activities of Mount Ontake in Japan. In this study, in order to analyze Ohtakigawa water quality affected by artificial infrastructures such as the Makio Dam, we mainly observed suspended solids (SS), Aluminum (Al) and Chlorophyll-a (Chl.a) in the Ohtakigawa river, where SS and Al prevent algae from growing, and Chl.a is contained in algae. In usual discharge cases from the Makio Dam through water pipes, the concentrations of Al and SS were decreased 0.1 times and 0.2 times, respectively, and the concentration of Chl.a was increased 3.3 times. In heavy rain cases, where overflow discharge through flood sluice gates were carried out, their concentrations showed the tendency similar to the above usual cases. And, laboratory experiments showed 80% of SS was deposited. Thereby, it is implied that both sedimentation and dilution effects caused algae inhibitors such as SS and Al to decrease and hence algae grew in the Makio Dam. In conclusion, the Makio Dam is capable of rehabilitation of the Ohtakigawa river water quality.