[A-HW26] Isotope Hydrology 2022

[AHW26-P06] Estimation of Inorganic Ions Load in Otakigawa River Branch at Mt. Ontake by Using Tank Model

*Kazunori Ebata¹, Yoshitaka Matsumoto¹, Akiko Usami², Tomomasa Taniguchi³ (1.National Institute of Technology, Toyota college, 2.Disaster Mitigation Research Center, Nagoya University, 3. Faculty of Humanity, Mie University)

Keywords: Mt.Ontake, Tank model, Inorganic Ions load

Estimation of volcanic compounds impact in volcanic river is important for the assessment of the river ecosystems as well as for the local water quality control. Mt.Ontake erupted in 2014, volcanic product was flow into the Otakigawa river and reached at Makio dam reservoir. Especially, inorganic ions from the volcanic compounds were seeping into the Otakigawa river. Also, the Otakigawa river flow wasis affected by human activity, for instance, Otakigawa dam outflow and also intake water usage for hydroelectrically power generation at each branch. Hence, evaluation of inorganic ions concentration but also inorganic ions load consideration of volcanic activity and anthropogenic dam operation is important to carry out the dam water management. In this study, we investigated in the Otakigawa river branches including Nigorisawa river, Denjyogawa river, Shimokurosawa river, and Uguigawa river from 2018 to 2020. We calculated each branch discharge in the Otakigawa river by using 3step of tank model and then integrating with empirical regression model for calculation of inorganic ions load. In tank model, the results of discharge were reasonably obtained less Pbias value at each branch. After the calculation discharge, inorganic ions load were calculated at each branch. Sulfate ion load in the Nigorisawa river was highest among the four branches due to the piling up the volcanic compounds at upper stream or volcanic gas seeping into the river. It was 15.0 times, 89.2 times, 462.8 times higher than Denjyogawa river, Shimokurosawa river and Uguigawa river, as respectively. On the other hand, Denjyogawa river which located next to the Nigorisawa river was highest bicarbonate ions load. Therefore, Nigorisawa river and Denjyogawa river flow into the Otakigawa river interacting with each other water quality. Also, sulfate and sodium loads in the Shimokurosawa river were as well as highest among the other ions loads. On the other hand, each ions load was found lowest among the four branches in the Uguigawa river. As a result of calculation inorganic ions loads at each branch, the Nigorisawa river had tremendous impact for acidic condition to the Otakigawa river. It is necessary to quantify and evaluate the volcanic compounds impact of the Nigorisawa river on the Otakigawa river.