Evaluation of hot spring discharge in the Hikaruma District of Matsunoyama, Tokamachi City, Niigata Prefecture, using groundwater drainage wells installed for landslide mitigation

Abstract

This study conducted an evaluation of hot spring discharge using five groundwater drainage wells in Hikaruma District of Matsunoyama, Tokamachi City, Niigata Prefecture. The samples collected from two groundwater drain wells were Na–Cl type water and had heavier oxygen and hydrogen isotope ratios than the other samples. The isotope ratio results indicated that the two samples formed by mixing between hot spring water and groundwater originated from meteoric water. An evaluation of the mixing ratio of the hot spring water and the groundwater originated from meteoric water, with a two-component mixing model using Cl⁻ concentration, showed that the mixing ratio of hot spring water was approximately 5 to 14%. When the mixing ratio was multiplied by the drainage amount of the two groundwater drain wells, the annual hot spring discharge from the two groundwater drain wells was estimated to be approximately 4.5×10⁵ L.