5:15 PM - 6:30 PM
[AHW22-P14] Estimation of groundwater flow and a river water contribution to it in an alluvial plain of western Japan, using tracer methods
Keywords:Coastal alluvial plain, groundwater flow, stable oxygen and hydrogen isotope
The purpose of this study was to confirm groundwater flow and a river water contribution to it in an alluvial plain of western Japan, using tracer methods. The research area is located on the Kurashiki alluvial plain, the downstream area of Takahashi River, Okayama Prefecture, Japan. We monitored the water level and water temperature at the 30minutes interval, and collected water samples weekly at Sakazu intake weir station of Takahashi River and at one borehole since May 2017. The observation borehole has the depth of about 11 m. The water samples were analyzed the main anion and cation by the ion chromatography, and hydrogen and oxygen stable isotope ratios by PICARO.
The water temperature in the Takahashi River showed a similar trend to the air temperature in Kurashiki weather station, on the other hand the water temperature in the observation boreholes showed a maximum in the seasonal variation with the delay of 6 months at the depth of 10 m and of 3 months at the depth of 3 m below the ground, respectively. The isotope ratios of hydrogen and oxygen in the river water and groundwater showed some variation. These results suggested groundwater recharge from the river to the underground on the alluvial plain, and the groundwater flow velocity was extremely large. In addition, the hydrogen and oxygen isotope ratios of the river water were significantly decreased in July 2018 and September 2018 during the large outflow. These water was good tracer to detect the influence of river water on groundwater
The water temperature in the Takahashi River showed a similar trend to the air temperature in Kurashiki weather station, on the other hand the water temperature in the observation boreholes showed a maximum in the seasonal variation with the delay of 6 months at the depth of 10 m and of 3 months at the depth of 3 m below the ground, respectively. The isotope ratios of hydrogen and oxygen in the river water and groundwater showed some variation. These results suggested groundwater recharge from the river to the underground on the alluvial plain, and the groundwater flow velocity was extremely large. In addition, the hydrogen and oxygen isotope ratios of the river water were significantly decreased in July 2018 and September 2018 during the large outflow. These water was good tracer to detect the influence of river water on groundwater