Numerical approach to understand hydrological and thermal signals to infer dynamic interaction between groundwater and river water in a GWHP operated riverside area

The riverside area is a suitable place to operate the Groundwater Heat Pump (GWHP) system with abundant groundwater quantity. In the riverside area, the interface between the river and the groundwater can be dynamically changed according to the hydraulic gradient variations. These dynamic movements cause mixing of the two waters, and the concentration and temperature of the groundwater change. In particular, it is important to understand the mixing between groundwater and river water because the change of groundwater temperature could affect efficiency of the GWHP system. In this study, we collected data on groundwater levels, concentrations at chemical constituents, and temperatures in riverside area where active mixing of groundwater and rivers occurs. Numerical model for groundwater flow system was established based on wellbore data, hydraulic properties of aquifer, and monitoring data of river water and groundwater levels. In order to investigate river-aquifer interaction, three-dimensional finite element models of the coupled variably saturated groundwater flow and solute/heat transport were established. Solute transport model was applied to calculate the mixing ratio of two water bodies, and the result was compared with the estimated mixing ratio. Heat transport model computed temperature variations and compared with the observed dynamic changes during the interaction. Through heat transport modeling in shallow aquifer near river, we simulated the temperature distribution of groundwater considering the influence of the hydraulic gradient between groundwater and river water. In addition, the model results on temperature distribution is essential for maintaining the operational efficiency of the GWHP system.

Acknowledgement : This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT(2017R1A2B3002119)