[A-HW25] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW25-04] Characterization of flow dynamics in a tidal-influenced coastal aquifer by using multilevel active heating tests

*Chuen-Fa Ni^1,2,3, Yu-Huan Chang¹, Chi-Ping Lin³, Chia-Yu Hsu⁴, An-Yi Hsu⁵, Nguyen Hoang Hiep^1,6, Doan Thi Thanh Thuy¹ (1.Graduate Institute of Applied Geology, National Central University, 2.Department of Earth Sciences, National Central University, 3.Center for Environmental Studies, National Central University, 4.Chuan Long Co., Ltd., 5.Industrial Technology Research Institute, 6.Department of Building Services and Built Environment, Faculty of Environmental Engineering, Hanoi University of Civil Engineering)

Keywords:submarine groundwater discharge, fiber optic distributed temperature sensing, active heating test, coastal aquifer, tidal

Aquifer storage and recovery have gained attention as a solution that utilizes submarine groundwater discharge (SGD) as a surrogate water resource to alleviate water scarcity and fill the demand gap. Characterizing SGD is crucial for using coastal groundwater and improving understanding of the interaction between continental water and seawater. This study employs fi-ber-optical distributed temperature sensing (FODTS) and the heat tracer to quantify the groundwater flux in a coastal aquifer in northern Taiwan. The fluxes in different sections along the borehole were estimated from the temperature response caused by the active heating tests and campier groundwater flux under different tidal conditions, providing information on potential water resources for water resource planning and management. According to the active heating tests, the material of the sections with high-temperature response mainly consists of a gravel-sand mixture. Based on the estimations of groundwater fluxes along the well, the sections with low sensitivity of temperature response have low hydraulic conductivity and low groundwater flux. The estimated thermal parameters at the site are consistent with those obtained from the borehole samples in the laboratory tests. The groundwater fluxes in different sections are calculated based on the temperature response observed from the FODTS. The groundwater fluxes along the well vary between 0.02 and ~1.77 m/day. There are considerable differences between the estimated fluxes during the tidal cycle in a heterogeneous coastal aquifer, indicating the high uncertainty of estimated SGD along coastal lines.