[A-HW21] Surface and subsurface hydrologic models: Technical advances and applications for water management

[AHW21-P07] Characterization of flow dynamics in coastal aquifers based on integrated observations from cross-hole hydraulic tests and temperature monitoring.

*YI-JING CHEN¹, Chuen-Fa Ni¹, Yu-Huan Chang¹, Chi-Ping Lin², Chia-Yu Hsu¹, Hsin-Po Wang¹, AN-YI HSU¹ (1.Graduate Institute of Applied Geology, National Central University, 2.Center for Environmental Studies, National Central University)

Keywords:Aquifer parameter, Hydraulic tomography, Groundwater flow fields

Water shortage in recent years has become a crucial issue in Taiwan, groundwater is an essential alternative water resource to support the water supply system. How to characterize the aquifer system and evaluate the groundwater flow are critical issues of water resource management. This study combines different approaches, field and laboratory hydrogeological experiments and inversion models, to estimate the spatial distribution of hydrogeological parameters and assess the groundwater system's temporal and spatial dynamic characteristics. There are 14 observation wells installed in the research site, which were used to conduct cross-hole pumping tests and multi-layered water level observations to analyze the hydraulic conduction of the site. The inversion model, VSAFT2, was selected to estimate the spatial distribution of hydraulic conductivity. Water level variation were measured for setting initial conditions and verification of numerical model. The numerical model will use to integrate the long-term observation data of coastal groundwater level and the spatial distribution of aquifer characteristic parameters obtained from hydraulic tests to carry out the numerical simulation of the time-series dynamic flow field of groundwater. The variation of water level is used as the time-series variable head control condition, and the model verification is carried out with the spatial distribution of temperature and flow field. This model will be used to analyze the characteristic of the interaction between groundwater and seawater at this site, and discuss the development benefits of groundwater in coastal areas and the usability of this model in actual situations. According to the core samples, the aquifer could be roughly separated into two layers by the material of the porous media at a depth of 18.5 m. this the consistency with the results of the pumping test, which has different drawdown responses in different depths under the same pumping event. The estimations of hydraulic conductivity from the pumping test are falling in the reasonable range compared to the reference values. The results indicated that, with a fair amount of observation points, the inversion model would efficiently describe the heterogeneity of the aquifer system.