Coastal flowing artesian wells and submarine groundwater discharge driven by tidal variation at TaiCOAST site in Taoyuan, Taiwan

Study region: This study was conducted at the TaiCOAST site, Taoyuan City, Taiwan. Study focus: Three coastal flowing artesian wells (FAWs) were observed at the TaiCOAST site that do not match the well-known driving mechanisms of geological or topographical control. The observed phenomenon has not been discussed in the literature. This study collected hydraulic head data for the three coastal FAWs and one onshore well at the TaiCOAST site. A multi-phase (freshwater and seawater) model of groundwater in porous media was constructed to investigate the mechanism of the coastal FAWs and quantify submarine groundwater discharge (SGD). New hydrological insights for the region: The rare observations of coastal FAWs at the TaiCOAST site were found to be neither geologically, topographically, nor recharge controlled. The constructed numerical model indicates that the coastal FAWs are driven by an upward flow due to the sharp interface between freshwater and seawater, which acts as a barrier. The depth profile of Darcy's velocity was obtained from the calibrated model. The average Darcy's velocity of SGD is (2.96 ± 0.61) × 10⁻⁶ m/s, which is similar to value reported in the literature. This study provides new insight into the mechanism of FAWs in coastal areas. The results can serve as an important reference for investigations of SGD.