Loading effect of phreatic level variations induced by river tide on groundwater head fluctuations in tidal river aquifer systems

The unconfined groundwater level variations caused by the river tide can impact the fluctuation of the groundwater head in the underlying confined aquifer by loading effect. In this study, we proposed a mathematical model and provided an analytical solution for a confined aquifer system considering the loading effect when the aquifer system is eroded by the tidal river to varying extents. The results demonstrated that the loading effect tends to amplify the amplitude of the tide-induced head fluctuation while reduce its phase shift in the confined aquifer. These effects are more significant with a larger tidal loading efficiency, a wider tidal river, and a smaller tidal propagation parameter of the unconfined aquifer. The analytical solution was validated by the observed groundwater level fluctuations from a groundwater level monitoring well near a tidal river in the Peral River Delta of China, and provided reliable estimations of aquifer parameters in the region.