No abstract

The problem of the groundwater dynamics and water balance of a confined aquifer in the aquifer system has been solved in previous studies, whereas that in the aquitard adjacent to the confined aquifer has seldom been considered. In reality, the groundwater dynamics of the aquitard are closely related to the exploitation of groundwater resources, groundwater contamination, underground storage utilization and land subsidence. In this paper, an analytical solution is derived to describe the drawdown variation in the aquitard when the head in the adjacent confined aquifer declines by a constant value. The characteristics of groundwater dynamics and water balance of the aquitard are analyzed using a dimensionless analytical solution. There is obvious delayed behavior in the response of groundwater dynamics in the aquitard, which is characterized by the delay index  0 . The delayed behavior in the response of groundwater dynamics is not only dependent on the properties of the aquitard, but also proportional to the square of the thickness of the aquitard. The law of the delayed release of water is described in terms of the ratio of the delayed release of water. A water balance equation for the aquitard is established. Three stages of the water balance and the corresponding characteristics are presented with the water balance curves of the aquitard. The analytical solution is given to analyze the flux per unit horizontal area of the aquitard. The hydrogeological parameters of the aquitard, namely the hydraulic conductivity, specific storativity and hydraulic diffusivity, are estimated according to type-curve fitting between the analytical solution and observed flux. The parameters are identified and validated in an experiment. aquitard, water balance, parameter identification, delayed release of water Citation:Zhou Z F, Guo Q N, Dou Z. Delayed drainage of aquitard in response to sudden change in groundwater level in adjacent confined aquifer: Analytical and experimental studies.

[1] This paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach. Field observations of water table, pore water salinity were performed. The two-dimensional finite element model MARUN was used to simulate observed water table and salinity. Based on field observations and model calibrations, a two-layered beach structure was identified which is characterized by a high-permeability surface layer underlain by a low-permeability lower layer. The salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone. The presence of the two layers prevented the presence of a freshwater discharge "tube" between the upper saline plume and salt wedge. This is in contrast with the previous works where freshwater discharge tube was observed. The tide-induced submarine groundwater discharge (SGD) was estimated at 9 m 3 d, a large value that is probably due to the large tidal range of ∼4.8 m and the very permeable surface layer. The freshwater-seawater dynamics revealed here may provide new insights into the complexity, intensity, and time scales of mixing between fresh groundwater and seawater in tidal beaches. The simulated water table of the beach was higher than the interface between the surface layer and the lower layer, which prevented Exxon Valdez oil from penetrating into the lower layer in 1989.