Analytical Solution Of Tidal Loading Effect In A Submarine Leaky Confined Aquifer System

With the developing of the coastal society and economy, a series of environmental problems arises such as sea water pollution, degradation of wetland in the coastal zone. Research on the groundwater dynamic in the coastal aquifer can reveal the mechanism of various coastal environment problems, and provide theoretical support for the solving these environmental problems. So the study of tidal groundwater head fluctuation in the coastal system is of great importance. Analytical studies of tidal groundwater flow in coastal aquifer system are gradually from the simplest study of a single layer aquifer to multilayer aquifer systems.In this thesis, an analytical study was conducted based on conceptual model of a submarine confined aquifer system, which is composed of a confined aquifer and an overlying semi-permeable layer. All the layers in system are horizontal, with constant thickness, and extended infinitely in all directions. A mathematical model is set up to describe the groundwater head fluctuation in the submarine aquifer system, and the analytical solution is derived. Sensitivity analysis was carried out on the various dimensionless model parameters such as the tidal loading coefficient, dimensionless leakage of the semi-permeable layer, elastic storage of the confined aquifer and the semi-permeable layer. The results show that with the increase of tidal loading efficiency of the confined aquifer, the amplitude of the groundwater head fluctuation in the confined aquifer or in the semi-permeable layer increases, and the phase shift decreases.In addition, we considered the influences of the thickness ratio of the aquifer to the semi-permeable layer and hydraulic conductivity ratio on the groundwater fluctuations in the aquifer system. The results show that the amplitude of the groundwater fluctuation in the confined aquifer becomes larger as the thickness ratio or the ratio of hydraulic conductivity increases.Lastly, we compared the groundwater fluctuations at the top and bottom of the confined aquifer. It is found that the differences between the groundwater head fluctuations at the top and bottom of the confined aquifer become larger as the dimensionless thickness of the semi-permeable layer increases and/or the tidal loading efficiency decreases. Note that the differences include both the discrepancy in amplitude the discrepancy in phase shift.Synthesizing all the factors affecting groundwater head fluctuation in the submarine aquifer system, we find that there is a relatively fixed sensitive value range of the dimensionless aquifer thickness(product of the aquifer’s thickness and tidal propagation parameter). Within this value range(-2.5 < lg(ab)< 1.0), the groundwater head fluctuation is influenced by various model parameters very strongly. However, outside this value range, the groundwater head fluctuation is insensitive to the variation of various model parameters.