Tidal Effect on Groundwater Fluctuations and Saltwater Intrusion in Coastal Heterogeneous Aquifers.

Document Type : Research Studies

Authors

1 Professor of Hydraulics., Mansoura University, Dean of Mansoura High Institute of Eng. And Technology

2 Assistant prof., Irrigation & Hydraulics Dept., Faculty of Engineering, Mansoura University, Egypt.

3 M.Sc. Student, Irrigation & Hydraulics Dept., Faculty of Engineering, Mansoura University, Egypt

Abstract

Groundwater table and saltwater wedge in coastal areas are commonly affected by tidal waves fluctuations. In this research, for the first time, a two-dimensional numerical model in plan is developed for simulating both the tidal fluctuation of the beach groundwater table and movement of interface between saltwater and freshwater in both coastal confined and unconfined heterogeneous aquifers. The sharp interface philosophy is adopted to simulate dynamics of freshwater flow. Tidal waves are simulated by simple harmonic motions in time. The solution is based on an approach of separating large and small time scales motions of groundwater fluctuations. The proposed model consists of two sub-models. The first one applied Finite Element Method (FEM) to simulate the hydraulic responses of the aquifer in large time scale and it is coupled with Finite Difference Method (FDM), in the second sub-model, to simulate the corresponding ones in small time scale. The model is verified against analytical solutions presented by other previous researchers in case of homogenous aquifer. To simulate the aquifer heterogeneity, unconditional random log-hydraulic conductivity fields are generated to present different hydraulic conductivity realizations for the aquifer under consideration. The application is carried out on both the hypothetical confined aquifer and the real Quaternary unconfined aquifer in El Arish-Rafah area, Egypt. Results show that both the groundwater fluctuation and saltwater intrusion due to tidal waves are affected by the aquifers heterogeneity and the tidal waves effects in confined aquifers are more significant than in unconfined aquifers.

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