A new approach to study seawater intrusion problems in coastal aquifers is presented. The approach is
demonstrated for the case of the Nile Delta aquifer in Egypt. FEFLOW, a 3D finite element variable density
model, is employed, however, because of the lack of 3D data, and to demonstrate the proposed approach,
the simulations are performed in 2D horizontal views. The concept of equivalent freshwater head (usually
implemented in 2D vertical simulations) is adapted in the horizontal (areal) simulations. After calibration
against field observations, the simulations are conducted at four horizontal sections located at
different levels (100, 200, 300 and 400 m) below the mean seawater level. The depth of the horizontal
section is identified through assigning an appropriate pressure ‘‘equivalent freshwater’’ head at the
boundaries. The study domain is modified for the horizontal sections at 300 and 400 m, respectively,
to account for the aquifer geometry at these depths. The effect of freshwater recharge from the Nile River
on the seawater intrusion is observed in the upper layer around its two main branches. The results of the
horizontal simulations clearly demonstrate the variation of water concentration in the vertical direction.
As the depth increases, the transition zone (in which the concentration varies from the seawater to the
freshwater concentration) is shifted toward the landside and become more extensive. At the lower levels
of the Nile Delta aquifer, the seawater migrates much further inland as compared to the shallower levels.
The concept of horizontal simulations at different levels is further developed to produce meaningful concentration
distributions in the vertical sections. This approach allows for a better realization of seawater
intrusion in coastal aquifers.