Numerical Modeling of the Freshwater Lens in Small Islands (Case Study of Kish Island)

The groundwater system in many small islands consists of a freshwater lens surrounded by seawater.
A transition zone exists between the freshwater and the seawater in which relative salinity gradually
changes from zero to 100 percent. Saltwater intrusion is the most important hazard to groundwater
quality in small islands. Kish Island is one of the few islands in the Persian Gulf with extractable fresh
groundwater resources. This paper presents details of a comprehensive study conducted to model
seawater intrusion in Kish Island. Three dimensional numerical simulations were carried out using
SUTRA a density dependent flow and transport numerical model. Model calibration was performed by
Inverse modeling. For this purpose the PEST inverse code was combined with SUTRA. Finally model
sensitivity was evaluated for aquifer recharge and permeability. This study shows that SUTRA can be
regarded as a valuable tool in saltwater intrusion modeling. This is mainly due to the model`s ability to
simultaneously solve flow and solute transport equations, as well as other key features of the model
such as its ability to simulate the transition zone and the unsaturated layer above the main aquifer and
to model the groundwater system in three dimensions.