Investigation of Regional Saltwater Intrusion in Two Coastal Aquifers in Florida Using the SWI Package for MODFLOW-2000

The Sea Water Intrusion (SWI) Package for MODFLOW-2000 was developed by Bakker and Schaars (2004) to simulate regional saltwater intrusion using a sharp interface approach.  The package utilizes the Dupuit approximation, which allows an aquifer to be represented as a single model layer.  The design allows saltwater intrusion to be simulated at the regional scale while providing substantial computational benefits over full variable-density flow models which require multiple layers (Dausman et al. 2010).  The USGS is currently working with Bakker and Schaars to update the SWI Package to MODFLOW-2005. 

The SWI package is being tested by two independent models that represent regional Atlantic coastal aquifers in Florida; the Biscayne aquifer and the Floridan aquifer system. Transient simulations were developed to test the ability of SWI to simulate the movement of the saltwater interface in response to predicted sea-level rise and increases in municipal well-field withdrawal rates. These model tests involved multiple simulations to determine the sensitivity of model results and run times with different grid discretizations, boundary conditions and initial SWI freshwater-saltwater interface locations. 

Bakker, M. and F. Schaars. (2004) The Sea Water Intrusion (SWI) Package Manual Version 1.2, Department of Biological and Agricultural Engineering, University of Georgia and Artesia Water Research, Unlimited

Dausman, Alyssa M. (2010) A comparison between SWI and SEAWAT – the importance of dispersion, inversion and vertical anisotropy, Proceedings of the 21^st Saltwater Intrusion Meeting, Azores 2010.