Documentation of the seawater intrusion (SWI2) package for MODFLOW

Abstract

The Seawater Intrusion (SWI2) Package was written for use with the U.S. Geological Survey (USGS) MODFLOW-2005 groundwater model. The SWI2 Package is designed to simulate regional seawater intrusion in coastal aquifer systems. The performance of this computer program has been tested in models of hypothetical and actual coastal aquifers; however, future applications of the programs may reveal errors that were not detected in the test simulations. Users are requested to notify the USGS if errors are found in the documentation report or in the computer program. Although the computer program has been written and used by the USGS, no warranty, expressed or implied, is made by the USGS or the United States Government as to the accuracy and functionality of the program and related program material. Nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith.

Thematic Issue on HYDRUS Software Applications to Subsurface Fluid Flow and Contaminant Transport

“…MODFLOW is the U.S. Geological Survey (USGS) modular finitedifference flow model (McDonald and Harbaugh, 2003), which is considered to be the de facto standard code for simulating groundwater flow. The SWI2 package for MODFLOW may be used to represent in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers (Bakker et al, 2013).…”

“…The HYDRUS package for MOD-FLOW is one such package that considers processes in the vadose zone (Beegum et al, 2018;Twarakavi et al, 2008). The SWI2 package is another package, which may be used to represent in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers (Bakker et al, 2013). Szymkiewicz et al (this issue) used both packages simultaneously to highlight the sensitivity of calculated recharge rates to the temporal resolution of weather data (similarly as Batalha et al, this issue), leading to different trends in the evolution of freshwater-saltwater interfaces.…”

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

“…We used the updated version of HYDRUS for MODFLOW (Beegum et al, 2018), which represents an improvement over the original version as described by Seo et al (2007) and Twarakavi et al (2008), and which is compatible with MODFLOW-2005 and MODFLOW-OWHM. Here, we provide a more detailed description of the current version of the HYDRUS package, while details about MODFLOW-OWHM and SWI2 can be found in Hanson et al (2014) and Bakker et al (2013), respectively.…”

“…The vertical boundaries and the bottom of the domain were assumed impermeable. A third-type boundary condition (a general head boundary, GHB) was prescribed on those parts of the soil surface that were below the sea level, similarly as in the examples described by Bakker et al (2013), using the GHB package of MODFLOW. The total freshwater head, H = h+z, was assumed to be 0 m for the GHB cells, while the conductivity was set to 100 m 2 /d.…”

Fresh groundwater for Wajir—ex-ante assessment of uncertain benefits for multiple stakeholders in a water supply project in Northern Kenya

“…To establish the chance of the upward movement of saline water resulting in pumping of saline water, we extended the MODFLOW model with the SWI2 package, which allows simulation of a three-dimensional vertically integrated variable-density groundwater flow (Bakker et al, 2013). The SWI2 package incorporates density effects into MODFLOW-2005, without the need to solve a separate advective-dispersive transport equation.…”