Using Visual MODFLOW and SEAWAT for Saltwater Intrusion Applications
Saltwater intrusion is defined as the inland movement of seawater into aquifers previously occupied by freshwater. The causes include: climate change, groundwater pumping, higher evapotranspiration, lower recharge, anthropogenic causes, urban development (buildings, pavement, sewers, …), channelization of wetlands, agricultural practices, natural causes, etc.
In standard transport modeling (using MT3DMS), it is assumed that the solute is dilute and miscible (soluble within groundwater), and that solute density does not affect the groundwater flow behaviour. This is typical for groundwater contaminant plumes with small concentrations (i.e. < 1000 mg/L). However, when solute density differs from the density of water, the flow behaviour will be affected:
changes in concentration = changes in equivalent freshwater head (EFH);
changes in head = changes in the groundwater flow regime.
Density is also a contributing factor in applications such as transport of dense mine tailings/leachate, transport of sewage wastewater, and flow beneath brine storage ponds.
SEAWAT was developed to simulate 3-dimensional, variable-density, transient groundwater flow in porous media. SEAWAT is a combination of the USGS MODFLOW code and the MT3DMS code. Most Applications of saltwater intrusion will utilize the USGS SEAWAT code. SEAWAT is currently only supported in the VMOD Classic interface. If you require instructions on how to access this, please contact us.
Barlow, P.M. (2003) “Groundwater in Freshwater-Saltwater Environments of the Atlantic Coast”. USGS Circular 1262, United States Geological Survey, Reston, VA.
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