Groundwater flow modeling / modelling with GMS software
True Layer Approach
When setting up a multi-layer MODFLOW model, defining the layer array data has traditionally been a difficult and time-consuming task. GMS provides a special option for streamlining layer data input called the "true layer" approach. When this option is selected, top and bottom elevations and Kh and Kv values are defined for each layer regardless of the layer type. When the MODFLOW files are saved, geometry dependent parameters such as transmissivity and leakance are automatically computed.
GMS includes a powerful suite of customized interpolation tools that make it possible to simulate complex stratigraphy when using the True Layer option.
When using the True Layer approach, the MODFLOW layer geometry can be displayed in a highly realistic fashion in both cross section and oblique view.
MODPATH
MODPATH is a particle tracking code that is used in conjunction with MODFLOW. After running a MODFLOW simulation, the user can designate the location of a set of particles. The particles are then tracked through time assuming they are transported by advection using the flow field computed by MODFLOW. Particles can be tracked either forward in time or backward in time. Particle tracking analyses are particularly useful for delineating capture zones or areas of influence for wells.
Capture Zone Analysis
The backward tracking option in MODPATH can be used to delineate capture zones for wells for a given time period.
MT3DMS
MT3DMS is a modular three-dimensional transport model for the simulation of advection, dispersion, and chemical reactions of dissolved constituents in groundwater systems. MT3DMS uses a modular structure similar to the structure utilized by MODFLOW. MT3DMS is used in conjunction with MODFLOW in a two step flow and transport simulation. Heads and cell by cell flux terms are computed by MODFLOW during the flow simulation and are written to a specially formatted file. This file is then read by MT3DMS and utilized as the flow field for the transport portion of the simulation.
MT3DMS is a newer version of the MT3D model distributed with earlier versions of GMS. MT3DMS differs from MT3D in that it allows for multi-species transport, supports additional solvers, and allows for cell-by-cell input of all model parameters.
MT3DMS is ideally suited for simulating the migration of contaminant plumes over time.
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