GMS:MDT Package
| MODFLOW | |
|---|---|
| Pre-processing | |
| MODFLOW Commands | |
| Building a MODFLOW Model | |
| Map to MODFLOW | |
| Calibration | |
| Packages Supported in GMS | |
| Saving a MODFLOW Simulation | |
| Importing MODFLOW Files | |
| Unsupported MODFLOW Features | |
| Run MODFLOW | |
| Post-processing | |
| MODFLOW Display Options | |
| MODFLOW Post-Processing Viewing Options | |
| Reading a MODFLOW Simulation | |
| Tutorials | |
| Packages | |
| Flow: | BCF6, HUF, LPF, UPW |
| Solvers: | SMS |
| Other: | UZF1 |
MODFLOW-USG Transport is a version of MODFLOW that can be used to model groundwater flow and contaminate transport. To model the effects of matrix diffusion, it can be paired with the Matrix Diffusion Transport (MDT) package.
- Note: The MDT package is not an official package released by USGS. The MDT package provided with GMS is still being developed and may change in the future. Newer versions of the package may not be compatible with older projects.
The MDT Package dialog is divided into two parts: one on the left which shows the main sections, and one on the right which shows the inputs for the current section.
Contents
COMMENTS
Comment lines can be added and will appear at the top of the MDT file.
VARIABLES
The Variables tab outlines key parameters and controls related to mass flux, immobile domain concentration, hydraulic conductivity, and matrix diffusion in flow simulations.
- Cell-by-cell mass flux unit (IMDTCB) – Controls whether cell-by-cell mass flux terms are written to a specified unit number or listing file.
- Immobile domain concentration unit (IMDTCF) – Controls whether matrix coefficients and immobile domain concentrations are saved to a specified unit number or the listing file.
- Hydraulic conductivity for fracture only (FRAHK) – Specifies whether the hydraulic conductivity and storage terms apply only to the fracture (mobile) domain or to the entire medium during flow simulations.
- Darcy flux hydraulic conductivity for fracture only (FRADARCY) – Specifies that the Darcy flux is computed only for the fracture domain, with hydraulic conductivity adjusted by the fracture volume fraction, and storage terms apply only to the fracture domain.
- Shift matrix diffusion start time (TSHIFTMD) – Indicates that the MODFLOW start time is not the start time for matrix diffusion, and the variable TSHIFT represents the time elapsed since matrix diffusion began; the AIOLD1MD and AIOLD2MD coefficients are also input when TSHIFTMD is used.
- Time elapsed since matrix diffusion began (tshift) – Represents the time elapsed since matrix diffusion began.
AQUIFER PROPERTIES
The Aquifer Properties tab outlines key properties and characteristics related to matrix diffusion, permeability, porosity, and diffusion behavior in the matrix domain during flow simulations.
- MDFLAG – An integer that controls how matrix diffusion is modeled in the system.
- VOLFRACMD – The portion of a grid cell occupied by a higher permeability material, representing the mobile domain's volume fraction.
- PORMD – The porosity of the low-permeability material in the matrix domain, showing the amount of space in a grid cell filled with immobile material.
- RHOBMD – The dry bulk density of the low-permeability material in the matrix domain.
- DIFFLENMD – The length over which diffusion occurs in the low-permeability material, indicating how far molecules travel during diffusion.
- TORTMD – The tortuosity of the matrix domain, representing the path that a molecule must travel during diffusion in the low-permeability material.
SPECIES PROPERTIES
The Species Properties tab outlines key aspects of contaminant behavior, decay, diffusion, and concentration integrals in the matrix domain, including adsorption, degradation, and diffusion processes in low-permeability materials.
- KDMD – The adsorption coefficient in the matrix domain, showing how a contaminant binds to the low-permeability material.
- DECAYMD – The rate at which a substance degrades in the low-permeability material, based on a first-order decay process.
- YIELDMD – The yield coefficient for chain decay at any location, representing the amount of mass produced by the decay of the parent component.
- DIFFMD – The diffusion coefficient for each species in the matrix domain, representing how quickly a substance spreads through the low-permeability material.
- AIOLD1MD – The concentration integral (equation 8) of each species in an element associated with matrix diffusion into an infinite acting adjacent aquitard (MDFLAG = 1, 3, 4, 5, 6, or 7). This value is used to restart a simulation with prior matrix diffusion.
- AIOLD2MD – The concentration integral (equation 8) of each species in an element associated with matrix diffusion in low permeability zones that are embedded in the volume element (MDFLAG = 2, 5, 6, or 7). This value is used to restart a simulation with prior matrix diffusion.
Conversion from MODFLOW 6
When converting a MODFLOW 6 model to MODFLOW-USG Transport, use the following table when converting the MDT package:
| MODFLOW 6 | MODFLOW-USG Transport | ||
| Package | Variable | Package | Variable |
| CNC | PCB | ||
| DSP | DIFFC | BCT | DIFFNC |
| MST | POROSITY | BCT | PRSITY |
| MST | BULK_DENSITY | BCT | BULKD |
| MST | DISTCOEF | BCT | ADSORB |
| MDT | MD_TYPE_FLAG | MDT | MDFLAG |
| MDT | MD_FRACTION | MDT | VOLFRACMD |
| MDT | MD_POROSITY | MDT | PORMD |
| MDT | BULK_DENSITY | MDT | RHOBMD |
| MDT | MD_DIFF_LENGTH | MDT | DIFFLENMD |
| MDT | MD_TORTUOSITY | MDT | TORTMD |
| MDT | MD_DIFF_COEFF | MDT | DIFFMD |
Related Topics
| [hide]GMS – Groundwater Modeling System | ||
|---|---|---|
| Modules: | 2D Grid • 2D Mesh • 2D Scatter Point • 3D Grid • 3D Mesh • 3D Scatter Point • Boreholes • GIS • Map • Solid • TINs • UGrids |  |
| Models: | FEFLOW • FEMWATER • HydroGeoSphere • MODAEM • MODFLOW • MODPATH • mod-PATH3DU • MT3DMS • MT3D-USGS • PEST • PHT3D • RT3D • SEAM3D • SEAWAT • SEEP2D • T-PROGS • ZONEBUDGET | |
| Aquaveo | ||
