The GWT Model can also run separately from a GWF Model by reading the heads and flows saved by a previously run GWF Model. The GWF and GWT Models operate simultaneously during a MODFLOW 6 simulation to represent coupled groundwater flow and solute transport. The GWT Model is designed to work with most of the new capabilities released with the GWF Model, including the Newton flow formulation, unstructured grids, advanced packages, and the movement of water between packages. The GWT Model solves the solute transport equation using numerical methods and a generalized CVFD approach, which can be used with regular MODFLOW grids or with unstructured grids. The GWT model for MODFLOW 6 simulates three-dimensional transport of a single solute species in flowing groundwater. The GWF Model also has packages for obtaining and controlling output from the model.
A package is the part of the model that deals with a single aspect of simulation. The GWF Model is divided into "packages," as was done in previous MODFLOW versions. a general unstructured grid based on concepts developed for MODFLOW-USG.įor complex problems involving water-table conditions, an optional Newton-Raphson formulation, based on the formulations in MODFLOW-NWT and MODFLOW-USG, can be activated.a layered grid defined by (x, y) vertex pairs, or.a regular MODFLOW grid consisting of layers, rows, and columns,.The GWF Model for MODFLOW 6 is based on a generalized control-volume finite-difference (CVFD) approach in which a cell can be hydraulically connected to any number of surrounding cells. MODFLOW 6 presently contains two types of hydrologic models, the Groundwater Flow (GWF) Model and the Groundwater Transport (GWT) Model. Groundwater Flow (GWF) and Groundwater Transport (GWT) Models The framework naturally allows for future extensions to include the simulation of solute transport. Or, a surface-water flow model could be coupled to multiple groundwater flow models. Within this new framework, a regional-scale groundwater model may be coupled with multiple local-scale groundwater models. Transfer of information between models is isolated to exchange objects, which allow models to be developed and used independently of one another.
These models can be independent of one another with no interaction, they can exchange information with one another, or they can be tightly coupled at the matrix level by adding them to the same numerical solution.
In the new design, any number of models can be included in a simulation. This version of MODFLOW is labeled with a "6" because it is the sixth core version of MODFLOW to be released by the USGS (previous core versions were released in 1984, 1988, 1996, 2000, and 2005). MODFLOW 6 is an object-oriented program and framework developed to provide a platform for supporting multiple models and multiple types of models within the same simulation. This type of layered grid can be represented using the Discretization by Vertices (DISV) Package in MODFLOW 6. This figure shows a triangular grid in which the size of the triangular cells is reduced in areas with relatively large hydraulic gradients, such as around the shoreline of a lake, near pumping wells, and along a stream.
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