Boundary Conditions

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Boundary conditions represent locations in the model where water flows into or out of the model region due to external factors. Lakes, streams, recharge, evapotranspiration and wells are all examples of boundary conditions. There a three types of boundary conditions in MODFLOW, (1) Specified heads, (2) Specified fluxes, and (3) head dependant fluxes. In specified head boundaries, the head remains constant. Fluid is simulated as moving in or out of the groundwater at a rate sufficient to maintain the specified head. In specified flux boundaries, the rate of fluid moving into or out of the groundwater is specified.  The head at the specified flux cell changes in response to the flux. In head dependant flux boundaries, the rate of flow from the boundary into or out of the groundwater varies in response to changes in head in the boundary cell.

The locations of all boundary conditions are defined using Objects.

MODFLOW experts may be surprised to find that ModelMuse does not support defining specified-head boundaries using a combination of the IBOUND and STRT arrays. Instead specified heads are defined using the CHD package. The other function of the IBOUND array, to define which cells are part of the modeled area, is specified in the Active data set.