The Flow and Head Boundary (FHB) Package allows the user to define specified heads and flows in a way that is independent of the stress periods and time steps in the model. The pane for this package is on the MODFLOW Packages and Programs dialog box under both Specified Head and Specified Flux.
The times defined in the FHB package need not correspond to the times when stress periods or time steps start or end. The FHB package will interpolate flow rates and heads between the times that are specified by the user. For example, if the user has specified a flow rate of 1 at time 0 and a flow rate of 2 at time 1, the FHB package will calculate a flow rate of 1.1 at time 0.1.
For specified flows, the flow rate for a time step will be the average specified flow for the time step. For specified heads, the head will be the interpolated head at the end of the time step.
Specified heads in the FHB package override those specified in the CHD package.
