The Flows in FHB: Flow and Head Boundary package pane is on the MODFLOW Features tab of the Object Properties dialog box.
The data that can be specified for the specified flows in the FHB package are the Time and Flow rate. The Flow rate is the volumetric recharge rate. A positive value indicates recharge and a negative value indicates discharge (pumping).
Time is the starting time for the specified flow rate or head. The times 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.
The flow rate used for an individual time step will be the average flow rate specified for the entire duration of the time step. For example, if the flow rate at the beginning of the time step is 1.0 and at the end of the time step is 1.1, the average flow rate for the time step is 1.05.
In many cases, if a polyline or polygon is used to specify a group of wells, it may be advantageous to specify the flow rate as a rate per unit length or rate per unit area and then multiply by ObjectIntersectLength or ObjectIntersectArea. Doing so makes it possible to modify the grid without reentering information. If the Flow rate interpretation is set to Calculated, those functions will be included automatically.
Sometimes it may be desirable to specify the total well flux for an object. One way to do this would be to use a formula of the form (Total Rate)/ObjectArea*ObjectIntersectArea or (Total Rate)/ObjectLength*ObjectIntersectLength. If the Flow rate interpretation is set to Total, those functions will be included automatically.
If an object defines a flow boundary in the FHB package in MODFLOW and the object has more than one section, each section will be used to define a separate set of flow boundaries. If two or more sections of the same object occur in the same cell, a single flow boundary will be defined for that cell with the total flow rate being the sum of the flow rates for each section considered separately.
