The River package is used to boundaries in which the flow into or out of the groundwater system is a function of the head. If the head is above a threshold value the flow is a linear function of head. However, if the head in the cell falls below the threshold, the flow from the river to the model cell is set to a specified lower bound. The pane for this package is on the MODFLOW Packages and Programs dialog box under Head Dependant Flux.
On the RIV: River package pane, the user can define parameters for the river boundaries. These parameters will be multiplied by user-specified multipliers to determine the river conductances defined by parameters. The user can also set up river boundaries that do not involve parameters. Objects must be used to define the locations of the river boundaries.
In MODFLOW 6 models, "multipliers" can be used with river boundaries. Multipliers will be used if the "Use Multiplier (MODFLOW 6)" checkbox is checked.. Ordinarily, multipliers are not needed. If multipliers are used, the river conductance is multiplied by the value of the multiplier. One use for multipliers might be when the river conductances are defined using a time-series and it is desired to multiply the river conductance values in the time series by a different amount at different locations.
The River package is similar to the Drain package except that in the Drain package there can never be flow from the drain to the groundwater system.
Parameters can also be edited in the Manage Parameters dialog box.
