The Reservoir Boundary package simulates leakage between a reservoir and an underlying groundwater system as the reservoir area expands and contracts in response to changes in reservoir stage. The user can specify beginning and ending stages for the reservoir in each stress period.

Unlike the Lake package, the head in reservoirs is unaffected by the interaction between the reservoir and the groundwater.

NRES is the number of reservoirs to be simulated. The minimum number of reservoirs that can be simulated is one and the maximum number is the number of active cells in the model grid.

If IRESCB > 0, it is the unit number on which cell-by-cell flow terms will be recorded whenever ICBCFL is set or "Save Budget" is specified in Output Control (see McDonald and Harbaugh, 1988, chap. 4, p. 14–15).

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If IRESCB ≤ 0, cell-by-cell flow terms will not be recorded.

NPTS is the number of values in printed table of stage, volume, and area for each reservoir. First and last stage value are minimum and maximum elevations within area of potential inundation. A value of 15 or greater is recommended for detailed representation of stage-volume and stage-area relations.

IRES is an array that specifies the model cells that are included in each reservoir. Array values of “0" or less indicate the absence of reservoirs at corresponding cell locations. Values greater than “0” indicate that the cell is part of the corresponding reservoir. For example, values of “1” indicate the location of the first of NRES reservoirs and values of “2" indicate the location of the second of NRES reservoirs.

BRES is an array that specifies land-surface elevation for all reservoirs. Values in the array are assigned to the reservoir denoted by the corresponding element in the IRES array. Values are not used for cells where the corresponding element in the IRES array is less than or equal to zero.

HCres is an array that specifies vertical hydraulic conductivity of the reservoir bed for all reservoirs. Values in the array are assigned to the reservoir denoted by the corresponding element in the IRES array. Values are not used for cells where the corresponding element in the IRES array is less than or equal to zero.

Rbthck is an array that specifies thickness of reservoir-bed sediments for all reservoirs. Values in the array are assigned to the reservoir denoted by the corresponding element in the IRES array. Values are not used for cells where the corresponding element in the IRES array is less than or equal to zero.

Ststage is the value of reservoir stage at the start of the stress period. Because the package assigns stage values on the basis of linear interpolation to the end of each time step, the assigned reservoir stage will never equal Ststage unless Ststage and Endstage are equal. A total of NRES records with values of Ststage and Endstage are read at the start of each stress period.

Endstage is the value of reservoir stage at the end of the stress period. Endstage is the value that will be assigned as stage for the corresponding reservoir for the last time step in the stress period.