Key values are used to parameterize the MODFLOW input. Key values can be used for both the zonation and pilot points methods of defining parameters. A key value is a number that is assigned as input that marks the input values as belonging to a parameter. When selecting a key value, a number should be chosen that is not likely to occur in typical input for that parameter. We recommend using negative numbers in most cases.
For example, a model may have four K zones and three recharge zones. The four K zones would be marked by assigning -100, -200, -300, and -400 to the cells in the K array for each of the four zones. Likewise, the recharge zones would be marked by assigning -500, -600, and -700 to the appropriate cells in the recharge array.
Key values can be assigned either by editing the cell array values directly in the 3D grid module or by assigning the values to a set of polygons or arcs in the conceptual model and selecting the Map -> MODFLOW command.
Related Links:
Automated Parameter Estimation
Parameter Dialog