Pilot Point Conditioning

With GMS v4.0, we introduced the pilot point method for interpolating K and recharge values within a parameter zone for MODFLOW simulations.  The user defines K or recharge values at a series of scatter point locations and the specified values are interpolated to all cells within a parameter zone.  The pilot point method is particularly useful for parameter estimation.  During the model inversion process, the parameter estimation utility PEST can be used to solve for an optimal set of parameter values at the pilot point locations.  The "parameter warping" resulting from the pilot point interpolation can lead to an excellent fit between computed and observed head values.

For pilot point interpolation of hydraulic conductivity, it is sometimes useful to include one or more measured K values with the pilot point set.  These measured values could represent K values extracted from a field pump test.  In version 4.0, there was no way to utilize a "fixed" K value for a pilot point in the parameter estimation process.  In version 5.0, we have introduced a new Pilot Point Conditioning option.  One of the properties associated with scatter points is a Fixed pilot point toggle.  If this toggle is on and the corresponding scatter point set is used for pilot point interpolation, the K value assigned to the point is not allowed to vary during the parameter estimation process.