Calibration using PEST help

[myersg]

Hello all,

I am working on a model that consists of 4 different materials and 8 layers.  The model is two sand aquifers separated by clay till in places and bounded on top and bottom by clay till as well.  The model runs fine in forward mode but I can't get the pest to refine it to better than -3m error based on observation wells.  I am using the pilot point method and set the larger aquifer as the pilot points with the perched aquifer, recharge and clay till layers allowed to vary as well.  When I run the model using pest it will refine the error on or two times then all of the parameters begin to get out of bounds and are frozen.  I am using Modflow 2005 with direct solver. Current version is 10.0.11 and let me know if any more details or images are needed to help with this problem.

Any suggestions are appreciated,

Greg

Edited March 16, 2016 by myersg

[speedy]

try the following:

-increase parameter bounds in PEST

-increase number of runs in PEST

-decrease the threshold error in MODFLOW

-if using regularisation, try first without it.

[myersg]

Thanks for your suggestions, I ended up having to modify the top cell materials to allow more recharge to the aquifer which brought most of the observation wells to within 1m.