Friday, July 17, 2009

New Pest Pilot Point Option

I have added a new Pest feature to Groundwater Vistas based on a suggestion from John Doherty. This new option is another way of using pilot points for model calibration. Currently, Groundwater Vistas (and all other GUI’s for that matter) adjusts aquifer properties on a layer basis. If you have a hydrostratigraphic unit (zone) that spans more than one layer, then each layer would be kriged independently. In the new procedure, you place pilot points throughout each zone but they are kriged by zone and not by layer. The same properties are used at each row,column location in each zone regardless of layer.

There are a couple of advantages of this strategy. First, you get a more consistent property distribution within each stratigraphic unit. Second, you use a lot less pilot points, which speeds up the calibration process.

The trick is to make sure you don’t have multiple pilot points at the same X,Y location within the same zone (i.e., same X,Y but different layers). To assist with this, Groundwater Vistas will check for pilot points of the same type (e.g. Kx, Kz, S, Recharge) in the same zone at the same X,Y location. If overlapping points are found, one of them is converted to a constraint target (not used by Pest). You can see these points as green symbols instead of the standard red for pilot points. If you agree with the one that has been “turned off”, then you can just delete them. If not, you can convert back to a pilot point and delete the other duplicates. This check is done when you create Pest datasets.

The new pilot point zone-based kriging is activated on the main Pest options dialog as a check-box to the right of the check-box that turns on the use of Pilot Points. You will need Groundwater Vistas version 5.36 Build 5 or higher.