Mud-Dauber

Quicksurf Unstable

3 posts in this topic

I'm using Quicksurf for ACAD 2011 to map a complex water table located next to a river and am having problems with Quicksurf reporting "unstable" and stopping during grid processing. The area I'm mapping contains a variety of elevation points, including randomly scattered well elevation data, an interceptor trench with a central pumping well and a elevation data from a group of pumping wells adjacent to the trench. I'm trying to model the trench with a three-dimensional array of points that are configured to approximate a drawdown cone within the trench, based on elevations at one end and in the middle. The array is currently set up as a 2'x2' grid extending over a 4'x268' area. The river margin is represented by a series of polylines extracted from a photogrammetric topographic map, which contains all topographic elements in 3D. The drawing doesn't contain any extraneous extreme high or low elevation points.

I'd like to model the area with a very tight (2'x2') grid, if I can, with exponential kriging, so I'll get nice, smooth contours and honor all the trench and pumping well data.

Any suggestions on getting this model to work other than coarsening up the grid to 4'x4' or greater?

I'm attaching a zip file containing the DWG with the points, a configuration file that represents what I'd like to use, and a surface file with a successful model at 4'x4' and the point data.

BS.zip

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Hi Mud,

The "unstable" message indicates that the variogram settings are not appropriate for the data set. Change the variogram settings to see if you can get a better kriging grid.

Kriging can run into problems if the surface has any discontinuities, and pumping in the trench could be causing a discontinuity.

Thanks,

Tom B

RockWare Inc

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Looks like I fixed it by reducing the density of the trench grid to 4'x4'. The surface computes with no difficulty with that grid and the remaining points and polylines.

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