groundwater volume balance residual raster - values too large?

Discussion created by zack.benedetto on Jan 11, 2014

I am attempting to make a groundwater flow model using the Darcy Flow tool in Arcmap 10.1 (using a 1-meter DEM, well level data and geologic characteristics. However, the groundwater volume balance residual raster from my output has large values, and I've read that if the values are too large (from error of groundwater elevations not matching transmissivity values) then the output is practically meaningless. Can someone clarify for me what range of residuals (and in what units) is reasonable? I would also think that the residuals near zero would not be normal because of places of discharge and recharge.

See attachment below.

First of all, the checkerboard pattern I believe is a result of the transmissivity values not matching the head values well enough, but I am still investigating issues with that too because it may be related to the size of the data too. Green areas are closest to zero but still vary from -1000 to 1000 mostly. I'm not even sure what the units of that is but I used units of feet and days throughout the rest of the data. There are also those pockets of yellow and blue that could potentially be areas of recharge and discharge, respectively, or could just be errors from the transmissivity values too.

Can anybody provide me with insight concerning the issues with the residuals and the strange checkerboard effect?


Zachary Benedetto
B.S. Civil Engineering '14
B.A. Geology '14
Lafayette College