Process for specifying constant head in top model layer

[tlillys]

Hi all,

I am not a constant user of GMS so I am often re-learning data processing techniques.  I am looking for help with a procedure to accomplish the following objective. 

I have a 10 layer, steady state flow model of a coastal plain. The top layer predominantly represents a confining clay layer (material 1 in brown) with several small discontinuous regions where the underlying aquifer is exposed (material 2 in green) and some inactive regions (in red). Regions where the underlying aquifer are exposed have specified values for recharge (using polygon feature objects derived from shapefile). Other BC's are defined on the top layer: (CHD for ocean - in cyan; rivers in blue; drains appearing only in material 2 - not shown).

I would like to specify a constant head in layer 1 equal to (TOP-1m) for every cell where clay is present but not interfere with other BCs subject to the following constraints:

If (TOP -1) > BOT,

   Constant head = TOP - 1

Else

   Constant head = BOT + (TOP - BOT) * 0.1

Any help on a process for accomplishing this task would be greatly appreciated.

Thanks

Ted

Edited September 13, 2019 by tlillys

[tlillys]

My solution was to use QGIS to first create a raster from the DEM that followed the rules above. Then I created a polygon shape for the entire grid and then used the Difference algorithm to cut away the other features in the region that are represented by polygon shapes, one by one, first the ocean, rivers, green and red areas, leaving a polygon that represented the exposed clay layer at the surface.  I imported the polygon shapes and used the raster to define the CHD head stage value.