GMS, SMS, and WMS User Forum

# GHB conductance

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Ok this is a simple question, but I can't find the answer anywhere and I am use to how Vis Modflow calculates GHB conductance.

How do you calculate the conductance for a GHB in GMS. The units are in ft^2/day/ft. Maybe a more appropriate question is does GMS calculate the GHB cond as a polygon or a line? Based on the units it looks like a line and the ft^2/day is a transmissivity value, however when reading FAQ it indicates (in a round about way) that the K is multiplied by the length of the arc and divided by the distance to the assigned head.

Any help is appreciated - Greg

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Greg

I assume that you are using the points, lines, or polygons in the Map tools in GMS to create your GHB. If so, here is how it works:

For points: the value of conductance assigned to the point is assigned to the GHB of the cell that contains the point. The units for conductance on the point are length^2/time.

For arcs (polylines): the value of conductance assigned to the arc is multiplied by the length of the arc that intersects the cell where the GHB is created. Thus for arcs the units on conductance are length^2/time/length so that when you multiply by the length of the arc that intersects the cell you get length^2/time.

For polygons: the value of conductance assigned to the polygon is multiplied by the area of the polygon that intersects the cell where the GHB is created. So for polygons the units of conductance are listed as length^2/time/length^2 so that when you multiply by the area you get length^2/time.

If you are editing a GHB bc directly on the grid then the units are length^2/time.

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