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Boundary condition: specified flow


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I've build a 3D Modflow 4 layers model with Constant Head Boundary condition (CHD, specified head) and Specified Flow Boundary condition.

The CHD refers to 1-4 layers while the Speficied Flow referes to 3-4 layers.

I get the Flow Budget by selecting the cells intersecting the Specified Flow coverage. I get the same values of Q for wells for each layer.

So, my question: is the Q set in the coverage (Specified Flow) divided by the number of layers regardless of each layer width?

I need to divide the input Q (100) among the layers proportional to the width of each layer (20, 20 60) and not equal to the total Q divided by layers' number (33, 33, 33).

Should I set different coverages, one for each layer?

Thank you

D Lattuada

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If you are using the "specified flow" attribute type in a coverage and assigning it to an arc or a polygon then the flow into a column of cells (layer 1 to layer N) depends on the length of arc that intersects the cell (or in the case of a polygon the area that intersects the cell) and then the flow is divided equally among the cells. There is no accounting for the change in Transmissivity between the cells.

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Thank you Michael, I was dealing with Specified Flow Boundary condition as Alan explained very well.

Thank you Alan.

A workround could be to set up different coverages (arc), each one applied to a single layer, and assign it the desired flow.

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