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Boundary Condition Issue


Umur
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Hi everyone,

I am trying to build a conceptual model with 3 layer and with a river, well and general head boundary conditions. I interpolate my layer elevations from raster data. For river and general head boundary conditions I enter head-stage then map to MODFLOW. After I build the model the heads of river and general head boundary conditions and the elevation data doesnt match at all. Anyone can help me on this? I am stuck right now and need help.

Thanks.

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Such as for ghb condition I enter 810 m for head value as starting point of arc and 770 m for the end of it. It interpolate through the arc when I mapped to modflow. When I check the cells with ghb conditions the top elevation mostly is below the head value after the interpolation. Because of that the model doesnt converge. This happens also for the river boundary condition too.

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Have you tried to add nodes to your river and GHB boundaries and assign elevations to them?

If you add a vertex to a line within the conceptual model, right-click on the vertex and choose convert to node, then you can right-click on the new node and assign an elevation and head value. Do this is a few locations along your arc/line and convert to MODFLOW again.

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I already have nodes on arcs of river and ghb conditions and I assign head values to them. Actually that's my problem. The elevation and head values on arcs is different when I mapped them to Modflow. Most of the head values are above of top elevation.

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When mapping to MODFLOW the values assigned to the cells are taken by linearly interpolating the node values along the arc. It may be that the elevation values for the grid don't match the linearly interpolated values so an arc needs to be split into more arcs as bjacoby mentioned. Then the head and elevation values on the new nodes could be set to match the grid. An arc can be split either by selecting the create node tool and clicking somewhere along the arc, or selecting the select vertices tool, right clicking on a vertex along the arc, and selecting Vertex -> Node.

If the boundary conditions are getting assigned to the incorrect cell vertically, it may be the layer range needs to be adjusted. The default layer range can be set in the Coverage Setup dialog, or each arc has a layer range attribute when Layer range is checked in the Sources/Sinks/BCs section of the Coverage Setup dialog.

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