tlillys

Coverage Setup for Wells

2 posts in this topic

I'm a newer user building a MODFLOW model that I will then need to teach others how the model was constructed, I am establishing a coverage for the WEL package that will use a point shapefile from another model to inform the location and pumping/abstraction rates.  One of the attributes in the shapefile is "Layer", identifying the layer of the well in the 10 layers of the model.  I was shown how to create the coverage but I wanted to understand the rationale for selecting the Layer Range item in the Source/Sink/BCs list.  I'm guessing this allows the use of the Layer attribute to map the points to specific layers in the Solid and Grid models, assuming they appear within layers 1 to 10, as specified.

Also, I had a question about the "Use to define model boundary (active area)" check box.  I have conflicting information as to when that should be checked in a coverage.  My intuition tells me that is would only apply to feature objects that define the model boundary and not necessarily other boundary conditions that are applied to the model boundary conditions.  For example, given one coverage (a polygon) that defines the extent of the active region of the model across all layers is create with the "Use to define..." item checked. If separate coverage was created that defines a constant head on layers along one edge of the active model domain, already identified as active in the other coverage, does the box need to be checked?  When should it be check and not?  Is there a danger in checking the box when it shouldn't.

Any insights are appreciated

Ted

coverage setup.jpg

Edited by tlillys
clarifying and correcting typos

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The layer range can be used to assign one to many layers over which a boundary condition is applied. When turned on, three fields are added to the attribute table including Auto assign layer, From layer, and To layer. If you would like to use your shape file to determine the well layer you could turn this on, set Auto assign layer to Use layer range, and then map the layer field from the shape file to the from and to layer fields.

When "Use to define model boundary" is checked, any polygons defined in the coverage get added to the model area that is used when running the "Activate Cells in Coverage(s)" command. For no flow boundary cells a majority of the cell has to be with a polygon for it to be active. For specified head cells if any portion of the cell is inside a boundary polygon then it is activated. The "Activate Cells in Coverage(s) command is described in more detail here: http://www.xmswiki.com/wiki/GMS:Activate_Cells_in_Coverage.

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