MODFLOW-USG Calibration Workflow

To calibrate an existing MODFLOW-USG model, use the following steps:

1. Begin with an existing MODFLOW-USG project.
The existing model can be created using the conceptual model or grid based approach. If necessary convert an existing MODFLOW model to a MODFLOW-USG model by: Right-click on the “MODFLOW” item in the Project Explorer and select Convert to MODFLOW-USG Simulation.

2. Create observation data.

1. Create an observation coverage. Create a coverage with at least one Observation Points option turned on. 1. Create new coverage from scratch. Use the New Coverage right-click command. Use the Coverage Setup dialog to create a new coverage by selecting the desired coverage properties and naming the coverage. 2. Create new coverage from an existing coverage. Use the Duplicate command on an existing coverage. This will copy any feature objects on the coverage. Use the Rename command to give the coverage a new name. Change the coverage setup. 2. Create observation points or arcs. 1. Create feature points, arcs, nodes and vertices. In the map module, create feature objects in the active coverage. Use the Create Arc tool to create arcs in the map coverage. Begin creating a new arc by clicking in the graphics window at either arc end. If clicking on an existing feature node, vertex or arc, the new arc will snap to that object. Double-click or press the Enter key to terminate the arc. Use the Create Point tool to create additional nodes alone or to split arcs. 2. Modify arcs. Feature arcs, whether digitized or incorporated from a boundary condition or a material coverage, often need to be edited after initial creation. 1. Create additional vertices on arcs. Use the Create Vertex tool to add vertices along arcs. 2. Refine the arc shape. Use the Select Vertices tool and the Select Points\Nodes tool to move/edit existing arcs and refine the shape by dragging the nodes/vertices. Use the Select Arcs tool to move entire arcs . 3. Split arcs. An existing arc can be split by: 1. Converting a vertex to a node. Use the Select Vertices tool. Select the Feature Objects | Vertices → Nodes command to split the arc into two arcs. 2. Add a node to the arc. Use the Create Point tool to add a node on an arc in order to split it into two arcs. 3. Connect the end of an existing arc to the middle of the arc. Use the Select Points\Nodes tool to drag the node of an existing arc to anywhere in the middle of another arc. This will split the second arc into two arcs. 4. Add a new connecting arc. Use the Create Arc tool to start or end a new arc on an existing arc to split the existing arc into two arcs. 5. Split overlapping arcs using the Clean Options dialog. Select overlapping arcs using the Select Arcs tool. Use the Feature Objects | Clean command to bring up the Clean Options dialog. Select the Intersect selected arcs option (for selected arcs) or Intersect arcs option (for all overlapping arcs) to split the arcs. 4. Merge arcs. Two arcs that share an end node can be merged together. Select the shared node using the Select Points\Nodes tool. Click on the Feature Objects | Nodes → Vertices menu command to merge the arcs. If desired, the Select Vertices tool can be used to select and delete the new vertex. 5. Transform arcs. Select the arc using the Select Arcs tool. Use the Edit | Transform command. Use the Transform dialog to scale, translate or rotate the arc. 3. Set observation point or arc attributes. With the Select Point/Node tool, right-click on the observation point and select the Attribute Table command. Set the observation attributes in the Attributes Table dialog. With the Select Arc tool, right-click on the observation arc and select the Attribute Table command. Set the observation attributes in the Attributes Table dialog. 4. Re-run MODFLOW. Save the project. Run MODFLOW .

3. Generate observation data for MODFLOW-USG.
With the desired UGrid active, select the MODFLOW | Observations menu command. In the MODFLOW-USG Observations dialog, select Generate PEST Obs. Data. Select observation coverages in the Generate Observations dialog.

4. Change parameters.

1. Change model parameters. Model parameters are usually adjusted in the Map model on the appropriate coverage—usually the coverage with recharge or hydraulic conductivity values. With the Select Arc , Select Point/Node , or Select Polygon tool, right-click on the desired feature object and select the Attribute Table command. Adjust the attributes in the Attributes Table dialog to calibrate the model. 2. Map new parameters to MODFLOW. Select the conceptual model . Select Feature Objects | Map → MODFLOW . Select the appropriate options in the Map → Model dialog. 3. Re-run MODFLOW. Save the project. Run MODFLOW .