Pruning

Pruning involves removing pipes that are not significant enough to be included in the model.

As part of the pruning process, storage compensation can be carried out to ensure that no storage volume is lost from the system when a section of the system is pruned. See Storage Compensation during Merging and Pruning for more details.

The Pruning Process

The pruning process comes in two parts. In the first stage, you set up options for use with future pruning operations. You then carry out subsequent stages for each pruning operation.

Stage 1. Setting up Pruning Parameters

Set up the parameters used by the pruning process on the Prune dialog.

1. Choose SimplifySimplification options on the Model menu. This displays the Simplification Options dialog.
2. Go to the Network Simplification page.
3. Click Define in the Prune section. This displays the Prune dialog.
4. On the Include page,choose what existing storage will be applied to nearby nodes as part of the storage compensation process. If you leave an item unchecked that particular storage type will be lost to the system when you prune.
5. On the Distribution page, decide where to apply storage during storage compensation. See Storage Compensation during Merging and Pruning for more.
6. On the Selection Refinement page of the Prune dialog, set options for refining the selection before pruning. You use these options in Stage 3.
7. On the Network Simplification page you can set a flag to apply to all storage compensation values changed during the pruning process.

Stage 2: Selecting pipe types

The second stage of pruning is to select the pipes that are to be removed from the model. You could select pipes individually, or by any of the other methods available for Selecting Network Objects. One method that might be useful is using SQL to select all pipes below a particular size:

1. From the Selection menu, choose SQL select.
2. In the SQL Table tab, select the Conduits table.
3. In the Where Clause tab, create a query that will select the required links.

   For example, to select all links with a width less than 300mm, enter the query: conduit_width < 300

4. Click Test to see how many links are affected by the selection. Then either click Apply to select the links and keep the SQL Query dialog open; or Run to select the links and close the dialog.

Stage 3. Checking the Refined Selection

Having selected a group of pipes, the third stage of the pruning process is to refine the selection if necessary.

1. Make sure you have set up your refine selection options on the Selection Refinement Page of the Prune dialog. You can:
   • keep selected only those links that are part of a wholly selected run of links that terminates at the end of a branch
   • keep selected any nodes which are only connected to pruned links, or are not connected to any links at all
   • de-select any nodes which are connected to links that will not be pruned
2. From the Model menu, choose SimplifyRefine selection for pruning. InfoWorks ICM will refine the selection based on the settings in the Prune dialog. The objects that meet the selection requirements are highlighted on the GeoPlan.

   When determining which objects are to be pruned based on the selection criteria, ICM finds the most downstream selected link and then examines all selected upstream links and nodes from it. ICM expects that all selected links in a network have the same system type but, when it cannot find an upstream node for a link with the same system type, it may accept a selected upstream node with any system type if the link's downstream node is not selected or has a different system type. However, if this is not the case, ICM terminates the current pruning area (a connected set of links and nodes) at that upstream node and creates a new pruning area starting from there. This may result in a difference between the number of areas of the network you would expect to be affected by pruning and the number that are actually are.

3. You can also adjust the selection by selecting or de-selecting nodes or links in GeoPlan Window by holding down CTRL and clicking on individual nodes or links.

Stage 4. Pruning links and nodes

The final stage of the pruning process is to remove the selected links and nodes.

1. From the Model menu, choose SimplifyPrune selection.
2. The number of sections about to be pruned is given. Click OK.

   InfoWorks ICM now completes the pruning process. Subcatchments linked to pruned nodes are reassigned to the nearest downstream node. Additional storage is added to adjacent nodes as part of the storage compensation process depending on the options you chose on the Distribution Page of the Prune dialog.

Working with pruned objects

The pruned links are displayed in the GeoPlan Window as a line with no nodes. By default this line is coloured orange.

View the properties of a pruned section of the network in the same way as any other network object. Select the tool and then click on the pruned object on the GeoPlan Window. This displays the pruned object property sheet in the Object Properties Window.

Note that pruned objects are given an automatically generated name of the form {96D15462-93A0-4b4d-9430-41B93BCE73D9}. This is called a GUID, or Globally Unique IDentifier.

Restoring pruned objects

The original nodes and links that were removed when the network was pruned can be restored from the pruned objects property sheet.

To restore pruned objects, click on the button next to the Merge Details field to display the Pruned Link dialog. Click Restore button on the dialog. The original nodes and links are re-instated and any subcatchments moved as part of the pruning process are reassigned to their original nodes. Any additional storage added to adjacent nodes is removed.