Merging

Merging involves joining together a run of pipes with very similar gradients and diameters to create one pipe that has the cumulative length of the original run of pipes. Note that you can only merge pipes of the same shape and that have the same number of barrels. Any pipe that has no value set for the Number of barrels can be merged with another one whose Number of barrels is either not set or set to one.

As part of the merging 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 merged. See Storage Compensation during Merging and Pruning for more details.

The Merging Process

There are two parts to the process. Carry out stages 1 and 2 to set up parameters used for future merging processes. Then carry out stage 3 to merge individual runs of pipes.

Stage 1: Setting up Merge Options

The first stage is to set up the storage compensation options:

1. Choose Simplify | Simplification options on the Model menu. This displays the Simplification Options Dialog.
2. Go to the Network Simplification Page.
3. Click on the Define button in the Merge section. This displays the Merge 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 merge.
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 Network Simplification Page you can set a flag to apply to all storage compensation values changed during the merge process

Stage 2. Setting similarity criteria

The second stage is to set the criteria for which pipes are deemed to be similar to one another.

1. Choose Simplify | Simplification options on the Model menu. This displays the Simplification Options Dialog.
2. Go to the Similarity Specification Page.
3. Enter a value for gradient similarity. An absolute value indicates that, to be similar, pipes must have gradients differing by not more than that value. A relative value indicates that, to be similar, pipes must have gradients within that percentage of each other. By default, the gradients must be within 10% of each other.
4. Enter a value for dimension similarity. An absolute value indicates that, to be similar, pipes must have dimensions (both width and height) differing by not more than that value. A relative value indicates that, to be similar, pipes must have dimensions within that percentage of each other. By default, the dimensions must be within 10% of each other.
5. Enter a value for invert tolerance. To be merged, pipes must have inverts differing by not more than this value. By default, the inverts must be within 0.1m of each other.

Stage 3. Merging a run of pipes

Having set the similarity criteria and storage compensation options, the final stage is to merge the selected pipes.

1. Click on the icon in the toolbar or choose Simplify | Select similar links mode for merging on the Model menu. The cursor changes to the merge cursor.
2. Click on a pipe. InfoWorks ICM selects all similar pipes in the same run as your chosen pipe. It will not select past a junction.
3. You can also select or deselect individual pipes by holding down CTRL and clicking on them in the GeoPlan Window.
4. From the Model menu, choose Simplify | Merge selection. This displays the Network Simplification Dialog.
5. The dialog tells you how many nodes and links will be removed as part of the merge. You must reassign the subcatchments from those nodes that will be removed. Choose to reassign the subcatchments to either the remaining upstream node or the remaining downstream node.
6. If pipes about to be merged belong to different system types, you will have to choose what system type to apply to the merged pipe
7. Click on OK to complete the merge process. InfoWorks ICM merges all of the original pipes into one pipe, which has the gradient and dimension of the pipe furthest upstream in the run and the cumulative length of the original pipes.

Finding Merged Pipes

In order to find merged pipes:

1. Open the Link Grid windows by clicking the  button or choosing Grid windows | New links window from the Window menu.
2. Select the Conduit tab. This displays the Conduit Grid Window of the Links Grid.
3. One of the Conduit Data Fields is a check-box called Is Merged. Sort this column in descending order, and all merged links (where the box is checked) will be moved to the top of the grid. You sort the column by right clicking on the column and choosing Sort Descending from the popup menu.
4. You can now view the merged pipe properties by double clicking on the appropriate row. Pipes can be un-merged on the Simplified Page of the Conduit Property Sheet.

Unmerging pipes

To unmerge a run of pipes that have been merged into one pipe during simplification:

1. Display the property sheet for a merged pipe by clicking on the symbol on the tool bar, and then clicking on the merged pipe in the GeoPlan Window, or by double clicking on the merged pipe on the Conduit Grid Window of the Links Grid.
2. Click on the button next to the Merge Details field to display the Simplified Conduit Dialog. This lists the original links, nodes and subcatchments that were merged to produce this pipe.
3. To unmerge, click on the Un-merge button. This restores the original links, nodes and subcatchments, and removes any additional storage added to adjacent nodes as part of the merging process.