For the network algorithms to process correctly all polylines must be single part polylines. Multi-part polylines are often generated during editing, especially if the original data capture had a purpose other than a topologically connected network. 

You can "explode" multi-part polylines into single parts manually or by using a Geo-processing tool. 

WarningExploding the multi-part polyline into it's individual parts will result in the attributes of the original polyline being passed into all subsequent parts.  Whilst this is useful when the attribute is common to all parts (e.g. river name); node ID numbers would be incorrect. Exploding a multi-part polyline is altering the topology of the network,  you must re-run your network through the Extract Network Topology and write to Workspace tool to rebuild and correctly attribute the node and polyline fields in your river network.

Exploding Multi-part features manually

You can manually deal with a multi-part in one of two ways: 

  1. Manipulating the individual parts and vertices through the edit vertices panel.

  1. Start an edit session, select the multi-part polyline and click on the Edit Vertices tool. Note the vertices are shown as a sequence of green squares, terminating at a red square.  The red vertex is the To-node of the polyline, which in the example below is illogically is at the junction in the middle of the selected feature.

Edit vertices.

  1. Review the Edit Vertices panel. In this example the multi-part feature consists of two parts.   If this polyline was a "Z aware" feature it would also be showing Z information. Right clicking on different parts of the Edit Vertices panel will display different context menus and you can use these to remove whole parts of a multi-part feature or just a single vertex

Modify Features

  1. Use the Explode tool to separate out the parts into separate polylines then deal with any disconnections.

  1. Start an edit session, select the multi-part polyline and click on the Explode tool. To run the tool click on the Explode button in bottom right of the tool panel.

.Explode tool

  1. The explode tool will separate out the parts into individual polylines, but it will not resolve the disconnection that it has created. In this example a polyline has been selected after the exploding step, note the selection continues past the junction (red circle) indicating that the incoming tributary is simply touching the polyline and not connecting at a node.  You need to split the selected line and snap the incoming tributary to the new junction.

Disconnection created by exploding out parts

Exploding Multi-part features using the Geo-processing tool

You can run your entire dataset or a selection through the Multipart to Singlepart Geo-processing tool.  It will search for multi-part shapes and explode them into individual parts.  You must check the orientation of the newly created polylines to ensure they are flowing in a downstream direction.  If you find a polyline created from a multi-part to be flowing in an upstream direction then you can edit it and flip its direction.  You will have to deal any disconnections created by the multipart becoming single parts.  The Multipart to singlepart tool is found in the Data management tool box > Features tool set.

Multipart to Singlepart geo-processing tool

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