If a gap or "break" exists within the network then RivEX will be unable to trace beyond the gap. Gaps in a river network can be digitising errors or cartographic in origin, such as a bridge.  They can be small and often very hard to see with the naked eye. Gaps will have a significant negative impact on many of the attribution tools in RivEX resulting in plausible values but completely wrong!  You must edit the network and close the gaps ensuring the network is connected at nodes.

RivEX provides a suite of tools for finding errors and reporting errors in an error log table. It is often helpful to visualise gaps to focus your attention on the sections of the network that need correcting.  Extracting out mouth nodes will allow you to quickly spot locations that need your attention.  You are expecting to see mouths ONLY at the coastline and not within the interior of the catchment.



Processing Task


You have run through steps 1 and 2 in preparing a river network and used some of the quality control tools which returned no errors. You then attributed your network with Strahler Order and as with any output created by RivEX you checked it!  But you noticed that results of the stream ordering didn't make sense.  You decide to extract out the mouths of the network to see if breaks exist within the network as this would account for the unusual results in stream ordering.


The river network; at this scale the network appears fully connected with the river mouths at the coastline.

Broken Rivers


Run the Create a node layer tool exporting only mouth nodes. Output is written to the Nodes geodatabase.

Create a node layer tool.


The results of this tool are added to the map and we can see 3 mouth nodes highlighted by the black boxes within the interior of the network and not at the coast.



Zooming into one of these erroneous mouths it is clear that there is a gap in the network and when measured it represents a gap of just 18cm.  This example is where the downstream end of a tributary has not been snapped to the junction.

The Break


Not all gaps are un-snapped junctions, they may be a gap created by:

  • A section of river missing, this might be due to a bulk select and delete run on the network.
  • Gaps from cartographic origins such as a bridge and the centreline network has not been connected up.
  • The polyline is a malformed multi-part, multi-part geometry are invalid and must be corrected.

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