Preparing the river network is the first step in any workflow.  You must create a workspace which is a folder that RivEX writes outputs to and records changes to the river network through the settings file. Having created the RivEX workspace you then must extract the network topology.  If you make edits to the network you will typically need to re-run the extract topology tool so the logical network (stored as topological dictionaries) is in sync with the geometry of the network.  The two preparation tools are: