The program determines the model upstream node(s) where an upstream boundary condition in terms of discharge is required. It also determines the downstream node(s) where a downstream boundary condition (water level or a rating curve) has to be specified.

The upstream nodes of the model can never be simultaneously the downstream nodes of a reach. The downstream nodes can never also be the upstream nodes of a reach. A model which is neither branched nor looped, finally has only one upstream node, corresponding to the main sluice at the dam, and only one downstream node, corresponding to the tail end of the canal.