The implicit dynamic engine solves the St. Venant equations along straight branches of conduit or channel starting at the most downstream outfall. Branch 1 starts at the outfall and upstream until it reaches the first junction. There it follows the junction with the largest conduit and/or the conduit with the alignment that matches the outlet pipe alignment. This continues until the branch reaches the most upstream node. At this point a second branch starts from the largest pipe from the first junction that was not in branch 1. This branch continues to its most upstream point. Once these branches are numbered, branches that start at pump station wet wells are traced out to their source.

An example of the branch labeling is shown in the figure below. The red numbers indicate branches. In the figure, branch 1 is made up of 30 in. pipes; branch 2 is made up of 24 in. pipes while the other branches consist of 18 in. pipes.

Branch Labeling