When you say "velocity errors", I assume you are referring to the user notifications that say "Conduit does not meet minimum velocity constraint."
These messages are warnings (note the yellow color circle next to them) that do not prevent the model from computing. They are in reference to the automated design feature's design constraints. In the Design Alternative, you will see that the minimum velocity constraint is set to 0.61 m/s. The pipes in question have a velocity greater than this, so the user notifications in questions appear.
This model is set to Analysis mode (not Design), so it will not try to automatically change pipe sizes and slopes to meet the constraints. For Analysis mode, those notifications will still display for informational purposes.
Furthermore, even when running automated design, the minimum velocity constraints are at the bottom of the constraint priority order and are unlikely to be satisfied without violating another constraint (again though, those notifications will still display for informational purposes.) See:
Unable to meet minimum or maximum velocity constraint
Order of automated design priorities for StormCAD (GVF-Rational) and SewerCAD (GVF-Convex)
For minimum velocity problems, you may also want to look into Tractive Stress.
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.