I see where @dieterdreist is coming from. These lines do not provide any additional information that isn’t already present in the map. Existing inlets and outlets perfectly describe the fact(s) that a flowline purports to describe.
It’s not clear that there’s a real problem that is being solved here, except perhaps to make the waterways map look a little nicer, in which case we’re basically tagging for the render by suggesting a nice place to put labels and not mapping actual geodata.