I have problem with modeling side weir in the situation when diameter of the conduit changes for example from DN800 to DN300.
Side weir suppose to start working at crest elevation 97,55, but nothing happens when the water level in the conduit reaches this level. The water starts to overflow only at 97,7 only when water level reaches the maximum modeling point.
But when I change the diameter of the conduit to DN 800, so there is no change in the diameters in the profile line, side weir starts to work properly. If overflows as it should at elevation 97,30.
Please explain the hydraulics in these situations and why does side weir makes different effect in these two situations.