Problem with TabulatedRatingCurve for non-monotonic spillway rating curves

[AKhakurel3]

Hello!! I am trying to model a spillway with non-monotonic rating curves (due to changes in flow regime from free flow to submerged for higher flow due to narrow downstream section) (Attached) in RIBASIM. With TabulatedRatingCurve boundary, it seems like the discharge cannot decrease when water level is rising(i.e. should be monotonic). How can I implement this type of spillway using DiscreteControl boundary?

[Huite]

Hi @AKhakurel3

I happen to be the first one answering -- I briefly discussed this with @visr, he might give a more complete explanation.

With current capabilities, the easiest way is probably to switch to a different rating curve with DiscreteControl.
Flipping the figure so that level is on the x-axis, and discharge is on the y-axis, you could do something like:

This doesn't give a great fit, but it's better than nothing.

@visr also suggested that non-monotonic curves might not be essential, in principle the solver should be able to handle it. In which case, you could get an experimental version which doesn't do the monotonity check.