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Re: duck bill
If you have a channel and you want to model a weir that is non-linear in the channel, the highest wse will occur when you assume a linear weir across the length of the channel.
For instance, if you are designing a road alignment, then the finished surface grade of the road usually needs to be at least 1-3' above the upstream WSE.
What I would do is (going downstream before the start of the weir), stop at the station where the weir begins and model a linear weir at this point. This will give you the highest WSE possible. Just make sure you start the weir at the most upstream point.
This is how I would do it, because I do not believe HEC-RAS can efficiently model 2-D flow. However, the methodology I've explained is a good work-around. Let me know if you have any more questions.
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