Overflow channel modeling – parallel reaches or not?

[ss1211]

I am modeling a stream that splits about 450 ft upstream of a road (there is a main channel and an overflow channel, which only sees about 50-year and above events), passes through two culverts, and converges again almost immediately downstream of the outlets.
Is there a way to model this using two separate reaches? The water surfaces need to be the same at the approach section to the road for the design storm events, but the “overflow” culvert has a lower invert, and therefore inaccurately shows the lower frequency events passing through it.
Old HEC-2 data shows FEMA modeled the area using long cross sections containing both reaches, but obviously 1D analysis doesn’t accurately distribute the flow, especially for lower frequency events.

[Anonymous]

You could put a junction where it splits and where it comes together and do it as separate reaches. Without knowing more hard to say how good it would be.

[Author]

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