Inline Weir depth results

[pauld]

I wrote this message some time ago, but nobody answered me: tell me something about generic simulation with inline weir and tell me if any other had the same problem !!


OLD Message:
I try to perform a simulation in a prismatic rectangular channel in subcritial conditions and steady flow; I draw an inline thick (0,05 m) weir to analyze the answer of the software in an "hydraulic standard exercise" (so that I can control manually the result).
HecRAS 3 computed results where (for example):
AVERAGE DEPTH (over the weir) = 0,2 m
MAX DEPTH (over the weir) = 0,35 m
I was suprised because average depth corresponds to depth linked to flow rate by usual hydraulic expression Q = CH^1,5, but Max depth was assumed by the program as the hydraulic depth in cross sections before the weir, to estabilish profile.
I think it's strange first of all because the difference between the two computed Depths is high (I suppose a regular geometry in my channel, so the depth should be the same over the entire width of the weir).
Also, in a real situation (a real channel in the same geometric and flow conditions, as the one simulated) if I'd like to mesure the flow in the channel I tried to estimate the depth over the weir, or in a cross section just before the weir: in this real case I don't think I should find so a big difference between the two depths, and the depth over the weir should be more or less, the same of a previous cross section.

Can anyone make me undertand, or tell me were I'm wrong ???

Thank you

Pauld