Flows at d/s of the lateral structure and leaving it, after optimization does not add up to the flow in the u/s

[kmittal]

I would appreciate some help/advice on optimizing a lateral structure on a stream.

There is a lateral structure modeled as weir on the main stream. After 3 RS at the d/s of the structure, this main stream is splitting in one additional “Bypass stream”. Tail water connection at the lateral structure was set as the first RS (most u/s) of the “Bypass stream”.
I was trying to optimize flows in the lateral structure and the main stream. The result flows from lateral structure optimization (Flows at d/s of the lateral structure and leaving it) does not add up to the flow in the u/s of Lateral structure. The difference in flows is highly considerable.
I have a schematic which I can post if someone ask me.

Any assistance would be greatly appreciated!!

[cameron]

what is your weir coefficient? Does it make sense? Are you getting convergence when you turn on flow optimization or is it hitting the max iterations?

[kmittal]

Thanks for the reply!
I am using the Weir coefficient as 2.5 and yes flows are getting converged.
For your reference, kindly check the attached results of “Profile Output Table-Lateral_Structure”.
Q leavving total+Q d/s should be equal or at least nearer to Q u/s, which is not there for all the profiles.

[cameron]

First make sure your weir coefficient makes sense for a lateral structure (see link below) as 2.5 is out of range from what HEC recommends.

http://hecrasmodel.blogspot.com/2013/12/lateral-structure-coefficients.html

What is the discharge values downstream of the lateral weir in the cross-sections for both the main channel and the side channel? Do they match the table you presented? Have you done a simple hand calculation to make sure the values make sense from the model (CLH^(3/2)?

[kmittal]

Thanks again. I will check weir coefficient which you mentioned.
The discharge values at d/s of lateral weir for main channel are mentioned below

and for side channel are mentioned below

I have done the calculations using weir equation using the average head form results and flows are matching.

[cameron]

If you look at the 7097 and 648 values they add up to the total amount upstream of the lateral structure. The lateral structures span at least two cross-sections (could be more) so the total split flow would not be seen until after the lateral structure.

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