Lateral Weir Percent Q Leaving greater than 100%

[Anonymous]

I have a lateral weir modelling spillage along natural overbank channel into an adjacent ditch-line waterway. The existing condition version of this lateral weir is working fine, but in the proposed condition I am getting invalid results. The Lateral Structure output table shows 135 cfs coming at the weir from upstream, 135 cfs passing down the main channel, and 262 cfs passing over the weir (Percent Q leaving = 193%). However the 262 cfs it say is leaving never shows up in the adjacent ditch-line waterway. What is going on? Changing the number of iterations and tolerances changes the output results, but does not make the invalidity go away.

[cameron]

There is a thread that discusses a similar issue. Basically it came down to the placement of the lateral structure along the mesh elements.

[Anonymous]

I eventually found the answer to my own question. I had 2 problems. Turns out, if your weir coefficients are too high, as mine were, it wall cause model stability problems.

Secondly, if you rename the ‘River Name’ or ‘Reach Name’ on the upstream (HW) side of a lateral weir, the lateral structure will stop working. The software will calculate an amount of flow that should pass over the weir, but that flow will remain in the HW river reach, and will not appear in the TW river reach. If you rename the River/Reach back to what it was originally, the lateral weir will work again. The River/Reach on the downstream side of the lateral structure can be renamed without affecting the flow split results.

[Author]

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