Wrong formula in the culvert flow rate calculation with OPTBUSE=1

This issue was created automatically from an original CUE issue, opened by Agnes Leroy. Further discussion may take place here.

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The formulation for culverts should yield the same result as the siphon formulation in the specific case of the siphon.
This is the case with the option 2 for the culverts treatment but not with the option 1.
The test-case bridge (of TELEMAC-2D) is impacted.