Multiple Openings

[flood]

Good afternoon fellow engineers and designers,

I am trying to analyze a road crossing with three openings. One is a 1.5' RCP, the second is a 20' span x 13' h bridge, and the third is a 6' CMP. The channel flows through the 6' CMP with the other two acting as relief structures if the WSEL reaches them. Between the 6' CMP and the bridge is a levee 6.5' above the cmp inv and 4' above the bridge/road elevation.

I have reviewed the data more than once and found no error. But, the multiple opening analysis will not converge (30 iterations) and produces unreasonable results. It indicates that the EG is lower in the cross section 10' upstream of the culvert than at the culvert. This is not good, plus the levee works in the cross section 10' upstream of the culvert, but not at the culvert. All storm events (2 yr - 100 yr) have results that are in the critical regime, which, also does not seem practical.

Would anyone have an idea what is happening? Thank you for your assistance.

John Wood

[Hydraulics Tool]

Are you allowing the stagnation points to "wander"? In other words, overlap your multiple opening stations. That allows RAS to determine the stagnation points during the optimization process. If you force a given stagnation point (or points), RAS may not be able to come up with a solution. Check the manual on this.