Low Flow Profile WSEL > High Flow Profile

[Braden Olson]

I am wondering if anyone can help me understand some potential reasons why I have a 10 year flood water surface elevation that is greater than a 50, 100, and 500 year flow at my cross sections 3 and 4 upstream of a bridge.

I have ineffective flow areas placed near the abutments where the that flow is permanently ineffective and does not convey flow. The rest of the overbank does not have ineffective flow as it should convey flow topographically.

The 50, 100, and 500 year flood is showing that flow is conveyed around the bridge but for the 10 year flood the flow is being restricted to flow under the bridge which is causing the water surface elevation to rise above the other flood profiles at these cross sections.

My bridge data editor is currently set for broad crested weir with max submergence as the default of 0.98. No minimum weir flow elevation is in place. For my bridge modeling approach editor I have the low flow method to be computed as Energy (standard step) and to ‘use’ that computation. For my high flow method I have energy only selected (standard step). I do not think it would be appropriate to model the bridge high flow method as pressure and/or weir as non of the water surface elevations are greater than the low chord of my bridge.

I have tried running subcritical flow regime vs mixed flow regime. I have adjusted my critical depth calculation tolerance to its minimum of 0.0001. I have adjusted my water surface calculation to its minimum of 0.0001.

I appreciate your help. Thank you.

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