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HEC-RAS levees / ineffective flow issues

HEC-RAS levees / ineffective flow issues

HEC-RAS levees / ineffective flow issues

(OP)
All,

I am in the process of developing two models and need assistance with some wse issues. There are two creeks that run parallel to each other with a bridge crossing on both. The creeks converge a couple miles downstream so they are being modeled separate. The issue that I am having is there are berms on each bank of both creeks. When talking with property owners, they say that the water stays within the creek banks and only over tops due to debris clogging the bridge opening. So for the natural conditions model, I originally set levee station on the tops of the berms to contain the water. This caused the some wse issues where the 2-yr event is elevated above the 5- and 10-yr events and 5- through 200-yr events revert to critical depth at the furthest downstream cross section.

I have tried to solve the problem by adding ineffective flow stations to the levee stations so the top width would not very drastically and cause the model to use critical depth. I have tried adding interpolated cross section, adding cross sections, and even removing the cross sections with issues. So far no matter what I change, the furthest downstream cross section uses critical depth and the 2-yr event does not follow the other profiles.

I believe on the problems is near the bridge, there are large roadside ditches that enter the creek on the upstream and downstream sides. I do not have a cross section through the ditch, but the cross sections are close enough that they pick up some attributes of the roadside ditches. Specifically, the top of bank stations are wider than the typical creek section. The water having to contract and expand through this area I think is causing some of the problems.

Attached is a typical cross section and the profiles (levees removed). Let me know your thoughts.

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