r/HECRAS

https://preview.redd.it/rhdftwqax0kh1.png?width=1532&format=png&auto=webp&s=2e39213cb9ee0fbef99cca203ac03ddebccfd1e7

Modeling a proposed canal (left) that ties to an existing channel (right) with a culvert. I'm running into WSE backwatering issues which I believe have something to do with the following error warning I received for the XS immediately downstream of the junction.

• The energy equation could not be balanced within the specified number of iterations. The program used critical depth for the water surface and continued on with the calculations.

I have tried many tips and tricks for improving model stability like reducing XS spacing, making sure XS are as close to the junction as possible, cleaning up manning's n values, and increasing maximum iterations/tolerances for the steady flow analysis. I've looked into modeling the culvert as an inline structure and a lateral structure, but haven't yielded any good results. I also tried using a terrain modification to allow for cleaner XS along the existing channel.

How would you model this configuration? Or is a 1D-steady model too limited for a junction like this?

I really hit a wall with trying to figure out how to fix this error we have in this 2D model, rain on mesh. The weird part is it almost seems to bounce around, which is just making it harder to really find the root cause. In this case we have 9 scenarios we are trying to run, the only difference between the runs being rainfall depth. When the events are run, some 2-3 events will fail and give this error. After some trouble shooting attempts, I will rerun the models events, and some or all of the plans that failed before will run just fine, but then other events that ran correctly in the previous set up, will fail this time around. This model has been tossed around to a few people, and we have not made any progress and I think we are nearing the point where computers start getting thrown across the office.

We are using HEC RAS 6.6 for this project, but I have also gotten this same error in 7.0.1. We have 378 reference lines, and unfortunately they are all necessary. They can be moved some, but in general we need all reference lines. We are also using gridded rainfall data, and we have around 60 bridges/culverts. The model does run without the reference lines, but we cannot figure out what is wrong with them specifically. These reference lines were generated based on WSE contours, and we have used this methodology successfully in around 60 other models for this project. The reference lines are generated in a python script we have developed and imported into RAS Mapper. Again, we have done this for around 60 other models and no issues. Some of those other models had double the reference lines, or double the surveyed structures. The only thing that would make this model unique on paper is we are using the gridded rainfall data, and I think we have some initial condition points being used too. Cell size is generally 25-200ft based on what is being enforced, and total cell count is around 125k. I'll list everything we have tried for trouble shooting below in no particular order.

Restarting computer

Restarting HEC-RAS

Run in RAS 6.6, 7.0, 7.0.1, 6.4.1

Compute 2D Hydraulic tables in RAS Mapper instead of plan file

Run with start up time

Make copy of geometry

Creating new plan files

Deleting geometry HDF files

Make random cell edits in mesh in RAS Mapper, save edits to force recompute geometry

Creating a new model from a fresh start, and import the geometry over, and reimport all other features

Repair feature tool in ArcPro used on the reference line shapefiles and reimport into RAS Mapper

Run the model on different computers

Check and confirm correct and consistent projection across all features and terrain

Experimented with replacing gridded rainfall with hyetograph table for the perimeter

Confirmed there are no hidden boundary conditions unaccounted for.

I think that's pretty much it, but I would be willing to try just about anything else at this point.

EDIT: Just tried deleting all the reference lines and drawing random ones all over the place, maybe 10? Anyways same error, so may be an indicator that the underlying issue is somewhere other than the reference lines, and the reference lines are just the straw breaking the camels back.