[Justin M Palmer]

I’m converting multiple RAS 4.1 models to RAS 5.X, and running into this a lot too. RAS 5.0.5 seems to be more forgiving than RAS 5.0.3, so if you can switch to that, do it. If you have to use 5.0.3, or you are still having problems, maybe the below suggestion will help.

My models at issue are all non-georeferenced… I’m just trying to upgrade my simple 1-D models to use RAS 5. The XS interpolation surface isn’t very important for these models because my main goal is XS elevations and profiles, not a pretty map from RAS Mapper.

The fix for me was to re-arrange the stick diagram in geometric data editor. I had confluences where main-river XS lines overlapped with tributary XS lines, and similar things that would pose a problem for a computer trying to create an elevation surface in between those lines. I went to Edit… Move Points/Objects… and re-arranged the lines so they didn’t overlap and looked like something I could draw a surface in between.

This worked, but with larger models with many tribs and pseudo-georeferencing, it was frustrating, because some XSs would redraw way off the map unless I tweaked the furthest upstream and furthest downstream cross section for each reach.

The nice thing about this solution is that I’m not modifying the actual hydraulic model in any way. Other suggested solutions included moving bank stations and adding interpolated XS, but I wanted to avoid those because they technically create a change to the geometry/hydraulics.

[Justin M Palmer]

David, I came across this with my middle-Mississippi model 4.1 to 5.0.3 conversion as well. In the Unsteady Flow Analysis window under Options -> Calculation Options and Tolerances… I discovered the Water surface calculation tolerance was set to 0.5ft. I lowered this below the max of 0.2 and RAS 5.0.3 executes just fine.

It seems like when our models were set up or converted from DWOPER/FLDWAV, the modelers had lower expectations on the accuracy of calculations. Or maybe to keep runtimes down, they deemed a half foot of instability as acceptable. Somehow RAS 4.1 was ok with it, but RAS 5 is not.

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