It appears that this routine will draw polylines for cross sections at computed water surface elevations. I wonder how different it will be if I take the starting polylines from which the sample lines were created, and edit their elevations to match the computed water surface elevation at that section in RAS. then, add these polylines as breaklines to create a tin. this should yield similar results since the underlying assumption for RAS is that the water surface elevation does not vary within a given cross section (no slope for water surface looking in section view). I understand if you have hundreds of sample lines, this can be a bit of pain.
In that case, one other thing you possibly can do is export the water surface elevation table from RAS, then churn it through VBA to create a space delimited text file. this can be imported through "Profile from File", and can be use to create a corridor using a generic subassembly mimicing a flat water surface for each section location. then create a TIN from the corridor.
![Autodesk Design & Make Report](https://forums.autodesk.com/t5/image/serverpage/image-id/1350519iCB55845EBFC43016/image-size/large?v=v2&px=999" "Autodesk Design & Make Report")