I'd like to find out from the ESRI\HEC community if anyone has experience in automatically (Python\Geoprocessing) identifying the river bank positions from the cross-sections. I found that delineating the bank lines is not necessarily the best method for determining the bank positions, especially in very flat river channels. If one could estimate the bank positions by looking at slope change within the cross-sections and identify the left and right bank position based on slope change and create a point at this position would greatly improve the bank lines positioning. Any advice or knowledge of possible scripts that could be used to determine the banks positions would greatly reduce the amount of time in having to alter these manually once importing the HEC-GeoRAS Geometry file into HEC-RAS.
We did some tests using Spatial Analyst Tools-> Slope to semi-automatically identify levees and other man made earthworks with DEMs that could potentially be used for the same thing. We found in our tests that the slopes between 1:1 and 2:1 would often also identify the stream banks. With the symbology of the slope process output raster set to the corresponding slope in degrees(I want to say 30-45 worked best) you can just draw along the outer limits. If you prefer TINS, 3dAnalyst tools->triangulated surface->Surface Slope I believe does the same thing as the spatial.
That said, unless you are dealing with hundreds of cross sections in your models you would likely be better served time wise just selecting your stream centerline and using Editor->copy parallel to create your approximate stream bank locations and then just use the graphical editor in RAS to manually adjust as needed. Its pretty rare that we bother trying to draw a bank line to match the stream banks for the same reason you specified...you end up having to fix it anyway.