I am working on a bridge project where the bridge opening needs to be skewed, but the upstream and downstream cross sections do not. In order to skew the bridge opening, I go into the Bridge Data Editor window and click on Bridge Skew to add my skew. Since my sections do not need to be skewed I click off the Skew upstream and Skew downstream option and then skew the bridge. The problem is that my bridge opening stationing gets multiplied by a factor which in effect pulls the opening towards the zero station. On this particular bridge the opening gets shifted far enough to the left that the ineffective flow areas are completely blocking off my bridge opening area.
Ideally the HEC-RAS program would include an option to set the station at the center of my stream so that when I skew the bridge opening it is scaled about my given point instead of the default of zero. That way my bridge opening would stay put instead of getting dragged towards zero. It would be relatively simple to program an option like that in, but I have never been able to find anything like that in the program. Does anyone know of any way to set the center of stream bed stationing so that this doesn’t become an issue?
On a side note, as a work-around on newer jobs I’ve started setting the station at the center of my channel to 0+00 (instead of say 10+00). Everything left of the stream has a negative distance and everything to the right has a positive distance. This works out great for things like skewing my bridge opening through HEC-RAS and for adding ineffective flow areas since I can go the same distance in the positive and negative direction. The only drawback to this solution is that my HEC-RAS stationing no longer matches my roadway stationing which is not a huge problem, but it is a bit of a hassle sometimes.