Smallest Opening

Dear Users,

Are there any tools out there (in RAS or out) that can determine the smallest possible opening that will either maintain a specific elevation or energy grade given a cross-section, steam centerline, and abutment type?? If this doesn't make sense, here is an example:

- I have a small bridge that I need to replace. An existing condtions model results in a WS = 1000'.
-I now want to see if I can replace the existing bridge a new one with the smallest possible opening.

Thanks,
Rich