<font color=blue>""I have been under the impression that to build a bridge that won't get washed away........ ""<font color=black>
Keep in mind that the answer depends on the creek. All creeks are not the same, and routing water between two concrete abutments will create all kinds of erosion action. If the water runs pretty calm year around, then it is less of a problem than if it is a torrent when spring comes, snow melts, and heavy rains come right along with it.
In my state, the State DNR would be highly involved in the construction of any bridge across any stream or creek, even if it was a dry run most of the year. (Includes just cutting brush along the creek banks as well). Just don't want to see anyone get in over their heads, so to speak.