I had a 16' bridge of mine float away (made it out of 6x6's) when the 2" deep creek flooded. Freak of nature... anyway, in order to hopefully help this from never happening again, I fastened thick rebar to the side of it. I got some metal brackets to hold the rebar in place. Then I drove the rebar 4' into the ground. I don't know if it will work, but I sure hope so.
Sounds like what my dad did to bridge at his old pond. Steel t-posts driven almost all the way into the ground with steel cables anchoring the telephone poles that made up the base of the bridge, it still washed out and into the pond after heavy rains.
