Bridge looks good. If you have access to a backhoe...you could attach a very heavy chain to a log & bury it(deadhead), on the easy access side of the waterway. If the water rises high enough to take it, it'll just swing away to one side. I would guess deadheading both sides might tear the living crap out of it, if it washed out. At least if it just swung over to one side, you could winch it back into place. I've seen similar bridges wadded up like paper, when anchored on both sides, so low/close to the water.