Deere Dude said:Nice project. I would consider trying to anchoring the ends down somehow and not count on trees to do that, because if the water raises a foot it might push the whole thing downstream or turn it and dump it in the river somehow. There will be a tremendous amount of force on the whole side of the bridge.
I made a wooden bridge out of barn beams which worked great until I had to pick it up about 1/2 mile downstream after some flooding. But it wasn't made of steel like yours and was lighter, but you have too cool of a bridge to have something happen to it.
Not sure what you mean by trees anchoring it, perhaps the fallen down tree that landed in it? It's locked in pretty good. I set the lower grade of the bridge above the high water level of the banks. Should be fine.