This is a piston based bridge. I made it so that each section rises and falls in sequence. The video tells the whole story. I made this a long time ago so some the the lever wiring is a little sloppy, but it still works pretty good.

After designing this I recreated it in game over in water from scratch with no mods of inv hacks just to prove to myself that it wasn't horribly impracticable to make in the vanilla environment.