The commercial certificated pilot was taxiing an amphibious float-equipped airplane to a seaplane dock after landing on a scheduled air taxi flight. The pilot shut-off the engine as the airplane approached the dock. A tidal current carried the airplane beyond the intended docking area, and the airplane drifted backward into a wooden piling. The operator reported that the left aileron was removed for repair. A 37-inch portion of the aileron trailing edge was replaced. Probable Cause: The pilot’s misjudgment of the airplane’s speed/distance from a dock resulting in the airplane drifting into a wooden piling during a taxi from landing. A factor in the accident was the presence of a tidal current.