N1778CCessna 180

The pilot of the tailwheel equipped airplane reported that he decided to land on a gravel bar. Slightly before the gravel bar, he touched the main landing gear on the water prior to the gravel bar. He realized the airplane’s ground speed was too low and the airplane’s tail “started to come up”. He added full engine power and “up elevator,” but the airplane nosed over and came to rest inverted, in 1-2 feet of water. The rudder was substantially damaged. The pilot reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.