On September 24, 1994, approximately 1645 Alaska daylight time, a Piper PA-18-160, N7513K, was substantially damaged during landing near Galena, Alaska. There was no flight plan filed and visual meteorological conditions prevailed. The pilot, the sole occupant, was not injured. The pilot was on a local flight when he decided to land at his hunting base camp on the Dulbi River. The landing area was a gravel bar in the river. The pilot estimated that it was 800 feet by 35 feet at its narrowest. The river banks were vegetated with trees and brush. He stated that he set up his normal approach to the gravel bar and noted on the homemade wind indicator that he would be landing with a left to right cross wind. He further stated that, after touchdown, he raised the flaps and applied the brakes. As he applied the brakes the tail came up and the airplane nosed over onto its back. He said that after extricating himself from the airplane and walking to the hunting camp, he noticed the wind appeared to be shifting frequently and had changed into a tail wind. He estimated the wind speed to be about 15 knots, gusting to 20 knots.