THE PILOT WAS LANDING ON A RIVER GRAVEL BAR NEAR A REMOTE LODGE. THE LANDING AREA WAS ORIENTED ON A 090 DEGREE HEADING. IT WAS ABOUT 375 FEET LONG AT 2,300 FEET MEAN SEA LEVEL. A SLIGHT TAILWIND WAS PRESENT FROM THE WEST OF ABOUT 4 KNOTS. AFTER TOUCHDOWN, THE PILOT APPLIED THE BRAKES, AND THE AIRPLANE STARTED TO NOSE DOWN. HE RELEASED THE BRAKES, BUT WAS APPROACHING THE END OF THE LANDING AREA. THE AIRPLANE ENCOUNTERED A DIP IN THE GRAVEL SURFACE WHEN THE PILOT APPLIED BRAKING ACTION ONCE AGAIN. THE AIRPLANE THEN NOSED OVER AND RECEIVED DAMAGE TO THE WING RIBS.