THE PLT ATTEMPTED A TAKEOFF FROM A ROUGH AND UNEVEN FROZEN RIVER IN THE SKI EQUIPPED ACFT. THE TAKEOFF WAS MADE INTO WINDS OF 20 KTS GUSTING TO 35 KTS. AS THE ACFT REACHED A SPEED OF APRX 35 KTS, A GUST OF WIND, COMBINED WITH THE ACFT BOUNCING ON THE ROUGH TERRAIN, TIPPED THE ACFT, CAUSING THE WING TO DRAG AND THE ACFT TO CARTWHEEL.