THE PILOT WAS CRUISING AT 3500 FEET WHEN HE EXPERIENCED A POWER LOSS. DURING A FORCED LANDING, HE STRUCK A DITCH AND THE AIRPLANE FLIPPED OVER. THE ENGINE WAS RUN SATISFACTORILY AFTER THE ACCIDENT. EXAMINATION OF A CARBURETOR ICING PROBABILITY CHART REVEALED THE PILOT WAS OPERATING IN CONDITIONS OF MODERATE ICING PROBABILITY WITH CRUISE POWER.