An extreme flood deemed to be the maximum flood likely to occur.

A flood so severe and statistically remote that the probability of its occurrence cannot be measured. Its magnitude far exceeds 100-year and 500-year floods and would result from a combination of the worst hydrological and weather conditions. For example, a PMF would occur if 36 inches of rain fell in a 72-hour period when the Highland Lakes were full. Although a PMF has not occurred in the lower Colorado River basin since LCRA was created, a $50 million project is in its final phase to ensure that all the Highland Lakes dams can withstand the greatest possible water load.

The largest flood that could conceivably occur at a particular location