The Definition Of Probable Maximum Flood

Floods can cause great harm and sudden misfortune.

The Probable Maximum Flood (PMF) is the most severe possible flood in a particular drainage area. It is calculated by combining information about the precipitation, geology and water management strategies of a particular area.


According to the Ohio Department of Natural Resources, the Probable Maximum Flood is “the flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in a particular drainage area.”


The PMF is determined in large part by the Probable Maximum Precipitation (PMP) which is determined by looking at historical weather records as well as studying the meteorological conditions possible in an area to determine the greatest theoretical amount of precipitation for an area. PMP is considered with the drainage capacity of an area to determine the PMF.


Knowing the Probable Maximum Flood for an area enables engineers to build dams and other water-control structures to withstand the PMP and prevent flooding. Calculating the PMF helps governments develop specific disaster-preparedness plans.

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