Authors: R. D. Zhou, C. R.Donnelly, and D.G. Judge
HydroVision 2008
Abstract
In many jurisdictions, the use of the Probable Maximum Flood (PMF) is mandated as the upper limit extreme event for assessing the safety of a dam that could present an unacceptably high risk to the public or the environment. It is assumed that this deterministically derived flood event is superior to extreme floods determined using probabilistic approaches. Indeed, the literature has shown that extrapolating flood events more than two to four times the historical record will lead to inaccuracies.
However, this does not necessarily mean that the PMF is an inherently more accurate method
of establishing an extreme event. The theoretical relationship between the PMF and the 10,000
year flood was explored in an attempt to establish the validity of probabilistic assessments for
defining extreme events, particularly in reference to the use of these events in dam safety risk
assessments. The establishment of a theoretical relationship between the two extreme events
also serves as a tool to check the reasonability of extreme event estimates. This later function
may be of significant economic benefit for some dam owners to avoid either dangerously under
designing or wastefully over designing spillway capacity.
