2011 – ACHIEVING CONSISTENCY IN DERIVATION OF THE PROBABLE MAXIMUM FLOOD

R.J. Nathan, P.I. Hill, and P.E. Weinmann

The current definition of the Probable Maximum Flood (PMF) is open to subjective interpretation, and this lack of objectivity can lead to inconsistencies in the application of risk-based and standards-based criteria. This paper summarises the different approaches used to estimate the PMF, and highlights how these reflect differences in the availability of design information and local tradition and experience. A number of approaches are available that can aid the objective definition of the PMF. These approaches attempt to define the “reasonableness” of the manner in which the various flood producing factors are combined by reference to the relative shift in the annual exceedance probability of the event. The implications of the different approaches to deriving the PMF are summarised for a number of dams from across Australia. Guidance on deriving the PMF is provided in the paper with a view to seeking feedback from industry and consideration for inclusion in relevant guidelines.