An empirical equation for estimation of probable maximum floods in Ontario

Dequan Zhou


In engineering design of critical infrastructures, such as dams and nuclear power plants, the probable maximum flood (PMF) is often required as the inflow design flood (IDF). The failure of these critical infrastructures can lead to large number of loss of life (LOL), social and economical damages (SED) and environmental impacts (EI). The derivation of PMF requires extensive efforts on extreme storm and streamflow data collection and analysis, the estimation of probable maximum precipitation and comprehensive hydrologic modeling. The determination of a site specific PMF requires the corporation of multiple experts from different disciplines, which is costly and time consuming. A way of quickly estimating the magnitude of PMF for preliminary evaluation would be valuable for engineers, dam owners, companies and regulatory agencies. If the preliminary evaluation proves that a more detailed and reliable PMF is needed, a site specific PMF can then be derived. A set of 92 PMF estimates was collected over a long time period, for sites across Ontario, Canada. Based on the PMF database, an empirical equation was developed which can be applied to obtain a preliminary PMF estimation when the drainage area of the study site is known. One important result from this analysis indicates that the Creager Curve with C number of 45 provides good approximation for the upper bound of PMFs in Ontario Canada. A method for predicting the impacts of climate change on PMF is also proposed. This equation may be used for evaluating the future’s PMF given a projected increment of the regional average temperature in the future.

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