Sensitivity to probable maximum flood

The probable maximum flood (PMF) is a function of numerous factors, both meteorological and hydrologic. An accurate estimate of the PMF, required for high-hazard design problems, requires finding the optimum combination of factors. The PMP/UH (probable maximum precipitation/unit hydrograph) method is the currently accepted method to estimate the PMF. Difficulties with the current trial-and-error process used to estimate the PMF include: (1) Finding the optimum combination of factors; and (2) assessing the relative effect and precision of the underlying assumptions. The first difficulty may lead to an inadequate design, and the second difficulty may result in an inaccurate estimate of the risk involved in the design. An experiment was designed to perform a sensitivity analysis of the PMF to its contributing factors. A set of guidelines were developed for assessing the effects of causative factors on the PMF, so that: (1) The optimum value of the PMF is more likely to be computed; and (2) the effort to find the optimum PMF is reduced. Preliminary verification of the results was conducted using Seneca Creek, Maryland, as a case study.