Impact of parameter uncertainty on the design of small flood water retarding structures
1991
Salem, E.B. | Haan, C.T.
A simulation approach that accounted for the random variability of the SCS retention parameter, S, and 24-hour rainfall, R, was used to determine the T-year flood storage height for reservoirs on small watersheds. A sample of flood storage heights was simulated and a frequency analysis conducted to determine the T-year flood storage height. This storage was compared to the storage requirement based on the standard approach of using the T-year rainfall and the average value for S. The standard approach was found to underpredict the required storage when compared to the more realistic probabilistic approach. The degree of underprediction was found to be a function of the average curve number with smaller curve numbers having the largest error. Correction factors for the curve numbers are presented that make it possible to find the correct storage requirement based on the T-year rain and the corrected curve number for this application. This work points to the need for considering variability in all of the factors contributing to run off, not simply rainfall probabilities, if an accurate estimate of a return period design is required.
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