The authors propose a procedure for estimating the discharge of a given return period based on the use of the rational formula in probabilistic form, with reference to a generic flood event observable within the year. In this manner it is possible to represent the natural variability in the runoff coefficient and at the same time to relate rainfall depths to the corresponding flood events. The link with annual maximum rainfall depths, on the one hand, and annual maximum peak discharges on the other, is established through relations deriving from the assumption of Poissonian occurrences over the year. The proposed procedure makes it possible to display the effect of the first and second moments of the random variable “runoff coefficient” on the shape of the flood frequency curve. In particular, it may be shown analytically that the second moment of the probability distribution of the runoff coefficient controls the third moment of the distribution of annual maximum peak discharges and hence its curvature. The paper also describes an application of the procedure to several basins of the Romagna-Marches region (Italy), for which the results of a regional analysis conducted using the index flood method were already available, both in relation to annual maximum rainfall depths and peak discharges. Comparing the results obtained with the two different procedures has provided a basis for advancing some considerations regarding the potential of the proposed procedure and which further aspects warrant investigation.
Deriving the flood frequency curve through the partial duration series analysis and the probability representation of the runoff coefficient
FRANCHINI, Marco;LOLLI, Marco
2005
Abstract
The authors propose a procedure for estimating the discharge of a given return period based on the use of the rational formula in probabilistic form, with reference to a generic flood event observable within the year. In this manner it is possible to represent the natural variability in the runoff coefficient and at the same time to relate rainfall depths to the corresponding flood events. The link with annual maximum rainfall depths, on the one hand, and annual maximum peak discharges on the other, is established through relations deriving from the assumption of Poissonian occurrences over the year. The proposed procedure makes it possible to display the effect of the first and second moments of the random variable “runoff coefficient” on the shape of the flood frequency curve. In particular, it may be shown analytically that the second moment of the probability distribution of the runoff coefficient controls the third moment of the distribution of annual maximum peak discharges and hence its curvature. The paper also describes an application of the procedure to several basins of the Romagna-Marches region (Italy), for which the results of a regional analysis conducted using the index flood method were already available, both in relation to annual maximum rainfall depths and peak discharges. Comparing the results obtained with the two different procedures has provided a basis for advancing some considerations regarding the potential of the proposed procedure and which further aspects warrant investigation.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
