VERIFICATION OF EMPIRICAL FORMULAS FOR CALCULATING ANNUAL PEAK FLOWS WITH SPECIFIC RETURN PERIOD IN THE UPPER VISTULA BASIN

The study evaluated the selected empirical formulas for calculating annual peak flows with specific return period (Q(T)) in southern Poland. Data used in the calculations in the form of observation series of peak annual flows were derived from the Institute of Meteorology and Water Management in Warsaw and covered a multi-year period of 1986-2015. The data were statistically verified for their homogeneity, significance of monotonic trends, outliers, and equality of variance. Peak flows with set return period were estimated with a statistical method of Pearson Type III distribution and empirical formulas (area regression equation and Punzet formula). The analysis showed significant differences between Q(T) for the investigated catchments derived from the statistical method and empirical formulas. This was evidenced by the values of mean relative errors of quantile estimation that reached 64% for the Punzet formula, and 62% for area regression equation. The obtained results indicated the need to update the empirical formulas used for calculating Q(T) in the Upper Vistula region.