Trend changes and frequency analysis of the annual maximum volumes for various runoff duration on the Morava River at Moravský Svätý Ján

In the present paper we analyzed, the occurrence of annual maximum runoff volumes with t-day durations for a 99-year series (1920–2020) of mean daily discharge of the Morava River at Moravský Svätý Ján gauge (Slovakia). The runoff volume is, apart from the peak runoff, another very important hydrological characteristic of a river for flood hazard assessment. The maximum runoff volumes with t -day duration were determined. Subsequently, trends of the annual maximum runoff volumes with t -day durations were identified. We analyzed how the annual maximum runoff volumes of the Morava River have changed over the period 1922–2020 and how they have changed over dry and wet periods. The results indicate that the trends of the annual maximum runoff volumes with t -day durations decrease, especially in wet periods. On the Morava River usually the maximum annual discharges occur simultaneously with the annual maximum runoff volume of waves with a given duration t . However, the corresponding values in terms of significance are not equivalent. Based on the exceeding probability curves of the annual maximum runoff volumes, it is possible to determine to the selected volume V tmax for different t-days the probability of its exceeding and return period. The Log-Pearson distribution type III was used to determine the T-year values of the maximum runoff volumes with t-day duration.