A comprehensive approach to determining the Drava River flood hydrographs for hydrotechnical design

Ovaj je rad posvećen određivanju teorijskih hidrograma velikih voda rijeke Drave u profilu hidrološke postaje Donji Miholjac. Primijenjena se procedura temelji na jednom novom sveobuhvatnom pristupu koji usporedno vodi računa o dva osnovna parametra hidrograma velikih voda – maksimalnoj ordinati hidrograma (vrhu) i zapremini poplavnog vala. Razrađena procedura u osnovi se oslanja na praktičnu primjenu, usporedno, metode „graničnog intenziteta otjecanja“ (GIO) za proračun teorijskih hidrograma velikih voda različitih vjerojatnosti pojave i teorije dvodimenzionalnog definiranja funkcija raspodjele (koincidencije) navedenih parametara hidrograma velikih voda. Važna pretpostavka je da se, u konkretnom slučaju, tretiraju osnovni parametri hidrograma velikih voda – ordinate maksimalnih godišnjih protoka i maksimalne zapremine hidrograma velikih voda u istoj kalendarskoj godini. Kalibracija parametara metode GIO vrši se u uvjetima izjednačavanja teorijskih vrijednosti maksimalnih godišnjih protoka i maksimalnih godišnjih zapremina istih vjerojatnosti pojave, koji se dobivaju primjenom metode GIO, odnosno standardne procedure prilagođavanja navedenih vremenskih serija teorijskim funkcijama raspodjele koje se najčešće koriste u hidrološkoj praksi. Za definiranje vjerojatnosti istovremene pojave navedenih parametara hidrograma velikih voda (vrha i maksimalne zapremine hidrograma velikih voda) korištena je procedura koincidencije dvije slučajne varijable, prikazana u literaturi (Prohaska et al., 1999.; Prohaska et al., 2016.). Definirane koincidencije vjerojatnosti prekoračenja dva promatrana parametra hidrograma velikih voda služe za odabir kombinacija koje će se koristiti za kalibraciju parametara metode GIO. Na kraju je prikazan praktični primjer definiranja teorijskih hidrograma velikih voda različitih vjerojatnosti pojave na rijeci Dravi u profilu hidrološke postaje Donji Miholjac.The paper deals with the determination of theoretical hydrographs of the Drava floods at the Donji Miholjac hydrological station profile. The applied procedure is based on a recent comprehensive approach which simultaneously considers two basic flood hydrograph parameters- maximum hydrograph ordinate (peak) and flood wave volume. The elaborated procedure primarily relies on the practical, simultaneous application of two methods – the method of "limit discharge intensity" (GIO method) for the calculation of theoretical flood hydrographs of different probabilities of occurrence and the theory of two-dimensional definition of the distribution function (coincidence) of the mentioned flood hydrograph parameters. In this specific case, an important assumption is that the basic parameters of the flood hydrograph (ordinate of maximum annual discharges and maximum volume of flood hydrograph) are from the same calendar year. The calibration of the GIO method parameters is carried out in the conditions of equalizing the theoretical values of maximum annual discharges and maximum annual volumes of the same probability of occurrence which are obtained by applying the GIO method, i.e. standard procedure of adjusting the mentioned temporal series to the theoretical functions of distribution which are the most frequently used in the hydrological practice. In order to define the probability of a simultaneous occurrence of the stated flood hydrograph parameters (peak and maximum volume of the flood hydrograph), the procedure of two random variable coincidence was used, as shown in literature (Prohaska et al., 1999; Prohaska et al., 2016). The defined coincidences of probability for exceeding two monitored flood hydrograph parameters serve to facilitate a selection of combinations to be used for the calibration of the GIO method parameters. Finally, the paper includes a practical example of defining theoretical flood hydrographs with different probabilities of occurrence in the Drava River at the Donji Miholjac hydrological station profile