The paper presents review of occurrence frequency of extreme hydrological events in a small agricultural basin in the flysh region over the period of 40 years (1964/65 - 2003/04). No human alterations were carried out in the basin over the period studied and hence influence of climatic changes on intensification of water cycle could be evaluated. Peaks over threshold (POT) method was applied separately to winter and summer hydrological events. In comparison with annual maximum series, all mean daily discharge values over a certain thresholds were taken into account for POT frequency analysis. The frequency of POT events has decreased in the past two decades (1984/85 - 1993/94 and 1994/95 - 2003/04). The results reveal that the most extreme values occurred in the 1964/65 - 1973/74 decade, mostly caused by summer rainfall. High event frequency also emerges in the 1974/75 - 1983/84 decade, especially in winter seasons as the consequence of snow melting. It is most likely that influence of climatic changes has not resulted yet in increase of occurrence frequency of POT events in the basin studied over the 40 years period. and Príspevok sa zaoberá frekvenciou výskytu extrémnych hydrologických udalostí na malom poľnohospodárskom povodí vo flyšovom pásme počas 40-ročnej periódy (1964/65-2003/04). Počas tohto obdobia nebolo povodie ovplyvnené významnými zmenami ľudskej činnosti a preto mohol byť zhodnotený vplyv klimatických zmien na intenzifikáciu hydrologického cyklu. POT metóda bola aplikovaná zvlášť pre zimné a letné hydrologické udalosti. V porovnaní so sériami ročných maxím, všetky priemerné denné prietoky nad určitou prahovou hodnotou boli zahrnuté do POT frekvenčných analýz. Frekvencia POT udalostí (nad zvolenou prahovou hodnotou) klesla v posledných dvoch dekádach (1984/85-1993/94 a 1994/95- 2003/04). Výsledky ukazujú, že najextrémnejšie hodnoty priemerných denných prietokov, spôsobené prevažne letnými prívalovými zrážkami sa objavili v dekáde 1964/65-1973/74. Vysoké hodnoty prietokov, spôsobené prevažne topením snehovej pokrývky sa vyskytli tiež v dekáde 1974/75-1983/84. Je nanajvýš pravdepodobné, že v študovanom povodí za obdobie 40-tich rokov klimatické zmeny nemali zatiaľ vplyv na zvyšovanie frekvencie extrémnych udalostí.
In this paper we focused on the history of floods and extreme flood frequency analysis of the upper Danube River at Bratislava. Firstly, we briefly describe the flood marks found on the Danube River in the region of Bratislava, Slovakia, and provide an account of the floods’ consequences. Secondly, we analyzed the annual maximum discharge series for the period 1876–2012, including the most recent flood of June 2013. Thirdly, we compare the values of T-year design discharge computed with and without incorporating the historic floods (floods of the years 1501, 1682, and 1787 into the 138-year series of annual discharge peaks). There are unfortunately only a few historic flood marks preserved in Bratislava, but there are very important and old marks in neighbouring Hainburg and other Austrian cities upstream to Passau. The calculated T-year maximum discharge of the Danube at Bratislava for the period 1876-2010 without and with historic flood values have been compared. Our analysis showed that without incorporating the historic floods from the years 1501, 1682, and 1787 the 1000-year discharge calculated only with data from the instrumented period 1876- 2013 is 14,188 m3 s -1 , and it is lower compared to the 1000-year discharge of 14,803 m3 s -1 when the three historic floods are included. In general, the T-year discharge is higher throughout the whole spectrum of T-year discharges (10, 20, 50, 100, 200, 500-year discharge) when the three historic floods are included. Incorporating historic floods into a time series of maximum annual discharge seems to exert a significant effect on the estimates of low probability floods. This has important implications for flood managements and estimation of flood design discharge.
The problem of understand natural processes as factors that restrict, limit or even jeopardize the interests of human society is currently of great concern. The natural transformation of flood waves is increasingly affected and disturbed by artificial interventions in river basins. The Danube River basin is an area of high economic and water management importance. Channel training can result in changes in the transformation of flood waves and different hydrographic shapes of flood waves compared with the past. The estimation and evolution of the transformation of historical flood waves under recent river conditions is only possible by model simulations. For this purpose a nonlinear reservoir cascade model was constructed. The NLN-Danube nonlinear reservoir river model was used to simulate the transformation of flood waves in four sections of the Danube River from Kienstock (Austria) to Štúrovo (Slovakia) under relatively recent river reach conditions. The model was individually calibrated for two extreme events in August 2002 and June 2013. Some floods that occurred on the Danube during the period of 1991-2002 were used for the validation of the model. The model was used to identify changes in the transformational properties of the Danube channel in the selected river reach for some historical summer floods (1899, 1954 1965 and 1975). Finally, a simulation of flood wave propagation of the most destructive Danube flood of the last millennium (August 1501) is discussed.
The study is focused on the analysis and statistical evaluation of the joint probability of the occurrence of hydrological variables such as peak discharge (Q), volume (V) and duration (t). In our case study, we focus on the bivariate statistical analysis of these hydrological variables of the Danube River in Bratislava gauging station, during the period of 1876-2013. The study presents the methodology of the bivariate statistical analysis, choice of appropriate marginal distributions and appropriate copula functions in representing the joint distribution. Finally, the joint return periods and conditional return periods for some hydrological pairs (Q-V, V-t, Q-t) were calculated. The approach using copulas can reproduce a wide range of correlation (nonlinear) frequently observed in hydrology. Results of this study provide comprehensive information about flood where a devastating effect may be increased in the case where its three basic components (or at least two of them) Q, V and t have the same significance.