Vízügyi Közlemények, 2004 (86. évfolyam)

3-4. füzet - Stelczer Károly: az 1954. évi dunai árvíz

372 Stelczer Károly Plotting the 20

t

h Century floods of the Danube for the Budapest station in time sequence (Figure 18) one might simply (but rather superficially, as far a physical facts are concerned) arrive to a conclusion that the „floods are continuously rising". The generally known theory that „floods are continuously raising" (supported by climate change considerations and the devastation of the vegetation) can only be contradicted by unambiguously proven facts only in the case of Danube floods. Namely, upstream of Vienna the Danube flows in a channel, which is bordered alongside by hills and mountains. This fact provided the possibility to identify the marks of historic floods in several sections. In this way we do know about the height of the extreme Danube flood in August, 1501. which rendered the theory of "continuously rising floods" nil and void. This also means that the viewing of the history of floods in a century is not sufficient for defining, and not even estimating, the height of the thousand-year flood. Figure 19 indicates well that in March 1595 there was another large flood the peaks of which had exceeded that of the year 1954. The water levels of the flood of 1501 (Table VIII) were plotted in Figure 20 in conjunction with those of the flood of 1899. The water stages of the flood of 1501 were frighteningly high in the river reach between Passau and Vienna. From the Hungarian point of view we are mostly interested in the expectable highest water levels in the Danube reach downstream of Pozsony/Bratislava (and especially in Budapest) in the case if the peak water levels of the flood of 1501 would occur in the Danube reach upstream of Vienna. To answer such a question (even if roughly) one would need a detailed exploratory research. There is, however, a good reason to question those assuring opinions, which state that the flood control works of the Hungarian Danube are sufficiently built up to the height needed (including those of Budapest). In this regard one must emphasise that Budapest could not be protected against the flood levels of 1501 with the presently existing flood control works. This means that on one hand the flood of 1501 contradicted the theory of "ever rising floods" and, on the other hand, had proven that it is insufficient to rely on the more-or-less homogenous records of a hundred year for the determination of the "design flood level". Thus we shall be happy to have the data of this five hundred year earlier flood of the Danube for the river reach between Passau and Vienna. This flood obliges us in a compulsory way to re-evaluate the safety conditions of the flood protection works of the Hungarian Danube. It is not acceptable to provide less safety than a total safety for the protection of Budapest, which represents the highest national values of Hungary. Knowing the flood of 1501 and the data of other extreme floods of the Danube (Table VIII) the author estimated the expectable flood levels at Budapest: - The peak level of a flood like that of 1501 (corresponding to a flow of 14 000 m

3 s"') would be around 1051 cm on the basis of the Q-H discharge rating curve; - Using the ever observed highest Austrian water stages of the flood of 1501 in the floodforecasting model of the research centre VITUKI Psc (and considering the flow of 14 000 m

3 s"

1), the respective expectable water stage of Budapest would be about 1045 cm; - Considering the flood of 1954, as increased by the flood flows of the rivers Traun and Enns measured in 1899 (Figure 5), and assuming their joining the 1501 flood at Vienna, then the expectable Budapest flood peak would be about 930 cm. - If one transforms the water stage time series of the flood of 2002 to the Vienna station (Figure 5), then the expectable Budapest flood peak would be about 970 cm (Figure 20). In the occasion of the 50 year anniversary of the 1954 flood that had devastated the large part of the Szigetköz area the North-Transdanubian Environmental and Water Management Directorate organised a series of memorial events. Monuments (ancient Hungarian wooden tomb headboards) were erected (Figure 21) on the sites of the breeches of the flood levee and a memorial meeting was organised in Mosonmagyaróvár (Figure 22).