Vízügyi Közlemények, 2004 (86. évfolyam)
3-4. füzet - Stelczer Károly: az 1954. évi dunai árvíz
Az 1954. évi dunai ár\'íz 371 excavated from sites right behind the dike, creating this way the danger of the development of boils. A large boil had developed early on the 20 t h of July and the breech of the dike followed this. The expectable peaking of floods in the Hungarian Danube might need a new approach, along with that for considering flood-safety, when one compares the peak flood levels of the period after 1954 to those of the flood of 1954 (Figure 14). Figure 14 unambiguously indicate that all of the floods of the period after 1954 (and especially those of 1965, 1991 and 2002) reached maximum levels in Hungary while the flood levels upstream of Vienna remained below those of 1954. The series of floods in 1965 were caused by precipitation of a special characteristic. Namely, in the catchment basin upstream of Pozsony/Bratislava received a nearly continuous rainfall in the period between 17 March and 14 June (Table IV). Flood levels of the Hungarian river reach were further increased by the impact of large precipitation events that occurred in the period 18-23 April on the eastern slopes of the Alps (resulting in devastating floods in the catchments of the rivers Rába, Pinka, Répce and Lajta). This was followed by similar conditions in the period 8-11 June in the High Tátra Mountain, especially in the catchment of the river Árva. The flood of 1965 was composed of six larger and several smaller floods (Figure 15). The series of smaller and larger tributary floods joined each other on the Danube reach in the vicinity of Gönyű, where the river has low slopes. Finally the last, the sixth, flood hydrograph raised the flood level to elevation, which exceeded that of the flood of 1954 (Figure 15). The flood of 1991 was induced by two subsequent floods following rainy periods of few day lengths. In the period between the two floods there were only two days (29-30 June) with no precipitation (Table V). This rainy period resulted in a smaller and a larger flood that were still separated from each other in the Danube reach upstream of Pozsony/Bratislava, while they got nearly superimposed on each other in the vicinity of Mohács (Figure 16). The peaking levels of the flood of 1991 in the Danube reach Vienna-Komárom (Table II) point out the nearly century long problem, that in the vicinity of Dunaremete the elevation of the flood- and mean water channels have been steadily increasing in spite of the intensive river training activities. The rate of the rising of flood peaks have increased since the flood of 1975. The flood of 1991 resulted in extremely high peaking water level at Dunaremete (Table VI). This picture becomes even more frightening when one compares the Dunaremete flood peaks to that of the Gönyű station, where the channel is relatively stable (with a smaller rise. Figure 17). In the Danube the first extremely high flood of the 21 s 1 Century occurred in August, 2002. Table VII shows the area-averaged precipitation that caused this flood. This table indicates that the area distribution of this precipitation was again different from those, which had caused the extreme floods earlier: - The highest precipitation occurred on the catchments of the rivers Traun, Enns and Salzach (without the River Inn); The rainfall that caused the flood of 2002 fell in two parts and induced two flood waves The flood of 2002 was similar to that of 1954, as there was again a "preparatory" flood. The difference was that in 2002 the floods of the rivers Traun, Enns and Salzach had also contributed to the extreme situation. It is to be noted that the River Inn, which generally causes the floods of the Danube, was not flooding this time. At Pozsony/Bratislava the flood of 2002 was peaking by only 7 cm higher than the peak of the flood of 1954. The flood of 2002 was higher than that of 1965 along the Hungarian river reach down to Nagymaros, if one considers the calculated flood levels (without the effect of the levee breeches. The extreme floods of the Danube were caused, in the period of 1899-2002, by different precipitation events (different in height, intensity and area distribution). Eventually one may rise the question; how big would (could) be the Danube flood when it is induced by simultaneous (coincidental) large precipitation events in all the three upstream river basins. One may call this theoretical flood the "highest probable flood". Another related questions are; what is the probability that such a meteorological situation occurs and what is the amount of precipitation that could fall onto the entire upper river basin of Danube at the same time?
