Vízügyi Közlemények, Kivonatok, 1965

Dégen Imre: Az 1965. évi dunai árvíz és árvízvédelmünk fejlődése

(32) Stages which would have occurred in the absence of ruptures were also estimated (Fig. 10) and their trends of development without ruptures were determined. Estimates were based on the completion of stage hydrographs with the help of gage relationships for adjacent gages, while checks were run using discharges through the ruptures. Results of these computation are presented in Table VII. Probability values of stages, discharges and peaks of the flood have been determined in Chapter 3. Different opinions were voiced in connection with peak stages and discharges, discussing their effect on present design flood stages and considering the necessity of modifications in relevant specifications. On the basis of basic data available, stages and discharges of different probability were estimated with the help of mathematical statistics (Figs. 11 and 12). Probabilities of peak stages of sucessive flood waves during the 1965 flood, as well as those for stages actually observed and estimated in the absence of ruptures during the sixth wave have been compiled in Table XI. As will be perceived from the table, the probability of peak stages of the sixth wave decreases progressively from Bratislava towards Mohács. At Mohács the estimated probability of actual stages — including the effect of ruptures — was 0.5 %, whereas that of the stage which would have occurred in the absence of ruptures, was found to be 0.2 % At Dunaremete, on the other hand, which was unaffected by levee ruptures, the peak stage of the sixth flood wave was of 1.8 % probability. From a comparison of peak stages during the sixth wave of the 1965 flood and the 1954 flood, it will be seen that stages observed over the Danube reach between Bratislava and Komárom in 1954 were of a higher probability than those in 1965, while they remain considerably below the probability values of 1965 over the lower reaches. A similar relation was found to exist between probabilities estimated for peak stages in the absence of ruptures. Probabilities were determined also for the peak discharges of the 1965 flood waves and were compared with the probabilities of peak discharges during the 1954 flood (Table XI). It could be concluded therefrom that in the case of the sixth flood wave in 1965, the probability value of stages was in general lower than that of discharges, indicating that exceptionally high stages were not accompanied by exceptionally great discharges. An important conclusion from this result is, that owing to the influence of tributaries and overtaking flood waves the sixth flood wave in 1965 passed under to a certain degree raised conditions. One of the most important features of the sixth flood wave in 1965 was its exceptionally long duration. The probability of flood waves of similar duration was estimated on the basis of data relating to the Mohács gage. The probability of duration for the sixth wave in 1965 was found to be surprisingly high — as much as 3% — so that the wave was exceptional as regards stage rather than duration.