Vízügyi Közlemények, Kivonatok, 1965

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

(31) remained well below those of 1965 (Fig. 7). The only flood since 1830 with peak stages and duration comparable to that of 1965, occurred in 1876. The development of discharges and waterhousehold conditions of the flood are also enlarged upon in the paper. For determining discharges, series of measurements were carried out in four cross sections, the results of which have been compiled in Table VIII. Phenomena of considerable interest and in contrast with familiar phenomena of flood waves were detected during the processing of data. Results of flow measurements are plotted versus stage in Fig. 8. From the looped curves traced with the help of pairs of points it can be concluded that the entire loop is situated invariably in every section above the rating curves reflecting steady conditions. Considering results of flow measurements at Medvedov (Czechoslovakia) it will be seen that the familiar flood loop appears in an inverted form as a consequence of the levee failure which occurred downstream from the gaging section. The loop curve traced for the Nagymaros gage shows a regular shape, but is shifted upward as a consequence of the levee breech. The results of flow measurements were used to trace the hydrograph of discharges (Fig. 9). Good agreement was found between daily discharges in individual sections; discharge maxima waves are transformed and attenuated gradually as a consequence of bed storage. The sixth flood wave, where the time sequence of peak discharges is disturbed by levee crevasses, is exceptional in this respect. Changes of slope caused by crevasses may be offered as an explanation for the fact that practically no increase of discharge occurred at both the Nagymaros and Budapest gages after the 15th June, although stages continued to rise. Runoff volumes conveyed during the 1965 flood were determined on the basis of discharge hydrographs (Table IX). Discharges through individual gaging sections were estimated for each month and for the total duration of the flood. In the knowledge of catchment areas pertaining to individual sections, specific runoff values were computed for individual months and for the total flood period. Values obtained were compared with average values for the period 1951 to 1960 and total runoff during the flood was found to be 1.6 times higher, while specific runoff greater by 9.6 litres/sec per sq.km than the corresponding averages. Runoff volumes conveyed by the 1954 and 1965 floods were also compared. From this comparison it could be established that the runoff conveyed in June, 1965 exceeded by 4.4 thousand million cubic metres the total runoff of the 1954 flood. As will be recalled flood levees ruptured at several points during the 1965 flood. Main data on these ruptures have been compiled in Table X. \