Vízügyi Közlemények, Kivonatok, 1965

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

(30) garian reach these flood waves overtook each other and resulted downstream of Gönyü in a flood of unparallelled duration with stages exceeding the 1954 peaks by as much as 20 to 60 cm. Chapter 2 is devoted to the development of stages and discharges. The 1965 flood commenced in the second half of March with the passage of a preliminary wave of medium height, which combined over the Austrian reach of several smaller waves, and which, by peaking for six days over the Hungarian reach, filled the bed. The second and third waves appeared on the 11th and 23rd March, respectively, of which the latter coincided with the disastrous flood wave of the Rába River. The fifth flood wave built up in the middle of May causing at Mohács a stage which remained only 34 m lower than the 1954 peak. The sixth wave arrived at the Rajka gage around the 10th of June and caused a rise of about 1 metre. Even thus, peak stages over the upper reach remained below the 1954 level, but downstream from Gönyü they gradually approached and below Komárom they exceeded considerably the highest stages on record, those observed during the 1954 flood. The development of individual flood waves was affected considerably by the tributaries, which contributed large volumes of water to the discharge carried in the Danube, and moreover, as in the case of the Vág River, raised Danube stages in the most critical period. The stage hydrograph reproduced in Fig. 1 presents a fair picture on successive phases of development of individual flood waves on the Danube and its major tributaries. As will be perceived from the data compiled in Table VI, the net rise at Mohács over the first peak was only 196 cm at the sixth peak. The fall at Mohács was invariably considerably less than at Vienna, or Bratislava. From an analysis of changes in surface slope it could be established that surface slope over the upper reach responds fairly well to rising, or falling stages, as demonstrated in Fig. 4. The envelope curve of corresponding peak stages during individual flood waves was also traced (Fig. 5) and reflects also changes of slope. Changes of slope over the reach between Baja and Vukovár are illustrated in Fig. 6. These changes can be attributed primarily to discharge fluctuations of the Dráva River and to the drawdown effect of levee crevasses in Yugoslavia. Peak stages of the 1965 flood were compared with the 1954 peaks (Table VII), as well as with present design stages for ice-run- and ice-free floods. From available data peak stages of the 1965 and 1954 floods were found to lie on non-parallel lines. The slope of the 1965 flood wave was considerably flatter over the entire Hungarian reach than that of the 1954 flood. The 1965 flood was compared with past floods on record and floods with extended peaks were actually found to occur, but these peak stages