Vízügyi Közlemények, 1996 (78. évfolyam)

3. füzet - Laczay István: A paksi Duna-szakasz mederváltozásának ellenőrzése

A paksi Duna-szakasz mederváltozásának ellenőrzése 327 Ikeda-Parker: River Meandering. AGV. Wat. Res. Monograph 12, Washington D. C. 1989. VITUKI: Paksi kisvizállások vizsgálata. С) Mederváltozások vizsgálata és előrejelzése. Kézirat. Témaszám: 7623/1/1. Témafelelős: Laczay István. 1984. VITUKI: A paksi Duna-szakasz mederváltozásának ellenőrzése. Kézirat. Témaszám: 7624/1/58. Témafelelős: Laczay István. 1989. * * * Review of the channel changes of the Danube reach of Paks by Dr. István LACZAY, C.E. The year 1995 was a wetter year than those of the previous decade (Figure 1.). Discharge measurements of Danube at Paks, which have been performed during the 11 years since 1988, indicate the dynamic stability of the discharge rating curve and thus of the channel of the river reach in concern (Figure 2.). Water surface profiles, which has been measured since 1984, were converted to those corresponding to identical flows. Figure 3. also indicates the stability of low flow water levels (that of the channel), upstream of river kilometre 1525 and the mild and attenuating subsidence downstream of this section. Theoretical investigations (Delft-VITUKI, 1995) indicated that commercial gravel dredging operations which had been performed in the river reach upstream of Paks might have a lasting effect downstream of river kilometre 1525 and might cause, by the year 2015, a water level subsidence of 0.4-0.5 m. This does not include the effects of potentially continuing dredging operations. Investigations supported the findings of 1984, on the basis of which latter commercial dredging had been banned in 1985 over a 10 km long reach upstream of the water intake. It has also been proposed to extend the restriction even further upstream. This resulted in the concentration of dredging operations downstream of the bridge of Dunaföldvár (Table /., Figure 4.). Although the site of gravel abstraction was moved towards upstream and the rate was also reduced, it has been stabilized at about 0.5 million m

3/year. One might suspect that demands for gravel will again shift dredging sites nearer to Paks. Figure 5 shows the annual channel changes for the period 1984-1995. Calculating on the basis of volume changes of partial reaches of 100 m length over 25 km total length and 450 m channel width the average specific channel bed sinking was obtained as 6.5 mm/annum, for the period of 11 years. The channel of the river reach has been in equilibrium (Figure 6.), with the exception of 1987/89 and even a low rate of sedimentation was observed in 1990/95. Calculations with other methods (Figure 7.) identified a uniform subsidence of 7.0 mm/annum. * * * Überprüfung der FlulJbettveränderung der Donaustrecke bei Paks von Dr.-Ing. István LACZAY Das Abflußregime der Donau war im Jahr 1995 wasserreicher, als im Durchschnitt der vorangegangenen Jahrzehtes (Bildes 1). Die während dieser 11 Jahre im Donauquerschnitt von Paks durchgeführten Abflußmessungen bestätigen, daß ab 1988 der Niedrigwasser-Abschnitt der Schlüsselkurve und somit auch die betrachtete Stromstrecke sich in dynamischem Gleichgewicht befanden (Bild 2). Die seit 1984 gemessenen Wasseroberflächen-Längsschnitte wurden auf denselben Abflußwert reduziert. Auch Bild 3 weist flußaufwärts von Strom-km 1525 auf die Stetigkeit der Niedrig-