Vízügyi Közlemények, 1995 (77. évfolyam)

1. füzet - Rákóczi L.-Sass J.: A Felső-Duna és a szigetközi mellékágak mederalakulása a dunacsúni duzzasztómű üzembehelyezése után

A Felső-Duna és a szigetkőzi mellékágak mederalakulása... 67 the Bős/Gabcikovo power plant. Changes of the channels were numerically quantified by the comparison of the channel survey data of measurements made just before the diversion of the Danube in October 1992 to those of May and June of 1994. These data provided basis for forecasting further channel changes as well. Channel bed samples have also been taken during these measurements in selected points of the measured cross-sections and the particle size distribution was also determined. The channel has been surveyed with 100 m spacing between the river banks in order to be able to determine the changes of the channel more precisely (Figure 1.). No channel bed samples were taken in course of this intensified measurements. The authors analyze the changes of the channel volume below a plane which is positioned 2 meters below the low flow navigation depth of 1990. These data are compared to the changes of the particle size distribution curves of the bottom sediment samples. The shape of the cross-sections (Figures 3., 5., 8., 10., 12. and 14.) and the particle size composition curves (Figures 2., 4., 7., 9., 11. and 13.) are presented for selected sections (Figure 1.). Particle size distribution curves are characteristic to filling, deepening and dynamically balanced cross-sections and thus they can be compared to the data of channel surveys made in different points of time. Results obtained by the two methods (on the basis of channel bed surveys and on that of particle size distribution curves of channel bed materials) are in harmony with each other and can also supplement each other in a useful manner. The advantage of the particle size distribution curve method is that the changes of the particle size distribution curves of 5-7 samples of the same cross-section well indicate the velocity distribution of the cross-section, the effect of iinpoundage and of the stagnant spaces, if any. Repeated channel surveys, however, identify and quantify numerically the site and extent of channel bed subsidence or rise. It seem to be thus advantageous to use the two methods simultaneously also in the future with special regard to locations where substantial channel changes are expectable in the Danube channel and in the channels of the side river arms, affected by the water diversion in concern. The growth and shrinking of the channel volume is illustrated by Figure 6., showing the longitudinal variation of these changes, as calculated on the basis of channel surveys made at 100 m specing. In the three side arm systems investigated (Figure 1.) channel filling increased towards the downstream (Figure 15.). Between 1992 and 1994 the total sedimentation amounted to about 33,000 m

3 in the side arm system of Bodak, while it amounted to 72,000 m

3 in the side arm system of Ásványráró. In the side arm system of Bagomér, falling into the impounded area, the total deposition amounted to 434,000 m

3. * * * Flußbettentwicklung der Oberen Donau und ihrer Nebenarme in der Kleinen Schiittinsel (Szigetköz) seit der Inbetriebnahme der Stauanlage von Cunovo von Dr.-ing. László RAKOCZl, CSc. und Dipl.-Ing. Jenő SASS Die Flußbetten der Donaustrecke Rajka-Palkovicovo sowie ihrer in der Kleinen Schüttinsel (Szigetköz) mäandrierenden Nebenarme wurden durch die im oktober 1992 bei Cunovo erfolgte Absperrung des Hauptstrombettes der Donau sowie die Uberleitung des Großteiles des Abflusses in den Betriebswasserkanal des Wasserkraftwerkes Gabcikovo in bedeutendem Maße verädert. Die Flußbettveräderungen konnten numerisch nachgewiesen und ihre weiteren Trends vorausgesagt werden, weil die Evidenzhaltungs-Querschnitte ( VO-Querschnitte) des I lauptflußbettes und der Nebenarme zuerts im Oktober 1992 (also unmittelbar vor der Inbetriebnahme des Umleitungskanals) und dann im Mai-Juni 1994 von neuem vermessen worden sind. Gleichzeitig mit beiden Vermessungen wurden den bestimmten Lotrechten der Querschnitte auch Proben des Flußbettmaterials ent-