Vízügyi Közlemények, 1989 (71. évfolyam)

1. füzet - Rákóczi László: Vízlépcsők hatása a hordalék- és mederviszonyokra

Vízlépcsők hatása a hordalék- és mederviszonyokra 23 шенное прохождение воды при установившемся движении. Важной задачей является двухмерный расчет намыва при неустановившемся движении воды. По опыту, полученному в зоне гидроузла Кишкере, можно констатировать, что мелкозернистые наносы, осаждающиеся на пойме в результате силы сцепления, вряд ли придут опять в движение во время прохождения паводков. Транспортирующее влияние прохождения паводков и искусственных волн в результате пикового режима ГЭС ожидается лишь в русле, которое наполняется средними расходами. Результаты одномерных расчетов ожидаемых изменений русла в верхнем бьефе гидроузла Надьмарош приведены на рис. 5-8. Из них вытекает, что пиковый режим работы ГЭС с увеличением расходов воды приводит к промывке русла, ограничивая намыв на коротких участках, и увеличивает соотношение крупных фракций гравийного дна и вместе с этим и прочность русла. * * * The effect of river barrages on sediment- and bed-condition by Dr. L. RÁKÓCZI, С. E., candidate of technical science The characteristics of deposition, wash out and other changes of the river bed are discussed by the author along the upstream and downstream river reaches of existing, constructed or planned barrages of two Hungarian rivers, the Danube and the Tisza. VITUKI (Research Centre for Water Resources Development) conducted regular observations to register bed-changes and other processes at the barrage of Tiszalök but mainly in the vicinity of the barrage of Kisköre operated since 1973 on the Tisza river. It has been concluded that about 600 000 m

3 of sediment was annually deposited in the backwater reach of the latter project. Floods are practically incapable to flush out the material deposited in the flood-plain, unless that in the low-flow river-bed. The sandy bed load deposited at the back water edge is regularly carried away by the flood waves. Downstream from the barrage deposition is the governing process increasing toward the site of the ship-lock. Farther downstream, scouring and bank erosion are dominating due mainly to the erosive effect or artificial flood waves produced by the intermittently operated hydroelectric plant. Over the Danube-stretch influenced by the River Barrage System of Gabcikovo-Nagymaros, a gradual decrease of the concentration and volume of the sediment has been described by Bogárdi (1971) as in Figs. 1 and 2. This trend has been observed also today due to the sediment retention ot the recently constructed barrages over the Austrian Danube-section. Bed-load arriving from the same reach has also been considerably reduced and by far it is not sufficient to refill the pits of large-scale industrial dredging activities executed during the past two decades by Czechoslovakians and the Hungarians. This evidence was supported by a continuous drop of the low-flow water level observed at the gauges of Pozsony and at the majority of gauges over the Hungarian reach. According to the different sources of estimation, about 60 years are needed for the passive storage-volume of the reservoir of Dunakiliti to be filled up completely. However, the accuracy of this estimate is influenced by a series of factors water regime in the first years after inauguration, magnitude and schedule of dredging over the stretch between Rajka and Devin the starting date of the peak-power production at Gabcikovo, etc., (Fig. 3). Distribution of sediment deposits are - at the moment - estimates of a Slovakian physical model experiment and calculations assuming an undisturbed passage of the steady-flow discharges. An urgent task is to carry out two-dimensional computations for non-steady flow in the near future to improve the reliability of estimations. According to experinces at Kisköre, the fine sediment deposited over the flood-plain cannot be set into motion by the flood-waves because of its cohesive characteristics. Flood-waves and artificial waves generated by peak-operation are able to flush out primarily the mean-flow river bed.