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PL
Zmienność morfologii koryta Wisły warszawskiej w rejonie rezerwatu Wyspy Zawadowskie oceniono na podstawie analizy materiałów kartograficznych i fotogrametrycznych, obejmujących okres od końca XIX wieku do czasów współczesnych. Dodatkowo przeprowadzono badania terenowe, obejmujące kartowanie geomorfologiczne oraz wiercenia geologiczne w korycie Wisły. Porównanie zmian układu głównego nurtu oraz zmian morfologii mezoform korytowych z budową geologiczną analizowanej strefy umożliwiło identyfikację stabilnych elementów analizowanego odcinka koryta Wisły.
EN
Variability of the Vistula River channel morphology of the Zawadowskie Islands zone has been assessed in the base of analysis of the cartographic and photogrammetric materials covers period from late XIX century up to present times. In addition field works consist of geomorphologic mapping and geologic drillings of the channel zone were accomplished. Comparison between thalweg, as well as channel mesoform location changes with geology of the channel zone enabled recognition of the stable elements of the examined reach.
EN
Because of large amount of deposited material and the varied discharge of water, the Middle Vistula possesses the morphologic and lithological characteristics of braided river. During a geological survey of the valley which holds the bed of the Vistula River, culminations of the alluvia basement was detected in channel zone. There were outcrops of Mesozoic rocks — gaizes, marls and limestones, Paleogene and Neogene sediments as clays and sands and Pleistocene sediments as boulder clays, ice-dam deposits and compressed coarse grains fluvioglacial sediments are occasionally found. On the surface of these structures, the presence of residual lags was detected. The shallow location of these types of structures in the river channel proves its erosion-resistant nature. In long section of river bottom they are marked by a considerable increase of their gradient. Resistant steps of this kind are crucial for the natural stability of the river valley in longi-tudinal profile. They can also cause culmination of flood flows. The presence of the culminations of the alluvia basement in the river channel may be a factor increasing the probability of ice jam formation and ice jam floods. Those phenomena are causes of characteristic morphology of terrace surface — presence of erosional troughs of flood event flows. They also affect depositional processes. In the paper the morphologic characteristics of the Middle Vistula (braided lowland river) in the zones of various lithological types of alluvial basement culminations are presented, as well as characteristic structures of channel and flood deposits.
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