piatok 25. januára 2008

Evolution of meandering lower Morava River (W Slovakia) during the first half of 20th Century.

Pišút, P.: Evolution of meandering lower Morava River (W Slovakia) during the first half of 20th Century. Geomorphologia Slovaca, 2006, 1, 3 figs., 4 tabs., 36 refs., 9 map. refs.

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This paper examines a development of the lower Morava river (Slovak – Austrian stretch) in the time period from 1896 until the river regulation (1951-1962), using historic cadastral maps. Study reach is located between Vysoká p. Morave and Marchegg (river kilometres 16-21). Morphometrical analysis, reconstruction of morphogenesis and morphochronology based on map superposition were aimed to describe channel forms and river planform development over time. Meandering Morava was a dynamic river system here with a continuous bend development at least since 1807. Retreat of outer banks after 1896 averaged 88 m (11-184 m), thus representing mean annual rate of lateral erosion 1.68 m.yr-1 (between 0.6 – 3.2 m dependent on a bend). Despite local channel shortening after a natural meander cutoff around 1906, there was a steady increase in sinuosity of model reach during the studied period, from 2.04 in 1896 to 2.27 in 1950s (present-day channelized Morava is only slightly sinuous river with s2000 = 1.183). The mainchannel development was significantly more dynamic (= narrower channel, minor radii of bends, almost twofold rates of lateral erosion) as of the synchronous evolution of a reference reach at Moravský Sv. Ján (rkm. 62 - 67). Correspondingly, a 100 m wide riverine belt with a soft floodplain woodland site had been forming at Moravský Sv. Ján almost twice as slowly as near Vysoká p. Morave (100 years in comparision to 60 yr). Research findings are of a key importance for predicting future channel changes in the case of Morava restoration by mainflow diversion back into selected cutoff sections.