Channel evolution of the pre-channelized Danube River in Bratislava, Slovakia (1712-1886)

Channel adjustments of the Danube River near Bratislava, Slovakia, are reconstructed from historical river maps for 1712-1886, the period preceding mid-course channelization. The study reach comprised an anastomosing-meandering planform, characteristic of the upper area of a large alluvial fan. The key mechanisms of channel change Were avulsions through channel switching into chute channels, meander development through progression and cutoffs, and abandonment of secondary channels. The gravel-bed Danube River was characterized by rapid rates of lateral erosion (maxima from 7.5 to 37 in a(-1)), and extensive areas of point bars and gravel bars. Within three to seven years, new bars were stabilized by Salici-Populetum Woodlands which subsequently developed into more stable vegetated islands. Human interventions were relatively common and frequent in the past, though increasing fluvial activity during the 18th century was responsible for their limited effectiveness. Uncontrollable lateral erosion at Petrzalka village, terminated only by a switch in position of the Danube River upstream from Bratislava (1766-1774), appears to be closely related to increasing ice-floods and other high magnitude flood events in the latter half of the 18th century. These events were coincident with the peak of the Little Ice Age. The effect of floods was probably amplified by human works which resulted in stabilization of secondary channels, simplification of the river pattern, and concentration and widening of the main channel. A further sign of channel readjustment to new conditions was the evolution of new large meanders, a tendency for channel switching and production of new anastomosing-meandering parallel channels. Copyright (C) 2002 John Wiley Sons, Ltd.