CONTROLS ON GEOMORPHOLOGICAL EFFECTS CAUSED BY CATASTROPHIC FLOODING IN A SMALL MID-MOUNTAIN DRAINAGE BASIN 

Roman Zurawek Department of Geomorphology, Geographical Institute, University of Wroclaw, Poland
E-Mail: zurawek@geogr.uni.wroc.pl

Geomorphological mapping was carried out in a small mid-mountain drainage basin in the East Sudetes, SW Poland, in order to identify geomorphic changes resulting from the catastrophic rainfall and floods in July 1997. Spectacular landscape changes due to erosion and accumulation were the consequence of abnormally high discharge, estimated to be at least 90 times higher than the mean discharge. Intensity and character of geomorphological processes were primarily controlled by three factors: (1) geomorphological setting within the catchment, (2) anthropogenic influence on the environment and (3) natural vegetation cover. The longest avulsion of the river as well as the most intensive lateral erosion, have taken place in the alluvial fan setting below a high fault-generated mountain front. The river has changed its planform from a single channel pattern into the braided one and destroyed the village situated at the foot of the mountain front. Upstream from the mountain margin, in valley sections with the slope exceeding 30m/km, downcutting and, occasionally, mass movements on the valley sides have dominated. In the lower course of the river erosion has not been significantly active. Distribution of gully erosion and sheet wash was controlled by the degree of human impact on mountain slopes.