HRADEK M.
The Dangerous Role of Dells in Agricultural Landscapes of south Moravia (Czechoslovakia)
Abstract
Dangerous processes are often associated with particular relief forms. In the hilly lands of the Bohemian Massif and the Western Carpathians, such forms include dells in which most erosion phenomena are concentrated. The dells represent natural catchments and form a relatively dense network. Problems arise when areas with numerous dells are subject to intensive agriculture. Many forms of cultivation have been carried out without respect to the relief. In spring when the soil is relatively unprotected and the winter snow is melting, slope processes become active. The incidence of snow-melt depends on slope orientation and weather conditions. During anticyclonic weather, snow sublimation dominates and there is little erosion, but during cyclonic weather, slope and nivation processes, such as supranival mud-flow and subnival thermoerosion, intensify. The worst situation so far occured in 1981. The effects of nivation processes are aided by periods of rain. Such activity has greatly increased in the last three years when rainstorms have been more frequent. In some areas with a dense network of dells, the soil was destroyed down to bedrock. In addition to crop demage, a train was derailed, and in one dell, floodwater caused a bus accident, costing human lives. Overland runoff from the dells can contribute to the formation of destructive flooding, as seen in a few cases in 1988. Study of hazards associated with dells has been aided by geomorphological mapping and remote sensing techniques. The results were compared with data acquired with the method of mathematical modelling of runoff.