The influence of river training on the location of erosion and accumulation zones (Kłodzko County, South West Poland)

Abstract

The channels of the main rivers in the Kłodzko County, South West Poland, have been strongly influenced by human activities since the end of the nineteenth century. The reasons, type, and time frame of these changes are very similar to those which occurred in other European mountain regions but the magnitude is different. Kłodzko County is an area with a well-developed river network. Since the Middle Ages, human activities were noticed in the river valleys of this region. The main cause of the most anthropogenic transformations of the river channels was changes in the volume of sediment supply and, thus, the channel load and its erosive and transport capacities. The ultimate effects of human impact are manifested in the changes of channel pattern, depth and sinuosity, and the location of erosion and accumulation zones. Morphological transformations are most intensive immediately after the regulation works. The influence of channel training is noticeable; however, there is no clear correlation between the occurrence of engineering structures and the development of channel forms. The channel changes are mostly local. The highest efficiency of channel processes is observed in the direct vicinity of the damming objects and in the peripheral fragments of bank-protection structures. Below the damming structures, the rate of channel downcutting increases because of sediment retention in dam and weir reservoirs, and above the transversal structures bed aggradation takes place; lateral erosion intensifies below the bank reinforcements, and sediment shadows are common below the transversal structures. The types of morphological changes observed in the regulated channels of the Kłodzko County are in most cases similar to the effects of training works in other mountain river systems in Poland and around the world; however, the scale of morphological influence is much smaller, which indicates greater stability of the river channels of the Sudetes than the Carpathian and Alpine river channels.