Effects of flood abrasion of the Carpathian alluvial gravels

Granulometrical characteristics of the sediments changed markedly after the floods. Both increase and decrease in mean size of largest clasts in gravel bars were observed. The results point to the important role played by the tributaries, which control the characteristics of clasts in the main rivers. In the foreland, lateral supply is not so important, because the bedrock consists of argillaceous rocks which do not produce gravels. The processes observed there include selection of material and changes in its composition caused by the presence of dams. Conglomerates are the least resistant to flood transport among gravel components. The most resistant are quartz clasts, but they are present only in the finest size classes. The most persistent characteristic of the clasts is their shape. The influence of the dams on clasts characteristics, contrary to expectations, is only slight. It is visible only in the greater proportion of quartz clasts in the alluvium of the Soła where the dams are present.