Morphometric change due to altered hydrological conditionsin relation with human impact, River Hernad, Hungary

摘要

On the slightly regulated Hungarian section of the meandering River Hernad significant morphological transformations were identified. The aim of the paper is to analyse the hydrological changes of the river and to reveal the morphological consequences of the altered regime. The temporal change of morphological parameters due to hydrological transitions in relation with human impact was assessed. In order to evaluate the morphological changes, aerial photographs (1953, 1966, 1975, 1988, 1997 and 2002) and long term daily hydrological data were analysed. The hydrological parameters reflected stable, equilibrium conditions until the late 1950s, and the channel morphology adjusted to hydrology, thus the River Hernad was relatively wide and the size of the meanders was diverse. From the late 1950s the hydrological regime significantly altered due to urbanisation processes in Slovakia, and later partly due to climatic effects. Declining discharge values altered the river morphology. The channel became narrower, incised and the channel pattern became more uniform. On large meanders secondary bends started to develop. Morphological changes partly depend on bed material and slope, thus on the upper study reach, where the slope is greater and bed material is coarser, meander distortions were more intensive and parameters decreased continuously. On the other hand in case of the lower reach with smaller slope and finer bed material cyclic changes were observed. The intensive channel transformation periods were the same on both reaches.