Anthropogenic and environmental impacts on the recent morphological degradation of the meandering Hornád River

Abstract

Anthropogenic and environmental impacts morphological degrada- tion the meandering Hornád River In the 19th century, the Hornád River in Slovakia was an unmanaged river system with well - developed free meanders. However, there has been a significant reduction of these free meanders in the last 70 years. The aim of this paper was to evaluate the morphological response to human intervention and flood events on three types of river segments (natural, regulated and water - gap) of 72 - km - long river reach of the mean- dering Hornád River in Slovakia over the last 197 years. Based on the dataset from the 2nd (1819 – 1827) and 3rd military survey maps (1869 – 1887), aerial photos (1949 and 1986) and orthophoto mosaics (2002, 2013 and 2016) the in - channel morphological, as well as the land cover changes, were identified. The four evolutionary periods of morphological response were identified: a pre - regulation period of 1819 – 1948, and three regulation periods with mutual effect of flood discharges of 1949 – 2001, 2002 – 2012, and 2013 – 2016. The Hornád River in the pre - regulation period was represented by a natural meandering river planform (45.8%) with a high occur- rence of in - channel landforms, where the lateral bar area prevailed. The intensive anthropogenic impact in the second half of the 20th century mainly affected its plan- form evolution, and resulted in channel shortening and narrowing, river sinuosity index and erosion - accumulation processes decreasing and loss of free meanders. The long - term low flood magnitude series coupled with land - cover changes (increasing the built - up area and communications) during the intensive regulation period led to the simplification of river channel planform by stabilization of the erosion accumulation processes. It caused simplification of river channel planform, mainly of the natural river segments (down to 26%). The low flood series was reversed by the flood events after the year 2004 (5 – 50 - year recurrence interval), which tend to in- crease of the river sinuosity, channel widening as well as the migration of free meanders.