engleski

The impact of river engineering works and flood events on channel migration rates on the Orljava River (the Pannonian Basin, Croatia)

Since the 19th century, hydromorphology of many lowland rivers in the Central Europe has been modified due to human interventions. River management measures often involve hard engineering strategies such as channelization and dredging in order to ensure flood protection and drainage. Unlike the majority of lowland rivers in Croatia, the Orljava River has not been extensively channelized. Still, its morphodynamics has been under significant human impact due to removal of riparian vegetation, artificial cut-offs, and construction of weirs. This study investigates changes in lateral channel migration rates on the Orljava River since the mid-20th century based on the analysis of topographic maps and aerial images in a GIS environment on selected river reaches. In addition, changes in the channel bank line have been monitored on distinct meanders using an unmanned aerial vehicle (UAV) and a GNSS receiver since 2021. According to preliminary results, the acceleration of lateral channel migration after 2011 seems to be strongly connected with recent engineering works, particularly removal of vegetation from river banks, since the occurrence of higher discharges in the previous decades was not followed by such high channel migration rates. Nevertheless, the largest reach-averaged migration rate of 3.5 m per year was apparently induced by a major flood event in 2014. In general, the largest rates of channel migration in the studied period were recorded downstream of artificial cutoffs and upstream and downstream of a breached mill weir. Since recently increased erosion of riverbanks leads to the loss of adjacent agricultural land, a change in the approach to river management is needed.

channel migration ; flood events ; engineering works ; aerial images ; Pannonian basin

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