Geomorphological changes of the Cetina River channels since the end of the nineteenth century, natural vs anthropogenic impacts (the Dinarides, Croatia)

摘要

This study investigates changes in channel morphology of the Cetina River over the last 130 years affected by climate changes and various human impacts. A detailed digitalisation and analysis of the channel features was performed by using historical maps from the 1880s, archival aerial images from the 1950/60s, and contemporary orthophoto maps from the 2010s. According to these sources, we defined three study periods, and distinguished changes in the pre-dam phase (1880s-1950/60s) and the post-dam phase (1950/60s-2010s). In the pre-dam phase, a partial channel narrowing and drying of marsh zones in the source area were recorded, possibly due to reduced humidity and discharge following the end of the Little Ice Age. A drop in discharge and an increase in sediment supply caused by agricultural intensification most probably affected the expansion of fluvial bars. The increase in sediment supply is particularly evident in considerable river delta progradation of 500 m during this period. In the last 50 years, five hydroelectric power plants were built in the catchment. Consequently, severe reductions in discharge led to channel narrowing by about 50% which occurred in the third of the river length. Apart from the dam construction, a reduction in the area of bars by 85% and an increase in the number of islands by 103% can be related to decreased sediment supply following land abandonment and natural reforestation. This study adds to the knowledge on river morphology and channel adjustments following natural and strong human disturbances in the Mediterranean environment.