Abstract
The consequences of river regulation work and other human interventions from the past can still be followed and cause various effects on the Danube river, especially on the formation and state of the islands. We aimed to compile an inventory of the islands along the Hungarian Danube stretch between Vének (1797 rkm) and Budapest (1647 rkm) during the past 250 years, focusing on their landscape history. Real islands were defined as gravel bars that are permanently covered with pioneer woody vegetation, constantly surrounded by water (side-branch is not closed), and their surface remains unflooded at an average water level. We identified 123 real islands that existed on this 150 km long river stretch in the last centuries. These were real islands for a shorter or longer period between the 18th and the 21st century. A total of 66 of them existed at the same time about 200 years ago, i.e., before the large-scale water regulation works, while today this number is only 18, meaning that 73% of current potential Danube islands are at a stage of side-branch succession. Before the river regulation works, the natural successional changes of a real island occurred over hundreds of years, but today they happen rapidly. The formation of new islands became very limited compared to the past due to the lack of sediments and the altered river dynamics. In order to conserve this unique ecological corridor and green infrastructure element in the long run, and restore its damaged floodplain habitats, no more hard-tech interventions should be allowed in the fluvial system. These aspects need to be taken into consideration in decision-making processes with an integrated approach.
Highlights
The Danube is the most international river in the world [1], and Europe’s secondlargest
Integrating data from historical maps to see the various transformations and shifts of the riverbanks (e.g., [18]) is of high importance in order to provide a perspective on the required land management and necessary interventions to maintain them sustainably. This is why we aimed to explore how many islands existed during historical times, follow their natural changes, and those changes which are determined by artificial interventions, and to see how many islands are formed or disappeared compared to the past and which ones could survive as real islands till nowadays
Smaller dikes already had been built during the Roman age, but adaptation to the natural floods had been typical for a long time
Summary
The Danube is the most international river in the world [1], and Europe’s secondlargest. The. Hungarian stretch has remained free-flowing, which is of unique value, but during the last centuries, many other artificial interventions have harmed the river, causing significant effects on its islands and their habitats [2]. The formation of gravel bars and islands as well as the meandering characteristics of the river depend on the water-level gradient and runoff [5]. In order to explore the time horizon of geomorphological processes, literature regarding terrace-formation during the age of the Danube riverbed and its geomorphology should be reviewed. Late Pleistocene and Holocene climatic changes led to the development of the Danube floodplain and the formation of the islands. The more intensive riverbed incision led to the formation of Sustainability 2022, 14, 1829.
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