PROJEKT: Restoration and management of Danube floodplain habitats

Various types of man-made barriers such as dams, weirs, steps, fords, culverts, etc. create obstacles in streams and cause water levels to rise. This creates non-native lake ecosystems with many negative effects, above the barriers due to the slowing of the flow and below the barriers due to the disturbed water regime and sediment transport regime.

The weir before restoration acting as a barrier

One of the implemented measures towards improvement of water regime was the partial removal of the weir designated as B-Old, under the “B” line. This weir, which was not possible to manipulate and impassable barrier was a remnant of the original damming of the branch system. From its total width of 130 m, 28.6 m was demolished from the left side of the flow, and the overflow edge was lowered by 1.3 m. This adjustment ensured the removal of the migration barrier and levelling of water surfaces above and below the barrier. The difference in water levels before implementation was 80 to 100 cm in the normal regime, which represented an impassable barrier for most fish. This also contributed to the extension of flowing sections, which is significant for rheophilic fish species that currently suffer from a lack of suitable habitats in the branch system, due to which their population numbers have decreased by 70%. And we also believe that in addition to fish, boaters will also appreciate this measure.

The weir after partial demolition – migration barrier removed