Alpine-Carpathian River Corridor

The project "Alpine Carpathian River Corridor" is of importance for the improvement of the Green Infrastructure in the Alpine-Carpathian Corridor. It was funded by the INTERREG V-A SK AT programme of the EU and supported by the Federal Government, the Province of Lower Austria and the “Schwechat Wasserverband”. The focus is on connecting the mountain ranges of the Alps and Carpathians through their flowing waters and their immediate surroundings. A total of 19 institutions participated in this project under the leadership of the Donau-Auen National Park with the aim of strengthening the flowing waters in the Slovak-Austrian border region as an ecological network between the Alps and the Carpathians.

Several detailed studies were carried out through the project. For example, the fish fauna of the Rudava was studied. With 35 fish species mapped here, the water body represents an important fish habitat. Especially the relict occurrence of the Ukrainian brook lamprey is remarkable. Another study was devoted to the occurrence of the kingfisher on the rivers Fischa, Schwechat, Močiarka and Rudava. Suggestions for measures to improve riparian structures for the kingfisher were made. In the study "Cross-border floodplain restoration concept & old-growth forest protection", 138 floodplain objects covering a total of 10,797 ha in the processing area were documented. The study discusses the restoration potential in the individual sections. It is thus an important basis for further work on the creation of continuity (connectivity) and restoration of floodplains in this area. The study "Survey of water-related landscape elements in the region of the Alpine-Carpathian River Corridor" focuses on potential connectivity opportunities of water-related landscape elements in the Alpine-Carpathian Corridor. A very high connectivity potential exists where soil conditions are still humid to wet today or were wet in the past.

A total of 13 pilot measures (seven in Austria, six in the Slovak Republic) could be implemented within the framework of the "Alpine Carpathian River Corridor" at different locations of the waterbody network. These serve to improve the habitat and increase the connectivity of the flowing waterbodies with their immediate surroundings.

Schwechat

The tributaries of the Schwechat originate in the area of the Schöpfl in the Wienerwald. The Schwechat flows through the southern Vienna Basin and flows into the Danube near the town of Schwechat. It is noteworthy that the river “Schwechat” has largely natural bedload dynamics. This makes the river particularly valuable as a spawning ground for various fish species. On the other hand, the Schwechat is very heavily obstructed by bank reinforcements along most of its 62 km long flow section. This prevents exchange with the few remaining natural floodplains and severely limits resilience, i.e. resistance to external influences such as heavy rainfall events or droughts. Even though the river has low flows most of the year, flood events are very prominent. The natural and semi-natural retention areas, floodplains and meadows, are therefore particularly valuable and worth preserving not only for their biodiversity but also to minimize extreme weather events.

Obere Schwechat

The main focus in the area of the Schwechat tributary streams in the Wienerwald Biosphere Reserve was on the conversion of spruce forests as an initial stage for natural alder-ash floodplain forest stands. In total, more than 42.1 ha of forest conversion measures were implemented. Conifers such as spruce were removed - natural rejuvenation and thus the emergence of site-appropriate vegetation is promoted. In addition, black poplars were planted at suitable locations to achieve local improvements and to create a stepping stone for the propagation of this autochthonous poplar species in Austria.

In addition, hydromorphological improvements were made to small waterbodies in the Wienerwald at seven sites. The measures ranged from the removal of pipe culverts to the deconstruction of bank regulations.

Schwechat Traiskirchen

Below the Schwechat-Auen (wetlands) natural monument near Traiskirchen is the Kaiserau. Here, the Schwechat is heavily straightened and thus limited in its radius to shape the landscape.

The aim of the revitalization was therefore to allow the riverbed and the bank to develop as freely as possible by removing as much of the bank reinforcement as possible. In addition to the removal of the bank stones, initial measures were also implemented, such as the creation of widening areas and the construction of groynes on the opposite bank. These are intended to support the dynamic development of the riverbed and banks.

Around two years after completion, gravel and sand banks as well as bank demolitions have already occurred, which are used by kingfisher and co.

Schwechat Stadtgebiet (City area)

During the revitalization in the town area of Schwechat, small-scale structural improvement measures were implemented within the existing flood protection. The construction of five alternating groynes created an oscillating line of the watercourse. This contributes above all to the improvement of the habitats for water-bound species and thus to an increase in biodiversity. At the level of the groynes, the watercourse bed was deepened to generate a deep channel. Such structures are especially important for fish as a shelter or for feeding. Furthermore, deadwood elements were installed, which leads to a diversification of the habitat for insect larvae, among others. These in turn are an important food source for fish and amphibians.

Fischa

The Fischa rises in the Steinfeld near Haschendorf in the municipality of Ebenfurth, flows through eleven municipalities in the southern Vienna Basin and flows into the Danube at Maria Ellend. It is 35 km long, the difference in altitude is very small at 86 m. Its catchment area is 563.1 km². The source is located on the eastern edge of the Piestinger gravel fan (also called Wöllersdorfer Schuttkegel) and the Fischa drains it. It is a flowing waterbody almost exclusively characterized by groundwater supply, therefore it has a very stable water level and a rather constant water temperature. At Gramatneusiedl the Piesting flows into the Fischa.

Fischa Kleine Au

In the local area of Fischamend, the Fischa river splits into three arms. Fish passability in this section was restored in the area of the right arm at the dividing spur by constructing an asymmetrical ramp.

In spring 2021, the fish ladder on the Fischa in the Kleine Au of the municipality of Fischamend was completed. In combination with the revitalization of the Fischa mouth, this measure serves to improve the passability of the Fischa and, above all, the spawning situation for ascending fish from the Danube.

In order to be able to measure the potential of these species to travel upstream and thus also the functionality of the fish passage, monitoring was established at the beginning of spring and a control trap was set up at the upper end of the fish passage. This trap is used to catch the specimens that ascend via the fish ladder. The fish trap is emptied daily to count and measure the fish. They are then gently released back into the water.

After more than 100 days of fish trap monitoring, the first positive results can be drawn. To date, 21 species of fish have found their way up the ladder - including all the leading species typical for the waterbody. Furthermore, during the spawning season in spring, spawning fish could be captured by fish traps, i.e. the situation for the spawning migration of Danube fish has already improved due to the installation. Unfortunately, the total number of documented fish was not in the desired range. This may be due to several factors. For example, in 2022 extreme drought caused long-term low water levels in the Fischa River, which also affects the biomass of upstream fish. In order to assess the long-term effect of the measure, it is therefore important to continue the monitoring program over the next years.

Fischa Mündungsbereich

The objectives of this revitalization were the restoration of river, riparian and bank structures typical for the site as well as fish ecological improvements in the area where the Fischa flows into the Danube. The hard bank obstruction was mitigated at the end of 2019. Upstream of the river mouth, the obstruction was lowered over a length of 125 m, and downstream about 130 m of block stones were completely removed.

In a further revitalization step in the fall of 2020, the level of the hinterland above the mouth was lowered to create a shallow side arm with a temporary downstream connection to the Fischa River. The affected area used to be a water area and was backfilled in the course of the then usual maintenance activities of the waterway. The Danube gravel now present there, was removed and the material was returned to the bedload cycle of the Danube.

A habitat was created that significantly improves water connectivity, providing aquatic and semi-aquatic habitats, particularly for juvenile fish and amphibians, as well as macrozoobenthos and waterfowl. In addition, reduced gravel thickness will promote the emergence of vegetation typical for the site.

Together with the restoration of passability in the Kleine Au near Fischamend, the habitat situation for many aquatic species in the Fischa has already improved considerably shortly after completion.