Description of the project area
The project area extends over about 100 km from the source of the river Leitha (river kilometre 121) to the border with Hungary (river kilometre 18,5).
The Leitha originates in the municipality of Lanzenkirchen (Lower Austria), at the confluence of the rivers Schwarza and Pitten. The Leitha leaves Austrian territory in Nickelsdorf in Burgenland and flows into the Moson-Danube at Mosonmagyaróvár (HU). The area of the catchment area upstream the Austrian-Hungarian border is 2,131 km².
The discharge of the Leitha is strongly influenced by its geologically and hydrogeologically different main source rivers: the Schwarza originates in the limestone massif of the Rax and Schneeberg region, the Pitten in the crystalline rock of the Wechsel and the Bucklige Welt.
As a result, the flow regime is also essentially determined by snowmelt, which is rather atypical for a lowland river in the Pannonian region.
Another peculiarity of the Leitha is that the highest flood quantities occur immediately after the confluence of the rivers Schwarza and Pitten rivers, but then gradually decrease. This is due to large-scale flooding-areas over the entire length of the river. As a result, the flood wave of 100-year flood event (HQ100), for example, is reduced from around 330 m³/s to approx. 130 m³/s. During an HQ30 flood event about 50 km² of the floodplain are flooded, an HQ100 floods about 75 km².
Originally, the Leitha was a meandering river in the project area. In the course of systematic regulation works, numerous meanders were cut off and the straightened channel was stabilised by longitudinal bank protection measures.
Hot Spots & Highlights
The Leitha in the project area is part of the Natura 2000-FFH European protected area “Feuchte Ebene-Leithaauen”. Due to river regulations, the natural floodplain forests only exist in small areas. In some places there are also oatgrass meadows in the floodplains.
Need for action
In addition to the flood protection measures already implemented or under construction, further measures along the Leitha are necessary. In order to achieve continuous protection against 100-year flood events in the future, linear flood protection measures as well as a retention area of approx. 5 million m³ is required for sufficient flood retention.
Regarding ecology, there is a great need for action, as the Leitha shows a moderate to poor ecological status. From the mouth of the Warme Fischa to the Kotzenmühle, morphological deficits and continuity interruptions (obstacles to fish migration) lead to deviations in the type-specific species composition and subsequently to a moderate ecological status of fish.
The Leitha section from the Kotzenmühle to Bruck (diversion Trautmannsdorfer Kanal) is characterised by low residual water flow and falls periodically dry. This pressure in addition to the interrupted longitudinal continuity in this river section cause extremely low fish biomasses and accordingly, the ecological status of fish is poor. However, a relatively high species spectrum and good juvenile fish habitats indicate a high potential for ecological improvement.
The full water flow of the Leitha from Bruck to Gattendorf results in an improvement of the ecological status of fish to moderate.
Morphological improvements and the re-establishment of the longitudinal continuity at the Gattendorf weir would be essential prerequisites for the achievement of a good ecological status.
The aim of the GE-RM Leitha is to coordinate flood protection measures with the necessary measures to achieve good ecological status in the river. The agendas of nature conservation (Natura 2000, floodplain protection), but also existing uses (e.g. water abstractions, tourism and recreational functions) must be taken into account with the goal to find synergies.
Outlook and time plan
By the end of 2021, the River Development and Risk Management Concept (GE-RM) for the river Leitha will be finalised. On this basis, the detailed planning of pilot projects will start. The structural implementation of the pilot measures is planned for 2022.