Drava - River Widening Rosenheim
Drava - River Widening Rosenheim
The Drau river is the fourth longest tributary of the Donau with a length of 707 km. The source of the river is in the Italian municipality Toblach where it continues its flow through Austria, Slovenia, Croatia and Hungary. The mouth of the river in the Donau is near the city of Osijek.
The Upper Drau in Austria is an European protected area with the largest grey alder riparian forests of Austria and over 140 species of birds, including 51 red-listed species. The LIFE project ‘Life vein – Upper Drau River’ was carried out to counteract the trend of too narrow channels that are vulnerable for erosion and flooding by widening the river. Location Rosenheim is close to a town of Drauhofen, St. Gertraud and Rosenheim.
Pressures and Drivers
The Upper Drau is the last free-flowing, not dammed stretch of the river Drau. Nevertheless, human activity has changed the river and its floodplains. When a rail road line was build through the valley in 1870, regulatory procedures were carried out in order to reduce the flood danger and to expand intensive agricultural lands and settlements. The embankments created a narrow channel which suffered from bed erosion. The river bed deepened and wetlands and agricultural lands went dry with the sinking groundwater level. The stability of bank protection structures also suffered from the erosion.
The project has 4 global objectives
- Further stabilization of the Drau river bed through widening and strengthening of bed load influx from tributary brooks.
- More pristine, dynamic shaped river habitats
- Improved information and visitor management on site
- International cooperation with the respective authorities of the Drau neighboring states
No specific objectives could be found in the available project documents
No success criteria could be found in the available project documents
At location Rosenheim (see figure above), a new side channel (1) and wetland ponds (5) were constructed. The side channel was fitted with steep banks on one side of the channel (3). An dead side channel was reconnected to the Drava (2) and a gravel bank was made (4).
A pre-restoration monitoring scheme was carried out to assess the current state of the location. The monitoring focuses on:
- Habitats and animals on the Habitat and Birds Directive
- Fish (presence of species and number of individuals)
- Carabid beetles and other macro-invertebrates (number of species)
- Amphibians (number of individuals)
- River morphology (soil depth and flow velocity)
The same indicators used in the pre-restoration monitoring were monitored during the post-monitoring program in 2010 and 2011.
Expectations and Response
It was expected that new habitats would develop by the natural dynamics in the widened river section. The animal species would benefit from the new aquatic habitats. At the same time, the flood protection was improved by bank stabilization and a higher retention area.
Ecology The synopsis of the monitoring carried out in 2010 and 2011 do not show the monitoring results for the location Rosenheim for fish. The results of the monitoring for the combined projects of the LIFE project and the older GBK Obere Drau project show that the Grayling (Thymallus thymallus) has increased considerably with a doubling of the caught biomass, but it is still below the values measured in the end of the 1980s. Two species that show no improvement are the Danube salmon (Hucho hucho), which is close to complete extinction in the Upper Drava and self-sustaining reproduction could not be determined. The presence of common nase (Chondrostoma nasus) could only be determined by few individuals, but the population has not improved.
Also for macro-invertebrates no results for the individual project Rosenheim were presented in the synopsis, but for all the projects 5 new species of spider and 8 species of carabid beetles were found of the total 130 species. One of these species was the spider Arctosa cinerea, a species strictly related to gravelly-sandy river banks and nearly extinct in Austria. In Rosenheim, a new population of a few individuals was sighted.
The number of amphibian species rapidly increased from 3 to 6 species with numerous sightings of adult Yellow-Bellied Toad (Bombina variegata). Close to location Rosenheim, slow worm (Anguis fragilis), grass snake (Natrix natrix) and Aesculapian Snake (Zamenis longissimus) were sighted.
In Rosenheim, a sediment deficit is prevalent, causing deepening of the soil of 12 cm. This is less than when the old state of the river (29 to 23 cm). Only a small extent of the dynamic morphological processes took place at Rosenheim, due to the low sediment input into the widened section. This reduces the effectiveness of the measures. A reason for the high sediment deficit could be the tributary of the Möll river upstream. The tributary enlarges the discharge of the Drava, but does not transport the needed sediment.
The project was carried out by the Federal Ministry of Agriculture, Forestry, Environment and Water Management in cooperation with the Carinthian State Government and Torrent and avalanche control, section Carinthia.
The main stakeholders were the land owners of the agricultural lands bordering the Drau river.
The communication with stakeholders and the general public was diverse. The project was opened with a large ceremony with a large attendance from the general public and politicians. A total of 70 project team meetings, 13 action days and 25 excursions were carried out.
Approximate cost (total project): €4,600,000
%EU Funding: 32.5 (€1,500,000)
%State: 58.5 (€2,600,000) Federal Ministry of Agriculture, Forestry, Environment and Water Management
%Regional authority: 4.5 (€200,000) Carinthian State Government
%other partners: 4.5 (€200,000) Torrent and avalanche control
Name: Norbert Sereign
Role: Project leader
Phone-Number: + 43 14762 5301 62312
Unterlercher, M. and Petutschnig, W. (ed.) (2011) Lebensader Obere Drau: F2. Monitoring Synthesebericht, Amt der Kärntner Landesregierung
Life vein – Upper Drau River (2011)
- Improve water retention
- Link flood reduction with ecological restoration
- Initiate natural channel dynamics to promote natural regeneration
- Construct semi-natural/articificial wetlands or aquatic habitats