GE-RM Lafnitz

The Lafnitz: A river of mystery

The project area studied within the GE-RM (River Development and Risk Management Concept) covers the entire course of the Lafnitz from the Waldbach retention basin in the Wechsel region to the Austrian national border. A special feature of the Lafnitz is that along large parts of its course it forms the state border between Styria and Burgenland. Therefore, the close cooperation between the two federal states was particularly important in the preparation of the GE-RM Lafnitz. In some sections of its middle course, the Lafnitz is still in a very near-natural state. In these segments, the Lafnitz forms the typical meandering bends that wind through the landscape and are constantly changing. Nevertheless, its ecological condition is worse than it seems at first glance. The explanations for this are manifold (fish predators, sediment input, etc.), but cannot be clearly identified in the course of the GE-RM study.

GE-RM Lafnitz

The Lafnitz: A river of mystery

The project area studied within the GE-RM (River Development and Risk Management Concept) covers the entire course of the Lafnitz from the Waldbach retention basin in the Wechsel region to the Austrian national border. A special feature of the Lafnitz is that along large parts of its course it forms the state border between Styria and Burgenland. Therefore, the close cooperation between the two federal states was particularly important in the preparation of the GE-RM Lafnitz. In some sections of its middle course, the Lafnitz is still in a very near-natural state. In these segments, the Lafnitz forms the typical meandering bends that wind through the landscape and are constantly changing. Nevertheless, its ecological condition is worse than it seems at first glance. The explanations for this are manifold (fish predators, sediment input, etc.), but cannot be clearly identified in the course of the GE-RM study.

Overview of flood risk and ecological status of water bodies

Following the preliminary study, the inventories were used to close knowledge gaps regarding flood risk and water ecology and to identify sectoral deficits. After a comparison with the existing objectives, a concept of measures was drawn up based on this. The graphic shows a summary of the deficits on the Lafnitz.

In almost all sections, the Lafnitz is in an unsatisfactory or poor condition in terms of aquatic ecology. This classification is mainly due to the lack of fish biomass. In terms of flood risk, many of the settlement areas are protected against floods with a medium probability (HQ100) by flood protection structures or the planning of such structures is well advanced. In the event of a major event, damage would nevertheless occur in these areas.

Map of LIFE-IRIS segments on the river Lafnitz.

Inventory details to download

Full details of the inventories can be found in the detailed reports. The results of the inventories are summarized in three reports on the following topics: Flood Risk Management (Hochwasserrisikomanagement), Watercourse Development (Gewässerentwicklung) and Planning Framework Conditions (Planungsrahmenbedingungen).

Only available in German.

Section Waldbach retention basin to Rohrbach

 

Deficits

Passability of the Lafnitz

There are several lateral structures in this section that are problematic for both ecology and flood control. The lateral structures prevent fish and other organisms from migrating upstream. At the same time, bedload cannot be transported downstream. Within the scope of maintenance measures, dredging to remove bedload is repeatedly carried out at these lateral elements. This not only impairs the natural bedload balance of the Lafnitz, but also represents a recurring intervention in the aquatic habitat.

Landwirtschaftliche Felder neben dem Fluss Lafnitz.

Influx of fine sediment into the Lafnitz River

Another deficit that affects the entire Lafnitz is the influx of fine sediments from the river’s surroundings. The entry of fine sediments has increased on the Lafnitz due to the expansion of arable land, a decrease in meadows and pastures and a general change in land management in recent years. In particular, open agricultural areas, as seen in the photo, cause a high sediment influx. In the watercourse, these fine sediments lead to so-called colmation: gravel islands or banks silt up and become muddy, resulting in the loss of important habitats.

Low habitat diversity

In this area, the Lafnitz is almost continuously secured and regulated with heavy bank stones. As a result, the dynamics of the river are largely inhibited. Important key habitats for fish such as ford-kolk sequences, deadwood structures or areas with shallow banks are hardly present. The poor river structure and lack of important habitats are also reflected in low fish populations.

Opportunities

Cost effective measures for improvement

Even if the ecological condition of the river in this section is unsatisfactory, low-cost measures can bring about rapid improvements. This is because the bed of the Lafnitz is wide enough in many areas here to implement structuring measures within the current riverbed without taking up additional land. Such measures would benefit, for example, the dwindling population of the Lafnitz grayling.

One way to create important key habitats is to install groynes and deadwood in the watercourse. With this first step, different habitats can be created with only one measure. The example photo shows such structures on the example of a groyne at the Michelbach in Lower Austria. A deep area forms around the groyne – a so-called kolk, which can be used by fish as a place of refuge (for example, from predators or high water temperatures). Meanwhile, shallow areas and gravel banks develop in areas close to the shore.

Der Fluss Lafnitz in der Buhne Michelbach aus der Vogelperspektive.

Section Rohrbach to the mouth of the Feistritz in Rudersdorf

Deficits

Flood risk

Due to the flattening landscape, the Lafnitz bursts its banks early during floods. The areas affected by flooding are therefore relatively large. Although many residential areas are already protected by technical flood protection systems, the potential for flood damage in Neudau and Rudersdorf is still high. For both areas, however, technical flood protection measures are already planned. The flood protection measure in Neudau will be implemented in close coordination with an IRIS pilot measure over the next few years. In Rudersdorf, negotiations are underway with the landowners to enable the construction of a retention basin.

In the villages of Burgau, Lafnitz and Rohbach a.d. Lafnitz, there is still a remaining risk in the event of a severe flood despite the technical protection systems, as the protection systems are only designed for flood events of a certain magnitude. If this magnitude is exceeded, damage to the villages can be expected here too.

Fish stock

Although the Lafnitz has many near-natural areas in this section, the fish population is far too low. This is mainly due to the lack of passability. Many lateral structures are not passable for fish and other organisms and the majority of fish ladders do not meet the current requirements of various fish species. Weirs and other lateral structures represent a clear barrier for fish and are the main reason for the disappearance of many species upstream of the structures. The fine sediment input mentioned above further worsens the living conditions for fish and other organisms.

Opportunities

Near-natural and natural sections

The river morphology in this section can largely be classified as near-natural to largely natural. Overall, almost three quarters of the stretch is in this condition. A special feature here are the meander bends with their steep banks. The preservation and improvement of these near-natural sections is a great opportunity for animals and plants along the Lafnitz.

A colorful resident

The meanders of the Lafnitz are particularly popular with the kingfisher, which finds an ideal habitat here. It uses the deadwood in and around the Lafnitz as a perch to catch prey. The kingfisher prefers to feed on young fish and small amphibians, which, however, require an intact ecosystem. Therefore, balanced habitat conditions on the Lafnitz are also essential for the kingfisher.

Section Rudersdorf to national border

Deficits

Strongly altered river course

Under natural conditions, the Lafnitz would have a winding course in this section. The former course can be seen, for example, on the Franzisco-Josephinian land survey (ca. 1870). Due to the straightening of the river, however, the winding course has completely disappeared in this area. As a result, ecologically important key habitats have also been lost. The loss of these habitats is also one of the main reasons for the sharp decline in fish stocks.

Signs of climate change

Like many other rivers in Austria, the Lafnitz is also affected by the effects of climate change. Evaluations of the water level data show a decrease in discharge during periods of low precipitation. At the same time, the air temperature has risen in recent decades. At the Fürstenfeld measuring station, for example, the average monthly temperature rose by 1.2°C between 1981 and 2019 (from 8.8°C to 10.0°C). The rise in air temperature in combination with low water levels leads to an increase in water temperature. The effects are particularly strong in areas where runoff is already reduced to a minimum due to power plant use. In the future, therefore, measures will be needed to keep water in the landscape, for example, or to prevent a further rise in water temperature through shading.

Opportunities

Space for the Lafnitz

One opportunity for the ecological revitalization of the Lafnitz in this area is to give the river more space again. Even local widening of the river course can have a major impact and create new key habitats. For this purpose, a development corridor has been designated for the Lafnitz, which is also shown in the maps of measures. Here, the Lafnitz is to be given space for its own dynamic development.

Measures

​​The concept of measures for the Lafnitz is based on the deficits and opportunities described and was developed by the entire interdisciplinary team. Suitable types of measures from a nationwide standardized list of measures were selected and localized. The individual measures and packages of measures are described in a separate report in the form of fact sheets and illustrated in measure maps. Each measure or bundle of measures was assessed from a technical perspective in terms of its relevance for achieving the objectives and assigned a corresponding priority. The process concluded with a public participation event at which feedback on the measures concept was collected and taken into account for further planning.

Overview of Lafnitz measures

Symbol Hydropmorphologie

Measures to improve the river morphology

Many of our rivers have been straightened and regulated to make way for settlements and agriculture. The typical river morphology has been severely restricted as a result. Consequently, important habitats in the water and on land are often missing. Gravel banks and islands are one example. These habitats are crucial for substrate spawners, i.e. fish that rely on substrate for spawning, or birds that breed in these places. For the Lafnitz, 48 measures were defined that focus on improving the morphology of the watercourse, but also contribute in part to flood protection.

Symbol Hochwasserschutz

Measures to reduce flood risk

Measures to reduce and prevent flood risks can be very diverse. The most effective measures are combinations of structural and non-structural measures. In the GE-RM for the Lafnitz, 15 measures were defined to protect people from flooding. These range from the preservation of existing retention areas to the renovation of existing facilities and property protection. During the planning process, these measures were harmonized with ecological objectives in order to exploit synergies.

Symbol Verbesserung der Durchgängigkeit

Measures to improve passability

Fish migrate by nature. This allows them to use different habitats. For example, different places are important for reproduction than for growth or feeding. This is why fish migrate within river systems in order to find the optimal conditions for their respective needs. Nowadays, numerous artificial barriers impede this. In order to allow fish and other organisms to migrate as freely as possible, 41 measures have been defined for the Lafnitz, which primarily involve the reconnection of tributary river mouths.

Symbol Hydrologischer Verbesserungen

Measures to reduce the impact of power plant operation

Hydropower is one of the most important pillars of Austrian energy production. However, hydropower plants can have a considerable impact on the environment. Therefore, when planning, operating and modernizing power plants, it is essential to assess the ecological impact. In the GE-RM for the Lafnitz, 11 measures were defined to minimize negative environmental impacts. The focus is on measures that reduce the effects of hydropeaking and increase residual water discharge.

Example of concept of measures

The map below provides an insight into the concept of measures for the Lafnitz. The map shows the municipalities of Rudersdorf and Fürstenfeld with a combination of different measures. With specific measures for water retention during floods, flood protection in Rudersdorf is to be improved. At the same time, additional measures should improve the dynamic flow of the Lafnitz in this area. One of the depicted measures in the area of the Alte Lafnitz in Rudersdorf is also being implemented as a pilot measure within the LIFE IP IRIS project.

All profiles of measures and maps on the main measures from the GE-RM Lafnitz are presented in comprehensive documents.

Photo credits:

Pictures of the Lafnitz and implemented measures: EZB Fluss & Werner Consult