Nationalpark Thayatal

Nationalparkhaus
2082 Hardegg
Austria

T +43 (0) 2949 / 7005 - 0
F +43 (0) 2949 / 7005 - 50

office@np-thayatal.at
www.np-thayatal.at


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Watercourses, ecology


Nature | Habitat management
 

View from Raven's Rock (Rabenfelsen)
View from Raven's Rock (Rabenfelsen)
View from Raven's Rock (Rabenfelsen)

The Thaya - The river

The most northern border of Lower Austria is for large parts determined by the Thaya. Although it only runs as a real border river on a few kilometers, it shaped the landscape. The Thaya changes sides several times. It is a border river in the physical and geographical sense only four times: near Hardegg in the National Park, near Laa an der Thaya and then again south-east of Břeclav, before it joins the March at the triangle of countries, Czech Republic-Austria- Slovakia.

The name "Thaya", or "Dyje" in Czech, comes from the Illyrian and means something like "murmur" or "murmuring river".
 

Aerial view of the meander mountain
Aerial view of the meander mountain
Aerial view of the meander mountain
If one looks at the Thaya from a satellite perspective, it could also be called "the meandering". In particular between Raabs and Znojmo it winds itself as if it tried desperately to escape from the tightness of its deep bed - a bed that was formed about five million years ago, when the Thaya was working against the rise of the Bohemian Massif, a granite massif, with all its water power. Following crevasses and disturbances of the rising massif, the old meanders cut deeply through the primary rocks.

The Thaya takes its most beautiful meander near Merkersdorf, a cadastral commune of the town of Hardegg, around the meander mountain in the National Park Thayatal. There the two sides of the Thaya get as close as 120 m. after an almost full circle, but the breakthrough is blocked by a hard rocky boulder. On the top of the immediately following Czech meander mountain lies castle Nový Hrádek. From there the Thaya can be viewed from three sides.
 

Fugnitz floods
Fugnitz floods
Fugnitz floods

A power plant changes the river

The construction of the Vranov power plant has strongly changed the characteristics of the Thaya (for more details, go to "Water ecology”).

For years, both national park administrations have been trying in vain to achieve an alignment of the outflow to its natural state, or at least an increase of the minimum outflow.

In its recommendations while awarding the European Diploma, the Council of Europe also criticized the present status.
 

Grafik: Vranov Hamry Dyje
Grafik: Vranov Hamry Dyje
Grafik: Vranov Hamry Dyje

Floods



Heavy rainfalls can turn the Thaya and its tributaries into torrential streams. This happened three times over the last years, in August 2002 and March 2006, the Thaya's tide rose, and in June 2006, floods from the Fugnitz caused a lot of damage in Hardegg.

A diagram showing the flood tides below the dam in Vranov in 2006 gives an idea of how dramatic the situation was. The top graph shows the water level in centimeters, the bottom one gives the flow rate in cubic meters per second. As of a flow rate of over 230 m3/sec. water no longer flows over the turbines but over the weir fields of the dam crest.

Information on the current water levels of the Thaya can be obtained from the office of the Lower Austrian government (D) and the Povodi Moravi (CZ):

Water level status notification of the Lower Austrian government
click here
 
Water level status notification of the Czech Republic
click here
 

Fugnitz valley
Fugnitz valley
Fugnitz valley

The Fugnitz and other tributaries

The nicest and longest tributary of the Thaya in the National Park is the Fugnitz, which shaped the basin of Hardegg together with the Thaya. Its catchment area goes beyond Geras and is about 140 km2. The Kaja brook, which has its source near Niederfladnitz, created a romantic valley which hikers can discover on the Thayatal track.

The tributaries of the Thaya are of particular importance as habitats. This is where crayfish and otter live. The ballast banks of the rivers are of particular importance for the reproduction of Thaya fish.
 

Power plant in Vranov
View of power plant in Vranov with storage wall and lake
Power plant in Vranov

River Ecology

In 1933 the storage power plant in Vranov (Czech Republic) was completed. The hydro-peaking of this power plant massively disturbs the hydrology and ecology of the Thaya. Two to four times a day a surge of water is released which increases the flow rate to 30 m³/sec. or 45 m³/sec. respectively. In between the flood peaks the flow rate goes down to nearly one m³/sec. during which some river banks dry out. Moreover the temperature regime has been altered since the construction of the power plant. The release of cold deep water resulted in fauna corresponding to that of a grayling area instead of a barb area. Other impacts include the deepening of the river, an absence of substratum shifting due to missing high tides and a modification in the dissemination of grain sizes.
 

Trout fishing in the Thaya
Fishermen in the Thaya near a fortification
Trout fishing in the Thaya

Impact on Fish Populations

The long-term objective is to establish a fish population suited to the river type, able to reproduce and possibly support itself under the given conditions (hydro-peaking, homogenous water flow).

When the Nationalpark was established, three out of five fishing grounds were closed. As the National Park administration owns the fishing rights for the rest of the Thaya and the tributary brooks, it was up to the administration to establish a national park-friendly fishery. In difficult negotiations with the Národny park Podyjí and the Moravian fishing union, a first alignment of fishing regulations and other general conditions was achieved. Nevertheless fishing regulations are not totally harmonized yet.
 

Electro fishing to monitor the fish population
Men electro fishing
Electro fishing to monitor the fish population

Basic Studies



The next steps were measures to improve river ecology. In 2006, in a transborder INTERREG project supported by the Region of Lower Austria, the Ministry of Environment and the National Park Thayatal, important parameters started to be compiled which were used as a basis for future measures. This is further being done with regard to the implementation of the EU Water Framework Directive. After all, the ecological situation of the part of the Thaya within the National Park Thayatal should be improved and almost restored to its former state. In September 2006 and April 2007, as part of a study, a survey of the fish population was made along the Czech-Austrian borders of the Thaya. The research was carried out in accordance with the policy manual of the Federal Ministry of Agriculture, Forestry, Environment and Water Management. Depending on the type of river, several fishing methods were applied. The results can be found on the project homepage www.project-dyje-thaya.info (in German only; not up-dated).
 

Spawning boxes-Evaluation
Scientists and fishermen emptying spawning boxes
Spawning boxes-Evaluation
Additionally the hatching success of river trouts was analysed by means of spawning boxes that had been buried in the Thaya in January 2007. The fish eggs came from five different breeders. At the end of the development period the boxes were lifted and the development rate evaluated. The result leaves room for hope: despite strong variations in water levels, fish larvae are able to develop. However there are vast differences from one breeder to the other. For one of the breeders, it was a complete failure; two others had a survival rate of less than one third. Another two breeders had better news: almost 90% of the eggs developed into larvae. Further measures should help to build up a fish population adapted to the river type and that reproduces itself.

During the floods of 2002 and 2006 drift wood from the National Park area gathered in the storage area of the reservoir in Znojmo. The problem of log jam was largely solved through the alteration of the outlet. Additionally a mapping of dead wood at river banks was carried out, the report can be downloaded here (in German only).


Dead wood at the Thaya (German only) [PDF]