AUSTRIA’S FIRST FISH LIFT AT THE WEIR RUNSERAU ON THE INN IN TYROL

Autor: Ing. M. Oberwalder and Dr. M. Schletterer , 05.12.2016

The fish lift design was chosen to provide a continuous passage at the existing weir Runserau on the River Inn, where space is limited and the water level is subject to considerable fluctuation.

The project was implemented between 2014 and 2015 in accordance with the National Water Management Plan by Tiroler Wasserkraft AG (TIWAG), with the support of the Austrian as well as the the Tyrolean government under the “Environmental Support Act”. As Austria’s first fish lift, the Runserau fish lift is an innovative undertaking.

Restoring the continuity of water courses to enable the free migration of fish in their natural habitat and the interconnection of biotopes is one of the central measures under the 2009 National Water Management Plan. To comply with the Water Framework Directive, the state governor of Tyrol on December 1st, 2011 issued an action plan for the restoration of watercourses throughout the federal state of Tyrol. The designated “goal for 2015” was to restore continuity at migration obstacles throughout the prioratory water courses. Located within this prioritised restoration area are three TIWAG hydropower plants: Langkampfen, Kirchbichl and Imst (which includes the weir Runserau and the water intake at Wenns ). Three sites were suitable for “standard solutions” (a vertical slot design in combination with a near-natural bypass channel). At the Runserau weir structure, however, the situation was a bit more difficult.

GENERAL CONDITIONS OF FISH PASSAGE CONTINUITY AT THE RUNSERAU WEIR GATE
Hydropower plant Imst was built between 1953 and 1956. This runof-river power plant with a reservoir uses the relatively high head of the Inn between the Prutz and Imst facilities. The Runserau weir structure comprises three inlet gates with a clear width of 13 m and a height of 10 m, which are equipped with hook gates. The water (85 m³/sec design flow rate) is abstracted on the right river bank through a vertical inlet rack and passes over the desilting basin to the 12.3 km pressure tunnel. Space at the Runserau intake is rather limited: On the orographic left side, the structure is integrated into solid rock, with the silt basin located the orographic right side. Due to the heavily fluctuating headwater level, implementing a fish pass with conventional methods was not feasible. An assessment of viable alternatives led to a “fish lift” construction as the optimum solution.

FISH LIFT AS A SPECIAL SOLUTION
Due to the lack of experience with fish lifts in Austria, we conducted a comprehensive study of the available literature and engaged in an exchange of ideas with operators abroad. Like fish locks, fish lifts are used worldwide in locations where considerable height differences between the headwater and tailwater levels are to be overcome and where the available space is insufficient for ‘conventional’ fish pass constructions. Fish lifts, as well as fish locks, have been used successfully for decades and are proven to be highly efficient, especially with diadromous fish species. International examples show that fish lifts work very well, provided they are positioned correctly and equipped with a properly constructed inlet.

TARGET SPECIES: BROWN TROUT AND GRAYLING
From an ecological point of view, the stretches of the Inn around the Runserau intake belong to the designated hyporhithral (grayling region) and metarhithral (lower trout region) habitats in the “non-glaciated central Alps” bioregion (special type ‘large river’). The primary species are therefore the brown trout and grayling (standard size: 50 cm), although rainbow trout, brook trout, bullhead and minnow can be found there as well.

AUSTRIA’S VERY FIRST FISH LIFT
The fish lift design was chosen to provide a continuous passage at the existing weir Runserau on the River Inn where space is limited and the water level is subject to considerable fluctuation. Two inlets in the tailwater section and a conventional slot pass construction ensure findability. The lift itself matches the design of recent functional reference projects in other European countries. The conveyance height of the lift exceeds the height of the obstruction, allowing the fish to be released into the headwater at a considerable distance from the migration obstacle. As a result, the integration of the fish pass was optimised with respect to the given flow characteristics both on the headwater and tailwater levels. Construction work began in September 2014. Before its commissioning in December 2015, the “fish lift” had to pass an operational safety acceptance test, which was performed by the TÜV in accordance with the Austrian Machinery Safety Directive (MSV 2010 BGBl. 282/2008), the Tyrolean Lift and Elevation Systems Act (LGBl. 153/2012) and the applicable lift engineering standard. With the test successfully completed, the Runserau fish lift was inaugurated in time on December 22nd last year.

FIRST MONITORING DATA & OUTLOOK
Due to its conventional intake construction (a vertical slot design with 2 inlets), the Runserau fish lift can be described as an “easy-to-find slot pass with a continuously operated fyke in the last pool and automatic discharge of the fish at a suitable location 600 m further upstream”. This has been confirmed by initial monitoring data that were collected with a VAKI RiverWatcher installed in the slot pass area and a camera installed above the fyke; this proved between January and May 2016 already more than 500 fish were conveyed successfully upstream. Besides confirming the proper functionality of the lift, the monitoring data also provide valuable information about the timing and intensity of the spawning and migration activity of the fish. Based on this data, it would be possible, for example to extract graylings in a controlled manner at the Runserau fish lift for use in the “Inn grayling” species protection project of the Tyrolean Fishing Association. In addition to ensuring the continuity of the watercourse, the adapted minimum flow of 5 m³/s in the residual flow reach led to a considerable improvement of the habitat of the benthic fauna and the habitat suitability for the brown trout and grayling species. The result is a positive impact on the entire residual water stretch downstream towards the point of discharge near Imst.

Reference: Martin Schletterer, Robert Reindl and Stefan Thonhauser (2015): Ökologische Grundlagen und Randbedingungen für die Planung des 1. Fischliftes Österreichs an der Wehranlage Runserau, Tirol. WasserWirtschaft 7/8: 91-98.

 

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Panoramic birds-eye view of the complete Runserau weir gate structure.

photo credits: TIWAG

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The restricted spatial conditions required an innovative technical solution: Since 2015, fish at the weir Runserau (HPP Imst) can migrate to the headwater via a lift system.

picture credits: TIWAG

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Building excavation for an upstream slot pass structure in the tailwater of the weir gate structure.

photo credits: TIWAG

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Concreting work nearing completion at the slot pass construction.

photo credits: TIWAG

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Monitoring data proves that between January and May 2016 already more than 500 fish were conveyed successfully upstream.

photo credits: TIWAG

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Construction of a water intake structure in the backwater area.

photo credits: TIWAG

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Intake rack of the finished residual water intake structure.

photo credits: TIWAG

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TIWAG has implemented Austria’s first ‘fish lift’ at the weir Runserau.

photo credits: TIWAG

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The fyke conveys fish to the headwater level.

photo credits: TIWAG

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Cross-walls in the pools of the ‘vertical slot’ type fish pass.

photo credits: TIWAG