It was already in the late 1970s that Schaldorf in the Styrian community of St. Marein was rated as suitable for future hydropower projects in a potential evaluation study.

Around 30 years later, hydropower specialist evn naturkraft went ahead and launched this bold project in the sensitive area between the Trieb and Mürzhofen power plants. Within an extremely short time, they implemented a veritable model project, both in terms of hydropower engineering and ecological compatibility.

When they are asked about hydropower construction in their area, the locals in the Styrian municipality of St Marein have a lot of positive things to say. This is not just the result of the marvellous opening ceremony for the new power station in late July, which operator evn naturkraft organised at the town’s sports grounds, with a free buffet as a token of gratitude to the community. Rather, from the time when construction work began in February 2011, the contractors had made it a priority to avoid as much as possible any interference with the quality of life of the nearby residents. For this reason they set up a separate motorway slip road. Martin Scharsching, DI, explains its purpose by saying, “With the slip road in place, we were able to transport material to and from the construction site directly via the motorway, sparing the local residents all the noise and dust. Our cooperation with the motorway operator, Asfinag, went very well. The road was in place for about a year and was then removed again.”

VALUABLE OLD ALLUVIAL LAND ACQUIRED
The operators took this sustainable approach not just with respect to the people of the region, but applied the same principles to the ecological requirements of the area where the new power plant was to be built. As a result, 3.2 hectares of alluvial forest were purchased and put out of commercial use. A dosing system now carries the annual flood flows towards the alluvial forest to help preserve the old woodland plot in its pristine state. Where ecological planning is concerned, evn relied on a collaboration with renowned river engineering expert Otmar Grober, who is known for his innovative approach to near-natural waterway development.

IMPROVED WATER STORAGE
The plans for the Schaldorf power plant called for a water storage space that should adapt as much as possible to the natural flow of the river. This is where the specially constr ucted, submerged groynes came in, which Otmar Grober had developed at the regional building directorate of Bruck an der Mur. These induce spiralling currents at the bottom of the river to ensure selectively dynamised flow rates. As Martin Scharsching explains, “These submerged groynes help to clear away the dregs within the storage area when the water level is high, and at normal water levels they prevent sediment from settling within their reach. This leaves the coarser, looser bottom substrate, which improves the ecological conditions for fish in the storage area quite a bit.” Adds Otmar Grober, “The advantage that this particular arrangement has against many other facilities is that the bottom level of the weir is only around a metre above the bottom level of the old River Mürz. This makes it easier for us to create dynamic conditions with the groynes within the storage area. In scenarios where the elevation of the weir is high above the bottom level, this can lead to problems due to the shearing stress, and then even groynes are useless.” The selected elevation of the weir has the added benefit of limiting the length of the storage area, which eliminates the possibility of interference with the Mürzhofen power station around 3 km further up the river.

COMBINED FISH PASS AND ACTIVATION BASIN
A fish pass in the form of a classic slot pass was installed as part of the project. At the half-way point, it leads into a generously spaced, near-natural basin pass, which also serves as a natural habitat in its own right for fish, invertebrates and amphibians. The outlet was installed with exemplary perfection, i.e., as far away from the weir as possible. When they installed the fish pass, the engineers were able to apply one of Otmar Grober’s ingenious innovations to optimise the attraction flow. Water is carried from the storage area via the bypass into a circular shaped activation basin, the walls of which are coated with silicate-based magnesite. From the bottom of the basin another bypass leads directly into the first reservoir of the fish pass at the intake on the tailwater side. The ‘sucking’ opening at the bottom of the activation basin creates a swirling motion in the river water that is fed into the circular reservoir. This is to cause the water to receive an electrical charge as it moves past the silicate containing reservoir wall in a rotational flowing motion. When ‘activated’ in this manner, the river water is supposed to improve the quality of the attraction flow water at the intake of the fish pass which, as Otmar Grober believes, is essential for the fish to find the fish pass in the first place. A fish pass based on the same activation principle has already been installed at the evn power station at the River Salza. There, local fishermen had to give up their favourite spots near the weir pothole, as too many of the graylings and brown trouts preferred the new fishway to the actual river.

SIMPLE, COMPACT POWER HOUSE
The hydropower facilities as a whole blend unobtrusively yet confidently into the surrounding landscape. According to project manager Martin Scharching, the main focus during construction was on functionailty, with a view to minimising future maintenance efforts: “The power house was designed so that, during the various stages of completion of the power house, the turbine components and generators could be transported directly into the building with a flatbed truck, hauled off the vehicle and installed straight away. If, decades from now, the machine need reconditioning, they can be removed and transported away quite easily with an indoor crane and flatbed truck.” Following the completion of the power house, the single-step installation of the turbine (i.e., installation without interfering with the building construction) was one of the reasons why the contractors were able to complete the entire plant facilities without problems and within a very short time.

TWIN-SET OF GENERATORS IN A MAINTENANCE-FRIENDLY DESIGN
The above-mentioned core element of the new hydropower plant is a machine combination that previous installations have shown to be a ‘match made in hydropower heaven.’ The two structurally identical, double-regulated Kaplan turbines by Upper Austrian family-owned manufacturer Jank, each combined with a direct coupled synchronous generator by Koncar, generate an overall annual total of 5.4 million kWh. With a flow rate of 14 m3/s per turbine and installed overall output of 1.15 megawatts, the plant will supply 1,500 households in St. Marein and the surrounding region with local eco-power. For the Schaldorf plant, a specially refined turbine design was chosen, which is particularly optimised for use in twin-machine arrangements. As a result, the two machines work at a high level of efficiency both under full load and when the drop head is lowered due to floods. The decision to go with a vertical alignment for the two turbines was also influenced by considerations of maintenance friendliness, as DI Scharsching confirms: “The reason we went for vertical Kaplan turbines was that this allows staff to access the entire mechanism by way of a shaft. We were also careful to avoid the need for gearings. At the end of the day, we are very happy with the solution that Jank and Koncar have implemented – everything is working perfectly. One thing I should mention particularly is the low noise level of the generators: they operate with very little vibration and very quietly.” Also, the vertical design makes the turbine arrangement more cost efficient than an alternative arrangement with bulb turbines.

REGIONAL TOUCH PROMOTES IDENTIFICATION WITH THE PROJECT
The fully automated control of the facility was implemented by Schubert Elektroanlagen. Haider of Kapfenberg (Styria) was responsible for the extensive earth works, concrete placement was contracted out separately to Leyrer + Graf. The contract for the extensive hydraulic steelwork installation went to specialist Mayrhofer of Wenigzell (also Styria). They supplied and installed the weir baffle, the buttomoutlet drain valve with flushing gate, as well as two intake valves, the horizontal fine-screen trash rack with 30 mm bar spacing, and a modular stop log system. Also the hydraulic system for the entire hydraulic steelwork was installed by Mayrhofer. Construction planning and on-site supervision was carried out by the offices of Mach & Partner ZT GmbH of Judendorf (Styria). This choice of local firms aptly reflects the overall local character of the entire project. This means that in additiom to the plant generating electricity for users in the immediate environment, the operator’s choice of contractors also ensured that most of the value generated by the plant remains within the region as well. This was another aspect of the project that found favourable reception with the local Mürztal citizenry. Meanwhile, operator evn is already focussing on the next generation of local citizens: when 2,000 trees and 14,000 shrubs were planted in the surrounding area of the plant’s premises, the pupils from the local schools of St Marein and Allerheiligen were invited to join in, which allowed them to learn first-hand about ecological aspects and the way a hydropower plant works.

OPEN-AIR CLASSROOM FOR THE NEXT GENERATION
At the start of the current school year, the project contractors are set to take a further step in supporting the local youth and promoting their understanding of the connections between various aspects of nature and responsible energy production: in the area of the purcased alluvial forest plot, they are planning to open an outdoor classroom for the students of the surrounding schools. In making Project Schaldorf a reality, evn naturkraft contributed know-how gained from new constructions and revitalisation projects of recent years, as well as the extensive experience as an operator of around 70 hydropower facilities. “We have been granted water rights until the year 2100,” says project manager Martin Scharsching. “It makes you think about the vast responsibility for the entire region that you are taking on for this long period of time.” Their model power plant stands as living proof that the project contractors are more than able to live up to the responsibility.