Floods like the ones in 1999 and in October 2012 showed the kind of natural forces at work in the area where the Ill flows into the Rhine – and the massive amounts of bed-load carried by the river in extreme situations.

It was reason enough for this aspect to be taken into consideration during the planning stages for the power plant, with a particular focus on robust, functional and reliable hydraulic steelwork structures. A project of this dimension demanded a hydro steel engineering specialist with extensive experience and a solid reputation – a provider like Hans Künz GmbH in Hard. The critical issues of high-water protection and bed-load movement in particular meant that the power plant constructors would have to come up with ultra-solid solutions. To the planners it was clear from the beginning that a job like this would require hydro steel structures of the highest quality. With all that in the background, the contract was awarded to renowned hydraulic steelwork engineering provider Hans Künz GmbH. The contract for the hydraulic architecture of hydropower plant Illspitz included three radial gates with flap gates for the weir structure, as well as two intake trash rakes, a set of dam beams, two outlet gates, two cable suspended trash rack cleaners, one coarse screen, and one needle rod. “The flood of 2012 was an important influencing factor for our project. Although Künz was not affected directly, the consequences of the event confronted us with numerous challenges throughout the project, while the Stadtwerke kept to their ambitious goal of going into trial operation in the summer of 2014. Thanks to the close cooperation of everyone involved and their constant focus on the goal ahead, we were finally able to celebrate the official inauguration of the plant on the first weekend in October,” says graduate engineer Johannes Galehr, project manager at Künz and joint project lead with his colleague Jürgen Feuerstein.

Alternative spillway solution wins the day
The core component of the hydraulic engineering structure are the 15 m wide radial gates with attached flap gates. However, this had not been the plan from the beginning. “Originally, the plans called for a different gate system with an automatic opening mechanism. However, in the end our solution with three structurally identical radial gates with attached flap gates won out, as it provides a larger overall outlet cross section,” explains Jürgen Feuerstein. Using the attached hydraulic flap gate, each of the gates can be used for impound regulation while providing an efficient way of clearing away driftwood and bedload material. Unlike the usual impound gates, the flap gates are rather large compared to the overall cross sectional area. This construction required a lot of expertise on the part of our engineers. At maximum storage level, each of the gates is able to drain 50 cubic metres of water per second. “The level-controlled opening mechanism for the gates provides extra protection, as they can drain the entire discharge volume of the river Ill, even in case of a power outage, by purely mechanical means,” says Feuerstein. In case of large discharge volumes, the weir gates are opened all the way to allow for the bedload to be carried off.

Customer-oriented solutions by Künz
Another essential hydraulic steelwork component, the turbine discharge gates, were installed facing towards the Rhine. Their control mechanism is linked to the turbines, which allows them to be deactivated in an emergency to prevent them from being damaged. Providing another important function, the new trash rack cleaners were designed by Künz as stationary cable-operated TRCMs. What makes these machines rather special is their ability to comply with hydro-ecological standards that require the bedload to be transported along to the tailwater area. For this purpose, Künz installed (( ?? Schwemmklappen – dredge flaps/gates? )) as well as a separate channel system, which runs parallel to the fish pass towards the tailwater area. This hydro-ecological feature not only ensures that essential organic substances remain in the water, it even saves operators the cost of separate disposal. Another special feature implemented by the experienced hydo steelwork engineers from Hard was a needle dam construction. As Johannes Galehr explains, “In general, the needle dam-type weir is a well-proven solution, although it is rather rare in these regions, and Künz had never done one of the required design before. The fact that the construction and commissioning went ahead without any problems gave impressive proof of the Künz team’s ability to provide an optimum response to special customer requirements. The needle frame is designed so it can be lifted into the water and pulled towards each of the three gates with minimal effort. This makes needle dam also perfectly suited as an closing device for revisions.”

Milestone in March 2013
As for the project schedule for the hydro steel engineers from Hard, manufacturing of the first components began in August 2012, following the general kick-off to manufacturing in April of the same year. Installation work began in January 2013. Over the following weeks, the Künz installation team had to put all their experience into fitting radial gates 2 and 3 with the weir segments within the scheduled time frame. “The two segments with attached flap gates were delivered on March 11th, and their installation was scheduled for the very next day. With the help of a telescopic crane, our engineers lifted, aligned and installed the 26-tonne components with millimetre precision. Everything went smoothly,” says Feuerstein. That completed the first milestone of the power plant project, and the overall facility was inaugurated in late July 2014. Hydropower plant Illspitz is one of the most significant reference projects in Künz’ company history, not just because of the geographic proximity and the future-oriented concept behind it, but primarily because it allowed the Künz team once again to demonstrate their competence. This competence is the result of decades of experience in heavy-duty hydraulic steelwork engineering, and it is being put into practice in all business areas by a young, creative team of highly motivated engineers.