Doubly safe

Marginal Column

Above: The eight central outlet gates are arranged symmetrically so that the water flows intersect just above the surface of the downstream basin.

Illustration | ERG insaat Magnifier

Location of the Deriner Dam.
Illustration: ERG insaat

March 2012

 

The Deriner Dam is one of Europe’s largest – and thanks to Rexroth hydraulics one of the safest as well.

 
 

The dimensions of the Deriner Dam on the Çoruh River in northeastern Turkey are gigantic in every respect. Over 3.5 million cubic meters of concrete were poured into this 249 meter high and 720 long structure. Work has been going on for ten years, with a budget that has grown to one and a half billion euros today. The heart of this mammoth project is an underground hydroelectric power plant – and that too is extraordinary. Every year, four giant turbines will generate 2,100 gigawatt hours – the annual consumption of a city of one million.

“To achieve this power output, we will impound almost two billion cubic litres of water,” explains Hilmi Kaplan, who is responsible for the electromechanical realization at ERG Trade and Industry. Since the 1970s, this Turkish company has specialized in major infrastructure projects and is responsible for large portions of the dam construction. “Safety is naturally a top priority in any project of this size,” continues Kaplan. The main risk for a dam is that the reservoir overflows, which would result in uncontrolled flooding. This could potentially be caused by earthquakes or extreme tides in the nearby Black Sea.

Priority for safety

Two large tilting gates with Rexroth drives provide flood discharge capability. They divert surplus water into the basin at the foot of the dam via two artificial diversion tunnels. “A total of 2,250 cubic meters per second can run off via these ducts,” Kaplan summarizes. “That’s enough for a lot of situations. But if a ‘flood of the century’ should occur, we need many times this capacity.” For this reason, eight central outlet gates have been integrated into the main dam structure. These can handle an additional volume of around 7,000 cubic meters per second. The openings are arranged symmetrically so that all eight water flows intersect just above the surface of the downstream basin. This reduces the impact of the outflowing water.

Keeping things flowing

As a project partner of ERG Trade and Industry , Bosch Rexroth was responsible for the drive and control solution for the central outlet gates and the two tilting gates. The local branch office supported the conceptualization, assembly and installation together with specialists in Germany. “The great advantage for us was that this meant we had just one partner for all flood discharge issues,” explains Kaplan. “Bosch Rexroth solved all tasks assigned to it internally – we were supplied a turnkey system.”

249 meter high, 720 meter long - they used more than 3.5 mio. cubic meter of concrete.

 

The opening drives for the massive central outlet gates represented a major challenge for the design of the hydraulic drives. Each gate is 2.8 by 5.6 meters and weighs 24 tons. Despite this weight, the corresponding drives must work in parallel with a high degree of precision so that the gates always open and close synchronously. This causes the streams of water to meet above the basin, thus dissipating their energy. For these volumes of water, this is essential to prevent erosion of the valley’s side walls and undercutting of the dam. Thanks to their experience from similar projects, the developers succeeded in arriving at a custom solution.

Their trick: the drive cylinders of the central outlet gates are mounted vertically in the drives. In addition, the cylinders are made of a lightweight special steel. “We were also subject to extreme constraints in the weight of the cylinder,” adds Kaplan. Each component of the dam could only be lowered using a special cable crane with a load capacity of 30 tons. Delay-free synchronization of all the gates is essential for efficiently opening and closing these additional flood discharge mechanisms as needed – but the sensor signals need to cover distances of up to 1,250 meters. “This is why a fiber optic network is used in the dam to transport each control command.” Like the central outlet gates, this network has also been installed and fully tested, so that the Deriner dam can safely go into service in 2013.