Safety given top priority at Europe's largest dam

The dimensions of the Deriner Dam on the Coruh River in north-eastern Turkey are gigantic in every respect. Over 3.5 million cubic metres of concrete were poured into this 249m high and 720m long structure. Construction has been going on for 10 years, with a budget that has grown to €1.5 billion.

At the heart of this mammoth project is an underground hydroelectric power plant. Every year, four giant turbines will generate 2100 gigawatt hours - the annual consumption of a big city.

Hilmi Kaplan, who is responsible for the electromechanical realisation at ERG Trade and Industry, explains: "To achieve this power output, we will impound almost two billion litres of water." Since the 1970s, this Turkish company has specialised in major infrastructure projects and is responsible for large portions of the dam construction. Kaplan continues: "Safety is naturally a top priority in any project of this size. 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."

Two large tilting gates, which feature Rexroth drives, provide flood discharge capability. The gates divert surplus water into the basin at the foot of the dam via two artificial diversion tunnels.

Kaplan summarises: "A total of 2,250 cubic metres per second can run off via these ducts. 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 gates can handle an additional volume of around 7000 cubic metres per second. The openings are arranged symmetrically in order that all eight water flows intersect just above the surface of the downstream basin. This reduces the impact of the outflowing water.

As a project partner of ERG Trade and Industry, Bosch Rexroth was responsible for the drive and control system for the central outlet gates and the two tilting gates. The local branch office supported the conceptualisation, assembly and installation, together with specialists in Germany. Kaplan explains: "The great advantage for us was that we had just one partner for all flood discharge issues. In effect, we were supplied a turnkey system."

Hydraulic drive design challenge

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 5.6m and weighs 24tonnes. Despite this weight, the corresponding drives must work in parallel with a high degree of precision to ensure that the gates always open and close in sync. This causes the streams of water to meet above the basin, thus dissipating their energy. This is essential to prevent erosion of the valley walls and the undercutting of the dam.

To solve this challenge the drive cylinders of the central outlet gates were mounted vertically in the drives. In addition, the cylinders are made of lightweight special steel. Kaplan adds: "We were also subject to extreme constraints in the weight of the cylinder. Each component of the dam could only be lowered using a special cable crane with a load capacity of 30 tonnes."

Delay-free synchronisation 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 1250m. Kaplan says: "For this reason, a fibre 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.

For further information on Bosch Rexroth hydraulics log on to www.boschrexroth.co.uk/civilengineering.