Hydro-Construct GmbH is an internationally renowned company from Steyr in Upper Austria. In 2019 and 2020 the company gained an initial foothold in the French market by installing two rubber dam systems. Hydro-Construct provided a single­field water-filled rubber dam across the River Arc for the new Aqua Bella hydropower plant, measuring 34.5 m across, holding a water depth of 4.15 m and serving 4 VLH (Very Low Head) turbines. Renewal of the Barrage de Vaux dam on the Yonne River near Auxerre involved replacing the ‘original’ 19th-century two-field, water-filled needle dam. Each individual weir field can be regulated in parallel with the other, ensure a dam-wall water depth of 1.9 m and is 27.3 m wide. Now these first two French reference systems have gone online, Hydro-Construct is confident they will lead to follow-on contracts in France in the near future.

There is one major benefit of deploying flexible rubber dam systems on broad, large-surface bodies of water. In con­trast to conventional damming or water-level regulation solutions, rubber tube dam systems can be installed across extremely broad rivers, without immense structural changes to the natural course or banks of the river. For several years Hydro-Construct GmbH from Upper Austria has been providing its tried-and-tested air- and water-filled rubber dam systems for a wide variety of purposes all over the world. Based in Steyr, in 2012 the company completed a project in Albania, installing Europe’s broadest rubber dam at 265 m end-to-end and a height of 2.3 m. Italy’s Casale Monferrato hydropower plant on the River Po commenced operation in 2020 and Hydro-Construct provided a rubber dam with the largest dam surface area in Europe. The Upper Austrians outdid their previous record with a bank-to-bank length of 200 m and a regulated depth of 4.3 m. In 2017 the largest rubber dam ever installed in India was set up in Uttar Pradesh, measuring 270 metres across and 3.2 m in depth. Hydro-Construct built its first two reference dams in France with the Aqua Bella weir in 2019, and the replacement Barrage de Vaux dam in 2020. “The French market is of great interest to us. We estimate in excess of 200 needle dams in the country, all of which, over time, will require renewal”, enthused Hydro-Construct’s CEO Rudolf Fritsch (Dipl.-Ing. Dr. tech.).

RUBBER DAM REGULATES WATER  LEVEL FOR VLH TURBINES
The Aqua Bella hydropower dam was built by the AKUO Group, specialists in technology harnessing renewable energy sources, on the territories of the towns of Aiguebelle and Randens in the Eastern French Département Savoie. Located on the Arc River, it integrates four VLH (Very Low Head) turbines that offer the advantage of limiting construction at power stations built to harness low heads and large flow volumes. When all four turbines work together at full capacity the machines can generate a maximum power output of 2.2MW. The power plant officially went online after completion in December 2019. In a regular year the plant can cover the demand for green electricity generated by 4800 aver­age­ households. The general above- and below-ground construction work required for the project was conducted by the French Léon Grosse construction company. As their subcontractor, Hydro-Construct provided 34.5 m of water-filled rubber damming for the single-field weir at a dam-wall height of 4.15 m. “The use of four VLH turbines necessitated rapid adjustment times for the dams in reaction to water-level fluctuations when one turbine started or stopped. The adjustment times for the entire weir system refer to the complete raising (90 minutes) or lowering (120 minutes for emptying) of the membrane under normal operating conditions. In special cases the entire rubber dam can be dropped completely in less than one hour”, explained Rudolf Fritsch.

TRIPLY-SECURED SYSTEM
A key challenge of the Aqua Bella project was posed by delivery of the rubber tubing. “The membranes are made with four material inlays with a total thickness of 18mm and an overall dam weight of 20 metric tons. This complicated the manoeuvring logistics. Lifting the membrane delivered in two rolls necessitated the deployment of a mobile heavy­-load crane. Furthermore, installation work had to be conducted in cramped conditions”, Rudolf Fritsch reported. The membrane was manufactured by one of Hydro-Construct’s associates and co-partners Rubena Nachod in Czechia. The extremely stress-resistant material is made using a vulcanising press and can, theoretically, be produced in any length required. Hydro-Construct was supported in the project engineering phase by another Czech co-partner, Aquatis from Brno. The regulation mechanisms within the rubber dam, such as the pumps, rams and reset drives are housed in a shaft built alongside the rock-bed lock of the power station. Continuous regulation of the water storage height, from full capacity to an empty rubber dam, is rea­lised using high-power pumps. Hydro-Cons­truct secures the plant dam in three ways: Firstly, by limiting the risks of pressure excesses. Secondly, by allowing water to be released from the dam manually via a ram or a valve. Thirdly, a pre-defined pressure overload triggers a water-release via gravity drive. Hydro-­Construct developed its own automation solution to regulate the rubber dam system. ESA from Wolfern near Steyr was the automation partner chosen to provide the control technology. The controls are hooked up to the overall power plant management technology, but also operate fully autonomously – so safe, fully-automated operation of the rubber dam system can be ensured at all times.

REDUCED VIBRATIONS
In 2019, the renewal of the Barrage de Vaux weir system in the eastern French Bourgogne-Franche-Comté region was Hydro-Cons­truct’s first chance to demonstrate its expertise on the French market. VNF is France’s national administrative body for French waterways, and was responsible for calls for bids for the project in the town of Vaux on the River Yonne. The needle dam weir was originally built in the 19th century and the last major rebuilding work had been carried out in 1896. The weir next to a ship lock was seriously damaged during floods in 2018 and the need for repair and renovation became urgent. In its role as the general contractor, VNF chose MAÏA SONNIER to conduct its construction work. For each of the two weir fields Hydro-Construct delivered a water-­filled rubber tube dam system – each 27.3 m across, with a maximum water level of 1.9 m. In contrast to the Aqua Bella project, cooperation was sought with a French company for the implementation of the dam controls. Rudolf Fritsch recounts that the main challenge for the Barrage de Vaux project was how to solve the issue of vibrations: “Basically it’s all about minimising dam vibrations caused by the constant underwater pressure of moving water on the dam to avoid operational da­mage to the membrane or the anchor points. Moreover, ahead of the project the Technical University of Graz conducted an analysis of the effects of vibrations on the components responsible for anchoring and securing the dam. We devised a general solution for the problem of vibrations based on the applicable guidelines and the experiences reported by other institutes. Ultimately, we developed a special regulating procedure for the two weir fields to minimise vibrations and optimise switching from parallel to serial operation for increased flow volumes, thus facilitating rapid passage through the critical parts of the rubber dam.”

AN ATTRACTIVE MARKET
Favourable weather and exemplary coopera­tion between the companies involved ensured the Barrage de Vaux project was completed in autumn 2019. The commissioning of the new and modern rubber dam system on the River Yonne has guaranteed local boats and ships in the Vaux area unlimited navigation of the river. Now Hydro-Construct has completed its first two French projects successfully, Mr. Fritsch is optimistic that subsequent orders in the ‘Grande Nation’ will soon appear further downstream, figuratively speaking: “We have installed two highly-impressive reference dams in France, and expect them to open more doors for us. Indeed, we are currently submitting offers for another rubber dam project in collaboration with the MAÏA SONNIER construction company. The AKUO Group, operators of the Aqua Bella plant, are also planning to build a new hydroelectric power station which will also include a rubber dam system. Based on positive feedback from the plant operators, it can be assumed that Hydro-Construct’s next French projects will soon be underway.”