The hydraulic engineering project to mitigate the Paks accident has begun: the first shipments of stone have arrived on site

The details have now been revealed regarding Hungary’s most urgent construction project at present: work has begun on the Danube riverbed sill near Paks to remedy the emergency situation. As we noted in yesterday’s report,

A stone bed is being laid in the riverbed; the sill constructed on top of this will help to raise the river’s water level on a permanent basis, whilst not causing any problems in the event of a flood later on.

Prime Minister Péter Magyar outlined the stages of the project at a press conference on Thursday, together with the relevant experts. According to this, the sill being built between Paks and Dunaszentbenedek will be constructed alongside the nuclear power station’s cold-water channel.

The details of the project’s design were presented by József Gacsályi, Deputy Director-General for Technical Affairs at the National Water Management Directorate. Brigadier General Dr Pál Kádár, Director-General of the Defence Administration Office, outlined the organisation and coordination of the works.

Different working methods on either side of the river

Water management experts, the appointed contractors and the armed forces are already at work on both banks. On the left bank, which can be accessed on dry land, soldiers from the armed forces have begun work. On the right bank, next to the power station – where the river is deeper and the water flow is greater – the designated contractors are working in collaboration with the water authority, the Prime Minister explained.

He added that a significant proportion of the heavy machinery is already on site, and that staging areas, transport routes and storage areas for large quantities of stone have been established. He noted that stone has already arrived on site, and work has begun on placing a small quantity of it by the Danube.

In parallel with all this, two 80-metre barges are being prepared, and if the water level falls below minus 132 centimetres, they will intervene by sinking them. In the short term, this intervention could raise the river’s water level by around 20 centimetres. It was stated at today’s briefing that the barges will not be positioned perpendicular to the bank, but at an upward angle of 45 degrees.

The waterworks will be completed within 30 days

József Gacsályi, Deputy Director-General for Technical Affairs at the National Water Management Directorate, outlined the hydrological and technical details of the riverbed sill planned for the Paks section of the Danube. In his presentation, he emphasised that, compared to the 1995 intervention at Dunakiliti, the current project poses a significantly greater challenge. This is because the structure must be constructed not in a still-water environment, but in a riverbed with a constantly flowing current, currently carrying a discharge of approximately 800 m³/s. The site of the works has been designated between Paks and Dunaszentbenedek, along a stretch of approximately 300 metres between the nuclear power station’s cold-water and hot-water channels.

The construction work is divided into two main areas. On the Paks side, on the right bank, high-capacity lorries are used to transport hydraulic engineering stones weighing between 40 and 200 kg to the site. These are deposited on the bank and then lowered into the riverbed from watercraft. At the same time, on the Dunaszentbenedek side, work is progressing towards the centre of the riverbed using dry construction technology: lorries drive in, the unloaded stone material is levelled by a bulldozer, and the machinery then continues along the stone foundation thus created.

The technical structure of the bottom sill will consist of two different cross-sections. In the deeper section of the riverbed on the right bank, a sunken sill profile will be constructed to ensure the international shipping route. This is a section approximately 200 metres long (with a lower surface 150 metres wide), the upper surface of which will remain at least half a metre above the current extremely low water level. On the left bank, on the Dunaszentbenedek side, a 300-metre-long stone structure (a retaining wall) is being built, which will rise approximately 50–60 centimetres above the current low water level. To ensure adequate stability, a layer of stone, one metre thick and 40 metres wide, laid on geotextile, is being placed beneath the left-bank stone structure, upon which the trapezoidal section with a crown width of 6 metres will be built.

Experts carried out detailed hydraulic modelling in collaboration with the Budapest University of Technology and Economics, using an extremely low water flow rate of 600 m³/s as the basis for their design calculations. The primary aim of the intervention is to raise this critical water level by nearly half a metre to ensure the security of the cooling water supply. At the same time, the models also confirmed that, in the event of a potential future flood wave (with a discharge of up to 7,500 m³/s), the structure would not pose a significant obstacle to the drainage of water.

The round-the-clock works are scheduled to last 30 days, but the installation of the structural widening works to ensure the waterworks’ stability will continue until October. Once the emergency situation has passed and hydrological conditions have stabilised, the sill on the 150-metre section of the navigation channel will be lowered by approximately one metre. To this end, approximately 2,500 m³ of rock material will be relocated to reinforce the riverbed, thereby ensuring conditions suitable for international shipping in the longer term.

Donations can be sent to this address

In his speech, the Prime Minister expressed special thanks to the experts in the energy, water management and defence sectors, the staff of the Defence Administration Office, the University of Technology and the design offices for „serving their country round the clock” in recent times.

The Prime Minister also expressed his gratitude for the donations received so far and asked anyone wishing to make a further donation to write to [email protected]. Péter Magyar particularly highlighted that the Austrian company Strabag had offered technology, transport and raw materials free of charge, and that a similar offer had also been received from the Hungarian-owned company KÉSZ Zrt..

Following the press conference, Market Építő Zrt. also stated on its social media page that, in response to the call from the Defence Administration Office, they are ready to support the engineering works by donating 10,000 tonnes of stone, which they will transport to the designated site using their own resources. At the same time, the Duna Aszfalt Zrt. has also on its Facebook page that the barge, which is currently surplus to requirements at the Mohács bridge construction site, set off yesterday and arrived safely in Paks, where it will support preparations for the next critical phase at the nuclear power station. Bayer Construct did the same. As their social media page: 25,000–30,000 tonnes of previously extracted and graded gravel are immediately available at their group’s gravel quarry in Kiskunlacháza, which they are offering free of charge to support the flood defence works taking place in Paks.