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Three Danube floods did not stop the Kvassay project – thus one of the most significant water management investments of the decade was realised.

Published

2026. 01. 01. 12:11
Photos: archive / magyarepitok.hu / Mihály Erdei / Mihály Nagy / Tamás Dernovics
Seven-metre-high concrete walls were built in Budapest in the drained bed of the Danube branch to serve a new pumping station. Despite three Danube floods, the modernisation of the Kvassay complex was completed in three years, providing a response to the water management challenges posed by climate change. The project, which was handed over this year, plays a key role in replenishing the Ráckeve–Soroksár branch of the Danube and the Homokhátság region.

One of Hungary's oldest and most complex water management facilities is the Kvassay water barrage, lock, power plant and pumping station at the northern tip of Csepel Island. One of the highlights of 2025 was the completion of the modernisation and expansion of the complex, which began in 2022 as part of an investment by the National Water Authority. The construction was carried out by Colas and STRABAG.

 

The construction, which will affect the area from Budapest to Baja

Approximately 450,000 people live in the area affected by the Kvassay complex. At the same time, more and more people are discovering the tourist and recreational opportunities offered by the Ráckeve–Soroksár branch of the Danube, which is also affected by the investment. This development is also significant from an agricultural point of view, as 400-450 million cubic metres of water, equivalent to a quarter of the volume of Lake Balaton, is discharged annually from the Ráckeve-Soroksár branch of the Danube into the Danube Valley water system. The impact of the Kvassay development has been felt as far as Baja.

 

Connection to the world

The Kvassay Lock is named after Jenő Kvassay, one of the most influential hydraulic engineers of the dualist period. Together with his contemporary, Elemér Sajó, who designed the lock, they played a decisive role in shaping the theory and practice of water management in Hungary. Thanks to their work, the canalisation of the Soroksár branch of the Danube and the construction of the Budapest-Csepel National and Free Port began in 1910. Kvassay's name is associated with the first water management law and the improvement of the standard of vocational and engineering training. His foresight was quickly vindicated by history, as the importance of the Danube increased dramatically after the Treaty of Trianon, as it was the only transport route that remained open to the country. A significant part of the railway network fell to neighbouring countries, which sought to make freight transport more difficult by imposing significant tariffs.  

 

Four new pumps ensure a balanced water level

Kvassay, Lord of the Danube

The Kvassay complex is also known as the Lord of the Danube due to its multifaceted and crucial role. At the northern tip of Csepel Island, the navigation lock was built first in 1911, followed by the inlet lock. Kvassay was expanded in the 1950s and 1960s with the addition of a pumping station and power plant.

  • It provides protection for the Budapest-Baja flood protection basin in the first-order flood protection line.
  • During periods of drought, it ensures a regulated water level in the Ráckeve–Soroksár branch of the Danube. From here, it feeds the fish ponds and irrigation systems of the Danube Valley, and also supports the water supply of the Danube-Tisza Interfluve and the Homokhátság region with up to 60-70 million cubic metres of water annually.
  • The lock and its surroundings are a popular destination for water sports enthusiasts and anglers.
  • The structure also plays a key role in regulating water quality, as ecological problems would arise if insufficient fresh water were to reach the Danube tributary, since the water treated by the South Pest sewage treatment plant flows into the river here.

 

A dramatic situation made the investment urgent

The decision to develop the Kvassay artwork was made in 2018. This was preceded by the lowest water level record of 51 centimetres, measured in 1947, being broken by ten centimetres in Budapest.  

During the drought, the water level in the Ráckeve–Soroksár branch of the Danube was 50 centimetres higher than in the main branch, which meant that water could not flow from the main branch into the branch by gravity. The installed pumps were unable to transfer water from the Danube to the tributary due to the low water level, so mobile pumps were used to supplement the required amount of water. As a long-term and cost-effective solution, decision-makers decided to build a new pumping station.

With this investment, Kvassay will be able to draw water from the main branch of the Danube at a water level that is 50 centimetres lower than the lowest level measured to date (to a water level of 17 cm measured at the Budapest water gauge).

Implementation became urgent, as history books had already recorded the consequences of insufficient water in the tributary.

The Danube branch condemned to death

In the 18th and 19th centuries, the Danube split into two branches of roughly equal size after passing through the narrows at Gellért Hill. Floods were common during this period, mainly caused by ice floes piling up on the sandbanks below Pest.

After the great destruction of Pest in 1838, it was decided that one of the two branches of the river, either Lágymányos–Budafok or Ráckeve–Soroksár, would be dredged to become the main channel, while the other would be closed off.

Based on a law passed in 1870, the Ráckeve branch was condemned to death. As a result of the intervention, shipping ceased and the riverbed began to silt up. The destruction caused by the lack of water affected not only the flora and fauna, but also the people living here through epidemics.

 

Model of the Kvassay complex

There were power stations at both ends of the island

In 1904, it was decided to reopen the branch of the Danube and to build a lock and sluice at the northern tip of Csepel Island. Under the design and construction management of Elemér Sajó, the lock was built in a drained riverbed. Timber structures were built and filled with reinforced concrete. The caissons were suspended on a beam frame and lowered into the riverbed using a lifting mechanism, then the spaces between the elements ensuring watertightness were filled. The water was pumped out of the sealed area. From an industrial history perspective, it is interesting to note that Sajó introduced the first Wolfsholz-type cement injection equipment to the country, which was first used in the dewatering of the Kvassay lock foundation pit. 

The structure, which took 16 months to build and was handed over in 1911, serves to facilitate ship traffic between sections with different water levels. The next phase of development was the construction of a floodgate.

At the southern tip of Csepel Island, after three years of work, the Tassi ship lock and drainage canal were completed in 1929, followed by the power plant in 1930. The latter was damaged during the 1956 floods and became inoperable. During the construction of the lock in 1924-25, the method of lowering the groundwater level (using the Siemens system) and concreting with a casting tower was used for the first time in Hungary, also at Sajó's request. The pumping station and power plant were constructed at the tip of Csepel Island between 1954 and 1962.

 

Competition inside and outside the project

After sixty years, construction began again at the Kvassay complex in 2022. As part of this, the specialists from Colas and STRABAG implemented the complex project in two major phases. In the first phase, they completed the construction of the flood protection wall and the laying of the pressure side pipes, as well as the construction of the structure. The work to be carried out included the renovation of the power plant's turbines and crane tracks, modernising the building's energy system, and beginning the modernisation of the sluice control building, which is a listed building, and the service apartment near the complex, as well as the beam storage facility and the development of the debris removal system. There was considerable pressure to complete these works in time for the World Athletics Championships to be held in September 2023, as the work site is adjacent to the stadium and the construction work could not interfere with the sporting event.

 

Construction traffic travelling in reverse 

After the World Cup, in November 2023, the second phase could begin with the extraction of 28,000 cubic metres of earth, when the area was prepared for the construction of the suction-side pipeline and structures. This work process was interrupted by the flood wave that lasted from December to mid-January. A total of three Danube floods affected the implementation of the investment. Another challenge was that the work area was adjacent to the sports facility, which could only be accessed by construction traffic through the stadium. Due to lack of space, the final section leading to the waterfront could only be accessed by vehicles in reverse. One of the largest of these was a 250-tonne mobile crane, which reversed between the two wall sections with a 10-10 centimetre gap to reach the work site. The cobblestone roads of the athletics stadium were protected from the load of construction traffic with a 10 cm load distribution layer and a 6 cm layer of asphalt.

The pumps can be controlled along a 60 km stretch of coastline at the touch of a button.

The modernisation of Kvassay was preceded in time by the renovation of the multifunctional water drainage structure designed by Elemér Sajó and built by Colas at the southern tip of Csepel Island. The complex, which is suitable for both pumped water lifting and gravity drainage, was handed over in 2021 and is capable of transferring water from the Ráckevei-Soroksári-Duna to the main branch and from the Danube to the side branch. During the work carried out at Kvassay, the control of the pumps serving the water demand of the tributaries was integrated into a single renewed control system along a 60 km stretch of the riverbank.

 

The power plant's turbines are ready for operation again

The turbines of the power plant were also renovated as part of the Kvassay project. The auxiliary controls and the entire hydraulic system were replaced on turbine number one, while turbine number two was completely refurbished. The equipment was fitted with a cooling system capable of utilising the waste heat generated by the turbine. In summer, river water is used for cooling, while in winter, the heat generated during pump operation is used to heat the power plant.

 

40 tonnes in free fall...

A special feature of the power plant is the 40-tonne drop gate in front of the turbine blades. In the event of a malfunction, a hydraulic system immediately lowers the seven-metre-wide and four-metre-high shut-off gate, which falls freely in the first section to prevent more water from reaching the blades. The new rake cleaning system also serves to ensure safe operation. Its function is to prevent debris carried by the water flowing in from the Great Danube by gravity from entering the turbine blades. With the modernisation, debris can be lifted out of the riverbed using an octopus arm, and the new system can transport it to the container via the extended crane track using remote control.

 

A monitoring system also ensured the safety of those working in the Danube riverbed.

During the construction of the new pumping station, the suction side pipeline and structures were built at a depth of 10 metres in the riverbed. To this end,
 

The largest weir in Hungary's history, measuring 150 metres long and 7 metres wide, was constructed in the bed of the Danube.

To create the work area, part of the riverbed was cordoned off with sheet piles. For this phase, an 80-metre-wide and 100-metre-long floating barge arrived in the tributary with two work machines weighing a total of 130 tonnes on board.

8,000 cubic metres of silt and clay were removed from the demarcated and dewatered work area, and the fish were returned to the main branch.

Excavators weighing 20-30 tonnes worked on the superstructure, and the tongue plates had to withstand their weight and the pressure of the water. Safety was ensured in a number of ways, one important measure being a measuring station that monitored the condition of the tongue plates. The system measured 150 points every half hour and indicated any movement of the sheet metal plates with millimetre precision.

 

Seven-metre concrete walls rose up in the bed of the Danube

In the drained riverbed, the Horizont Invest Szerkezet Kft. erected concrete walls to a height of more than seven metres during construction using the MEVA formwork systems. The purpose of the structure is to direct the water to the four pumps. The four pumps of the new plant are served by two parallel pipes, each with a diameter of 1.8 metres, which merge into a single pipe with a diameter of 2.4 metres. The steel pipes have been given a 30 mm thick porcelain-hard surface treatment to meet the 100-year service life required for water engineering projects.

 

The Kvassay project began in 2022 and was completed in the spring of 2025. It responds to the challenges of climate change by strengthening flood protection and, among other things, ensuring water replenishment in the Homokhátság region.

 

 

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