The Rijkswaterstaat or, Directorate-General for Public Works and Water Management is a government agency in the Netherlands responsible for the construction and maintenance of public infrastructure, including motorways and waterway facilities. As such, it is part of the Ministry of Infrastructure and Water Management of the Netherlands. In 1953 a flood caused by the North Sea ravaged the Netherlands. Johan van Veen, an employee of the company, initiated the Delta Plan project. The Deltawerken is the world’s largest water defence structure, located on the territory and on the southwest coast of the Netherlands. The implementation of the programme has seen the introduction of new engineering techniques. It definitely puts the Netherlands at the forefront of innovation in hydraulic engineering.
North Sea Canal tunnels
In the northern part of the country, the North Sea Canal runs through the province of North Holland. It connects the cities of Amsterdam and Ijmuiden (Velsen) over a distance of more than 20 km. Since its inauguration in 1876, five road tunnels have been built to cross the canal, managed by the Rijkswaterstaat.
One of them is the Velsertunnel, which is also the oldest national tunnel in the Netherlands. It is twinned with the Velserspoort railway tunnel. Their construction started in 1941 but stopped a year later, because of the Second World War. Construction work resumed in 1952 until the inauguration in 1957. The construction of the Velsertunnel was planned to be carried out at the same time as the widening of the North Sea Canal. It was built to allow the current A22 to pass under the canal. The total length of the car tunnel is 1,664 metres, with a covered area of 768 metres, it was built according to the cut-and-cover method. However, despite the quality of the work, the emblematic building of this tunnel is the ventilation building.
The ventilation building of the Velsertunnel was built by Dirk Roosenburg (1887-1962). He is a renowned architect that constructed many national and government buildings. Indeed, a part of his constructed work have been declared a national monument. He is also known to be the grandfather of the world-known architect Rem Koolhaas.
The Velsertunnel ventilation building is primarly recognized for its ventilation shafts. The four low shafts are for fresh air intake and are 16.20 metres above ground level; the four high shafts, for the discharge of polluted air, are 31.20 metres above ground level. The internal diameter of all wells is 3.10 metres.
The architectural elements of the ventilation shafts are entirely made of concrete. Each shaft extends slightly forward at the top and has a total of 50 openings, made of square concrete tubes. The whole forming an alveoli structure, ventilating the tunnels. The manufactured elements made it possible to build these towers in a hundred days.
Thanks to its architecture, it has become an emblematic building of the period of reconstruction of the Netherlands after the Second World War. As such, it appears in the list of national monuments.