The overlap of the Senna River ( February 13, 1867 - 1871 ; Fr. le voûtement de la Senne , niderl. De overwelving van de Zenne ) by a team of engineers led by Henri Mois became one of the most important milestones in the history of Brussels , which opened the way to architectural and logistical modernization of the city. Currently, underground pipes hide the river in the city. Above them are boulevards and highways.
Senna was historically the main waterway of a small medieval Brussels. However, after 1830, the city became the capital of the united Belgium. As a result of industrialization and the influx of migrants began an intensive growth of the city. As a result of intensive industrial and domestic water intake, the water level in the river fell. It has become more polluted and less navigable. In the working quarters, due to the lack of plots directly above the river, residential quarters were built on piles or in the form of balconies. Garbage was dumped into the river and sewage was drained. The stench from the shallow river spread over a radius of several kilometers. The sudden floods and the presence of a huge number of dead-end alleys in the slums of the lumpen-proletariat further complicated the ecological situation.
Numerous proposals were made to correct this problem, and in 1865, the mayor of Brussels, Jules Anspach , chose the project of the architect Leon Suiz, who proposed to cover the river with pipes and build a number of magnificent boulevards and public buildings above it. The project was extremely controversial, mainly because of its high cost, as well as the danger of a social explosion as a result of the destruction of the traditional quarters of the working class. The original coverage contract was signed by a British company. But after major financial embezzlement, control of the project was returned to the Belgian government. This somewhat slowed down the project, but it was generally completed by 1871. Buildings and boulevards of modern Brussels appeared on the site of Senna, although small areas of the uncovered bed continued to remain in places. The problem of water pollution was not solved.
By the 1930s, the further growth of the city forced architects to wall up the river along its entire course within the Brussels metropolitan area. The flow of Senna was changed. In 1976, disused tunnels were transformed into the lines of the underground system of the Brussels tram . At the same time, modern large-scale wastewater treatment in Brussels began only in March 2007, when two wastewater treatment plants appeared in the suburbs, designed for 1.1 million people.