Covering of the Senne
The covering of the Senne (French: Voûtement de la Senne, Dutch: Overwelving van de Zenne) was one of the defining events in the history of Brussels. The Senne/Zenne (French/Dutch) was historically the main waterway of Brussels, but it became more polluted and less navigable as the city grew. By the second half of the 19th century, it had become a serious health hazard and was filled with pollution, garbage and decaying organic matter. It flooded frequently, inundating the lower town and the working class neighbourhoods which surrounded it.
Numerous proposals were made to remedy this problem, and in 1865, the mayor of Brussels, Jules Anspach, selected a design by architect Léon Suys to cover the river and build a series of grand boulevards and public buildings. The project faced fierce opposition and controversy, mostly due to its cost and the need for expropriation and demolition of working-class neighbourhoods. The construction was contracted to a British company, but control was returned to the government following an embezzlement scandal. This delayed the project, but it was still completed in 1871. Its completion allowed the construction of the modern buildings and boulevards which are central to downtown Brussels today.
In the 1930s, plans were made to cover the Senne along its entire course within the greater Brussels area, which had grown significantly since the covering of the 19th century. The course of the Senne was changed to the downtown's peripheral boulevards. In 1976, the disused tunnels were converted into the north-south axis of Brussels' underground tram system, the premetro. Actual purification of the waste water from the Brussels-Capital Region was not completed until March 2007, when two treatment stations were built, thus finally cleansing the Senne after centuries of problems.
The Senne in Brussels
At the beginning of the 19th century, Brussels was still in many ways a medieval city. The royal quarter in the upper town, inhabited mainly by the nobility and the richer members of the bourgeoisie, was upscale and modern. The rest of the city, however, in particular the lower town, located in the western half of the Pentagon, was densely populated and industrial, characterized by an illogical street layout, back alleys, narrow streets, and numerous dead ends.
The Senne river split into two branches at Anderlecht, penetrating the Pentagon, the former site of the second city walls, in two places. The main and more southern arm entered through the Greater Sluice Gate, near today's Brussels-South railway station. The smaller northerly arm entered through the Lesser Sluice Gate, near today's Ninove Gate. The courses of the two traced a meandering path through the city centre, forming several islands, the largest of which was known as Saint Gaugericus Island. The two branches met up on the north side of Saint Gaugericus Island, exiting the Pentagon one block east of Antwerp Gate. A man-made arm, called the "Lesser Senne" (French: petite Senne, Dutch: kleine Zenne) continued on the borders of the Pentagon in the former moat, outside the sluice gates. It followed the Charleroi Canal before rejoining the main part of the Senne north of the city.
The Senne had long since lost its usefulness as a navigable waterway, being replaced by canals, including the Charleroi Canal. The Senne had always been a river with an inconsistent flow, often overflowing its banks. In times of heavy rainfall, even the sluice gates were unable to regulate the flow of the river which was often swollen by numerous creeks flowing down from higher ground. Making matters worse, within the city the river's bed was narrowed by encroaching construction due to demographic pressure. The supports of numerous unregulated bridges impeded water flow and caused water levels to rise even further, exacerbated by a riverbed of accumulated waste.
During dry periods, however, much of the Senne's water was diverted for the needs of the populace of the city as well as to maintain the water level in the Charleroi Canal. This left a flow too feeble to evacuate the filthy water, leaving the sewage, garbage, detritus and industrial waste that had been dumped into the river to accumulate in the stagnant water. The Senne, which a witness in 1853 described as "the most nauseous little river in the world", had become an open-air sewer spreading pestilential odours throughout the city. Early in the second half of the 19th century, Brussels saw numerous dry periods, floods and a cholera epidemic, caused as much by the river itself as by the poverty and the lack of hygiene and potable water in the lower city. This forced the governments of the Province of Brabant and the City of Brussels to act.
Attempts at purification
The first studies and propositions to clean up the river date back to 1859, and during the following years, many different commissions of engineers were assigned to examine possible solutions. Dozens of different ideas were submitted, many of which were completely unfeasible. Several of them proposed diverting large amounts of cleaner water from other rivers upstream to dilute the Senne, while greatly improving the drainage system in the city. Other proposals involved diverting the main course of the Senne completely to the Lesser Senne, which would then be enlarged and thus more useful for boat traffic and mills. Others considered any sort of sanitization impossible, and proposed covering the Senne without greatly changing its course. Among these was a proposal to double the size of the underground drainage tunnels, creating space for a subterranean railroad tunnel. The idea was ahead of its time, but would be implemented a century later with the North–South connection.
The municipal council chose the proposal by architect Léon Suys, submitted in 1865, which had the backing of mayor Jules Anspach. The plan involved suppressing the secondary arm of the Senne by closing the Lesser Sluice Gate. The main branch would be channelled into underground tunnels, to be placed directly beneath a long, straight 30 m (100 ft) wide boulevard, stretching from the Greater Sluice Gate to the Augustinian church (now De Brouckère Square) before splitting into two. One branch was to head towards the Brussels North railway station and present day Rogier Square, the other towards Antwerp Gate, thus forming a long, narrow "Y" shape.
Anspach's backing of Suys' proposal was a calculated decision, as he had radical plans to transform the city. Anspach saw the proposal as an unexpected boon, as it allowed him to accomplish several of his goals at once. It had long been his ambition to transform the impoverished lower city into a centre of business and commerce, suitable for a modern capital. He wanted to attract the middle class, most of whom had left the dingy downtown for the cleaner suburbs, including the Leopold Quarter (now often called the European quarter) and Avenue Louise, causing a large loss in tax revenue for the city. The elimination of the numerous alleys and dead-ends in the lower town in favour of a large, straight, wide, open-air boulevard, linking the two rapidly growing train stations, seemed both a necessity and an opportunity to beautify the city and improve both traffic circulation and hygiene.
Controversy and opposition
The Belgian Parliament had recently passed a law allowing the expropriation of privately owned land by the government when the land was to be used for the 'greater good.' This could be done even if the project was still speculative in nature, and allowed for more land to be taken beyond what was strictly necessary for a project. The city expropriated large swathes of the lower town, counting on reselling the land for a profit, which, after the project was complete, would be on a grandiose modern boulevard in an upper-class neighbourhood. The selling of land after the completion of the project was seen as a way of financing the project itself. That the poorer residents of the lower town were forced away into other already overcrowded districts or into the surrounding suburbs did not trouble the upper classes very much, as the displaced residents did not pay taxes or have the right to vote.
Even after Suys' proposal was officially adopted, Anspach faced strong opposition to the project. This opposition came first from engineers who felt that the covering was incompatible with Brussels’s geology, would accumulate potentially dangerous gases and would not be able to handle enough water to prevent floods. Others opposed to the project complained about the high taxes resulting from its high cost, poor compensation for seized property and the lack of public input into the project. The press accused Anspach of being responsible for demolishing Brussels' old town, and published numerous caricatures mocking him.
A liberal, Anspach feared the weakness and rigidity of the government and therefore gave the work of covering the river to a private British company, the Belgian Public Works Company (the English name was used), which was created for the task. However, partway through construction, it was forced to relinquish control to the city of Brussels after an embezzlement scandal in which a company director allegedly attempted to steal 2.5 million francs from the company. Anspach only barely kept his office in 1869 by-elections.
Excluding the important sewers built upriver and downriver in the adjacent suburbs, the covered section itself was to be 2.2 kilometres (1.4 mi) in length. Constructed from bricks, the covering was to consist of two parallel 6 m (20 ft) wide tunnels, and a set of two lateral drainage pipes, each taking in waste water from its respective side of the street.
The contract was signed on June 15, 1866 and the expropriation of the first 1,100 houses was completed in a few months. The work began on February 13, 1867. There were several technical difficulties that delayed the covering, many of which were due to the geology of Brussels, though they were not as bad as some engineers had forecast. The embezzlement scandal also caused a significant delay in construction, largely due to the change in control. The project was completed in 1871, with the municipal council ceremonially opening the reconstructed sluice gates on November 30.
The new central boulevards
The series of boulevards created by the project – Hainaut Boulevard (now Maurice Lemonnier Boulevard), Central Boulevard (now Boulevard Anspach), North Boulevard (now Adolphe Max Boulevard), and Senne Boulevard (now Émile Jacqmain Boulevard) – were progressively opened to traffic from 1871 to 1873.
The opening of these new routes offered a more efficient way to get into the lower town than the cramped streets of rue du Midi/Zuidstraat, rue des Fripiers/Kleerkopersstraat and rue Neuve and helped revitalize the lower quarters of the town. In order to accomplish this revitalization and attract investment, public buildings were constructed as part of the Léon Suys project including the Brussels Stock Exchange. The vast Halles Centrales/Centrale Hallen, a good example of metallic architecture, replaced unhygienic open-air markets, though it was torn down in 1958. The monumental fountain that was to break the monotony of the boulevards at Fontainas Square was abandoned for budgetary reasons.
The construction of private buildings on the boulevards and surrounding areas took place later. The middle class continued to prefer living in new suburbs rather than the cramped areas of the city center. The high prices of the land (expected to finance part of the construction costs) and the high rents were not within the means of the lower classes. Life in apartments was no longer desirable for residents of Brussels, who preferred to live in single family homes. The buildings constructed by private citizens had difficulty finding buyers.
To give builders an incentive to create elaborate and appealing facades on their works, an architecture competition was arranged in which twenty buildings built before January 1, 1876 would win prizes. The first prize of 20,000 francs was awarded to Henri Beyaert who designed the "Hier ist in den kater en de kat" (Loosely, "House of Cats") on North Boulevard. Nonetheless, it took another 20 years, until 1895, for buildings to solidly line the boulevards.
The former Augustinian church, built at the beginning of the 17th century in the baroque style, was the only remaining part of a convent destroyed in 1796 by French revolutionaries. After having been used as a Protestant church from 1815 to 1830, it subsequently saw use as a concert hall, a commercial exchange, and a post office. At the center of de Brouckère square, the church’s façade was intended by Léon Suys to be one of the focal points of the new boulevards. The work to cover the river, which nearly surrounded the church, preserved the integrity of the building at great trouble and expense, but the church was finally demolished in 1893, its style no longer popular with the people and its presence unsuitable for the area. The church was replaced by a fountain dedicated to the memory of Jules Anspach. The facade of the church, however, was preserved, being disassembled and moved to serve as the façade for the St. Trinity Church in the suburb of Ixelles.
Diversion and treatment
Although the original covering of the Senne resolved sanitary problems and flooding in Brussels’ old city, this was not the case in peripheral areas. The Senne was still very polluted, despite work done to the sewers and spillways in the canal. The drainage into the canal was not able to completely stop the floods that regularly affected certain outer areas of the city.
In 1930, a group was created whose objective was to channel the Senne into subterranean tunnels for nearly its entire course through the Brussels metropolitan area. This was done in order to expand the benefits that the covering achieved in the old city. In the centre, the course of the river was to be changed from the central boulevards to the peripheral boulevards of the small ring. The project, delayed by war and the work being done on the North–South connection, was only finished in 1955.
The disused channels of the central boulevards later facilitated the construction of the north-south line of the premetro, which opened in 1976. The conversion of the existing tunnels to metro tunnels ensured that there was minimal disruption on the surface. Some of the former pipes also served as storm drains. The Anspach Fountain was transferred to the Quartier des Quais/Kaaien. 
Actual purification of the waste water from the Brussels-Capital Region was not completed until the 21st century, when two purification stations were built. The south station treats refuse water from 360,000 inhabitants, which is about one third of the polluted water, and lies on the border of Anderlecht and Forest.  The north station, completed in March 2007, is located near the border of the Brussels-Capital Region, between the Senne and the Charleroi-Willebroek Canal, near Buda Bridge.  A portion of the cost was footed by the Flemish Government, as 7 of the adjacent municipalities lie within the Flemish Region.  This station is capable of treating the water of 1,100,000 inhabitants and should finally be capable of fully purifying the Senne, which had long caused much of the pollution of the Scheldt river.
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