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Water management in Brussels: knowledge gained from the long time data series of the Flowbru regional telemetry system

Notes de la rédaction

This is the press release related to the article from Nicolas de Ville and Michel Verbanck, published on May 22, 2017

The sewer system is an absolutely essential as well as inconspicuous urban infrastructure. People think about it only when something goes wrong – collapse due to its old age, flooding during storms, treatment plant interruption, etc. – as well as when the cost of its renovation is reflected in the water bills. The works related to maintenance and the creation of stormwater basins are among the major work sites seen in a city which is painfully rediscovering its dependency on underground infrastructures.

The challenges of Brussels water management are numerous and varied: flood mitigation, ever-increasing imperviousness, river pollution control and the management of a sewer network which was designed and built more than a century ago. There was one main objective at the time: to evacuate as quickly as possible the malodorous and foul wastewater produced by the growing city using every available waterway. Many small streams were therefore covered and turned into sewage collectors.

Today we must deal with this legacy, which is ill-adapted to more environmentally friendly management. The artificial and natural water systems are intermixed to the point that it is difficult to determine their limits, which has an impact on certain infrastructures. Therefore, water managers and engineers must gather information in order to improve system efficiency and respect river water quality standards while protecting the city from flooding hazards. For example, the wastewater treatment plants are designed to clean polluted water, but they are much less efficient during the massive influx of less polluted water, such as rainwater.

Therefore, a better understanding of the specific nature of what flows through the sewers is essential for efficient management. The long time data series provided by the Flowbru regional hydrometric network for surface water and wastewater, as well as the Brussels-Capital Region limnimeter, represent a true opportunity to gain knowledge on the hydrographical system in Brussels.

Issue number 111 of Brussels Studies summarises the information from the analysis of these data by Nicolas de Ville, bioengineer, and Michel Verbanck, civil engineer, both of whom work at Université libre de Bruxelles in the Faculté polytechnique. They are interested in particular in one of the collectors which leads to the North wastewater treatment plant. An overflow structure ensures that in the event of excess volumes, wastewater is discharged directly into the Zenne without being treated. This is called ‘overflow’. Based on the observation that these discharges are very frequent and greatly jeopardise the water quality improvement expected after the treatment plant was put into operation, the two engineers aimed to improve their understanding of the factors at the origin of this increase in polluting events, using Flowbru data.

The first element highlighted is the parasitic clear water infiltration in the sewer system. This infiltration reaches a maximum level in winter. Part of the burden on the sewer system could be removed by ensuring that parasitic water no longer infiltrates the system (by improving the impermeability of the collectors, for example) and that it is evacuated by streams and rivers. The decrease in the amount of parasitic clear water would contribute directly to improving treatment plant operations. However, this infiltration contributes to a self-cleansing process in the sewer system. The disappearance of this process could therefore lead to a clogging of the sewer system due to sedimentation.

The second factor identified as being at the origin of the frequent spills into the Zenne is sediment accumulation. By means of several converging analyses, the researchers show that the sediment layer at the bottom of the collector under study is five times thicker than it was in the mid 1980s. This, of course, greatly reduces the capacity of the collector and leads to an increase in episodes of system saturation.

Clearly, it is through the integration of new infrastructures (treatment plants, stormwater basins), sewer system renovation, the regular maintenance of collectors and the rehabilitation of natural water circulation that more efficient and sustainable management will be achieved.

References
Nicolas de Ville and Michel Verbanck, “Water management in Brussels: knowledge gained from the long time data series of the Flowbru regional telemetry system”, Brussels Studies [Online], General collection, No 111, 22 May 2017. URL: https://brussels.revues.org/1519
Contact
Benjamin Wayens, Senior Editor: bwayens[at]brusselsstudies.be

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