Image VUB & Urban Environmental Geosciences








  • 05/01/2012










The results of the previous project (BONat) on natural storm water reservoirs and their infiltration capacity in Brussels have been summarized in 9 maps.

A poster in Dutch and French has also been made for local administrations or citizens groups in order to reach a large number of inhabitants in Brussels.

You can see these maps in thumbnail view below (the resolution does not allow a good representation at real scale).

If you are interested in poster or maps, please contact us

Epaisseur Cum Sables Lédiens Cumulated thickness of Lede and Brussels Sands

These two formations are the most permeable in the Brussels area.

Their geographic distribution is not homogeneous and the thickness of the formations varies a lot.
Width Unsatured Zone

The depth of the water table varies significantly in Brussels. In general, the groundwater is located near the surface in the valleys but much deeper in the hills.

However, in some uplands, the groundwater can also be found near the surface.

The presence of impermeable layers (clays) prevents the groundwater percolation and creates perched aquifers.
Unsatured Zone
 Influence of compensatory measures

The use of compensatory measures will lead to an important decrease of run-off.

The flooding risk will be mitigated in the infiltration areas but also in the downhill zones where floods generally occur.
Urbanization of Natural Storm water Reservoirs zones

The type of rainwater infiltration measure will depends on the topographic and geological context but also on the density of urbanization.

Compensatory measures can be used in public spaces or in private gardens.
 Natural soils in Brussels

The different soils in Brussels and their specific infiltration capacity are related to the topographical and geological context. The valley soils are less permeable because of the presence of clays.

Silts have been deposited by wind on the hills, which makes the hills much more permeable. The presence of groundwater near the surface reduces the infiltration capacity of soils, which principally occurs in valleys and in few places on hills.
Floods in Brussels

In Brussels, floods are caused by intense rainfall. The sudden increase of run-off oversaturates the unitary sewer system, which is undersized in comparison of growing impervious surfaces.

The majority of inundations occurs on the lowest part of the slope zones or in the secondary valleys.
 Urbanization of Natural Storm water Reservoirs

Urbanization increases the number of impervious surfaces.

The natural storm water reservoir zones are the places where the rainwater recharges the aquifer systems.

In these areas, impervious surfaces have to be limited or at least compensated by infiltration techniques.
Geological formation constituting the Natural Storm water Reservoirs

The sandy geological formations of Brussels, Lede, Diest, Bolderberg and Sint-Huibrechts-Hern are the most permeable.

The zones where these formations are covered by a weak thickness of aeolian silt are called Natural Storm water Reservoirs.
 Depth of the Natural Storm water Reservoirs

These areas are covered by a thin blanket of aeolian silt, between 1 and 3 meters thick.

This uppermost layer can easily be removed to allow the rainwater to infiltrate through the permeable sands by using compensatory measures.

A poster summarizing the concept of Natural Storm water Reservoirs has been created in Dutch and French.

It is available for local and regional administration and/or citizen groups (please contact us if you desire to obtain a high resolution version).

© 2010 - 2011 - Vrije Universiteit Brussel - Pleinlaan 2 - 1050 Elsene - Email: Kevin De Bondt