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Execution of above-ground infiltration systems

Infiltration à ciel ouvert


The proper functioning of above-ground infiltration systems is crucial to meeting the objectives of integrated water management and flood prevention.

Above-ground storage and infiltration are increasingly imposed in the environmental permit.

In recent decades, there has been a considerable increase in the built-up area (buildings and paving). As a result, the natural water cycle, whereby rainwater can seep into the soil and the earth fulfils a sponge function, has been greatly disturbed. As a result, the groundwater table is insufficiently replenished and, on the one hand, dehydration occurs. On the other hand, much of the rainwater that falls on paved surfaces is discharged into the sewer system. In rainy periods, this causes a large influx of diluted sewage at the sewage treatment plants (WWTPs). As a result, the purification of the wastewater does not take place efficiently and, moreover, the WWTPs cannot process the water mass. At such times, overflows occur, causing wastewater to be discharged untreated into rivers and other surface waters. This can cause flooding, both of streams and rivers, and of sewers.

Due to the negative effects of the changing water cycle, we are facing a real water problem. In order to offer a solution to many problems, the disconnection of rainwater from the sewers is of great importance.

Solutions to the water problem consist first of all of limiting the built-up area as much as possible. When (re)building a structure or (re)constructing a paved surface, one should always consider whether one can do with 'a little less'. By allowing the rainwater to infiltrate the soil again, a more stable water balance will be created which will help to minimise the water problems mentioned above.


A WADI is an above ground infiltration system.

Principle: A wadi is a shallow infiltration basin with a filter bed (gravel, expanded clay granules or infiltration block) to break up a less permeable layer or to provide extra water storage.

The term wadi stands for 'Water Drainage by Drainage and Infiltration' and is Arabic for 'valley'.

A wadi works as an infiltrator when the groundwater level is below the wadi.


In 2021, COPRO will develop further the execution certification of above-ground infiltration systems.