Heavy rainfall causes significant runoff on soils that have become impermeable.

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ithin WASABI, the rain garden of Gembloux Agro-Bio Tech ULiège is considering responses to this problem. The aim is to illustrate the multifunctional hydrological management of an urban site. Bioengineering students and landscape architects, trained under the guidance of Professor Aurore Degré, will develop urban hydrology projects.  In addition, an open-air classroom will host life science courses, allowing direct interaction with the subjects developed there.   

How is a rain garden organised? It is a unique place that combines different devices for slowing down, storing, infiltrating and evaporating water (regulation service) while offering landscape, leisure and even refuge services for biodiversity.  

In concrete terms, the essential function of the rain garden is to filter a certain volume of water before letting it infiltrate into the soil or discharging it at a regulated rate to an outlet. The rain garden is based on the principle of bioretention. Rainwater and runoff are temporarily stored in the rain garden where they are partially purified.  

In addition to this functional aspect, in terms of urban runoff management, it will be a place for relaxation, aesthetics and social interactions. It will thus be a place of scientific advances where everyone will eventually be able to walk around and enjoy the surroundings.

A little technical information... 

The mechanisms involved are as follows:

  • sedimentation: as the water slows down, suspended particles settle in the ditches and the rain garden pond;
  • filtration: particles are filtered as they pass through the soil and the fibrous roots of plants;
  • assimilation: nutrients are consumed by plants for growth. Plants can also contribute to the assimilation of heavy metals; 
  • absorption: pollutants are temporarily attached to organic matter, soil particles and roots allowing the action of micro-organisms;
  • degradation and decomposition: the decomposition of organic matter and absorbed chemical compounds is promoted by soil micro-organisms;
  • evacuation: rainwater is evacuated to an outlet or by infiltration into the soil and evaporation. These different drainage methods can be combined according to their own capacity.

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