With regard to the surfaces of green spaces, drainage is considered necessary when the following conditions are met:
- Poor pitch soil texture.
- Low water permeability.
- Impermeable layer at a very shallow depth.
Drainage is carried out with the help of a network of underground perforated pipes (usually "herringbone") of different cross-sections which are buried in the sloping ground in order to collect and eliminate excess water from a surface, in order to avoid surface alteration. .
In most cases, this network of perforated pipes is "coated" with special permeability geotextile and covered with various cross-section stony materials.