Pipe swales are used for infiltrating stormwater underground. They consist of a perforated pipe or pipe system and a gravel bedding around the pipe. The runoff is channelled underground into the pipe system and infiltrates through the pipe system into the gravel swale. The fast water distribution in the swale requires pipes with a nominal diameter of 300 mm and a large perforation area. One or more inspection shafts must be arranged per pipe for flushing and inspection purposes.
Planning and dimensioing of infiltration systems are regulated in the DWA worksheet A138. Decentralised infiltration systems must be dimensioned according to the applicable local mean heavy rainfall (e. g. KOSTRA data). The consistence of the soil is of great importance to the dimensioning of the infiltration system. A vortex outlet is required if the permeability value kf is lower than 1 x 10-6 m/s.