Underdrained swale systems are used for the treatment of contaminated stormwater and the downstream infiltration into the soil. Dirt particles and dissolved pollutants are absorbed and detained by the soil layer. Underdrained swale systems are suitable for use in any soil. Depending on the soil infiltration capacity, the infiltration effect will outweigh the detention effect or vice versa, with a significantly throttled, delayed discharge into the sewer or the natural receiving waters. This makes the system particularly suitable for areas where impermeable soils with unfavourable kf values prevail. The vegetation/soil layer of the trough provides a superior cleaning effect. This makes underdrained swale systems also suitable for heavily polluted surface water, e.g. road runoff from heavily trafficked areas, and industrial and commercial areas. Stormwater is stored in the underdrained swale before it filters through the manmade vegetation layer and enters the swale. In the swale, the water evenly seeps into the void spaces between the gravel. MuriPipe then controls the flow and infiltration of the water. We generally recommend accommodating an emergency overflow from the underdrained swale into the swale. An emergency overflow is essential if the frequency of overflows in the underdrained swale exceeds that of the entire underdrained swale system. If soil is sufficiently permeable for water (kf ≥ 1 x 10-6 m/s), water completely infiltrates through the swale into the ground. Water will only partially infiltrate on soils with a relatively low permeability.