Adding ditches or fields next to paved surfaces to temporarily store runoff is a simple way to allow water to infiltrate from clean hard surfaces such as roofs and cycle paths. Besides the volume of precipitation that needs buffering, the permeability of the ground is another factor that determines the dimensions. Soil samples need to be taken to assess that permeability. As an indication, an area equalling 10-20% Geiger et al., 2009 of the impervious surface is required. In addition to infiltration ditches, infiltration meadows are also an option.
Infiltration systems with above-ground storage can be deep or shallow, and naturally the depth and area determine the buffering capacity. In residential areas, a maximum depth of 30 cm is sufficient, to present less of a hazard for playing children. The infiltration systems can be given natural, gentle and safe verges. Roots and the animal activity in the soil ensure that the ground’s permeability is retained. These systems should be designed in such a way that they are not used too much by playing children or other intensive activity when they are dry, which might cause the soil to be compacted and the infiltration capacity to diminish.