There are several types of draining facilities: concrete paving stones (with gravel/grass in the holes), plastic gratings (with gravel/grass in the holes) or permeable asphalt. Permeable (permeable) pavement is used as local disposal of stormwater, mainly on traditionally paved surfaces such as parking, pedestrian and bicycle paths and car roads. The solution is not well suited for steeper slopes.
The typical concentrations of land use are based on data from the Parking Area, but the stormwater concentrations have been reduced after a documented treatment effect from StormTac Database. The runoff coefficient should be selected depending on the design and material, but there are general (default) values and recommended values within ranges in the model and database. There is a great deal of uncertainty about the choice of value of the coefficient depending on the type of reinforcement, maintenance and the particle content in the stormwater, which, among other things, controls the degree to which clogging takes place. To avoid clogging, maintenance is required by vacuum suction and/or replacement of the top gravel layer, which should not contain smaller rock fractions than 2-4 or 4-8 mm (Larm and Blecken, 2019).