Because of multiple constraints, e.g. existing drainage systems, little available space and higher costs, Best Management Practices (BMP) for stormwater-runoff in existing urban areas is more difficult to apply than for new urban developments. For a large urban catchment (about 22 km2) with a separate drainage system in Berlin, Germany a combination of decentral (non-structural) and semi-central stormwater-management measures proved to be the best solution. It offers a high effectiveness concerning stormwater treatment at relatively low costs. Modern planning tools such as Geographic Information Systems (GIS) were used to investigate the possibilities of implementing decentral measures in larger areas. Correlations between field surveys and data from the ‘Environmental Information System’ of Berlin shows that even in highly urbanised areas a disconnection of 30% of the impervious area can easily be achieved. The resulting reduction of the discharge makes it possible to convert existing retention tanks to soil filter tanks. The purification efficiency of this combined measures is higher than of a central stormwater settling tank which has been simulated with a pollution load model.
Modelling stormwater runoff, quality, and pollutant loads in a large urban catchment