Dealing with Rainwater

A paradigm shift in dealing with rainfall runoff from residential areas is not only observed in Germany but also internationally in recent years. Whereas previously the "harmless drainage" was at the forefront, a decentralized management of runoffs is increasingly sought today.

The reason for this paradigm shift is that the previously practiced, drainage of precipitation via separate or combined systems led to enormous problems:

• high pollution load of waters

• intensification of the inflows into receiving waters after heavy precipitations

• reduction of the base runoff in dry seasons

• reduction of groundwater recharge and evaporation, disturbance of the water balance

The concept of decentralized rainwater management has proved to be alternative for a more sustainable use of stormwater. Stormwater management does not stands for a single process, but for a variety of measures, which are selected according to local conditions and requirements and can also be combined. In Germany there are now numerous examples of executed stormwater management systems, which are based on natural water resources and minimise the pollution of receiving waters (Sieker et al. 2006). The necessary technologies such as infiltration systems, swale-trench systems, green roofs or rainwater harvesting systems have been tested successfully for years. Corresponding technical regulations for planning, construction and operation are available (e.g. the DWA A138). Also a legal basis for these measures was created.