The installation of about 500 stormwater detention facilities (SDFs) led to a significant drop of the pollution originating from stormwater runoff in the river basin of the Ruhr which covers 4,488 km2. The German technical directives on the design of SDFs are briefly outlined and the specific costs for such plants are given. The average costs for one kilogram COD held back by SDFs in combined systems amount to € 3.73 (calculated without consideration of the subsequent removal in the municipal wastewater treatment plant (WWTP)). The tank volume for stormwater storage can be minimised by application of real-time management systems which allow a dynamic operation of all SDFs in a catchment area.

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