Next Generation Water Sensitive Stormwater Management Techniques

Decentralized stormwater retention and infiltration in urban areas has been used in Germany since the beginning of the 1980s as a sustainable and cost effective alternative to combined and separate sewers. In Germany, all new developments are required by law to retain/infiltrate rainwater on site. Infiltration can help in returning the urban water cycle to its pre-urbanized state. Infiltration supports groundwater recharge, allows smaller diameters for sewers (resulting in cost reduction) and improves water quality of receiving waters because pollutants and high peak flow are effectively controlled. On the other hand, pollutants in runoff originating from domestic and industry emissions and traffic can contaminate soil and groundwater if they are not removed from runoff before it infiltrates into the ground. A wide variety of different infiltration systems exist, such as sinks, swales and gravel filled trenches, and have been used and investigated in Germany. Legal requirements and grants support alternative drainage techniques. After 20 years of operation not only the advantages, but also the problems and disadvantages of such systems can be identified, and new solutions, education programs and management tools developed. In conclusion, decentralized retention and infiltration is sustainable and cost effective. However, planning, construction and maintenance have to be undertaken in line with current best practice.