OVERVIEW OF URBAN DRAINAGE - ENVIRONMENTAL IMPACTS AND CONCERNS, MEANS OF MITIGATION AND IMPLEMENTATION POLICIES

Recent developments in urban storm drainage are reviewed starting with drainage impacts on receiving waters, followed by a brief analysis of selected components of urban drainage systems, hydroinformatics, and regulatory programs. Further advancement in drainage planning will req uire considerations of the catchment, drainage system, groundwater, tr eatment plant and receiving waters as one entity, and ensuring sustain able integrated development and ecological enhancement of urban stream s and corridors. Such processes should be based on comprehensive model ling, which is well advanced for hydrological aspects, but further dev elopment is needed in water quality, sediment quality, transport and i mpacts, and ecological modelling. Mitigation of stormwater impacts is accomplished by best management practices, which form a part of the tr eatment train, and their sustainability has to be ensured by proper op eration and maintenance. Impacts of combined sewer overflow are mitiga ted either conventionally by storage (and return to the central wastew ater treatment plant), or more recently, by satellite treatment or pol lution separation at the overflow points. An improved utilization of t he available spare (idle) capacities in the drainage system can be ach ieved by real-time control. Finally, regulatory programs in various co untries indicated a great deal of uncertainty and some aspects of such programs may even impede effective environmental practices.