On-site stormwater detention systems in Sydney

On-site stormwater detention (OSD) requirements are applied by most municipalities in Sydney, Australia. Persons redeveloping properties served by existing drainage systems must provide storages for stormwater, to compensate for increased runoff from the new development. While OSD is widely accepted, procedures differ considerably between municipalities. Many designers criticise guidelines and design methods, and express doubts about the maintenance and economy of OSD systems. This paper surveys the application of OSD in Sydney, describes typical installations, and reviews their effectiveness. It sets out the main arguments for and against OSD systems, discusses alternatives, and indicates how systems and procedures will evolve in the future.