We have looked at the role of Sustainable Drainage Systems (SuDS) in tackling combined sewer overflows (CSOs) using case studies from Philadelphia, Portland and London.

Philadelphia aims to tackle 85 per cent of CSO discharges through SuDS measures over a 25 year period. This work has started, but cannot yet be deemed successful. A tunnel solution akin to the Thames Tideway Tunnel may still prove necessary to meet the required environmental standards.

Portland has removed approximately eight million m3 of storm water a year from the system using SuDS (35 per cent of total CSO volume), but tunnels still proved to be a necessity to meet the required levels of control.

London’s specific circumstances dictate that the proposed Thames Tideway Tunnel is essential to tackle the scale of the discharges in the timescale required. SuDS could and should play an important role in extending the life of the Thames Tideway Tunnel, but can in no way replace the need for it.

Download the complete case studies.

A grassed 'living' roof

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