Thames Tideway Tunnel: design responsibilities, phases and system-wide design challenges

The Thames Tideway Tunnel project is a deep tunnel system for combined sewer overflow (CSO) control in London, UK. The project comprises 20 shafts and 14 tunnels to actively manage flows from 34 CSOs by transferring flows to Beckton Sewage Treatment Works for treatment. Multiple parties have either influenced or been responsible for the design of this large ‘specified infrastructure project’. Most design responsibility sat with four NEC3 design and construct contractors, but Tideway retained responsibility for system-wide hydraulic, air and control aspects. New standards were developed for the design of tangential vortex drops and for vertical deaeration within large circular shafts. A new methodology was developed for the ventilation design that analysed how air moves in and out of the tunnel system, is controlled and treated. Qualitative design aspirations and stakeholder requirements for the integration of the infrastructure in the public realm were captured in design principles and an innovative approach to heritage interpretation was used. Although all the CSO interception sites feature similar components, each site was different, leading to innovative designs by the contractors.