The second round of public consultation is underway on the Thames Tunnel, a major new sewer project that will tackle the growing problem of overflows from London’s sewers into the tidal River Thames. HR Wallingford, the international hydraulic and environmental engineering consultancy, has been helping Thames Water understand the effects the potential construction work could have on the river’s hydrodynamic, sediment and morphological regimes.
London’s Victorian sewerage system is a combined system design to deal with both rain water from streets and buildings and foul water from homes and businesses. Part of the design allows the system to overflow into the River Thames when capacity is exceeded, so that it does not back up to streets and houses. Currently, when it rains, the capacity of the system is now reached more commonly resulting in sewage discharges happening more frequently. Such events have a detrimental effect on water quality in the river and in order to meet European environmental standards outlined in the Urban Waste Water Treatment Directive (UWWTD), the problem of overflows must be addressed.
To address the problem Thames Water plans to tackle the problem by intercepting selected combined sewer overflows (CSOs) and redirecting them in to the Thames Tunnel, a 15.5 mile long tunnel, up to 70 m deep underground with the width of three London buses. The Tunnel will broadly follow path of the River Thames across London. Once the overflow event is intercepted into the tunnel it will then be pumped for treatment at the sewage treatment works at Beckton.
The £4.1 billion project will involve major construction work at a number of sites alongside the River Thames. Engineering works in the river are challenging and have the potential to change the flow, sediment transport and morphological regime in the area. Since starting work on the project in 2009, HR Wallingford has helped Thames Water understand the impact these works will have on the river. They have carried out a comprehensive programme of fluvial modelling and assessment to evaluate these impacts. Results have been used to inform the development of the design of both temporary and permanent works, allowing Thames Water to devise a construction strategy that minimises the impact on the river environment. HR Wallingford’s findings are also providing a significant contribution to the Environmental Impact Assessment for the project.
HR Wallingford’s contributions to the project have included:
- detailed 2D models of each foreshore CSO interception site
- modelling the overall impact of the works on estuary hydrodynamics
- scour studies at each CSO interception site
- tidal physical models for three of the more challenging CSO interception sites.
Further information on the Thames Tunnel project can be found at the project website www.thamestunnelconsultation.co.uk
