Thames Water Ring Main Tunnel Extensions – AMP4 London Resilience Programme: 6DCF New River Head to Stoke Newington |
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Interim Client and Outline Design Award
Project Team:
Client: Thames Water Utilities Ltd
Designers: London
Clean Water Network (LCWN) and Mott MacDonald
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The Thames Water Ring Main (TWRM) northern extension from New River Head to Stoke Newington is one of the two TWRM tunnel extensions within the AMP4 London Resilience Programme. The southern extension project is 4DCF Brixton to Honor Oak.
During the early stages of the project, a decision was taken to register both projects for the CEEQUAL award scheme to ensure the highest standards of environmental good practice and design were achieved. The CEEQUAL award is divided into two stages representing the key project milestones, namely:
- Stage 1: Interim Award Stage for satisfactory completion of planning and the outline design phase.
- Stage 2: Whole Project Award Stage for satisfactory completion of the construction phase.
Following the successful completion of the interim award by the 4DCF Brixton to Honor Oak project, the 6DCF New River Head to Stoke Newington project has also completed the interim award. The 6DCF project was able to identify and pursue even more opportunities in developing environmental excellence during planning and design stage.
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6DCF New River Head to Stoke Newington
The northern tunnel extension from New River Head to Stoke Newington comprises a 2.5m internal diameter tunnel, driven 4.5km from a new 48-m-deep shaft at the Stoke Newington site to a new reception shaft at the New River Head site. The tunnel will be constructed using precast concrete segments and an earth pressure balance tunnel boring machine. The Stoke Newington site is partly located within a TWRM operational site and partly within Stoke Newington West Reservoir site, owned by LB Hackney. The Stoke Newington reservoir site is located on Metropolitan Open Land (MOL) and is classified as a Conservation Area. The site is a former water treatment works; the old pump house (The Castle Climbing Centre) and its environs, which date from the late 1800s, are classified as grade II listed buildings. The site shares a common access road with the West Reservoir Sports Centre, the listed Castle Climbing Centre and a children’s play centre. The New River Head site is located entirely within an existing operational site, which is bounded by residential houses and a school.
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During the early stages of the project, an EIA Screening Opinion Report was prepared, which concluded that the project would not lead to any significant environmental impacts and therefore the main tunnelling works should proceed as Permitted Development. In order to make the site suitable for construction traffic, it was necessary to obtain planning permissions for access widening works.
Works undertaken during the planning and outline design phase can significantly influence environmental impacts during the construction phase. By highlighting key environmental issues early and incorporating appropriate measures into the outline design, a better overall environmental performance will result.
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Key actions undertaken by the Client-Design team during Interim Award stage included:
- Reducing construction impact by careful consideration of locations for the tunnel drive and reception shaft site. The outline design removed the need to construct an intermediate access shaft.
- An Environmental Management Plan (EMP) was prepared, including an environmental risk register, identifying key risks and mitigation measures to be addressed by Thames Water and the contractor.
- A Tender Assessment Scoring method was used, which gave consideration to the contractor’s environmental track record.
- Environmental screening surveys were carried out to identify likely environmental impacts (e.g. traffic, noise, groundwater, archaeology and habitat surveys).
- A Project Communication Plan for liaising with all key stakeholders was prepared. The key stakeholders comprised local authorities, residents and users of the sports centre (sailing club), climbing centre and children’s play centre. Drop-in sessions were held at the main shaft site, the local church and the Islington Business Design Centre, where local residents and businesses were invited to hear about the project and raise any concerns, which were fed back to the project team.
- Landscaping and general access
improvements to Stoke Newington site. The landscaping
proposals were designed to complement the existing
site and improve pedestrian access to the sports centre
and New River Path.
Provision of a new wildlife area and environmental classroom facilities for the London Wildlife Trust at the Stoke Newington East Reservoir site. - Pre-construction enabling works were designed to improve access to the Stoke Newington site. Upgrades included provision of a new pedestrian walkway and guardrail, widening of entrance gates, removal of undesignated parking at the site entrance and between the trees with Tree Protection Orders, and provision of designated car parking within the sports centre.
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Future Works – Construction Phase
Both 4DCF and 6DCF projects have been procured as Design & Build contracts, using the Engineering Construction Contract (ECC). The appointed tunnelling contractors are required to develop the detailed design and carry out the construction works. Construction has the potential to create the largest environmental impact. Typically, the key environmental issues during construction include:
- construction traffic nuisance to local residents
- compliance with environmental legislations (Section 61 and EA approvals)
- detailed design of the tunnel-lining system
- recycling and/or disposal of tunnel arisings, e.g. via other project sites or aggregate/gravel pits.
- non-contamination of Source Protection Zones (SPZ)
With the first part of the journey complete, London Clean Water Network remain committed to working together with the Design & Build contractor to ensure the highest standards of environmental excellence are achieved.