The St Germans Pumping Station near the village of Wiggenhall St Germans in Norfolk drains some 700km2 of Fens land, whilst protecting more than 25,000 properties and extensive areas of high-grade agricultural land to the south-west of Kings Lynn. The existing installation serves the whole of the Middle Level System, transferring all drainage to near the village, where the flows are pumped into the tidal River Great Ouse.
However, at 74 years old, the station is approaching the end of its useful life and will soon no longer meet the required standard of protection. Following Defra funding approval for the estimated £38 million cost, work has now commenced on the construction of the new state-of-the-art pumping station.
Feasibility Study and EIA
Atkins Ltd has been working with the Middle Level Commissioners on the St Germans scheme since 2003 in three phases. The first, a feasibility study, involved an extensive option study and environmental impact assessment, culminating in the successful Defra application. The second phase consisted of detailed design, prequalification, planning and phased tendering (three distinct contracts). This took 18 months, with the third phase of site implementation works, expected to take approximately three years.
The EIA involved environmental surveys and a number of rounds of consultation with statutory and other interested parties. The output of the EIA formed a significant element in the derivation of the preferred option. Key features of the EIA were the traffic management plan, assessment and mitigation of any visual amenity disturbance, the introduction of mitigative ecological habitat and the assessment of construction noise on the surrounding environment.
Once complete, this new, modern station will ensure the sustainability of the Middle Level System for the long-term future and provide security from flooding for the large areas of high-grade agricultural land, numerous communities and businesses as well as a number of environmentally sensitive areas.
Civil Enabling Works
The site implementation can be broken down into civil enabling works, construction of the new pumping station and the demolition of the existing station.
The first part of the civil enabling works, by the contractor Costain Ltd, was the installation of a 1.7-km-long, stone-surfaced access road, running from High Road at Tilney cum Islington down to the main works area. This was completed in January 2007 and will ensure that site traffic is routed away from the local community.
The second part required the installation of a twin-walled, steel-sheet-piled cofferdam out into the tidal section of the Middle Level Drain. In addition to the cofferdam, the existing drainage channel was diverted around the works on the eastern bank of the channel to enable the continuing operation of the existing station.
Installation of the cofferdam enables Phase 2 of the site works – construction of the new station – to be erected in a dry environment. Continuous Flight Augured piles provide the platform from which to build the superstructure, which will house six concrete volute pumps capable of pumping 100 cubic metres of water per second.
In the later stages, the pumps and mechanical and electrical equipment will be installed by contractors KSB and Birse Water, with connection to a new electricity substation constructed for the station. Each pump is variable speed and has a dedicated 11-metre-long motor control centre, transformer and 1700-kVA stand-by generator.
The station will be commissioned on line, downstream from the existing station, using a sophisticated method to simulate operational conditions, which requires close cooperation of all three contractors, designers and the client. Completion of the fully operational pumping station will enable the final phase, demolition of the historic pumping station, to commence. The demolition will be carried out in two halves within another cofferdam, with completion due at the start of 2010.
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