North London Flood Relief

The contract for the complete Mechanical and Electrical works involved in the final stage (Phase III) of the North London Flood Relief Project was awarded to Naston in August 1996. The major element of the Mechanical and Electrical works was associated with the Return Pumping Station at Abbey Mills.

The pumping station, located at the end of the new 6.4km stormwater storage tunnel was some 30m deep with both wet and dry wells The ?0.88 million contract was successfully completed in February 1998.

Main Stormwater Return Pumps
The main stormwater return pumps (duty/assist) were dry well submersible fixed speed units rated up to 2000 litres per second and driven by 250 kW motors. The pumps discharge via DN600 ductile iron rising mains to a stormwater outlet chamber at ground level.

Wet Well Equipment
Located within the wet well section of the pumping station are removable bar screens (protecting the main pumps), final drain down submersible pumps, a high-pressure sparge system for wet well washdown and submersible mixers.

Tunnel Ventilation
In order to design the tunnel ventilation system it was necessary to complete a flow modelling exercise.

The final design covered the provision of variable speed axial fans (duty/standby) located at Abbey Mills, each with 55 kW motors to provide ambient ventilation of the tunnel at a velocity of 15 m?/sec and man entry ventilation at a velocity of 31m?/sec.

Air is discharged via acoustic splitters to a vent stack outlet. The fans and motors, complete with non-return dampers, are housed in an acoustic enclosure to limit the noise level up to 60 dBA.

Electrical Distribution and Control
Under this contract a 1000 kVA power transformer (11,000/433 V) and ring main unit were provided to serve the new Return Pumping Station facilities at Abbey Mills.

The electrical control panel housing the main switchgear and PLC control is some 7.6 m long and is installed in a fully air conditioned, purpose built GRP kiosk.

The equipment is controlled by three PLC's, the main unit with operator interface being located at Abbey Mills and the two remote units (Sandringham Road and Rectory Road) connected via modems and leased lines.