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Major overhaul for north London main water hatches


THAMES WATER is to inspect all the remaining hatches on the north London main that burst in March this year, causing nearly a week of major traffic disruption.

The investigation, which involves digging up 63 access points, follows the discovery that at least two of the 28 hatches inspected in a previous survey were in a critical condition and could have caused a similar burst. The original failure, under the heavily-trafficked A406 North Circular, released 26,000m3 of water and flooded a major underpass.

An independent report by the Defence Evaluation and Research Agency recommends that the additional steel access hatches must now be examined in sections 1, 2 and 3 of the 21km-long main. A contract for the inspection will be let shortly, with work beginning in mid-November.

The 1.5m diameter main runs across built-up areas of north London from Ashford Common water treatment works to Cricklewood pumping station.

But Thames claims traffic disruption will be kept to a minimum as most of the required access points are on dedicated land or where it has exclusive land use rights.

Failure of the original hatch, in section 4 of the main, occurred because of progressive corrosion of bolt threads over 30 years. At least two of the 28 hatches investigated by DERA had 'significant loss of nuts and threads resulting in inadequate sealing arrangements'.

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