Wed 11 Feb 2015

Building Opinions: Robert Nemeth on the sewer diversion

It is not the most glamorous of subjects, but is certainly one of the most fascinating. Brighton’s sewer system has proudly survived the test of time and works so well that it is rarely modified. But, from time to time, changes are required.

It was in 1865 that around 44 miles of sewers ranging from 12” to 8ft in diameter were introduced to Brighton. In 1871-4, an intercepting sewer was built along the seafront to the designs of Sir John Hawkshaw, using yellow engineering bricks from Keymer to take effluent all of the way to Telscombe Cliffs using just gravity. It has a length of 7.25 miles with a diameter of 5–7ft, and runs directly through the i360 site.

Rather than build over it, a decision was taken to divert around the i360’s huge foundations which will consist of 4,000 tonnes of concrete. The old sewer has been broken either side of what will be the base of the tower and a new sewer built in three sections around it. Rather than right angles, the joints are more generous to stop blockages. Four inspection chambers have been added – one for each corner.

I visited the morning after a difficult night of work which saw the connection of old to new.

Bearing in mind that the sewer cannot be shut off, much thought was required (a similar operation was recently carried out regarding one of the city’s principal electric cable routes).

Doughnut-like inflatables were used as plugs. Plastic pipes in their centres temporarily took the flow so that work could take place cleanly and efficiently. It is not hard to imagine how unpleasant a leak might have been.

The operation, carried out by a number of parties including Southern Water, Thorne Civil Engineers, Mackley Construction and Hollandia, was a complete success.