BY TOBY PORTER
Parts of South London are sinking as a result of work on the Northern line extension to Battersea.
Many families affected by drilling work are set to be compensated, but local campaigners say other homes are likely to be hit by water being extracted from the ground in the area.
They say the depression around Kennington Park, seen by satellite earlier this month, may be hitting far more homes than first thought.
Sentinel-1, a weather satellite which can detect the movement of earth, has found the ground in the area has sunk by almost half an inch in the past year.
The cause of families living in the area was taken up by the Kennington & Walworth Neighbourhood Action Group (KWNAG) last month, with Southwark MP Neil Coyle speaking to more than 70 residents about their concerns.
One resident, Bob Lentell, said: “The houses affected by tunnelling work are covered by special arrangements. But we don’t know of any claims being made yet because of the de-watering of the area.
“We believe that will cause much greater subsidence. It stretches about half a mile around Kennington Park.
“Residents are concerned. It was the only area in the whole of the south-east of England with the same level of subsidence.”
Geomatic Ventures, who used the satellite’s data, believe this issue has most likely been caused by drilling a vertical tunnel for the Northern line. They found a subsidence bowl where, at the epicentre, the movement is greater than 1cm per year.
Paul Bhatia from Geomatic Venture said: “They tell us it really is nothing to worry about. Because it’s a large area that’s about 500m wide, the whole area is moving down but if we don’t continue to monitor this, then we won’t know if it is something to worry about or not.
“It could, for example, affect large infrastructure or lead to cracks in the road if it continues.”
KWNAG also staged a meeting at Durning Library on the issue – but also about the fact that the extension work means the Bank branch of the Tube line will not be accessible from Kennington for four months.
They also believe commuter safety will be hit by the alterations as it will take 20 minutes to evacuate the station in an emergency once the extension begins to operate.
Mr Lentell said: “The Bank branch closure came as a bolt from the blue to all of us.
“Once the extension opens, there will be more people going through and bigger crowds when there is an emergency, all using the same small spiral staircase.
“It would be hard to get everyone out – even TfL say it would be 20 minutes. But six minutes is the standard length of time across the network.
“The Northern line extension is the most expensive piece of underground ever built, at a cost of £1.2billion – and Kennington is the oldest station, built in 1890.
“It is astonishing that the small spiral staircase remains the only way to evacuate it, all these years later.”
A TfL spokesman said: “Work on the Northern line extension (NLE) is progressing well, with major tunnelling finishing last year and the building of two new Tube stations well underway. The decision to keep the station open for the duration of the work was made earlier this year following detailed work to determine the safest and least disruptive solution.
“In a major civil engineering project of this size, small levels of short-term ground movement are completely safe and are associated with the removal of groundwater known as ‘dewatering’. This well-known technique is necessary to ensure safe tunnelling in wet ground and its impact will reduce once de-watering finishes this summer.
“The safety of our customers and staff is always our top priority.
“We keep our fire safety strategies under constant review, alongside the London Fire Brigade and have robust operational plans in place to ensure that Kennington station remains safe during and after the NLE works.”