Hampstead Heath dam to save 1,500 Gospel Oak residents from flood

Published: 20th January, 2011
by DAN CARRIER

A CATASTROPHIC flood sending millions of gallons of water sweeping through Hampstead Heath and swamping homes in Gospel Oak has been predicted by scientists.

The shock findings have prompted plans for massive a £12m dam-building project that will see swathes of the Heath closed to visitors while heavy diggers move in.

The research, commissioned by Heath managers the City of London and published this week in order to ensure the City complies with tough new environment laws,  includes the chilling statistic that if the dams failed – and the risk is big enough to warrant immediate action – up to 1,500 people in Gospel Oak, Dartmouth Park and Parliament Hill could drown.

Engineers are now working flat out to prepare plans, which include some new banks  three metres higher than they currently are, being built on the edges of the Highgate and Hampstead ponds. Images seen by the New Journal show radical changes to much-loved walks and views that have remained untouched for centuries. 

Heath chairman Michael Wellbank said scientists had warned there may be a 1 per cent chance every 100 years of dams that hold the ponds in place failing, it could happen tomorrow – and they had to act quickly.

He said: “Even though the dams are stable, new legislation means we have to do this work. Research shows flash floods could happen tomorrow, and there are more than 1,000 people at risk in a catastrophic event.”

The Environment Agency-backed report cites changing weather patterns in England, meaning tranquil ponds normally associated with ducks or swimming contain a hidden threat. 

Long dry spells followed by heavy rain mean there have been disastrous floods elsewhere and the City have been told this could happen on the Heath. 

The new legislation was partly in response to the floods in Boscastle, Cornwall, in 2004, which wrecked the picturesque village. 

The Heath has already suffered minor, yet telling, incidents: in May 2010 the boating pond burst its banks. The last major episode was in 1975, when homeowners in Gospel Oak were famously rescued in rowing boats by neighbours.

The layout of the Heath has also added to the threat. Streams and ponds zig-zag hills and valleys, while underneath fields lies hard, compacted clay that Heath superintendent Simon Lee describes as acting like a ‘sheet of glass’ so all rainfall that falls on the 900-acre Heath rushes into culverts and quickly fills the 23 ponds on the Heath.

Mr Lee added: “A tropical-style storm could cause a rush of water that would mean the dams by the ponds would fail.”

A computer map designed by the City and the Environment Agency shows areas that would be covered: they include homes across Dartmouth Park, Gospel Oak, Parliament Hill and northern areas of Kentish Town. But Mr Lee added that while the new dams would mean heavy engineering work, they would work as quickly as possible to return the ponds to a natural state. He said that trickling weirs would provide new focal points for views, and improve the water quality in the ponds, which in the summer are often stagnant. 

Work has already begun surveying which ponds need the new dams built first, and once planning permission is gained and user groups consulted, the scheme could be completed by 2014. 

Landscape architects will also be used to ensure the work leaves pond banks looking natural.