Heath ponds to be closed and re-built due to dangerous flood risk

HAMPSTEAD Heath’s ponds, much loved by swimmers, anglers and nature-enthusiasts are due to close to allow the waterway’s complex dam system to be completely re-built.

The dams will have to be transformed to prevent dangerous flooding into Dartmouth Park and from Gospel Oak down to King’s Cross which could cause hundreds of fatalities according to a government safety study.

To combat the risk Heath bosses must undertake a programme of work which will transform the look of the beloved green space and cause major disruption for Heath users.

New government legislation brought in last year means dams across the country need to be remodelled to prevent catastrophic flooding in the event of a tropical-style rainstorm.

The Heath has a series of 18 ponds, each of which has a dam. If they burst, which could happen in the event of a severe storm, swathes of Gospel Oak, Kentish Town and Dartmouth Park would be flooded and more than 1,000 lives put at risk.

A government engineer has deemed that the Heath dams are high risk and the project needs to be carried out urgently.

Michael Welbank, chairman of the City of London Heath management committee, said: “This is a fairly serious issue and the indications are the dams on the Heath are high risk, therefore we have to do something.

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“We are tackling the problem. We have carried out a detailed hydrology study and we have a much more sophisticated knowledge of what happens to the water now. We are moving forward with that knowledge in hand.

“We know what we have to do but the detail of how we do it has yet to come. It is unlikely the work would start before 2013 and would probably last one to two years.

“At the end of it people will be horrified because it will look crude. But if we have done the work correctly it will mature quite quickly and in 10 years time people will come along and not even realise.

“The ponds will obviously be affected but for how long they will close we just do not know yet. We want to make the proposals fit with the Heath and we have to consider the interests of the users of the Heath.”

Every dam on the Heath will need to be upgraded which will mean closure of the ponds, while work is carried out.

There is no doubt they will all look noticeably different afterwards but the speed of recovery will depend on the location of the ponds and how much change has taken place.

The Bird Pond is likely to go through the most upheaval as the dam is to be raised to three metres, meaning access to the pond will be very different, although bosses are looking at the feasibility of a riverside path on top of the dam.

Simon Lee, Hampstead Heath superintendent, said: “The risk of a tropical storm is very low but the consequences would be very severe.

“There is substantial work we have to do to the ponds – both the Hampstead and Highgate chains in order to ensure that god forbid, if we had a catastrophic event, we would be able to slow the flow of the water through the ponds.

“We expect people to be very resistant to change but we have got to do this. One of the things we recognise is the sensitivity of the Heath and its natural aspect that people love.

“The plans we are coming up with are to try to minimise as far as reasonably viable the impact of the work on the Heath.”

The Corporation has been working with the government engineer and a team of specialists on the plans and has spent �250,000 so far exploring the hydrology of the Heath.

Mr Welbank said: “The Heath is clay and very heavily used so it is like a concrete surface for the water.

“The quantity of the water and the speed of the water if the dams burst are what will cause the damage.

“It might only be a low amount of water – up to people’s legs or so – but it will be fatal because of the quantity and speed.”

The Heath already has an emergency warning system in place in case water levels start to rise or a heavy storm is heading for London and the Corporation has recently spent a further �70,000 upgrading these.

Hampstead Heath questions answered:

When will the ponds close?

The details have not been finalised yet as this is the beginning of a long process of consultation and development but any work is not likely to start before 2013. Details of the project will be hammered out over the upcoming year after which a complex environmental report will be prepared and planning permission will be sought.

How long will the ponds close for and will they all close at the same time?

The Corporation is looking at the feasibility of doing the work all at once or staggered over a few years but has not yet decided the best way forward. Bosses have said they will look at whether one pond could be left open for swimming while the others are closed.

How long will the work take?

The Corporation anticipates the project will take between one and two years to complete.

Why do they need to do this?

After the Boscastle dam in Cornwall burst in 2004 causing extensive flooding and the dam at the Ulley reservoir in Rotherham burst in 2007 flooding huge sections of the M1, the government introduced new legislation requiring dams to be more secure in the event of a severe tropical-style rainstorm, which are recognised as becoming more frequent.

What is the risk of flooding?

The dams are inspected yearly and have passed those inspections. The risk of a catastrophic flood is very low – one per cent in 100 years, although London came close in 1975.

What will happen if they do not do the work?

The government could force the Corporation to do the work if it does not comply as the Heath has been classified as high risk. If the dams burst large swathes of Gospel Oak, Kentish Town and Dartmouth Park would flood and the speed and quantity of the water would put more than 1,000 lives at risk. The overground railway line would also flood all the way down to King’s Cross. Once the work is done the lives at risk are fewer than 100.

How much will it cost?

The work looks set to cost around �10million which will all be paid for from the Corporation’s own resources.

How different will the Heath look and what does the work involve?

It will look very different. Every dam will be altered enlarged in some way although the changes will vary from between 200mm or 400mm bigger but the Bird Pond will be three metres higher and the Men’s Swimming Pond will be one metre higher. The current dams have trees on top of them, blending them in with the rest of the Heath but the new dams will not be able to hold large shrubbery or trees, although any trees lost will be replaced with others elsewhere on the Heath. Bosses have said they will be exploring the best type of grass for on top of the dams.

What will the dams look like?

Bosses are committed to building the dams from the most natural resources available. Some concrete will inevitably have to be used but the dams will be built using concrete together with clay soil. A plan to mature the flora around the dams within a decade will also be in place so that within 10 years the dams should look natural and people should not be able to realise what has gone on.

How will the scheme affect the wildlife?

Wildlife is going to continue to be a key priority for Heath bosses, although some disruption is unavoidable they will do their best to minimise disruption. There will be some opportunities to improve some habitats while work is going on.

Are there any positives?

Yes – the Corporation is planning to introduce a system to allow them to be able to flush water through the pond system in summer which will prevent the build up of algae in the ponds and keep the water fresher and free from dog faeces, which will benefit swimmers and wildlife. There are also plans to introduce new habitats around the ponds, including possible introducing a wetland around the boating pond.