Hampstead Heath is in good hands
By Virginia Rounding, Chairman of the City of London Corporation's Hampstead Heath Management Committee
Hampstead Heath is fortunate in having about 30 beautiful and much-loved ponds. Although they look natural, most are formed by man-made earth dams which are up to 300 years old.
Three of the ponds are big enough to be classed as 'large raised reservoirs' under the Reservoirs Act 1975, which means they hold over 25,000 cubic metres of water and so are legally subject to inspection by a government appointed expert panel engineer.
Detailed studies show that the existing earth dams on both chains of ponds, which sit above large residential populations, could fail in a large storm, putting at risk lives, property and infrastructure below. The original studies were carried out by the hydrologist Haycock. These were then checked by another engineering company, CARES. When Atkins were employed to design the scheme, they looked at all of the hydrology data again using industry standard best practice. This process of verification means we are absolutely confident the design we have is correct and absolutely the best for the Heath.
When sudden, extreme amounts of water flow over an earth dam they can cut it away, releasing all of the water in one go, with a potential 'domino-effect' on other dams downstream. In order to prevent this type of cascading, we have to carry out smaller works on some of the other ponds in both chains.
Destructive storms may be rare, but one happened in 1975 and the Heath’s earth dams were damaged. And in 2010 a brief storm resulted in the Stock Pond overtopping with earth washed away from the top of the dam, which risked its collapse. The work being done means that the Heath’s earth dams will be able to withstand these more regular types of storms as well as the stronger, less frequent ones.
We are also carrying out work on the smaller ponds, to allow us to spread the works across the two chains. If we did not employ this approach, large scale works including concrete dams would be needed on the three statutory ponds – something which I know everybody wishes to avoid.
The Ponds Project Stakeholder Group, which worked with us on the designs and includes the Heath and Hampstead Society, is in support of this strategy. Our obligation here is to protect the Heath’s landscape, which is central to the project’s delivery.
Early on in the consultation process, some ponds were identified as sensitive because of their landscape or ecology and this includes Vale of Health. As a result, the scale of work at this pond was minimised as far as possible.
As part of the designs, a new spillway is needed at the Vale of Health. This spillway will allow water to leave the pond safely, in the event of a large storm, without causing any damage to the earth dam.
The spillway will be grass-lined and sowed with a wild flower mix, which has been specifically designed to fit in with the Heath’s landscape. One tree has been removed, but the designs have been carefully considered to save the iconic Giant Redwood.
The existing dam crest also needs to be raised a very small amount and this is being done by simply installing a protective kerb which will sit along the path, in front of the fence on the downstream side of the dam. We will grow vegetation over this and it will blend into the surroundings, so it won’t be noticeable.
A key objective of this project is not only to fulfil our legal requirement as the Heath’s conservator, but also to improve water quality and conditions for wildlife.
There will be an aerator installed and the current reed bed will also be extended which will provide better habitat for aquatic life and the wildlife that depends on it.
The pond will remain open for anglers throughout the work and when complete, dogs will still be able to enter the water from the southern corner. Work will start here soon and will be finished this September.
I’d like to thank the many Heath users who are bearing with us as our contractors, BAM Nuttall, are carrying out this essential work. And I’d like to assure Ham&High readers that the Heath is in safe hands. Once the project is fully completed, in about a year’s time, the Heath will be a safer place for downstream residents and the ponds will benefit from greater ecological diversity, better water, views and paths, new reed beds and other important wildlife habitats.