Stabilising the Kenwood Dams

by Hazelle Jackson

The 'Thousand Pound' and the 'Wood Pond' dams on the Kenwood estate were constructed in the latter part of the 18th century and stand at the head of a series of ponds that stretch down across Hampstead Heath towards Parliament Fields.

The sham bridge at Kenwood

Thousand Pound Pond and the sham bridge before work was carried out

A survey in late 2005 by English Heritage, showed that both dams could be breached if heavy rainfall suddenly led to increased water levels and water flooded over the top. Additionally, experts were concerned that, if one of the mature trees were to be blown over in a storm, then the entire dam might collapse.

Expert hydrologists Land & Water Special Projects of Surrey were commissioned to implement a sustainable solution, which would protect the dams and have minimal impact on the character of the historic landscape and the ecology. The resulting scheme, agreed with English Nature and the Kenwood Landscape Forum, allowed mature trees to be retained whilst creating a new timber-clad piled dam face carefully hidden behind water plants. The scheme also included new water management sluices to allow water levels to be safely managed, and a new facility for the fire brigade to pump water from the pond if there were a fire at Kenwood.

Work commenced in the early part of 2006. On a bitterly cold day in March, I was invited to join members of Kenwood Landscape Forum to see at first hand the work being carried out on the dams and to review recent ground maintenance by Head Gardener Peter Jackson and his team.

Favourable Impression of Pruning

We started our tour by Kenwood House. Peter Jackson showed members the results of recent pruning of the laurel bushes, before we proceeded round the inner circuit to see the impact on the local views of tree pruning, holly reduction, and coppicing. This made such a favourable impression on the group that members were very receptive to Peter's proposals on opening up the lost view towards the house from Beech Mount.

Reaching the dams, Drew Bennellick, Head of Regional Partnerships for English Heritage in the London region, and Chris Spencer, Contracts Manager of Land & Water Special Projects, described vividly what might happen if the water level suddenly rose in the Thousand Pound Pond, the upper of the two ponds.

The bank of the dam was being restored by driving steel piles 3m deep between ponds to prevent a breach if a tree should fall. A new outfall was being built and, to minimise environmental damage caused by the essential use of heavy cranes, Land & Water were working from pontoons.

Replanting of the bank between the two ponds was in progress and huge coir (rope) sausages were being laid around the water's edge to be planted with water plants. These will be protected by hazel fencing while getting established.

Exciting Finds

At the time of our visit, work had been delayed by the exciting find of some 17th and 18th century timbers at the bottom of the ponds. One theory was that these were from an old mill, and the Museum of London archaeologists had been called in to investigate.

The road over the sham bridge needed reconstructing, as the access road to the site has sunk. Plans were to rebuild it to the correct level. The reconstructed road will act as an emergency weir in the event of a sudden downpour.

Since the visit, the dams project has been completed slightly behind schedule but ready for the summer season. Drew Bennellick of EH expresses satisfaction at the outcome: "All structures are working well and the water level has been adjusted on Thousand Pound Pond. For the first time in at least 20 years, the Sham Bridge reflects as a half moon - we think as originally intended."