Construction work will begin at Hampstead No. 1 pond next week and will last until March 2016. The works will be happening in an area of the Heath which is not accessible to the public and every care will be taken to avoid disruption to visitors.
Hampstead No. 1 Pond is the last pond in the Hampstead Chain and the closest to the community in South End Green. It is also one of the largest ponds on the Heath, with a capacity of just over 25,000 cubic meters of water. This also means it meets the threshold of the 1975 Reservoirs Act and is legally classified as a large raised reservoir.
The dam on this pond is already relatively high and does not need to be raised, but a 9.6m wide letter box culvert will be built in the current dam to allow water to leave the pond safely, without overtopping and possibly causing damage to the earth dam, in the event of a large storm.
Here is an artist impression of what the letter box culvert will look like from the pond side.
The new culvert will be located to the eastern side of the dam and will be buried in the earth bank to reduce visual impact. This location was chosen to minimise tree loss on the dam crest and on the downstream side where a concrete stilling basin will be constructed. This stilling basin will also be buried in earth and there will be trees and shrubs planted to camouflage it.
The environmental masterplan below shows the new structure in plan form (bottom centre). The square stilling basin is marked in a darker green colour.
You can view a zoom-able PDF version of this plan here: Hampstead No. 1 Pond Environmental Masterplan
To help improve water quality in the pond, an aerator will be installed and there will be some marginal planting along the south and east banks and some localised desilting in the area where the new structure is to be built. This pond is popular with birds and every effort will be made to avoid disrupting them during the work.