One of the main goals of the Ponds Project, as well as dam safety, is to improve water quality across the Heath. There are various measures being applied to help achieve better water quality, such as the addition of aerators on the ponds and more aquatic planting in key areas. Several ponds, including all of the bathing ponds, are also being desilted. This process involves the removal of sediment or silt which has built up on the bottom of the pond bed over the years. The silt is mostly made up of organic matter, like leaves and branches which have fallen into the ponds. Removing this material will have a great benefit to water quality
Surveys revealed that many of the ponds had high quantities of silt, and this was certainly the case at Model Boating Pond, where the silt was 4m in depth at the deepest point.
Some of the ponds on the Heath were desilted in the late 1980’s. In 1988, the Ladies Pond was drained and silt was excavated. The photograph below shows how messy and disruptive this process was, involving the draining of the entire pond. This has a high impact to the pond’s environment.
To avoid similar disruption during the Ponds Project, with the exception of the southern end of Model Boating Pond, the ponds will be desilted using an innovative suction technique.
This process involves a pontoon, called the DINO Six, excavating material from the pond using suction. The DINO Six is a uniquely portable dredge system developed to perform jobs inaccessible to other dredges and sediment removal equipment. A specialist contractor, P&D Environmental, will be carrying out this work on the Heath ponds.
The DINO Six, works its way across the pond on cables, so it covers all of the surface area of the pond. The dredged material is pumped through the pipeline (the larger of the black pipes in the photo below).
It is pumped to the cyclone unit, which is called the Normag Reclaimer. This piece of equipment provides an innovative solution to process sediment on site. This system will separate the solid material dredged from the pond, whilst processing and returning the water to the pond in a continuous cycle. The water is returned to the pond in the smaller of the black pipes.
The Normag Reclaimer removes solid material from the pond water in three separate stages. The first stage removes larger items such as stones and leaf material.
The second stage removes sand.
The third stage removes a muddy material.
The water is then passed through centrifuge and the final silt product is removed.
The clean water is returned to the pond, creating a healthier habitat and improving the ecosystem of the pond with as little environmental impact as possible and without the need for heavy machinery travelling across the Heath.
Stock Pond is being desilted using this process at the moment. Men’s Pond will then follow in November. On the Hampstead chain, it is Viaduct Pond, Mixed Bathing Pond and Hampstead No. 2 which are due to be desilted. Finally next year Ladies Pond will be desilted using the same process.