The origins of the Ponds Project go back to 2006, when a specialist hydrologist was appointed to to undertake a water quality and hydrological catchment assessment. Their investigation reviewed the hydrological functioning of the various lake chains around Hampstead Heath and provided recommendations for their management. The study identified issues with compaction and absorption of water. It was the first study to look in depth at the four water catchment areas that exist across the Heath and immediate environs of the site.
In July 2007 the Inspecting Engineer undertook a ten year statutory inspection of the three reservoirs on the Heath (Hampstead No. 1, Model Boating Pond and Men’s Bathing Pond), the resulting report stated that the overflow capacity on all the reservoirs was inadequate and recommended an assessment of the downstream impact and risk of breach be carried out.
In 2009, following the recommendation in the 2007 inspection, the City of London Corporation commissioned their then Supervising Engineer, CARES Ltd, to undertake a Flood Risk Study for the three reservoirs, as well as Swan Pond on the Golders Hill Chain. This concluded that the Hampstead No. 1 and Highgate No. 1 Ponds fell into the highest risk category and Swan Pond had a broadly acceptable risk of failure (due to the lower consequences of dam breach at this pond). The report recommended further modelling of the effect of the pond chains, and improvement work to the ponds.
In 2010, the City commissioned Haycocks Associates to undertake a review of the hydrology and hydraulics of the dams within Hampstead Heath. The aim of the study was to determine the current operation of these structures and their compliance with reservoir legislation. Under changes to the 1975 Act set out in the 2010 Act (not yet brought into force) the minimum size of a large raised reservoir will be reduced to 10,000 cubic metres. It is anticipated that the new regulations will also provide for all ponds in a chain that have a combined volume of 10,000 cubic metres to be classed as large raised reservoirs, which would include all of the ponds in the Hampstead and Highgate chain. It is also anticipated that these ponds will be assessed as high-risk reservoirs – the new designation for large raised reservoirs that are subject to the most rigorous safety and inspection regime.
Haycock’s report was reviewed by the Panel Engineer and published in April 2011. It identified the probable maximum flow and the implications arising from it. The report said that the “spillway’’ (or capacity for controlled overflow) is inadequate and presents a risk. Based on the findings of this study, it was considered that the three existing large raised reservoirs are inadequate to meet the current requirements of the 1975 Act. The report included concept ideas so that the reservoirs and ponds on both the Hampstead and Highgate chain of ponds comply with the existing and emerging reservoir legislation whilst also complying with the requirements of the Hampstead Heath Act 1871. This work also included draft visualisations and provision of estimated capital costs. Given the deficiencies identified with the dam structures, the Supervising Engineer advised the City Corporation that works would be required to ensure compliance with the Reservoirs Act. Failure to proceed on a timescale considered reasonable by the Supervising Engineer could result in a further statutory inspection and enforcement action by the Environment Agency to implement works within prescribed time frame (normally two to three years). Read the Haycock Report.
In July 2011, the City approved an Evaluation Report setting out the broad scope of works (circa £15M) to comply with existing and emerging reservoir legislation while also considering the Hampstead Heath Act 1871 and to improve water quality. Officers were instructed to commence production of a Detailed Design Report, taking the project to a position where a planning application could be submitted to the Local Planning Authority. In considering the need to meet public safety, whilst reconciling the works so that they fit with the character of the Heath, the City approved an outline scheme that upgrades all of the ponds. This approach (as opposed to one which only focussed on the three existing large raised reservoirs) was selected as it mitigates against the risk of dam failure at any of the ponds. It also reduces the visual impact of the works in any one place by spreading the impact across all of the ponds. It avoids works being carried out on the three large raised reservoirs that would become redundant in future, and ensures full compliance once the 2010 Act is in full force, avoiding the need for further works at that time.