Wanstead Park water levels

Wanstead ParkWanstead Park

Ahead of this month's summit about the future of Wanstead Park, the City of London Corporation offers an overview of the park's cascade of lakes and explains the issues surrounding the water level problems.

The lake system in Wanstead Park was mostly constructed in the 1730s and 1740s from existing water features, while the Ornamental Water used to be the River Roding, which was re-routed to form the lake.

The way the lake system works has changed over time with water once being sourced from a system of weirs and later from the park owners' right to temporarily dam the River Roding to top up the water or flush the lake out. The Basin and the southern chain of lakes, on the other hand, occupied a partly natural valley and were fed by groundwater supplemented by water channelled from the Leyton Flats area.

Years of changes in the landscape has meant the cascade system has been no stranger to water shortages. In particular, over the past 200 years, the cascade has seen the abandonment of no less than four lakes that were once part of the system. It has also seen the loss of the Holt Channel, which supplied water from the area around Leyton Flats, and the truncation of the Epping Ridge groundwater by the North Circular and the Central Line. Moreover, the cascade has had to contend with damage from Edwardian sewer digging, enemy action during World War II and the loss of river abstraction rights following water shortages in the late 20th century.

The Heronry Pond is a concrete-lined lake that leaks and has to be filled by pumping water from a borehole that takes water from an underground aquifer. However, following a £35,000 investment, the borehole pump, which stopped pumping in November 2016, has now been replaced and is pumping 288,000 litres of water each day to restore water levels in this part of the cascade. Fish from Heronry Pond were moved to Perch Pond as the former began to dry out. Once levels return to normal, we can restock the Heronry with fish.

The Ornamental Water, which is at the end of the cascade, has suffered greatly reduced water levels due to an issue arising further upstream in the cascade system. Water from Heronry Pond passes through Perch Pond and then into the Ornamental Water. However, Perch Pond has been contaminated with floating pennywort, an invasive non-native plant species. This North American exotic, which is able to propagate itself from both seeds and even the tiniest plant fragment, has the potential to inundate the entire lake cascade, out-competing all native plants and irreparably damaging the cascade's ecosystem. For this reason, until our work to control the pennywort succeeds, we cannot let water go from Perch Pond to the Ornamental Water. In 2016, around 40 tonnes of weed was removed from Perch Pond and a monthly herbicide treatment of remaining colonies was carried out with much greater success than we first hoped.

During this difficult period, we have investigated a variety of solutions to augment the water supply to Ornamental Water, including the possibility of installing a pipe to take water from the borehole directly to Ornamental Water or the winter pumping of water directly from the River Roding. As this would require a new pumping station, an investment of this magnitude would need to be carefully considered within an overall water conservation plan. Placing a filter on the current spillway outfall from Perch Pond to Ornamental Water was also considered; however, it was not permissible due to Reservoir Act 1975 dam safety precautions. The current lake cascade system is only viable if we pump 294 million litres of good quality drinking water from our 88m aquifer borehole. Our understanding is that this supply may become increasingly restricted over time, and in planning a long-term sustainable future, we need to put in place measures to reduce the cascade's demand for water from the aquifer.

We recognise the importance of Wanstead Park as the most extensively designed waterscape in London and we are currently examining the long-term future of this ailing Georgian lake system. The long-term solution to developing a sustainable cascade system is likely to rely on a series of measures, including improved catchment harvesting, such as recently achieved at Jubilee Pond on Wanstead Flats, improved water conservation through lake relining and the use of novel water sources, such as winter spate river pumping. Such a hybrid solution will demand significant investment by ourselves and potential partners, including the Heritage Lottery Fund, London Borough of Redbridge and Thames Water.

We will continue to keep residents updated as we progress with the options being explored. Thank you for your patience whilst we work hard to find a workable solution to this important part of Epping Forest.

This article is reproduced with the kind permission of City of London Corporation. For more information on Wanstead Park, visit cityoflondon.gov.uk/eppingforest

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