Water is a limited and valuable resource essential for plant growth. Water resources in the UK are under pressure from climate change and population growth. As part of Forestry England’s aim to be net carbon zero by 2030, a new rainwater harvesting and filtering system has been installed at Westonbirt, The National Arboretum. CMW installed an innovative slow sand filter system to pump, clean and use the rainwater collected in the underground tank.
This new rainwater filter system is a first for Forestry England and will reduce the amount of water being used; completing the facilities that support the new Quarantine House in the arboretum’s Propagation Unit. Based on an average year’s rainfall, the system has the capacity to collect a massive 90,000 litres of rainwater per year and its collection tanks can store nearly 26,000 litres which is equivalent to 132 bathtubs of water.
An old underground rainwater collection tank was discovered in the propagation area, under the existing glasshouses. Helped by CMW Horticulture, specialists who design and build large greenhouse systems throughout Europe, an innovative slow sand filter system has been installed to pump, clean and use the rainwater collected in the underground tank.
The system works by collecting rainwater from the quarantine house and two large glasshouse rooves via downpipes, pumping the rainwater from the underground collection tank into a large tank above ground filled with layers of pebbles and sand to biologically remove organic matter and pathogens from the water as it percolates through; avoiding the use of chemical additives to remove plant pathogens. The water is also filtered by UV light before being used for irrigation in the Propagation Unit.
Despite the drought conditions experienced this July and August, with more daily irrigation required to keep the plants hydrated, there was still plenty of water left in the system which proves its ability to provide sufficient water.
Rainwater collection system – technical details:
- The new system makes use of a re-discovered underground rainwater collection tank that holds 20,000 litres of water (over 110 bathtubs), 1.15-metre high x 1.5-metre wide x 10-metre length.
- A newly installed tank stored above ground (1.8m diameter x 2.4m height has collected water pumped to it, the tank contains sand at the top and larger cobbles at the base to slow-filter the water as it percolates through. This galvanised filtered water tank can hold 5,800 litres in 32 bathtubs.
- In a connected second tank, the filtered water is stored and drawn off. This second tank holds 5,880 litres (approx. 32 bathtubs) of filtered water.
- A pressurisation vessel keeps the water pressurised to draw from taps.
- The water passes through a UV filter on its way from the filtered water tank before the water is drawn off from taps to irrigate plants in the propagation area.
- Based on the square meter area of rooves, we have the capacity to collect 90,000 litres based on an average year’s rainfall.
The poly structure is the “quarantine house” for any new plant material delivered to the site
The left-hand tank is the disinfected water after passing through the sand filter, and the right-hand tank is the sand filter itself (full of filtration medium) with different grades of stone, then covered in a layer of sand
Westonbirt, The National Arboretum
Westonbirt, The National Arboretum is managed by Forestry England and is renowned worldwide for its tree and shrub collection. Home to five national collections, the arboretum covers 243 hectares (600 acres) and contains 15,000 labelled specimens. Visitor numbers are 500,000 a year, with a Friends of Westonbirt Arboretum membership of over 38,000 members. Westonbirt Arboretum was established in the 1850s by wealthy landowner Robert Holford and later developed by his son George Holford. Unlike many arboreta, Westonbirt is laid out according to aesthetic appeal rather than scientific or geographical criteria.
Forestry England manages and cares for the nation’s 1,500 woods and forests, with over 230 million visits per year. As England’s largest land manager, they shape landscapes and are enhancing forests for people to enjoy, wildlife to flourish and businesses to grow. Forestry England is an agency of the Forestry Commission.