Project overview
Solutions By Nature has built a new integrated constructed wetland (ICW) to further treat wastewater at Staplefield Wastewater Treatment Works in West Sussex. The wetland is a nature-based approach to phosphorus reduction and will deliver a range of co-benefits to the site and its surroundings.
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Our role
The wetland at Staplefield Wastewater Treatment Works is being delivered for Galliford Try Binnies Joint Venture as part of the AMP7 capital programme for Southern Water. In order to meet stricter phosphorus and suspended solid regulations, additional treatment capacity was required.
The wetland was chosen as a nature-based water treatment solution to remove pollutants from treated water before it is discharged back into the River Ouse. Planning for the wetland began in 2022. A feasibility study, groundwater risk assessments and other environmental assessments were completed, with construction beginning in May 2025.
This project was one of the first initiatives of its kind in England. With limited precedent, there was a steep learning curve for all involved. Beyond the capacity for water treatment, the wetland needed to blend into the surrounding landscape and support biodiversity, following principles from the Convention on Biological Diversity (CBD) to offer multiple ecosystem services such as habitat creation, carbon sequestration and aesthetic value.
The lowest point of the wetland site sits below the natural level of the floodplain of the River Ouse, restricting the space available for the wetland.
A strong emphasis on collaboration between businesses ensured the project delivered the right outcomes for the client. Assembling the appropriate expertise and stakeholders enabled the project to proceed smoothly despite the limited precedent.
The natural slope of the site was really well suited to enabling the gravity flow of water between the cells, and the shape of the cells was designed to maximise the hydraulic retention time and the treatment of the water. The existing clay soil created a natural seal on the bottom of the cells, making considerable cost savings compared with importing an artificial liner.
Excavating the lowest part of the site enabled its use as a separate stormwater retention area, adding to flood storage mitigation.
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The project will have clear benefits for local water quality and in improving biodiversity
According to Natural England, more than 90% of wetland habitats in the country have been lost over the last 500 years. Planting over 80,000 native wetland plants across 14 different species therefore creates an important and rare habitat.
When fully mature, it is estimated that the wetland will sequester approximately eight tonnes of CO₂ per year, and the site will add an additional 3500 m2 of flood storage mitigation.