Kingfishers, kestrels and buzzards are just some of the beneficiaries of two stunning new wetland habitats created at Durleigh Reservoir in Somerset, south-west England.

The enhancements for wildlife and plant-life are also delivering improvements to the way drinking water is processed for local people. The wetlands are just one part of a £50 million scheme to upgrade Durleigh water recycling centre and improve the quality of the raw water entering the plant.

At Durleigh, a complex adjustment to the acidity or alkalinity of the raw water - its pH value - had been necessary to ensure high quality drinking water, as the water entering the treatment works was experiencing high levels of algae during the summer months.

The water was also showing high levels of turbidity in the winter. Turbidity is a visual measure of water quality and can be seen when water seems hazy due to suspended particles of silt or other substances.

The upgrade means day-to-day operation of the plant has been simplified, making it easier and less costly to produce clean drinking water for the 44,500 people who depend on Durleigh for their supply.

An existing wet woodland acts as the final screening process before the water reaches the reservoir, where it is held before being treated at the recycling plant.

Dragonflies, damselflies, frogs and toads are just some of the wildlife attracted by the wetlands as they boost biodiversity, as well as providing a beautiful amenity for people living nearby. They have already brought about a reduction in water pollutants, with a 75% drop in ammonia levels, while phosphorus and sediments have dropped by around a third.

The wetlands are based at the head of the reservoir and are designed to filter out the silt and sediment that cause turbidity, as well as reducing the quantity of nutrients such as nitrogen and phosphorus present in the water. An overabundance of nutrients can cause algae and some aquatic plants to grow excessively, reducing oxygen available and risking harm to fish and other wildlife.

Phosphorus comes from a variety of sources including septic tank systems and wastewater treatment plants, soil erosion, animal and pet waste, fertilisers and everyday detergents and personal care products.

Wetlands are called nature’s kidneys - they are great at removing sediment and pollutants from water. They do this by slowing down the water flow so suspended silt drops to the bed of the wetland, or is trapped by roots and plants, leaving the water clearer.

Many harmful environmental contaminants do not dissolve in water and attach to the sediments. As the sediment settles out, these pollutants become bound up in the soil layer. Provided the sediments remain undisturbed, these contaminants stay locked away from harmful contact with plants and animals.

Slowing down the water is also important for naturally improving its chemistry. It provides time for bacteria to convert toxic nutrients from agriculture and other sources into less harmful forms. They can then be taken up by growing plants and microorganisms in the soil.

The wetlands support the work of Wessex Water’s catchment delivery team with local farmers to reduce pesticides and silt entering the Durleigh Brook.

They found that reverting cultivated land to a natural state, as well as restoring the river to its former location and reconnecting it to its floodplain, has resulted in the biodiversity in the surrounding habitats increasing by between 55 and 76%, using Natural England's biodiversity metric. This will continue to increase as the habitats mature, with Wessex Water regularly sampling and analysing the water and environment.

Ruth Barden, Wessex Water’s director of environmental solutions said, “Wessex Water is leading the way in applying nature-based solutions, such as wetlands and testing their effectiveness in tackling the environmental challenges that we all face.

“We are continuing to monitor the effectiveness of sites like Durleigh, examining chemical and biological data to inform our future investment decisions.’’ 

Wessex Water’s biodiversity & wetlands project manager, Sarah Williams said, “As well as enhancing wildlife and biodiversity these wetlands are a great example of how we can harness the power of nature to support our water supply operation.

“Each wetland at Durleigh has its own purpose. A naturalised wetland captures sediment and silt by connecting the Durleigh Brook back to its floodplain, while a constructed wetland area improves the quality of supply from the Bridgwater & Taunton Canal, as well as recycled water from the water treatment centre itself."

She added, “This area is one of our most biodiverse and is becoming home to lots of aquatic-loving species and the newly-created habitats have brought significant wildlife benefits, being home to amphibians, dragonflies, birds and wildflowers."

Species already logged include brightly coloured yellowhammers; little and great egrets; frogs, toads and newts; non-venomous grass snakes, and a wealth of dragonflies and damselflies. Flourishing flora include the ragged robin, yellow flag iris, flowering rush and purple loosestrife.

Durleigh gets the treatment

Spectacular as they are, the wetlands and their thriving wildlife and plant-life are only one part of the Durleigh story. A whole reconstruction of the treatment works was also undertaken - the largest single-value project ever delivered by Wessex Water’s engineering and sustainable delivery team.

Demand on the old Durleigh site had outgrown its design capacity and reconstruction was required to update water treatment processes and ensure it would continue to meet increasing demands from a rising population. Some 70% of old centre demolished and recycled, with outdated equipment decommissioned and removed, and 30% of structures repurposed or refurbished.

All the works had to take place within a very tight construction site, constrained by the reservoir, Durleigh brook and a local road. The poor condition of the ground onsite, including high groundwater levels, meant special foundations, or pilings, had to be bored into the ground for the construction of the water tanks.

Flood risk also had to be carefully assessed and the tight timeline meant the partners faced additional challenges posed by the Covid-19 pandemic. Working closely with infrastructure consulting firm AECOM, Wessex Water's construction team worked out that some large structures and tanks could be built offsite and craned into position, saving an estimated 20% programme time and £1.1 million in cost, as well as reducing waste by up to 20 per cent.

Wessex Water Project Manager Nigel Coates said, “Refurbishing the Durleigh centre has been a complex, large-scale project taking place within a tight working site and coming up against challenges such as poor ground conditions as well as the obvious difficulties caused by the pandemic.

“Teams across Wessex Water and all the partners involved have worked extremely hard to ensure any major delays have been avoided and they deserve enormous credit for making sure that the centre has returned to supply and delivering high-quality water to thousands of people in the area.’’

Lasers, drones and virtual reality

The emergence of new digital technologies for design and construction, including lasers, radar and drones, has transformed the way Wessex Water has delivered this large project, compared with traditional approaches, and will impact all projects going forward. Working closely with AECOM, they introduced digital engineering innovations that drove major efficiencies and a £2.5 million cost saving.

The use of laser scanning, ground-penetrating radar and drones to gather images and information meant an accurate digital representation of the site and planned changes could be created from the very start. This 3D model was combined with gaming technology to create a virtual reality (VR) simulation of the Durleigh site.

The VR site was hosted inside an 'igloo’ - a walk-in cylinder with 360-degree projection to create a fully immersive experience. This meant teams of up to 12 people could virtually stand on site and walk around the project in complete safety, using an Xbox controller.

Multiple reviews of the design and operation of the works could be carried out within the igloo, and all stakeholders could be included, without having to don protective clothing and carry out extra safety assessments. Wessex Water says the ability to visualise and rapidly 'build' alternative equipment layouts unlocked an estimated £300,000 in engineering savings by detecting over 100 potential design clashes.

Drones were used to undertake a structural survey of the roofs of existing buildings, creating a high-definition record of condition for future reference and to eliminate fall-from-height hazards associated with working on fragile roofs.

Wessex Water Delivery Manager Simon Osborne said: “The Durleigh project is part of our long-term water supply strategy for Somerset and the project has also led way in the water industry with the implementation and daily use of digital technology. These essential improvements will ensure we continue to deliver high-quality water to our customers and we thank the local community for their patience and understanding while this extensive project has been completed."

AECOM Water project manager Mark Badcock said, “As the design partner for this flagship project, our design leads and 3D-modellers worked with the Wessex Water team at Durleigh to achieve the optimum design.

“This was a technically complex project and the emphasis on digital collaboration and engineering were critical to its success. It’s a fantastic achievement all round to see it in operation.”

What next for Wessex Water?

Wetlands and reedbeds are among 28 natural solutions being developed throughout the Wessex Water region before 2025. These will help reduce instances of storm overflows operating by and preventing excess groundwater entering sewers and overloading the system.

The company’s catchment delivery team is working with farmers and landowners in the River Stour in Dorset and Somerset to identify more eco-landscaping opportunities to further offset phosphorus from water recycling centres and other developments, whilst providing biodiversity and carbon benefits.

Thanks to Wessex Water for sponsoring this Awesome Project and helping to Make Water Famous. If you have a project you would like to see featured, do get in touch.