WaDFAS & COPFAS: Shaping a New Era of Flood Resilience for Hull

The City of Hull is settled on flat land adjacent to the sea and close to sea level, making the region susceptible to intense flooding due to its surrounding valleys draining their rainwater into the basin in which Hull is built. Consequently, in 2007, extreme rainfall overwhelmed the drainage systems across Kingston upon Hull, over 14,000 properties were flooded, and roads through Willerby, Derringham, Cottingham, and Orchard Park turned into rivers, with no natural watercourse available to carry water away.

As part of Pell Frischmann’s centenary, we are revisiting two schemes that helped define a new era of flood resilience for Hull and the East Riding: the Willerby and Derringham Flood Alleviation Scheme (WaDFAS) and the Cottingham and Orchard Park Flood Alleviation Scheme (COPFAS).

The impact stretched beyond Hull itself and prompted an unprecedented partnership between the East Riding of Yorkshire Council and Hull City Council, supported by the Environment Agency and the Humber Local Enterprise Partnership, to find robust and sustainable answers to flood risk. As part of this joint effort, WaDFAS and later COPFAS were commissioned as major stormwater attenuation schemes by East Riding of Yorkshire Council designed to protect communities in Willerby, Derringham, Cottingham and Orchard Park.

From the outset, Pell Frischmann played a central role in shaping both WaDFAS and COPFAS. For WaDFAS, we undertook environmental surveys and assessments, ground investigations, hydraulic modelling, detailed design, and the preparation of contract documents. We also provided technical advice during construction, including archaeological supervision and Reservoir Construction Engineer services.

WaDFAS represented one of the largest floodwater attenuation schemes in Great Britain at the time, with four earth embankment reservoirs in the Great Gutter Valley serving Willerby and Derringham. Three of these reservoirs fall under the Reservoirs Act 1975 due to their scale and together provide a combined storage volume of 234,000 cubic metres. The system of reservoirs, control structures and culverts, with interconnecting ditches, delivers controlled releases into the lower drainage network. This has protected more than 8,900 homes and businesses across the Great Gutter Valley.

For COPFAS, Pell Frischmann was commissioned by East Riding of Yorkshire Council to undertake an outline design with hydraulic modelling, submit the planning application, and provide detailed design and on-site engineering consultancy. The scheme is divided between the Raywell Valley, which directs water into Cottingham, and Cottingham Parks, which drains towards Orchard Park. Across these catchments, a system of nine storage reservoirs, all under the Reservoir Act, was developed to retain up to 330,000 cubic metres of surface water and reduce flood risk, ultimately providing protection for approximately 4,000 homes and businesses.

Both projects exemplify Pell Frischmann’s leadership in flood modelling. For WaDFAS, our team used Infoworks ICM, combining a three dimensional overland mesh with underground drainage networks and one dimensional river modelling. This was the first time the software had been used for such a complex, large scale model. For COPFAS, we adapted the River Hull Integrated Catchment Model into a streamlined single catchment model, which informed the creation of eight reservoirs along Eppleworth and Westfield Road and a further reservoir near North Moor Lane in Cottingham.

Environmental protection also sat at the heart of both schemes. At the WaDFAS sites, the presence of great crested newts, water voles, and nesting birds demanded careful mitigation. Clay linings shielded the underlying aquifer, and emergency spillways ensured long-term resilience. Habitat compensation and species exclusion measures were adopted to maintain ecological integrity while delivering vital flood protection.

In COPFAS, environmental and water resource protection were equally prominent. As for WaDFAS, the entire construction site lies within a Source Protection Zone for a chalk aquifer that is essential to the drinking water supply for Hull and its surrounding areas. As a result, construction methods were constrained by the need to avoid groundwater contamination. Pell Frischmann carried out extensive geotechnical testing and worked closely with the Environment Agency and Yorkshire Water to agree on the reuse of on site clay to line the reservoirs and build embankments. This sustainable approach safeguarded the aquifer whilst saving millions in costs.

WaDFAS, awarded in 2013 and completed in 2016, transformed stormwater management in the Great Gutter Valley by introducing large scale flood attenuation that set a new standard for the region. COPFAS advanced this progress soon afterwards, with all nine reservoirs completed by the end of 2020. Together, the schemes now provide long term protection against a 1 in 75-year flood event with built in allowances for future climate change, illustrating how Pell Frischmann’s work has significantly strengthened climate resilient infrastructure across the area.

WaDFAS and COPFAS earned widespread industry recognition for their innovative and sustainable approaches to flood alleviation. WaDFAS received early acclaim, including honours at the Institution of Civil Engineers Yorkshire and Humber Centenary Award in 2017, the Innovation Award at the Constructing Excellence Yorkshire and Humber Awards the same year, and the Infrastructure Award at the RICS Yorkshire and Humber Awards in 2018, where judges praised its sustainable and power‑free operation.

COPFAS achieved similar success, winning the Institution of Civil Engineers Yorkshire and Humber Smeaton Award in 2020 and being shortlisted for the NCE100 Climate Resilience Award, with judges highlighting Pell Frischmann’s high‑quality design, protection of the water source zone and effective use of cascading reservoirs. These accolades demonstrate the strong standing of both schemes within the wider industry conversation on sustainable flood risk management.

WaDFAS and COPFAS represent a defining chapter in Pell Frischmann’s first hundred years. Emerging from the devastation of the 2007 floods, they were among our earliest flood alleviation schemes in the Hull area and now protect more than 12,000 homes and businesses combined. Each scheme brought together local authorities, national agencies, and our own specialists to deliver solutions that are technically advanced, environmentally responsible and economically efficient.