Using modelling to support better stormwater management in Yorkshire
At a glance
Yorkshire Water launched an ambitious programme to tackle storm overflows across its wastewater network and improve the quality of rivers and bathing waters across the region. We supported the utility in identifying cost-effective, evidence-based solutions to reduce storm spills and guide long-term investment planning. Our contribution focused on applying advanced data analysis and modelling techniques that underpin integrated stormwater management strategies across multiple catchments.
The challenge
Storm overflows are a persistent issue for water utilities, both from regulatory and environmental perspectives. Yorkshire Water manages 2,172 overflow points across its network, many of which are combined sewer overflows (CSOs) that discharge to sensitive locations, including bathing waters, rivers and sites of special scientific interest.
Yorkshire Water set a target to reduce storm spills by at least 20 percent, with some sites achieving reductions to fewer than 10 spills annually. To achieve this, Yorkshire Water needed a clear understanding of catchment behaviour, backed by reliable data and practical interventions that could also inform customer engagement and future funding bids.
Our response
Working alongside our partners, we conducted detailed investigations and modelling for 31 storm overflow sites under Yorkshire Water’s Storm Spill Reduction Programme. A further 14 projects were advanced to delivery, covering both wastewater treatment works and CSO locations.
Combining technical insight with a collaborative mindset, our team:
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Applied network hydraulic modelling to understand how overflows respond to varying rainfall and runoff conditions
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Addressed data gaps through catchment-based knowledge, GIS analysis and field validation
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Identified and prioritised interventions that offered measurable reductions in spills and improved sewer capacity
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Produced outputs to guide investment planning and customer communications
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Contributed to industry discussions on planning and regulatory frameworks for future flood management
This integrated process allowed Yorkshire Water and its delivery partners to make informed decisions about where to invest and which measures would achieve the greatest environmental and social return.
The impact
The programme covered a large part of the Yorkshire Water region, from Chesterfield to Leeds. In most cases, storm spills fell to fewer than 10 per year for each overflow. The work also delivered multiple community and environmental benefits:
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Partnerships with schools led to the installation of sustainable drainage systems, which manage roof runoff while offering educational opportunities.
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Innovative construction methods, including the use of plastic components, helped reduce concrete use.
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Water quality in rivers has significantly improved because of lower volumes of raw sewage entering watercourses.
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In-house innovation across teams drove sustainable and cost-effective delivery.
Our collaboration helped Yorkshire Water identify affordable and resilient solutions that continue to inform business planning, regulatory engagement and future investment strategies. The project improved river health and strengthened the region’s approach to managing water sustainably for decades to come.