From feasibility to futureproofing: Downpatrick Flood Alleviation Scheme
Partnering with Amey Consulting to deliver vital risk assessment, modelling and optioneering, helping build flood resilience for the community of Downpatrick.
Responding to fluvial flooding
Following severe flooding in Downpatrick on 1–2 November 2023, our project partner Amey Consulting was commissioned by DfI Rivers to undertake a feasibility study to address the town’s fluvial flood risk.
This flood event, triggered by prolonged rainfall and high spring tides, caused extensive disruption to homes and businesses in Downpatrick, particularly around Market Street and other low-lying areas. High spring tides acted to severely limit the Quoile River’s discharge into Strangford Lough, causing water to back up and overwhelm urban watercourses and drainage infrastructure.
- Client Amey Consulting, on behalf of the Department for Infrastructure (DfI) Rivers, Northern Ireland
- Partner Amey Consulting
- Location Downpatrick, Northern Ireland
How did we support Downpatrick Flood Alleviation Scheme?
Amey approached JBA to carry out hydrological analysis and fluvial model due to our expertise in the development and application of Integrated Catchment Models.
We updated the hydrological analysis and existing fluvial model of the catchment, and produced a long list of 14 flood mitigation options. The hydraulic model was used to test the feasibility of these 14 scenarios, as well as produce flood maps for the baseline and mitigation options.
We also carried out an economic assessment for both the Business As Usual (BAU) and preferred mitigation scenarios.
Of the 14 options, two were found to be cost-beneficial. Option N — comprising flood embankments, walls, enhanced culvert capacity, and pump installations for urban watercourse — was identified as the leading solution. Offering protection to 106 properties during a 1% AEP plus climate change event, with a Benefit Cost Ratio (BCR) of 1.15.
Innovating for flood resilience
Our team addressed the challenges of the complex catchment hydrology by integrating high-resolution LiDAR, topographic and bathymetric data, and historical flood records into an updated Integrated Catchment Model. Climate change allowances were also embedded to support long-term resilience.
We deployed the latest version of the Integrated Catchment Model (ICM v2024.5), enabling accurate simulation of flood scenarios, including climate change projections. By validating our model against real-world 2023 flood data, we increased confidence in the model outputs and supported robust comparison of the mitigation options.
Heritage considerations were also integrated into the design process, and sustainability was prioritised by maximising use of existing infrastructure and avoiding reliance on demountable defences. Future phases will focus on low-carbon materials and reuse of site materials.
The scheme is now progressing into Phase 2, which includes ground investigations and detailed development of project risks and costs.
Community-centred engagement
Early stakeholder expectations were high, with local communities and policymakers eager for immediate actions and robust answers. We engaged in active communication and updated stakeholders regularly to manage expectations, sharing interim findings, and incorporating local knowledge.
Contracted through Amey Consulting, we worked alongside DfI Rivers, Northern Ireland Water, and the Historic Environment Division. This partnership required close working relationships with regular updates, design workshops, and analytical review sessions to ensure alignment on technical outputs and project milestones.
Sustainable flood management
By using adaptive and resilient approaches, we delivered robust and actionable recommendations in support of Downpatrick’s future flood risk management. This scheme will see lasting benefits to Downpatrick and its surrounding communities, including:
- Protection for 106 properties
- £25.9M in flood damages avoided
- Improved understanding of catchment hydrology
- A valuable modelling asset for future planning and emergency response
The Downpatrick Flood Alleviation Scheme sets a benchmark for future flood risk management projects. It demonstrates how advanced modelling, stakeholder engagement, and sustainable design can deliver resilient, cost-effective solutions in complex hydrological settings.
Contact Alistair Clark for more information about our work on the Downpatrick Flood Alleviation Scheme.
