Shimna flood alleviation scheme earns BREEAM Infrastructure Excellent

Newcastle, Co Down, is vulnerable to severe flooding due to the Shimna River’s historical tendency to breach its banks during heavy rainfall. The devastating impact of these floods had made it essential to develop a robust flood management scheme. 

The Shimna Flood Alleviation Scheme addressed these challenges through engineering solutions designed to balance environmental sensitivity and functionality. Its primary components included: 

• 1,300m of reinforced concrete flood walls. 
• 150m of earth embankments. 
• 3,500 secant piles (average 9.5m long) to cut off water seepage. 
• An innovative ‘roughing grille’ to catch upstream debris and prevent blockages. 

The project faced significant challenges during its development and implementation. These included safeguarding the sensitive river environment, gaining community and stakeholder buy-in, and managing technical complexities. 

Developing controls to mitigate ecological risks was particularly important, as the Shimna River is home to diverse species and habitats. Securing necessary approvals, such as environmental permits and stakeholder agreements, required early and sustained engagement. In addition, the high bedrock areas along the project site demanded a tailored approach to minimise vibrations and disruptions. 

Key challenges included: 

• Protecting the Shimna River’s ecosystem while constructing extensive flood defences. 
• Addressing community concerns and gaining approval from property owners. 
• Designing a solution that could withstand high bedrock areas with minimal environmental impact.

The Shimna Flood Alleviation Scheme adopted innovative solutions guided by BREEAM Infrastructure criteria to meet its sustainability and engineering goals. The project team focused on resource efficiency, community involvement, and biodiversity protection throughout. 

A notable design optimisation replaced traditional steel sheet piling with secant piling, which significantly reduced vibration risks and ecological disruption. The construction process incorporated measures to minimise waste and carbon emissions, including the reuse of 97% of excavated material on-site. The team also employed an ecological clerk of works to ensure compliance with environmental guidelines. 

Highlights of the solutions implemented include: 

• Optimised design: Switched to secant piling to minimise vibrations and reduce the impact on wildlife. 
• Community engagement: Appointed a liaison officer and held information days to involve local residents and schools. 
• Ecological protection: Conducted extensive pre-construction surveys and implemented safeguards for local habitats. 
• Innovative flood management: Designed a bespoke ‘roughing grille’ to prevent downstream debris blockages.

The Shimna Flood Alleviation Scheme delivered significant benefits to the local community, environment, and economy. It provided long-term protection for over 300 properties, enhanced the local ecosystem, and demonstrated best practices in sustainable construction. 

The project achieved a 60% reduction in embodied carbon emissions, exceeding sustainability targets. By reusing 97% of excavated material on-site, it also minimised landfill waste while improving the local topography. Community engagement efforts ensured local support and raised awareness of the project’s importance. 

Key outcomes included: 

• Flood protection: Prevented flooding during Storm Betty in 2023, safeguarding Newcastle’s properties and residents. 
• Carbon reduction: Achieved a 60% reduction in embodied carbon emissions. 
• Waste management: Diverted 2,600 tonnes of material from landfill through reuse and recycling. 
• Social engagement: Conducted school outreach, exceeded ‘Buy Social’ targets, and raised funds for local charities.