The team at RAB have delivered a detailed design for rock armour erosion protection at Ferry Bridge in Clarina, County Limerick, on behalf of the Office of Public Works (OPW). The design was commissioned in response to a significant erosion defect highlighted during a previous RAB-led asset inspection project, which identified a risk to the nearby flood embankment and surrounding properties.
The project aimed to provide a robust, site-specific engineering solution to reduce erosion along the riverbank, protecting critical flood defence infrastructure. The scope of work included technical drawings and construction documentation to guide the implementation of erosion control measures. The use of rock armour was chosen as the most effective and durable method for stabilising the bank in this tidal river environment.
Outcomes
To develop the design, RAB began with a detailed topographic survey of the site to ensure accuracy in the ground profile and existing conditions. Tidal gauge data from Ferry Bridge was used to assess local water levels and flow ranges, forming the basis for hydraulic calculations such as Manning’s equation which was applied to calculate flow velocities within the channel, allowing the engineering team to appropriately size the rock armour required and define its placement in line with site-specific flow dynamics.
The final design incorporated key features such as geotextile layers for filtration and stability, correctly graded rock armour sized to withstand the calculated hydraulic forces, and toe protection at the base to resist undermining. The design restores the bank’s profile to its condition prior to erosion while reinforcing it for long-term performance. Securing pins and embedded overlap ensure that the armour integrates effectively with the existing embankment.
Two detailed cross sections were produced as part of the design, each providing a clear representation of the proposed structure at critical points along the eroded riverbank. These drawings show the relationship between existing and designed ground levels, the rock armour layers and accompanying construction elements such as embankment crests and substrate layers.
Alongside the engineering drawings, RAB delivered supporting materials to ensure readiness for construction. These included a design risk assessment outlining potential construction hazards and associated mitigations and a pre-construction information compliant with CDM (Construction Design and Management) regulations. All documentation was tailored to support the client’s engagement with contractors and streamline the transition to the construction phase.
Conclusion / Takeaways
The Ferry Bridge rock armour design project demonstrates how targeted, data-led engineering can address urgent flood risk and asset degradation challenges. The clients proactive defect response enabled RAB Consultants provided a fully engineered solution that balances practical constructability with long-term resilience.
This design not only protects a vulnerable section of riverbank but also shows how geospatial data, hydraulic modelling, and detailed CAD design can work in combination to deliver high-value outcomes for infrastructure clients. While traditional erosion control methods remain in use, this project illustrates the potential of more efficient, design-informed approaches to asset protection—particularly in flood-prone and environmentally sensitive areas.
Through this work, RAB have supported the OPW in proactively managing their flood defence infrastructure, ensuring both the protection of critical assets and the safety of nearby communities.
RAB deliver a wide range of asset management, public safety and engineering services for both public and private sector organisations. More information is available here on our website, or you can get in touch for an informal discussion on your specific project by email to enquiries@rabconsultants.co.uk or call our head office in Lichfield on 0330 223 6475.