The Shimna River in Newcastle, Northern Ireland, has flooded periodically over the last 50 years.
Following severe flooding in August 2008, a post flood investigation of the Burren and Shimna Rivers was undertaken. Despite the Burren Flood Alleviation Scheme, it was discovered that areas could still be flooded by the Shimna River. The Shimna River Flood Alleviation Scheme delivers an economical, environmentally and socially sensitive project which alleviates the flood risk to affected properties, infrastructure and businesses. AECOM collaborated with the Rivers division of the Department for Infrastructure to develop a detailed design to protect the community.
Design, modelling and delivery
At an early stage, we built a hydraulic model to replicate a digital twin of the river. It was determined that 312 properties were at risk of flooding during a 1% Annual Exceedance Probability (AEP) or a 1 in 100-year event i.e. an event that has a 1% probability of occurring in any given year. The detailed design provides enhanced protection to properties, with allowance for climate change.
The scheme consists of approximately 1.5km of secant piled flood wall and piled embankments. The walls are finished to seamlessly blend into the surrounding environment.
Flood gates and embankments were constructed at strategic locations which improve community accessibility around the flood defences. An upstream ‘roughing screen’ was designed to prevent debris from the forest potentially causing a blockage at a downstream bridge.
Safeguarding the environment
A full suite of environmental surveys were undertaken in the area to inform an Environmental Impact Assessment, as the river flows through an Area of Special Scientific Interest (ASSI) and the Mourne Area of Outstanding Natural Beauty (AONB). We worked with the contractor to facilitate fish rescue, silt curtains and environmental permits. Several public consultations were held to ensure community buy-in to the scheme. Local councils and schools were engaged with to erect bat boxes and to plant mature trees within the scheme.
Going beyond
We provided multi-disciplinary services to ensure that all aspects of the scheme were delivered in an efficient manner. This fostered good communication between multiple teams and enabled us to produce work under an accelerated programme to ensure the client met deadlines.
During construction, we worked closely with the contractor to ensure the scheme was constructed within budget and on programme. Being involved from design to delivery allowed us to manage the project in an efficient manner while ensuring the contractor and client were well informed throughout.
The Shimna River Flood Alleviation Scheme delivered over and above its primary aim of providing flood protection to 312 properties. The local community also benefit from; increased mobility for pedestrians and the creation of a new picnic area and upgraded play park.