“Our village is drowning.” Those were the words of one local councillor after 40 homes in the Welsh village of Llanfair Talhaiarn were flooded during Storm Ciara in 2020. The storm brought heavy rainfall to the area, with the River Elwy reaching record flow levels.
Flooding is a recurring problem for Llanfair Talhaiarn, due to its location at the confluence of the Nant Barrog watercourse and River Elwy. As climate change increases the occurrence and intensity of floods, local people and their properties are at risk.
As a result, Natural Resources Wales (NRW) – the Welsh body for environmental regulations and advice – appointed us to develop a flood risk scheme to safeguard the community and strengthen resilience from future flood events.
The scheme is designed to protect the village from the type of severe flooding that can happen once every hundred years – a one per cent Annual Exceedance Probability (AEP) event.
Using advanced hydraulic modelling techniques
To address flood risks and design an effective flood risk management scheme, we used hydrological and hydraulic modelling, civil engineering, conducted environmental assessments and provided construction support.
By employing advanced modelling techniques, our specialists were able to determine flood levels, flows and extents which informed the civil design.
This included:
- Replacing a deteriorated 40-metre brick arch culvert with a reinforced concrete bridge and flood walls over 75 metres long
- Installing a highway drainage system with non-return valves to manage excess water during heavy rainfall.
Enhancing environmental and community wellbeing
Aligning with NRW’s ecological priorities, we focused on restoring local habitats for migrating fish, eels, and otters.
For example, the scheme involved removing weirs to facilitate fish migration, installing an otter pass for the local otter population, and fitting a vegetated retaining wall to increase biodiversity. Additionally, rock armour was strategically placed to improve riverbed conditions.
Community engagement was central to this project. We involved local stakeholders – including businesses and landowners – to better understand their concerns and requirements.
As the scheme is situated within the Llanfair Talhaiarn conservation area and passes through the grounds of a Grade II-listed chapel, our landscape architects selected native plants and trees, as well as Victorian-style ornamental railings, to preserve the village’s aesthetic appeal and heritage.
Flood defence in action: protecting Llanfair Talhaiarn during Storm Babet
The completed Llanfair Talhaiarn flood defences have already been put to the test.
During Storm Babet in October 2023, the steel trash screen – an enhanced safety feature designed to block debris during storms – stopped a staggering 150 tonnes of material from reaching the village culvert, helping to safely control the flow of water through the village, protecting local people and their homes from flooding.