North Wales Eel Pass Programme

North Wales Eel Pass Programme

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We were appointed to produce detailed designs of eel pass solutions at eleven sites across North Wales. Our collaborative approach facilitated the integration of all client team requirements into our design work.

Design challenges in achieving gauging weir accuracy

The gauging infrastructure at the sites varied from low head crump weirs to compound crump weirs, with existing multi-species fish passage measures already installed.

A key design criterion at all sites was to minimise impacts on the hydrometric functioning and accuracy of the gauging weirs. However, some locations required pumped solutions as gauge sensitivity meant the existing weirs could not be broken into.

Integrated design approach: engineering solutions and hydrodynamic insights

The project's collaborative nature stemmed from the diverse design criteria set by each client team. Our civil, structural, mechanical, and electrical engineers collaborated with fish ecologists and Computational Fluid Dynamics (CFD) modellers, engaging in extensive consultations and ensuring the delivery of solutions that aligned with client expectations. This was facilitated through collaborative design workshops and teleconferences involving hydrometry and telemetry, fisheries and project delivery teams.

As part of the range of gravity solutions provided, we implemented eel tiles and mussel rope climbing substrate in seven locations, while proposing pumped solutions for three others. To aid the client team in comprehending the water flow needed to achieve a specific depth on an eel tile with lateral slope, we conducted Computational Fluid Dynamics (CFD) modelling. Additionally, CFD was employed to optimize pump sizing at a select few sites.

Enhanced construction efficiency and risk reduction

We devised strategies to reduce the operative risk of cold water exposure during future maintenance tasks. At the mid-catchment site (Nant Peris), we employed pre-cast, moulded concrete blocks to enhance construction efficiency. Eel passage opportunities have been significantly enhanced at six project sites, with construction completed by William Hughes. Work is set to commence construction at Pont y Capel in June 2024 led by Ebsford Environmental and two more sites are due to be constructed in 2026, dependent on funding. The valuable insights gained from the CFD modelling will inform upcoming projects involving pumped eel pass design, while the cold water exposure risk management feature will also be useful in the future.

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For more information on this project please contact Jon Whitmore. Find out more about our Environment and Sustainability work here.

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