Hinkley Point C fish return tunnel: design and interface notes for engineers
Reviewed by Joe Ashwell

First reported on New Civil Engineer
30 Second Briefing
Preparatory works have started at Hinkley Point C to drive a 620m-long fish return tunnel, using a tunnel boring machine to connect the cooling water system back to the Severn Estuary. The tunnel will allow fish and other marine organisms drawn into the 3.2GW plant’s cooling water intakes to be screened and safely returned offshore rather than discharged onshore. For designers and contractors, the project adds a short, small-diameter marine tunnel interface to an already dense underground works package of intake and outfall tunnels.
Technical Brief
- Similar short auxiliary tunnels on large energy schemes often become critical path items due to interface complexity.
Our Take
Among the 731 Infrastructure stories in our coverage, very few deal with nuclear-associated marine works in the United Kingdom, so the 620 m fish return tunnel at Hinkley Point C sits in a relatively specialised niche of coastal and estuarine tunnelling practice.
The Severn Estuary’s strong tides and high suspended sediment loads make TBM launch and recovery for a short tunnel like this technically closer to urban microtunnelling under rivers than to conventional long-distance power tunnels, which will influence segment design, abrasion allowances and maintenance strategy.
Positioned under the Sustainability tag within our database, this fish return tunnel highlights how UK nuclear new-build projects are now being engineered with dedicated infrastructure for aquatic ecology, which is likely to become a reference point for future cooling-water intakes on other large coastal plants.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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