Protecting a Severn Estuary intertidal habitat affected by jetty construction

This case study presents a coastal engineering scheme that addressed a unique environmental challenge on a marine construction site. Artificially bunded reservoirs were constructed on the rocky shore of the Bristol Channel, UK, to mitigate the potential impact to ecological features of the Severn Estuary/Môr Hafren Special Area of Conservation resulting from the construction of a jetty at the Hinkley Point C construction site. The installation of piles irreversibly altered the natural supply of seawater from several large rock pools to Corallina officinalis (red seaweed) waterfalls, that the developer, Electricité de France, was obliged to protect. Corallina can die within 30 min of drying out. Following rigorous topographic surveys of the foreshore, hydrodynamic modelling and an evolution of protective measures, concrete structures were designed and installed to ensure the Corallina waterfalls were passively supplied with a constant flow of seawater throughout the tidal cycle. The artificial bunds had to be sympathetic to the natural environment while sufficiently durable to withstand the high-energy conditions of the intertidal site. A local wave buoy 13.5-year dataset shows that the scheme has withstood the two highest wave heights recorded, one of which was the third highest storm peak.