A scheme to combat flooding by surrendering land to the sea will be completed on Monday on the south coast.
The £28m “managed realignment” at Medmerry in West Sussex has seen the building of 7km (four miles) of new sea walls up to 2km inland.
By letting the waters in, the Environment Agency says the risk of flooding for hundreds of homes will be reduced.
The surrendered land will become a wetland habitat for many species.
The sea has long been a threatening presence on the flat land of the Manhood Peninsula that juts into the English channel on the coast between Portsmouth and Worthing.
Caravan parks in Selsey and Bracklesham Bay have been flooded a number of times in recent years, as the shingle defences have yielded to the surging seas.