Somerset scheme set to absorb high tides and waves but critics say money should have gone on flood defences for residents

An ambitious and controversial coastal realignment scheme – billed as the largest in the UK in modern times – has been completed, with sea water pouring on to the Steart peninsula in Somerset for the first time in centuries.

The £20m project will create a 250-hectare (617-acre) salt marsh, which is designed to protect local communities and sea walls from erosion by naturally absorbing high tides and storm-whipped waves and to create a new valuable habitat for birdlife.

While the Environment Agency (EA) and the Wildfowl & Wetlands Trust (WWT) claim the scheme is good news for humans and wildlife, critics argue the money could be better spent on other projects to combat the sort of flooding that blighted parts of the nearby Somerset Levels last winter.

Ian Liddell-Grainger, the MP for Bridgwater and West Somerset, has led the opposition, calling the marsh an "extravagant, ridiculous scheme" that puts birds ahead of humans.

Coastal realignment sees sea water on the Steart peninsula for first time in centuries. Photograph: WWT

But the EA and the WWT argue that the Steart peninsula scheme is an example of working with nature to combat the challenges of rising sea levels and more frequent, violent winter storms.

WWT chief executive Martin Spray said: "We need to be brave and bold if we are going to deal with the impacts of climate change. WWT Steart Marshes proves you can protect homes and businesses by using wetland technology that works with nature, not against it."

The idea is that the shallow gradient and coarse vegetation of the salt marsh will naturally absorb wave energy. The EA and the WWT concedes the scheme will directly protect only a handful of homes. But it will also protect National Grid connections to the power station at Hinkley Point and ease pressure on other "hard" sea defences such as walls in the area, which help secure many more homes.

An artist's impression of the wildlife habitat to be created by the coastal realignment. Photograph: WWT

Half a million cubic metres of soil were dug and moved to create new and improved flood banks. At high tide on Monday morning, sea water was allowed to enter the low-lying land of the peninsula through a newly excavated 200m gap in the River Parrett coastal embankment.

The area is being managed as farmland and a nature reserve and in time its creek system could become a nursery for commercial fish stocks such as sea bass.

Richard Cox, of the EA, said: "The Steart project will directly protect homes, businesses and the surrounding infrastructure.

An aerial view of the Steart Marshes in Somerset, blasted by critics as a waste of money. Photograph: WWT

"Salt marsh is a natural flood risk management scheme. Like coral reefs or mangroves in the tropics, salt marsh takes energy out of the tide and reduces wave height."

Liddell-Grainger said on Monday that the scheme was a "national disgrace", adding: "It's a complete and utter waste of money." He claimed it cost £30m rather than the £20m declared by the EA and WWT and said the money should have been put towards the £40m needed to build a barrage on the river Parrett. "That would have protected the town of Bridgwater and the Somerset Levels. Instead it has been spent on a bird sanctuary."