Mud trial aims to protect harbour from erosion

Dredged mud from a south coast harbour is being used to restore eroding saltmarsh in a scheme aimed at protecting both the local economy and wildlife.

The trial at Lymington Harbour in Hampshire involves placing sediment at a height that allows plants to recolonise naturally.

The harbour - which has a ferry link to the Isle of Wight, 1,600 leisure moorings and about 20,000 visiting yachts a year - is worth tens of millions of pounds annually to the local economy.

But its saltmarsh has been eroding at a rate of two to three metres a year due to rising sea levels and increased bad weather linked to climate change.

Without the saltmarsh, much of the harbour would be exposed and could become unviable.

Rocky breakwaters and depositing dredged mud in front of the saltmarsh have previously been used to slow the erosion.

The new trial, led by Lymington Harbour Commissioners and Land and Water Group, aims to place sediment at the correct height so that vegetation can re-establish itself.

The Crown Estate, which owns most of the foreshore, seabed and tidal riverbed at Lymington Harbour, is backing the scheme.

Ryan Willegers, chief executive of Lymington Harbour Commissioners, said the harbour had seen a decline in saltmarsh since around 1920.

"At the beginning of this century we started to get very concerned that if it carried on, we would be in a situation where the saltmarsh that protects the harbour, most of it wouldn't exist," he said.

"Without the saltmarsh a lot of the harbour would be exposed and no longer viable to support the economy."

James Maclean, chief executive of Land and Water, said saltmarshes supported 80% of marine species that grow in inshore waters.

He said about 20 million tonnes of nutrient-rich sediment dredged from UK harbours and ports each year was almost entirely dumped offshore.

The project is testing different technologies and working to address regulatory issues to make it easier to use sediment in nearshore areas.

In 2024, the first year of the Environment Agency-funded trial, about 800 cubic metres of mud was placed in a sheltered part of the saltmarsh at a height designed to regenerate habitat.

Twelve months later, Mr Willegers said there was "really good quality saltmarsh growing in that location".

Last year, with funding from the Crown Estate, the team transported sediment a shorter distance, allowing them to move two-and-a-half times more material in a third of the time.

Willegers said the material had survived the winter and was expected to colonise in the spring.

Maclean said once sediment reached the correct height, it would naturally recolonise with wind-blown and bird-carried seeds.

"Everybody involved has been dumbfounded by how quickly in 2024 the material colonised," he said.

"So we know if we get that target height, nature will take over."

Caroline Price, head of nature and environment at the Crown Estate, said traditional methods of restoring saltmarsh could be slow and expensive.

She said the organisation wanted to explore innovative and scalable ways to use sediment removed to keep harbours operational, and hoped the approach could be replicated elsewhere.

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