Work costing £10 million is nearing completion, to help prevent the Dorset coastline from Studland to Highcliffe from flooding.
The old groyne at Hengistbury Head near Christchurch is being rebuilt larger and stronger, with rocks shipped from France and Norway and delivered to the site by the Jenny D tug.
The old groyne at Hengistbury Head is being rebuilt to protect the coastline from Durlston to Highcliffe
A map of the Dorset coastline shows how much land could be under threat by 2100 without a new, larger groyne
Important part in the vital exercise
The Hengistbury Long Groyne was built between 1937 and 1939, and has been responsible for protecting the beach environment along East Dorset and Purbeck coastline, but recent surveys have shown that the concrete structure is damaged and that the groyne had become unfit for purpose.
The work caught the attention of Swanage residents as the Jenny D tug has been spotted both at work and at anchor in Swanage Bay at various times since the start of May 2024
The 238 tonne Euro Carrier is playing an important part until the end of June 2024 in the vital exercise, to ferry rock brought from Norway to Hengistbury Head, where it is offloaded onto the shoreline and then retrieved by land based excavators.
She is a multi category utility vessel with an onboard deck crane and a carrying capacity of up to 35 tonnes, making her ideal for marine civil engineering projects at sea.
The tug also boasts air-conditioned living spaces for a crew of six people, with three double cabins, a galley, a mess and an onboard sewage treatment plant.
Her presence in the bay has caused a lot of questions, especially as she been a repeat visitor, occasionally working at night under floodlights.
In Swanage Bay, the Jenny D loads up rock from the French ship
The work has continued at night
Making use of sheltered Swanage Bay, the Jenny D is part of a £10 million operation to rebuild a groyne at Hengistbury Head
A threat to Studland Bay
Depending on prevailing winds, the Jenny D shelters at Cowes on the Isle of Wight or returns to the protected waters of Swanage Bay to collect a new consignment of rock from Norway or France.
Meanwhile, the shore based excavators then load the rock into articulated dumper trucks and take it along the beach to Hengistbury’s Long Groyne, where work takes place to update the 1930s sea defence.
Although the new groyne will be much the same length as the old one at just over 150 metres, it will be one and a half metres taller and twice as wide, to cope with a predicted sea level rise of a metre in the next century.
But without the groyne, which was already being breached by winter storms, there would be rapid erosion of cliffs, loss of beaches and a threat to some 6,000 homes, with effects being felt throughout Christchurch Bay, Poole Bay and Studland Bay.
The handover of rock taking place in Swanage Bay before the Jenny D heads over to Hengistbury
Work underway at Hengistbury Head to rebuild the groyne Inset: BCP portfolio holder for climate response, Andy Hadley
“Long Groyne is beyond the end of its life”
Bournemouth Christchurch and Poole Council (BCP) portfolio holder for climate response and the environment, councillor Andy Hadley, said:
“Modelling has shown that the sand and gravel moves around the bays in a circular motion and if we don’t intervene then the process will erode away what we know as Hengistbury Head and also some of the cliffs all the way along the beach from Durlston to Highcliffe.
“The Long Groyne plays a significant role in reducing the risks of coastal flooding and erosion from the Purbecks to Hurst Spit, and it’s great to see the work starting on site.
“But the current Long Groyne is beyond the end of its life and during storm events is frequently submerged by sea waves, compromising its performance as a coastal defence structure.
“These works will ensure our coastline is more resilient to projected sea level rise and the increasing number of storm events predicted over the next 100 years.”
Beach huts at Mudeford Sandbank, costing up to £500,000 each, would be first casualties of the encroaching sea
“Long term loss of land across Purbeck”
Councillor Andy Hadley added:
“If the rate of erosion wasn’t stopped, the long-term loss of land would extend across Purbeck, Bournemouth, Christchurch, Poole and the New Forest, including damage to infrastructure and thousands of properties.
“Mudeford Sandbank could be breached, creating further inlets to Christchurch Harbour and both Poole Bay and Christchurch Bay would weaken and eventually become one bay.
“The upgrade will also enable us to deliver innovative environmental enhancements to improve the natural environment.”
The reef cubes and hexagonal honeycombed blocks are ready to be placed when the new groyne is finished
The new marine habitat should be thriving within two years
New habitat for marine species
Over the next six months, before the project is finished in October 2024, the core of the groyne is being reshaped with voids being filled in with smaller rocks being brought over from Norway.
New rock armour is then being built on top of the existing structure, raising it in height by 1.5 metres and using rocks of six to ten tonnes brought over from France, chosen for their resistance to erosion.
In the lee of the groyne, reef cubes and honeycombed blocks are being installed to provide a habitat for marine species as well as an extra level of coastal defence.
They are perfectly designed for sea creatures of various sizes to make homes in and become quickly established shortly after being installed.
One of the BCP artificial ponds, built to the perfect specifications for natterjack toads to breed in
Saving the natterjack toad
A spokesperson for BCP Council said:
“The upgraded Long Groyne design will be taller to allow for increased storm events and predicted sea level rise, wider to provide additional stability in this exposed location and covered entirely in rock, using natural quarry stone from France and Norway, chosen for its durability.
“Material from the existing structure will be recycled wherever possible to avoid having to send material to landfill, and to minimise the amount of new rock required.”
And part of the £10 million budget from BCP will also go towards building new pools inland at Hengistbury Head which will be ideal environments for the endangered natterjack toad.
This scheme was highlighted on Springwatch in spring 2024, with Iolo Williams filming live from the Site of Special Scientific Interest in Dorset, who found toad burrows in the sandy cliffs.
Iolo Williams, on a search for natterjack toad burrows at Hengistbury Head
Iolo Williams demonstrates for the cameras how toad burrows keep the amphibians safe and cool
“A fine balance and difficult to manage”
Iolo Williams said:
“Natterjacks are a very, very rare nocturnal toad which emerge in early spring when the temperature is consistently above seven degrees centigrade, about four to eight weeks later than the common toad.
“They use these burrows through the summer to hide away from the sun. We have filmed them here, but they are so rare that you need to have a licence to film them and we believe that we were the first in the UK to film their emergence from the burrow.
“The temperature in these burrows is remarkably constant – even when the sun heats the surface of the sand to a scorching 60 degrees centigrade, it remains at a constant 24 degrees in the burrow, and in prolonged dry periods the toads can stay in their burrows for weeks on end.
“But they also need ponds to breed in, which need to have warm water – and that means shallow ponds which absorb the sun’s heat better, but not so shallow that they dry up. It’s a fine balance and very difficult to manage, which is why they need help.”
Further information
- Read more about the construction project at Hengistbury Head
