Current Project
Hengistbury Head Long Groyne works 2021-2024
As part of a 17-year Beach Management Scheme, the Long Groyne will be repaired & upgraded between April – October 2024
Lead Authority
BCP Council
Working with
Project start date
22 November 2021
Last Updated
19 May 2024
The works area at Hengistbury Head
What’s happening?
Construction is underway at Hengistbury Head. Our contractors are working with the tides around the clock. Rock deliveries are taking place until the end of June…
- Coaster ships laden with rock arrive in Poole Bay. The rock is transferred from Coaster to Barge.
- At high tide, the Barge places the rock as close to Hengistbury Head beach as possible.
- At low tide, land-based excavators retrieve the rock, load it into articulated dumper trucks and move it to the Long Groyne.
Access to the beach remains open. For your safety, please follow signage and keep your distance from large plant & machinery operating in the area. Dogs should be kept on leads. Marked pedestrian routes help you avoid walking across the environmentally protected Sand Dunes.
© Terry S NCI Coastwatch Hengistbury Head
Project Progress
- The old groyne is being dismantled in sections, with the material sorted to be re-used in the core of the upgraded design.
- New rock is being shipped in by sea.
- Deliveries of smaller rock (from Norway) were completed during the first two weeks of May.
- Deliveries of larger rock (from France on the coaster ship Liamare) began on 16 May and will continue until the end of June. Each piece of rock weighs between 6-10 tonnes.
- Local Notice to Mariners No. 10/2024 (pdf) was issued by Poole Harbour Commissioners.
The process
Our video showcase below demonstrates the process of moving 6-10 tonne rocks from the barge and along the beach to the construction site. The coaster ship that brings rock from France can be seen in the distance at the start of the first video:
The barge delivers the core rock onto the beach
The barge delivers the core rock onto the beach
The rock is loaded onto articulated trucks
The rock is loaded onto articulated trucks
The trucks are escorted 900m metres East to the Hengistbury Head Long Groyne
The trucks are escorted 900m metres East to the Hengistbury Head Long Groyne
Construction
- The existing groyne will be broken up in short sections at a time
- The old rock will be shaped into a new core base
- New rock armour to be placed on top in the same footprint as the existing groyne.
Cross section of the upgraded design
The upgraded long groyne design:
- Will use the same alignment and length as the existing groyne (approximately 150 metres).
- Will be 1.5 metres taller along its crest than the existing groyne to allow for increased storm events and predicted sea level rise.
- Will be wider than the existing groyne to provide additional stability in this exposed location.
- Will be covered entirely in rock, using a natural quarry stone (armour) from France & Norway, chosen for its durability.
- Will use larger rocks (6 – 10 tonnes) than those existing, to cope with the exposed location of the structure and the expected wave conditions.
- Material from the existing structure will be recycled wherever possible to avoid having to send material to landfill, and to minimise the amount to new rock required.
- Floating groyne markers will be placed at the sea end to aid navigation.
Project Overview
The long groyne at Hengistbury Head plays a critical role in reducing coastal erosion in Poole Bay and is a stabilising feature for Christchurch Bay. However, during storm events it is regularly submerged and its current condition means it is unable to continue to perform effectively, particularly with the additional threat of sea level rise.
A detailed inspection of the structure in 2019 revealed the groyne to be in very poor condition. Subsequent ground investigations and underwater surveys through 2021 & 2022 helped us prepare for the significant works required to protect the coastline from sea level rise over the next 100 years.
The project is explained by Richard Slee, ITV News
Video courtesy ITV Meridian, 20th July 2023
Why the works are needed
If we did nothing to repair or upgrade the long groyne, then;
- The rate of erosion would rapidly increase at Hengistbury Head, resulting in the loss of beach followed by erosion of the cliffs;
- 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;
- Both Poole Bay and Christchurch Bay would weaken and eventually become one bay.
Environmental enhancements
Hengistbury Head is a Scheduled Monument and site of international archaeological importance • a Site of Special Scientific Interest (SSSI) • Local Nature Reserve (LNR) • Special Area of Conservation (SAC) • Environmentally Sensitive Area (ESA) • Site of Nature Conservation Interest (SNCI) • Special Protection Area (SPA) and a Ramsar site.
We are improving the marine habitat by incorporating a number of specially designed structures:
Examples of another ReefSystems project (before and after installation):
We are also supporting the conservation of Natterjack Toads within Hengistbury Head Nature Reserve through the funding of a specialised pond.
Project background
A detailed inspection of the structure in 2019 (using sonar and laser equipment) revealed it to be in a very poor condition. Several voids were discovered in the foundations below the waterline, with an associated risk of localised collapse, so access was prohibited for safety reasons.
Ground Investigations, summer 2022
Underwater surveys mapped out the depth and land beneath the surface while borehole investigations revealed the composition of the ground below the structure. Boreholes up to 20m in depth were collected from both land and sea using a rotary drilling rig (on land) and a sea-based jack-up barge, as shown.
All data collected will help refine the most efficient and effective design for the new groyne structure to ensure the continued stability of the coastline, while protecting it from sea level rise over the next 100 years.
The Sandpiper jack-up barge worked on site during August, taking boreholes from five seabed locations immediately beside the long groyne.
The purpose of the long groyne
The Hengistbury Head groyne was constructed between 1937–1939 to protect the headland. It is now well recognised as an “anchor point” that is critical to stabilising and controlling coastal erosion in both Poole Bay and Christchurch Bay. Along with the beach and other shoreline structures, the long groyne helps to protect local communities and infrastructure.
Without it, beach material would rapidly wash away (estimated with in a year), and the cliffs could start to erode again. This would eventually progress to the sea breaching into Christchurch Harbour via locations at Double Dykes and Mudeford Sandbank. The impacts could extend to the Purbecks and New Forest.
The current national policy for most of this populated coastal frontage is ‘hold the line’. This means that existing coastal defences should be maintained, upgraded or replaced in their current position, where funding permits, to reduce the risk of coastal flooding and erosion.
More about coastal defence policies at Poole & Christchurch Bays Shoreline Management Plan
The angle of the long groyne
In recent years, there have been proposals to alter the angle of the groyne, including potentially creating new surfing opportunities. The proposal has been reported on in the local media although it cannot be supported for important reasons, which are summarised as follows:
- It is crucial that the long groyne continues in its main function to limit long term coastal erosion in Poole Bay and Christchurch Bay.
- Coast protection is manageable under its existing configuration as set out in strategic policy (i.e. Poole & Christchurch Bays SMP) which is economically justified*.
- For the last 50+ years the long groyne has profoundly influenced the transit and deposition of beach material from Poole Bay into Christchurch Bay. The volume of beach material from Avon Beach and Highcliffe has then been managed by local beach recycling, when required – for example Christchurch Beach Recycling and Rock Groyne Repairs, spring 2021.
- A change in the angle of the groyne would generate new and unknown hydrodynamics that would affect the entrance to Christchurch Harbour.
- Modelling and data underlines layout changes as being high-risk with high uncertainty (in terms of being able to predict long term implications). Layout changes could trigger wide-reaching impacts on interlinked coastal protection assets across Dorset and into Hampshire.
- Hengistbury Head and its surrounding areas have many environmental designations (both national and international) which must be carefully adhered to. Additionally, the area falls into a Coastal Nature Park, as supported by other BCP Council strategies.
- The legacy council in Bournemouth invested in Boscombe as a surf-based tourism destination. It is supported by local facilities including year-round lifeguard cover, car-parking, toilets, showers, food outlets and accommodation. Hengistbury Head does not have the same offer and is in a more remote, potentially more dangerous location; exposed to swell waves and ebb currents from the Harbour.
* The Environment Agency is responsible for the approval and allocation of all coastal capital funding in England. Capital investment schemes go through an appraisal & approval process both on technical and financial grounds to secure grant funding. To be considered for funding schemes should be in line with the strategic direction set out in the SMP or strategy; they must also contribute to outcome measures and be on the sanctioned list.
Construction of Hengistbury Head Long Groyne was completed in 1939. Its location has enabled beach material to accumulate around the headland, reducing erosion to the cliff face.
Groynes on Mudeford Sandbank were added from the 1980s to the early 2000s and have further helped stabilise the Sandbank in its current position.
Constructing the long groyne 1937-39, photo gallery
26th January 1937 26th January 1937 8th July 1937 8th July 1937 23rd August 1937 23rd August 1937 23rd August 1937 21st September 1937 21st September 1937 21st September 1937 20th October 1937 20th October 1937 19th November 1937 19th November 1937 16th March 1938 16th March 1938 14th April 1938 14th April 1938 15th May 1938 15th May 1938 2nd June 1938 13th August 1938 10th October 1938 10th October 1938 10th October 1938 10th October 1938 24th October 1938 1st June 1939 1st June 1939 1st June 1939 1st June 1939 1st June 1939 1st June 1939
26th January 1937
26th January 1937
8th July 1937
8th July 1937
23rd August 1937
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21st September 1937
21st September 1937
21st September 1937
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14th April 1938
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2nd June 1938
13th August 1938
10th October 1938
10th October 1938
10th October 1938
10th October 1938
24th October 1938
1st June 1939
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1st June 1939