Current projects
Hengistbury Head Long Groyne works 2021-24Part of a 17-year Beach Management Scheme to protect our coastal frontages, making them more climate resilient.
LEAD AUTHORITY
BCP Council
WORKING WITH
START DATE
22 November 2021
LATEST UPDATE
21 September 2023
Hengistbury Head Long Groyne plays a crucial role in shoreline stability.
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 (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.
Planning permission was granted on 21st September for the repair and upgrade Hengistbury Head Long Groyne; details can be found at the BCP Planning Portal – Application No 7-2023-15059-Y.
Project timeline:
Video courtesy ITV Meridian, 20th July 2023
Features of the proposed design
The upgraded groyne design is:
- Using the same alignment and length as the existing long groyne (approximately 150 metres).
- Raised 1.5 metres in height along its crest to allow for increased storm events and predicted sea level rise.
- Wider than the existing groyne, due to its increased height and the side slope needed to ensure the structure’s stability and ability to absorb wave energy.
- Covered entirely in rock, using a natural quarry stone (armour), chosen for its durability.
- Using larger rocks (6 – 10 tonnes) than those existing, to cope with the exposed location of the structure and the expected wave conditions.
- Recycling material from the existing site to avoid sending material to landfill wherever possible.
- Placing floating markers at the sea end to aid navigation.
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 considerations
In developing our proposed design, we’ve carefully considered that Hengistbury Head is a:
- Scheduled Monument and site of international archaeological importance
- Site of Special Scientific Interest
- Local Nature Reserve
- Special Area of Conservation
- Environmental Sensitive Area
- Site of Nature Conservation Interest
- Special Protection Area
- Ramsar site
Environmental enhancements
Specially designed structures, similar to those shown below (before and after installation), will be incorporated into the design to provide habitat for a range of marine species. The project will also support 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
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
The proposed project site layout 2024
Subject to our planning application being granted, works are scheduled to take place over spring/summer 2024
We’d like to remind everyone that the long groyne remains closed for safety reasons
Sea Safety
Please do not put yourself in danger by climbing onto or fishing from the long groyne, even at low tide, it is unsafe.
If you are fishing around the coastline the RNLI advise you to plan your trip. 
Tides and currents can be hard to predict. Even if the sea is relatively calm when you start out, a swell can quickly materialise producing rogue waves which, if in an exposed location, could drag you out to sea. Please respect the water and stay safe:
- wear a life jacket,
- carry a means of calling for help,
- check the weather forecast,
- tell someone where you are going and what time you will be back.
Read more about staying safe while you’re out fishing at: www.rnli.org