Seabed investigations and surveys have started at Hengistbury Head to prepare for the upgrade of a long groyne structure, which is critical for controlling coastal erosion in Poole Bay and Christchurch Bay.

The Hengistbury Head long groyne was closed to the public for safety reasons following a detailed inspection of the structure using sonar and laser equipment in 2019. The structure was revealed to be in a very poor condition.

Several voids were discovered in the foundations below the waterline, with an associated risk of localised collapse. The groyne is also regularly submerged in water.

Following ground investigations in November and December of 2021, Bournemouth, Christchurch and Poole Council is continuing the work this summer.

While land-based ground investigations have already been completed, further underwater surveys and investigations will take place over the next three weeks.

The seabed investigations will be carried out from Lankelma’s Sandpiper jack-up barge using a rotary drilling rig. The barge arrived on site in early August.

The borehole samples will be taken from five locations around the groyne.

The activity around the long groyne also includes underwater surveys to map out the depth and land beneath the surface, while the borehole investigations will show the composition of the ground below the structure.

All the borehole samples, both from land and sea, are up to 20m in depth.

The collected data will help the council’s Flood & Coastal Erosion Risk Management Team refine the most efficient and effective design for the new long groyne structure to ensure the continued stability of the coastline, while protecting it from sea level rise over the next 100 years.

Councillor Mark Anderson, portfolio holder for environment and place, said: “The 83 year old structure has been critical in stabilising and controlling coastal erosion in both Poole Bay and Christchurch Bay.

“Along with the beach and other shoreline structures, the long groyne helps protect local communities and infrastructure, so it is vital we upgrade it so it can continue to perform effectively, particularly with the additional threat of sea level rise and an increasing number of storm events.

“Without the long groyne, beach material would rapidly wash away, and the cliffs could start to erode again. This would eventually lead to the sea breaching Christchurch Harbour at Double Dykes and Mudeford Sandbank and the impacts could extend to the Purbecks and New Forest.”

The works form part of the Poole Bay Beach Management Scheme, which is running between 2015-2032. It is estimated that the entire scheme will cost in the region of £50M, with the majority funded by the Environment Agency.

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