The Need for Groynes, Rock Groyne Safety & Ecology

The whole of Poole Bay from Sandbanks to Hengistbury Head is an eroding coastline.  The cliffs and beach have been eroding since the last ice age, 8000 years ago.  The current rate of erosion is approximately one meter per year.

In relatively recent history much of the cliff erosion has been prevented by the construction of sea walls and a promenade.  However the beach itself is still eroding which has resulted in a lowering of beach levels against the sea wall.  Should this action be left unchecked beach levels will continue to drop until there is no dry beach left in front of the sea walls.  The sea walls could be undermined, and ultimately collapse, through constant wave action.  If the integrity of the sea wall and promenade is lost then the cliffs will start eroding again, resulting in a threat to cliff top infrastructure and properties.  To combat this problem the two councils responsible for the coast protection in Poole Bay (Poole and Bournemouth) have traditionally employed the construction of groynes and beach replenishment.  To maintain the coast into the future the Councils have established a coast protection policy which involves 'holding the line' (i.e. resist rather than permit coastal erosion).   The policy is set in the existing Shoreline Management Plan (SMP1), currently under review [more]. 

The need for beach control was identified in the Poole Bay Strategy Study (2004), which recommended a programme of beach renourishment together with the construction of defence structures (probably rock groynes).  For the Poole frontage this has been subsequently reinforced in two recent studies undertaken by HR Wallingford which initially considered over 20 options.  The preferred option is to construct 5 groynes at the eastern end of the Poole section of the bay.

Rock Groynes & Safety

Rock groynes are common structures around the coast of the UK and abroad.  It has been demonstrated in Poole and elsewhere that rock groynes are an appropriate and safe method of coast protection .

We acknowledge however, that some people may have concerns about the safety of people swimming near them.  For example with the existing groynes at Sandbanks there were some concerns that swimmers may graze skin against rock, so the Council moved the swim zones to reduce this minor risk. 

There were also concerns about the strong currents near the Harbour entrance in response to which we have now placed signs to warn swimmers of potential danger.

Whilst these issues may not arise with the new groynes at the Eastern end of the beach, the Council has consulted with the Royal National Lifeboat Institute (RNLI), who provide a Lifeguard Service for the Council’s beaches, in order to reduce any potential risk.  We will continue to work closely with the RNLI to identify and minimise any potential risks with the new groynes and to ensure that any new swim zones, safety equipment or operational procedures will be established as required.

Overall, the Council has received very positive feedback about the rock groynes at Sandbanks from beach users who enjoy being able to walk out seawards along the top of the groynes and we hope that this will also be the case with the new groynes.

Rock Groyne Ecology

Since the construction of rock groynes at Sandbanks various ecological benefits have become apparent as they became colonised firstly by lower plants such as algae and lichens.

Barnacles and seaweeds established themselves after a few years, followed by the limpets, anemones, crabs and other life forms that are able to adapt to the ever-changing tidal conditions of rocky shorelines. 

In this way, our rock groynes add to the diversity of beach life, and provide inspiration for a new generation of wildlife enthusiasts.

The Project • Project Diary • Project Photos • Proven Need • Construction