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Bournemouth Groynes New for Old

Bournemouth has implemented a coastal protection and beach managment scheme for the whole of this coastline. New Bournemouth groynes are currently being built west of Hengistbury Head and in the eastern end of Soutbourne Beach. This section of the work, replacing worn out groynes that were build 25 years ago willwill be finished well before the holiday season. The current Beach Managment scheme though is slated to last until 2032.

Longshore Drift

The groynes purpose is to limit the loss of sand from the beaches. Groynes inhibit longshore drift (the movement of sand along the beach by wave and tide action).  In Bournemouth Bay the prevailing wave action moves sand eastward from about Durley Chine and also westward from Durley Chine towards Poole Harbour.

 

Bournemouth Groynes -First a deep hole is drilled
First a deep hole is drilled – up to 10m deep

Longshore Drift has in the  past reduced Fishermans Walk and Southbourne Beach .  The groynes also protect the vulnerable western end of Hengistbury Head from rapid beach loss.

Transitional Groyne Field

The Bournemouth groynes on Southbourne beach are packed tighter than further west. As you go eastwards along Southbourne beach they get closer together. This area forms what is known as a transitional groyne field. The purpose is to slowly reduce the effect of the groynes until an undefended beach ( middle of Hengistbury Head Beach) is reached. This helps to protect the undefended beach from sediment starvation.

The groynes on Southbourne beach are mainly made from wood though a number of other groynes in this area are made from stone.

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Wooden groynes are (relatively speaking) a cheap method of controlling beach loss. Coupled with beach nourishment (that took place a couple of years ago on this beach) it is hoped that the new groynes will reduce and control the loss of sand from the eastern Bournemouth beaches while still maintaing an adaquate supply of sand to prevent sediment starvation from Hengistbury Head and further east.

The Bournemouth groynes being built are closed groynes and are built from a series of uprights which are then boarded. When complete they present a solid wooden wall at right angles to the shoreline.

Building a Groyne

A groyne is built by first drilling a deep hole using a specialist drill about 15 meters long. The upright is then placed in the hole and “shaken” down as far as possible. The final visible top of a groyne pillar may only be a meter or two above the beach while the actual pillar is perhap up to 12 meters in length.

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The majority of the pillar is deep in the sand. When the pillars have been placed, they may be pile driven and finally cut to present a uniform set of posts onto which the wooden wall is mounted. The wooden wall is made from long lengths of timber. They are attached with stainless steel bolts. Usually the wooden wall is at least 10cm thick and sometimes double skinned. All wood used is invariably imported hard wood. A groyne will typically have a design life of about 20 – 25 years.

More information on Bournemouth beach managment can be found On This Link

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