Beach Replenishment Winter 2005/06

Last update: 09 February 2008

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Poole Bay & Swanage Beach Replenishment

During the winter of 2005/2006 approximately 1.1 million cubic metres (1.65 million metric tonnes) of sand dredged from Poole Harbour channels and approaches was used to replenish beaches at Swanage, Poole & Bournemouth to protect them from erosion.

Dredgers pumped ashore 24 hours a day, 7 days a week, including Christmas and the New Year.

The contractors arrived on 22nd November 2005, and the beach at Swanage was replenished first;
Work at Poole started in December and was completed on Monday, 16th January 2006;
The Bournemouth Beach Replenishment Scheme (BIS4.1) replenished beaches between Hengistbury Head and Boscombe between 18th January - 18th March.

A second Bournemouth contract during winter 2006/07 (known as BIS4.2), replenished beaches between Boscombe Pier and the Borough Boundary with Poole.

The Need for Beach Replenishment

The standard of flood and coast protection at Poole Bay and Swanage depends mainly on the level and width of its beaches.

Construction of seawalls over the course of the last century put a stop to the natural supply of beach material from cliff erosion and it is necessary to occasionally replace beach material lost to longshore transport driven by wind and waves.

In the 30 years between 1970-2000 almost 2 million m³ of sand was used to replenish the beaches at Bournemouth and Poole. Since the predominant direction of longshore transport at Poole Bay is from west to east, new sand gradually feeds the beaches at Southbourne and Hengistbury Head to the east, and beyond into Christchurch Bay.

The on-going need for beach replenishment was first identified in the Poole and Christchurch Shoreline Management Plan 1999, and a subsequent report by Halcrow (2004) suggests that a further 3 million m³will be required over the next 50 years in order to maintain protective beach levels and widths.

Availability of Sand

Purchasing and transporting sand from commercial sources (from licensed dredging sites south of the Isle of Wight or at the Thames Estuary) can be very expensive. So when an opportunity arises to utilise sand from local dredging operations it saves Defra - and consequently the taxpayer - a considerable sum of money.

Poole Harbour Commissioners (PHC) dredged 2 million m³ of material from Poole Harbour Channels and Approaches, of which about 1.1 million m³ was suitable for beach replenishment.

The remainder of the material (silts and clays) were disposed of under licence at an offshore disposal ground located off Swanage. PHC have utilised this site for the disposal of dredged material from Poole Harbour for more than 50 years.

The dredging was necessary to deepen the harbour approach and channels from the present 6m to 7.5m below Chart Datum and by doing so secure the long-term viability of the Port. It was also necessary to widen the Middle Ship Channel to 100m.

Primarily, the deeper approach channel was required to meet the needs of modern ferries, the majority of which now have a minimum draft of over 6.5 metres.

In 2003 Brittany Ferries advised Poole Harbour Commissioners that they would be withdrawing the freight ferry M/V “Coutances” from the Poole/Cherbourg service due to the age of the vessel. The “Coutances” will be replaced with a vessel built to carry both freight and passengers. It will be of a similar design but larger than the M/V “Barfleur” that also operates out of Poole.

Environmental Considerations

Poole Harbour is internationally recognised as a sensitive environment in terms of wildlife, geology and landscape. It is also important for recreational boating and supports a significant fishing industry.

In view of this, and in accordance with the Harbour Works Regulations 1999, a full Environmental Impact Assessment (EIA) was carried out by Posford Haskoning on behalf of PHC and the local authorities. The document is available to download from the PHC website (see ‘Sources of Further Information’ below).

The EIA study and other extensive assessments of the likely effects of the channel deepening on, for instance, habitats, archaeology and water quality, has resulted in one of the most significant investigations ever undertaken into the morphology of Poole Harbour.

Replenishment Operations

The 1.1 million m³ of dredged material suitable for beach replenishment was distributed as follows:

	Swanage beach - 90,000 m³
	Poole beaches between Shore Road and Branksome Dene Chine - 450,000 m³
	Bournemouth beaches between Boscombe Pier and Double Dykes - 600,000 m³

The dredging and replenishment contract was awarded to Van Oord UK Ltd, a long established and reputable company specialising in dredging, coastal protection works and maritime engineering.

Dredgers took sand from Poole Harbour’s channels and approaches to close by the beach to be replenished.

Click image to enlarge map

The waters of Poole Bay are shallow and it was necessary to pump the sand ashore through a 750m long pipeline (500m at Bournemouth) called a sinkerline. This was achieved by mixing the sand with a considerable amount of water; as the mixture exits the pipe the water flows back to the sea leaving the sand behind. Bulldozers then levelled the beach [more].

Initially the pumped sand appeared to be darker than that forming the current beach, but very soon lightened to a normal colour with exposure to oxygen and daylight.

In the first few weeks small ledges or cliffs were cut into the front of the beach by wave action as it sorted the new material, but these soon disappeared as the sand was moved by wind and waves into a natural beach profile.

During replenishment beaches were regularly inspected for any unsuitable material.

In the interests of health and safety it was necessary to close short sections of the beach when the sand was pumped ashore, and being moved by heavy plant. The promenades remained open at all times.

Funding the Project

The estimated £5 million cost for beach replenishment was funded by the government Department for Environment, Food and Rural Affairs (Defra). PHC funded the majority of the dredging project, with Defra paying a proportion of the cost of dredging the sand used for replenishment.

The saving made by utilising locally dredged sand for beach replenishment is estimated to be between £8 million and £15 million.

Archaeology

A wreck (believed to be 16^th Century) was discovered during the EIA study for the dredging project, located on the edge of the proposed dredge area.

English Heritage was informed and the wreck site is now a designated area of national importance.

Whilst the wreck site and its immediate surroundings were undisturbed during the dredging operation, there is a chance that some material of archaeological importance may have been pumped onto the beach [more].

Sources of Further Information:

Poole & Christchurch Bays Shoreline Management Plan Review (SMP2) 2007-2010 at www.twobays.net
Poole Coast Protection Works 1996-2007 at www.boroughofpoole.com
Bournemouth Beach Replenishment information at www.bournemouth.gov.uk
Swanage Beach Replenishment information at www.purbeck-dc.gov.uk
Notices to Mariners will be published as work progresses at www.phc.co.uk
The Halcrow (2004) report Poole Bay & Harbour Strategy Study – Assessment of Flood & Coast Defence Options can be downloaded from www.bournemouth.gov.uk
The Environmental Impact Assessment for the Poole Harbour Approach Channel Deepening and Beneficial Use Scheme can be downloaded from www.phc.co.uk
UK Flood & Coastal Erosion Risk Management policy information is available from www.defra.gov.uk
More about the sediment transport and shoreline management of central southern England is available from www.scopac.org.uk
South-East England coastal process monitoring data can be found at www.channelcoast.org

Re web content or photos contact: Sarah Austin