Swanage Erosion Case Study

Durlston Bay / Studland Bay / Poole Harbour / Poole Bay / Christchurch Harbour / Christchurch Bay / Hurst Spit / Swanage Bay

Swanage Bay (SWA)

Peveril Point to Handfast Point

The southern half of this frontage includes Swanage Bay and the town of Swanage.  This is a popular recreational area for beach users, diving, fishing and sailing.   

The town has been developed on soft eroding cliffs and annual falls & slips have left some properties, such as The Pines Hotel, very close to the cliff top. 

Timber groynes were first constructed in 1925; eighteen of them were reconstructed in 2005/06 at the same time as the beach was replenished - an operation that made beneficial use of sediment dredged during essential works to Poole Harbour's port and approach channels (see www.poolebay.net for further information). 

The extreme southern part of this frontage includes Swanage Pier, a sewage treatment works and coastguard station.  Moving north beyond the groynes the coast is undeveloped and undefended.  From Ballard Point through to Handfast Point the coastline is characterised by actively eroding vegetated chalk sea cliffs.  This area is best known for the stacks, caves and chalk arches with "Old Harry Rocks" at the northern most point.

The coastline of the bay is of national and international ecological and geological importance (the occasional dinosaur remains have been found in the alluvial chalk strata) and the landscape is of high intrinsic value.  A bowl barrow and two round barrows (Scheduled Monuments) lie east of Ballard Down, close to the cliff edge.

The frontage is highly designated:

Dorset & East Devon World Heritage Site

Isle of Portland to Studland Cliffs SAC

Studland Cliffs SSSI

Purbeck Ridge SSSI

West Dorset Heritage Coast

Dorset AONB

 

AONB - Area of Outstanding Natural Beauty.  SAC - Special Area of Conservation.  SSSI - Site of Special Scientific Interest

Swanage Bay faces east and is protected by Peveril Point from major southwesterly storms.  The Isle of Wight provides a degree of shelter from easterly storms. 

Construction of the outfall jetty in 1993, at the southern end of the bay, obstructed sediment transport and resulted in falling beach levels immediately to the north.  Although this was offset by considerable accumulation of beach material to the south, the 2005/06 groyne replacement and beach recharge project has since addressed the problem. 

Beach modelling has shown that the effect of the outfall structure as a groyne precludes the need to replace the two groynes to the south of the outfall jetty which were removed during the recharge scheme.

Coastal management issues here include:

  • The potential impact of any coastal defence works on Swanage's tourism, inshore fisheries, offshore wrecks, archaeological value and the aesthetic and landscape quality of the coastline.

In SMP1 the shoreline of Swanage Bay is divided into 5 Management Units:

Process Unit

Management

Unit

Description

SWA

SWA1

Peveril Point to Swanage Pier

 

SWA2

Swanage Pier to Outfall Jetty

 

SWA3

Outfall Jetty to Sheps Hollow

 

SWA4

Sheps Hollow to Ballard Point

 

SWA5

Ballard Point to Handfast Point

Administrative Responsibility

Purbeck District Council

Headlands and bays

Bay and headland in New Zealand

Headlands are formed when the sea attacks a section of coast with alternating bands of hard and soft rock.

The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays.

Geology is the study of the types of rocks that make up the Earth's crust. Coastlines where the geology alternates between strata (or bands) of hard rock and soft rock are called discordant coastlines. A concordant coastline has the same type of rock along its length. Concordant coastlines tend to have fewer bays and headlands.

Discordant and concordant coasts in Dorset

Along the coastline of the Isle of Purbeck in Dorset, there are both discordant and concordant coastlines. The discordant coastline has been formed into Studland Bay (soft rock), Ballard Point (hard rock), Swanage Bay (soft rock) and Durlston Head (hard rock). After Durlston Head, the strata stop alternating and the coastline is made up of hard rock. This concordant coast has fewer features.

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