Swanage Case Study

• Swanage is in the South East of the UK in Dorset
• Sandy bay facing east and protected from major SW storms and winds.
• In southern part = low cliffs and banks of upper Purbeck Limestone, shale – largely built over.
• In northern part = cliff sections of Weldon strata, soft yellowish and brownish sands, and clay.
• Greater erosion of sand and clay than of the limestone and shale.
• LSD = S-N
• 18 groynes of the beach.
• Why protect this area:

  -5,300 dwellings in Swanage and a population of over 10,000+ and growing.

  -Wide range of attractions, historical trails, and exhibitions -European blue flag beach status.

  -Mowlem theatre, opened in 1967, seats 400. 200 films each year.

  -RNLI station and coastguard Waton house, oldest and busiest.

  -Series of services provided e.g. fire, schools, gyms, and banks.

  -Isle of Purbeck part of Dorset and East Devon coast world heritage site – outstanding natural beauty.
• Zone 1 of the SMP: At Sheps hollow there is no active intervention = area behind is low value land – farmland. The fossils found within the geology here are higher value.
• Zone 2 of the SMP: Inside Swanage Bay, they are holding the lone with an active intervention approach due to high land value. This includes groynes, cliff stabilisation and beach replenishment.
• Zone 3 of the SMP: Southern end of Swanage beach, they are holding the line. Only hard engineering = sea wall as there is the natural defence of Peverill point.
• Groynes = Most cost effective method, replace the 1930s groynes. 18 of them have been replaced in 2005. Reduces LSD and absorbs energy.

  Terminal groyne syndrome = build up of sediment as less LSD, can result in erosion in other locations.
• Cliff stabilisation and drainage = Reduces risk of mass movement and less excess water. Rip rap is at the base of cliff.
• Sea wall = Built in 1920s, provides promenade as well as a barrier to wave attack. Regularly maintained.
• Beach replenishment = In Nov. 2005, 90,000m3 of sand was deposited on the beach. Replenishment of 40,000m3 of sand every 20yrs. Works with groynes. Completed 2006 June. Cost = £2.2 million.
• 1920s –sea wall and groynes to south of bay put in place (Victorian). Further coastal defence works -extension of the sea wall and timber groynes – starved beach in N.
• 1980s -rock armour was put in place at base of cliffs and groundwater drained from rocks.
• 1990s -review of current defences – develop long term plans – develop best plant, retain sediment, and dissipate energy.
• 2005 -replacement of 1930s groynes and beach replenishment. 18 timber groynes. November = 90,000m3 of sand was deposited.
• 2006 -works completed in June = £2.2 million. Beach needed to be recharged around 40,000m3 every 20years. Current plans to protect beach are in place and supported until 2055 (50yr cycle). Aim to protect as if unaddressed damage to local properties and roads up to 2055 - £20million +
• 2023-25 -next beach recharge.
• 2040-41 -plans to undertake a capital programme to replace groynes if funded.

  Considerations = buried beach rip rap or sea wall drained for protection.
• 2055 - End of SMP, may not be suitable to protect, different approach may be needed.