Coastal Defence These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates that the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 24 © Boardworks Ltd 2005 Learning objectives Why does cliff recession occur? What are the effects of cliff recession? How can the coastline be protected? What are the disadvantages of coastal protection? What is the best method of coastal protection? 2 of 24 © Boardworks Ltd 2005 Why does cliff recession occur? 3 of 24 © Boardworks Ltd 2005 Why does cliff recession occur? What are the two main causes of this cliff collapsing? 4 of 24 © Boardworks Ltd 2005 Learning objectives Why does cliff recession occur? What are the effects of cliff recession? How can the coastline be protected? What are the disadvantages of coastal protection? What is the best method of coastal protection? 5 of 24 © Boardworks Ltd 2005 What are the effects of cliff recession? 6 of 24 © Boardworks Ltd 2005 Learning objectives Why does cliff recession occur? What are the effects of cliff recession? How can the coastline be protected? What are the disadvantages of coastal protection? What is the best method of coastal protection? 7 of 24 © Boardworks Ltd 2005 How can the coastline be protected? 8 of 24 © Boardworks Ltd 2005 How do groynes work? Groynes trap the sand which is carried along the coast by longshore drift. The sand acts as a natural protection against the force of the waves. The waves break onto the beach and not the cliffs. 9 of 24 © Boardworks Ltd 2005 Managed Retreat Managed retreat is also known as managed realignment. It involves breaching an existing coastal defence, such as a sea wall, and allowing the land behind to be flooded. This land is then left to be colonised by saltmarsh vegetation. When established, the vegetation disperses wave energy, reduces erosion rates and provides new habitats. The first attempt at managed retreat in the UK was on Northey Island, located in the Blackwater Estuary in Essex. 10 of 24 © Boardworks Ltd 2005 How can the coastline be protected? Hard engineering techniques aim to stop coastal processes from occurring. Soft engineering methods try to work with nature to protect the coast. 11 of 24 © Boardworks Ltd 2005 Swanage Bay Study the photo and map extract. Is this Peveril or Ballard Point? pier 12 of 24 © Boardworks Ltd 2005 What has been done to protect Swanage? 13 of 24 © Boardworks Ltd 2005 What has been done to protect Swanage? What is the purpose of each scheme at Swanage? Match the correct scheme to its purpose! 14 of 24 © Boardworks Ltd 2005 Learning objectives Why does cliff recession occur? What are the effects of cliff recession? How can the coastline be protected? What are the disadvantages of coastal protection? What is the best method of coastal protection? 15 of 24 © Boardworks Ltd 2005 What problems do sea walls create? Why might a sea wall cause more coastal erosion? 16 of 24 © Boardworks Ltd 2005 What are the disadvantages of groynes? Mappleton is located on the Holderness Coastline. 17 of 24 In 1991 a rock revetment and two rock groynes were built. Sand accumulated and halted erosion. South of Mappleton, the rate of erosion has increased significantly. Material that usually moves south via longshore drift is becoming trapped within the groynes. Now there is no beach to protect the cliffs - the sea reaches the base of the soft cliffs and erosion occurs. © Boardworks Ltd 2005 Learning objectives Why does cliff recession occur? What are the effects of cliff recession? How can the coastline be protected? What are the disadvantages of coastal protection? What is the best method of coastal protection? 18 of 24 © Boardworks Ltd 2005 What is the best method of coastal protection? This is the imaginary coastal town of ‘Seaview’. Seaview has been suffering from coastal erosion for the last 15 years since the nearby larger town of ‘Engleton’ had groynes built to protect its own coastline. 19 of 24 © Boardworks Ltd 2005 What is the best method of coastal protection? There are strong feelings about what should be done to protect Seaview! 20 of 24 © Boardworks Ltd 2005 What is the best method of coastal protection? Give each scheme a score from 1 (poor) to 5 (good). For example, an expensive scheme should have a low score. Would you choose the scheme with the highest score? Why? Which is the most important criteria? 21 of 24 © Boardworks Ltd 2005 Examination question Choose two of the sea defences and explain how they are used to protect cliffs from collapse. List three disadvantages of hard engineering solutions. Suggest one reason why some coastlines are not protected from the sea. 22 of 24 © Boardworks Ltd 2005 What do you know about coastal defences? 23 of 24 © Boardworks Ltd 2005 Key Ideas Cliff recession is caused by wave action and sub-aerial processes. Cliff recession can have major economic and social effects. Hard engineering solutions include sea walls, groynes, revetments, rip rap and gabions. Soft engineering solutions include cliff drainage, beach nourishment and managed retreat. All sea defence schemes have advantages and disadvantages. 24 of 24 © Boardworks Ltd 2005