1. Coastal Defence

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3. Swanage

4. Coastal erosion in Swanage
the soft, clay bedrock is prone to attack from the waves
river drains through Swanage and encourages slumping

5. Coastal defence in Swanage
Swanage Bay
GROYNES
PIER
CONCRETE REVETMENT
HEADLAND IS FENCED TO STOP TRAMPLING

6. Swanage Bay Study the photo and map extract.
Is this Peveril or Ballard Point?
pier

7. 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 on the beach and not the cliffs.

8. Decision making exercise
10m
Engleton
Why is Seaview being eroded?
Seaview
Should Seaview be protected from coastal erosion?
If so, how?
groynes
buildings
Roman
Palace
Prevailing wind
till
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. Seaview is built on ‘till’ (soft clay) and is losing up to 30cm of land per year. Why protect Seaview? The town is home to 20,000 residents. The remains of a Roman Palace are located here. This attracts tourists.

9. The options... Rip rap Sea wall Groynes Gabions Stone revetment
DO NOTHING!

10. Further information on the schemes
the waves break on the rip rap and not on the coastline
rip rap is simply boulders/stones
wire box with rip rap
Stone revetment acts as a barrier to the waves. Revetments can also support sea walls.

11. Problems with sea walls
Why might a sea wall cause more coastal erosion?

12. What are the advantages and disadvantages of each option?
SCHEME
COST
APPEARANCE
EFFECTIVENESS
Do Nothing !

13. Weighting table
Now you have thought about the advantages and disadvantages, give each scheme a score from 1 (poor) to 5 (good), using the same criteria. For example, an expensive scheme should have a low score. Add up the total for each scheme.
Would you choose the scheme with the highest score? Why?
Which is the most important criteria? Cost? Appearance? Effectiveness?
SCHEME
COST
APPEARANCE
EFFECTIVENESS
Do Nothing!