KQ2: How are coasts protected from the effects of natural processes? Flashcards
Name some hard engineering defences
- sea walls
- gabions
- rock armour
- revetments
- groynes
- cliff drainage
Name some soft engineering defences
- Beach replenishment
- Building bars
- Replanting vegetation
What are sea walls?
Curved, straight or stepped reinforced concetre structures to reflect waves back on themselves and dissipate energy
What are gabions?
Steel mesh cages filed with small rocks which absorb wave’s energy, making the waves less powerful, and stopping them from directly hitting the cliff
What are rock armour?
Large rocks placed at the foot of sea walls to absorb wave energy and also partially reflect the energy so to reduce scouring of the beach
What are revetments?
Wooden or concrete structures designed to absorb wave energy but still allow a flow of sediment
What are groynes?
Wooden of concrete structures designed to break waves and slow down longshore drift. They maintain beach width to protect cliff base.
What is beach replenishment?
Pumping sand or shingle back onto the beach to replace eroded material so the beach becomes a better natural defence against erosion. More energy is dissipated so the waves have a smaller impact on the cliffs and coastline
What are building bars?
Underwater bars to reduce wave energy
What is replanting vegetation?
To stabilise low-lying areas e.g. marram grass
What is cost benefit analysis?
A means of evaluating the economic/social and environmental costs and benefits of a project in order to reach a decision
What factors affect the type of sea defence method used?
- Strategy chosen
- Budget available
- Type and strength of coastal processes which need to be altered
- Environmental/aesthetic value of the coastline
What is ICZM?
Integrated Coastal Zonal Management
- method of managing shoreline but also the whole of the coastal zone
What is SMP?
Shoreline Management Plan
- a document which examines the risks associated with coastal processes, and presents a policy to manage those risks
Where is Sea Palling?
East Coast of Norfolk
Why is there a need for protection on the east coast of Norfolk?
• 1953: storm surge broke through the sand dunes and flooded parts of NE Norfolk
= ↓ in beach material to create a barrier against powerful waves
• Inland area of Norfolk Broads needs protection from flooding
What physical factors affect Sea Palling?
- High wave energy due to strong dominant wind with long fetch
- Incoherent rock type
- Weak rock structure (discordant)
- Strong LSD due to wave orientation at an angle
- Sea level rising
- Need for conservation of important natural habitats
What human factors affect Sea Palling?
- High value land e.g. fens inland of Sea Palling
- Significant human activities / high economic value
- Failure of earlier defences
What was done in Sea Palling?
• A sea wall built in front of sand dunes
• Groynes at Eccles to preserve local beaches + trap sediment moving S by LSD
o = wider beach + ↓ sediment reaching further S
• By 1990s: beach reduced so much that the sea reached the sea wall during storms
• 1991: rip rap in front of sea wall temporarily
What is the strategy for Sea Palling?
To hold the present line of defence (maintain existing defences)
What is the plan for Sea Palling?
• Over 100 000 tonnes of boulders in front of sea wall
• Offshore bars parallel to the coast constructed so waves break before reaching beach + waves absorb ℇ during storms
o Gaps between bars to allow LSD to take place, resulting in a ‘tombola’ effect when sediment has built up behind the reefs and connected them to the beach, creating bays = added protection + amenity value + ↓ sediment flow towards S ∴ Waxham needed beach replenishment
• Beach replenished with 1 million cubic metres of sand ∴ =wider beach
What does the SMP predict for the future of Sea Palling?
- The SMP predicts that there will be no property, land, dune, or site loss behind the existing defences, but there will also be maintenance to the beach, car parking, facilities and Sea Palling lifeboat station.
- Therefore, their recommendations for Sea Palling appear sustainable as they provide protection for now and the future for the area.
Where is Abbots Hall Farm?
Essex
What strategy is Abbots Hall Farm using?
Managed Retreat
Why is Abbots Hall Farm using managed retreat?
- Large areas of salt marsh and mudflats were being lost to coastal erosion
- Loss of salt marshes had an impact on flora and fauna
- Salt marshes can be cost-effective as a defence- it is inexpensive where there is lack of dev.
- Only a narrow strip of land between the existing 3km sea wall and 5m contour line. ∴ when the land was flooded, and a salt marsh developed, the vegetation and natural gradient of the land provided a natural defence against future storm events
Is managed retreat a suitable method for managing erosion in other coastal areas?
• Only where there is low value land
• Only when marshes can colonise
o Vegetation provide a defence so erosion rate is ↓, and can cause deposition to help salt marsh ↑more
How did Abbots Hall Farm allow managed retreat?
• The sea wall was breached in 3 places, allowing these areas to be flooded and develop estuaries where vegetation is colonising the salt marshes
Why does the Norfolk Coast need protecting?
- Global warming on lowland coast
- Cliffs are of low-resistant boulder clay (till) and outwash sands, and therefore susceptible to sub-aerial processes as well as marine erosion. Overstrand had 85m of erosion in the 3 years preceding the protection scheme in the late 90s.
- Coastline has some of the most important bird-breeding sites and winter migration sites for some birds in the UK, and some of the best salt marshes at Brancaster.
- 67km of existing man-made defences need to be maintained
- Coastline is of major recreation value
