2.3.1 Coastal Management Flashcards
Aim of coastal management
To protect homes, businesses and the environment from erosion and flooding.
This is because flooding and erosion of the coastline can have severe social, economic and environmental impacts.
How do local authorities choose which (and how) places are defended?
Using a cost-benefit analysis.
The money available is usually used to protect large settlements and important industrial sites, rather than isolated or small settlements.
Four main options for coastal management
- Hold the line
- Advance the line
- Managed retreat
- No active intervention (do nothing)
Hold the line
Maintain the current location of the coast usually by using hard engineering.
Advance the line
Extending the coastline further out to sea by reclaiming land or encouraging the build up of material.
Managed retreat
Allow the coast to retreat, but manage the retreat so that is causes least damage (typically by sacrificing low value land).
No active intervention (do nothing)
Build no coastal defences at all, and deal with erosion and flooding as it happens.
Soft engineering
Soft engineering encouraging natural processes to manage (but not necessarily prevent) erosion.
Soft engineering techniques
- Beach nourishment
- Beach stabilisation
- Dune regeneration
- Lane use management
- Creating marshland
- Coastal realignment (managed retreat)
Hard engineering techniques
- Sea wall
- Revetment
- Gabions
- Riprap
- Groynes
- Breakwaters
- Tidal barriers
[Soft engineering]
Beach nourishment
Where sand and shingle are added to breaches from elsewhere (e.g. dredged from offshore). This creates wide beaches, which reduce erosion of cliffs more than thin beaches
[Soft engineering]
Beach stabilisation
This is done by reducing the slope angle and planting vegetation. It also creates wide beaches, which reduce erosion of cliffs.
[Soft engineering]
Dune regeneration
Where sand dunes are created or restored by either nourishment or stabilisation of the sand.
Dune provide a barrier between land and sea, absorbing wave energy and preventing flooding and erosion.
[Soft engineering]
Lane use management
This is used for dune regeneration.
The vegetation needed to stabilise the dune can easily be trampled and destroyed, leaving the dune vulnerable to erosion.
Wooden walkways across dunes, and fenced-off areas that prevent walkers, cyclists or 4x4 drivers from gaining access to the dunes, all reducing vegetation loss.
[Soft engineering]
Creating marshland
Creating marshland from mudflats can be encouraged by planting appropriate vegetation. The vegetation stabilises the sediment, and the stems and leaves help reduce the speed of the waves. This reduces their erosive power and how far the waves reach inland, leading to less flooding of the area around the marsh.
[Soft engineering]
Coastal realignment (managed retreat)
This involves breaching an existing defence and allowing the sea to flood the land behind. Over time, vegetation will colonise the land and it will become marshland.
Hard engineering
Involves building strucures to prtoect the coastline.
[Hard engineering]
Sea wall
- The wall reflects energy back out to sea, preventing erosion of the coast. It also acts as a barrier to prevent flooding.
- Cost: Expensive to build and maintain.
- Disadvantage: It creates a strong backwash, which erodes under the wall.
[Hard engineering]
Revetment
- Revetments are slanted structures built at the foot of cliffs. They can be made from concrete, wood or rocks. Waves break against the revetments, which absorb the wave energy and so prevent cliff erosion.
- Cost: Expensive to build, but relatively cheap to maintain.
- Disadvantage: They create a strong backwash, as above.
[Hard engineering]
Gabions
- Gabions are rock-filled cages. A wall of gabions is usually built at the foot of cliffs. The gabions absorb wave energy and so reduce erosion.
- Cost: Cheap
- Disadvantage: Ugly
[Hard engineering]
Riprap
- Boulders piled up along the coast are called riprap. The boulders absorb wave energy and so reduce erosion.
- Cost: Fairly cheap
- Disadvantage: They can shift in storms
[Hard engineering]
Groynes
- Groynes are fences built at right angles to the coast. They trap beach material transported by longshore drift. This creates wider beaches, which slow the waves (reducing their energy) and so gives greater protection from flooding and erosion.
- Cost: Quite cheap
- Disadvantage: They starve down-drift beaches of sand. Thinner beaches don’t protect the coast as well, leading to greater erosion and flooding.
[Hard engineering]
Breakwaters
- Breakwaters are usually concrete blocks or boulders deposited off the coast. They force waves to break offshore. The waves’ energy and erosive power are reduced before they reach the shore.
- Cost: Expensive
- Disadvantage: Can be damaged in storms
[Hard engineering]
Tidal barrier
- Tidal barriers are built across river estuaries. They contain retractable floodgates that can be raised to prevent flooding from storm surges.
- Cost: Very expensive
- Disadvantage: Very expensive!
