8.4. Coastal Management Strategies Flashcards
Methods of Protecting against Coastal Erosion
- Hard engineering
- Soft engineering
Hard Engineering
Most common way of protecting vulnerable coastlines, which involves building large, solid structures to absorb or reflect the energy of the waves
Types of Hard Engineering
1) Vertical Sea Wall
2) Groynes
3) Breakwater
4) Gabions
Vertical Sea Wall
- Solid, vertical wall of masonry or concrete
- Deep foundations are needed to maintain stability
Vertical Sea Wall Advantages and Disadvantages
Advantages
- Solid structure that can withstand severe wave action
- Maintains the line of the coastline
Disadvantages
- High initial costs and high maintenance costs
- Reduced access to beach - steps have to be provided at regular intervals
- Basal scour is a problem
Groynes
- Usually of wood - a barrier of stout timber piles and planks built at right angles to the shore
- They control longshore drift and encourage deposition of beach material
- Can be made out of stones
Groynes Advantages and Disadvantages
Advantages
- Relatively cheap, but actual cost depends on length and spacing
- Encourages deposition of beach material, therefore making a wider beach which absorbs wave energy and encourages tourists
Disadvantages
- Only last 20 years so the maintenance costs are high
- Visually unappealing and rock groynes are dangerous if people walk on them
- Interfere with longshore drift so they can cause problems downdrift where beaches are depleted of sediment and erosion rates increase there
Breakwater
- Solid Structure made of masonry with a concrete caps
- Foundations go down to the bedrock
- They deflect waves and provide a sheltered environment behind them
Breakwater Advantages and Disadvantages
Advantages
- Protects the area behind them from wave action, reducing erosion and providing a sheltered harbour for small boats
- Slows longshore drift and encourages a build-up of sediment
Disadvantages
- Very expensive to build as they are broad and deep
- Maintenance expensive
- Basal scour is a problem
Gabions
- Wire cages filled with stones
- Can be wired together to make any shape or structure
Gabions Advantages and Disadvantages
Advantages
- Cheap to build
- Very flexible as they can be used to produce different shapes and structures
Disadvantages
- Very short lifespan - often no more than 5 years and maintenance costs are high
Unsightly and the wire can be dangerous once it rusts and the gabions burst
- If used as a sea wall they reduce access to the beach
Soft Engineering
These strategies are becoming more popular as our understanding of coastal processes improves. It involves working with nature to protect the coast by enhancing the natural, protective, coastal processes
Beach Nourishment
- Artificial addition of beach material (sand, shingle or pebbles) from another location
- The sediment can be brought by lorry or dredged from offshore
Beach Nourishment Advantages and Disadvantages
Advantages
- Builds up the beach, making it a bigger buffer to absorb wave energy
- Low initial costs - but this depends on how far the sediment has to be moved
- Bigger beach attracts tourists
- Natural and aesthetically pleasing
Disadvantages
- Requires constant maintenance, especially if longshore drift is vigorously removing the added sediment
- Often needs groynes to be built downdrift to reduce sediment loss
- Considerable local disruption during construction phase
Sand Dune Conservation
- Important ecosystems
- Provide areas inland from the dunes with protection from coastal erosion and flooding
Sand Dune Conservation Advantages and Disadvantages
Advantages
- Working with nature to protect an important coastal ecosystem as well as enhancing the natural protection that dunes provide
- Well-managed systems allow access to the dunes and the beach beyond without excess trampling
Disadvantages
- Initial costs may be quite high
- Maintenance is required
- Some areas of damaged dunes may need to be fenced-off, denying the public access
Cliff drainage
- Drainage pipes are inserted into the face of the cliff, especially where the cliff is made of soft or unconsolidated material
- This removes water from the cliff, lessening the potential for mass movements
Cliff drainage Advantages and Disadvantages
Advantages
- The cliff becomes dryer and less prone to slumping
- Very little environmental impact apart from during the construction phase
- Maintains the natural appearance and recreational value of the beach
Disadvantages
- Can be expensive
- Disruptive and unsightly during construction phase
Cliff Regrading
- A vertical cliff is turned into a more gently-sloping cliff by removing material from the cliff top and adding it to the bottom of the cliff (on the beach)
- Works best in unconsolidated or soft cliff material
Cliff Regrading Advantages and Disadvantages
Advantages
- The cliff becomes more stable and less prone to unexpected movements
- Once ‘naturalised’, the new cliff slope is not unsightly
- Maintains the natural appearance and recreational value of the beach
Disadvantages
- Often expensive
- Disruptive and unsightly during the construction phase
- Removes the natural cliff line
Major ecological impact e.g. on nesting seabirds
Types of Soft Engineering
1) Beach Nourishment
2) Sand Dune Conservation
3) Cliff Drainage
4) Cliff Regrading
Coastal Flooding
- Very real danger in low-lying coastal areas, especially in deltas and around estuaries
- Coastal flooding is a common consequence of tropical storms
Types of Protection from Coastal Flooding
1) Barrages
2) Embankments
3) Shelters
Barrages
- Example of a solid, hard-engineering scheme to prevent flooding on major estuaries and other large sea inlets
- Acts as a dam across an estuary and prevents incursion of seawater either a permanent or temporary basis
- Only work when combined with embankments on the seaward side, ensuring that high seas can’t outflank them
Barrages Advantages and Disadvantages
Advantages
- Create a freshwater lake behind them and often encourage the reclamation of land from this lake - encouraging economic development
Disadvantages
- Very expensive to build
- Very expensive to build
- Can destroy feeding grounds of migrating birds and can interfere with fish migration
- Economically, they can stop the movement of ships to ports further up the estuary
Embankments
- Barriers built along the coastline, physically stopping seawater from flooding low-lying land next to the sea
- Engineers have to decide on a design brief and that usually means protecting against a flood that has a long recurrence interval
Shelters
- Cheaper alternative to building embankments
- Flood-proof shelters which local people can use in the event of a flood
- Built of concrete and raised above flood level on stilts
- There has to be a reliable flood warning system in place so that people know when to move to the shelters, but they are capable of saving many lives
- However, they can’t save people’s homes and livestock and local infrastructure is still at risk
- This means that, although death is reduced, economic and social disruption is considerable
