Managing the Impacts of Coastal Erosion
- There are conflicting views about using a particular type of engineering for coastal defence
- Most coastal managers aim to use a range of methods depending on the value of what is being protected
- This method is known as Integrated Coastal Zone Management (ICZM)
- ICMZ aims to use a combination of methods to best reflect all stakeholder's needs
Soft engineering methods
- Soft engineering works with natural processes rather than against them
- Usually cheaper and do not damage the appearance of the coast
- Considered to be a more sustainable approach to coastal protection
- However, they are not as effective as hard engineering methods
Soft Engineered Defences
Strategy | Description | Advantages | Disadvantages |
Beach replenishment | Pumping or dumping sand and shingle back onto a beach to replace eroded material |
Beaches absorb wave energy Widens beach front |
Has be repeated regularly which is expensive Can impact sediment transportation down the coast |
Fencing, hedging, and replacing vegetation |
Helps to stabilise sand dunes or beaches Reduces wind erosion |
Cheap method to protect against flooding and erosion |
Hard to protect larger areas of coastline cliffs |
Cliff re-grading | The angle of a cliff is reduced to reduce mass movement |
Prevents sudden loss of large sections of cliff Regrading can also slow down wave cut notching at base of cliffs as wave energy is slowed |
Does not stop cliff erosion |
Managed retreat | Existing coastal defences are abandoned allowing the sea to flood inland until it reaches higher land or a new line of defences |
No expensive construction costs Creates new habitats such as salt marshes |
Disruptive to people where land and homes are lost Cost of relocation can be expensive Compensation to people and businesses may not be paid |
Hard engineering methods
- Hard engineering involves building some form of sea defence, usually from concrete, wood or rock
- Structures are expensive to build and need to be maintained
- Defences work against the power of the waves
- Each type of defence has its strengths and weaknesses
- Protecting one area can impact regions further along the coast, which results in faster erosion and flooding
- Hard engineering is used when settlements and expensive installations (power stations etc) are at risk - the economic benefit is greater than the costs to build
Hard Engineered Defences
Strategy | Description | Advantages | Disadvantages |
Sea Wall |
A wall, usually concrete, and curved outwards to deflect the power of the waves |
Most effective at preventing both erosion and flooding (if the wall is high enough) |
Very expensive to build and maintain It can be damaged if the material is not maintained in front of the wall Restricts access to the beach Unsightly to look at |
Groynes |
Wood, rock or steel piling built at right angles to the shore, which traps beach material being moved by longshore drift |
Slows down beach erosion Creates wider beaches |
Stops material moving down the coast where the material may have been building up and protecting the base of a cliff elsewhere Starves other beaches of sand. Wood groynes need maintenance to prevent wood rot Makes walking along the shoreline difficult |
Rip-rap |
Large boulders are piled up to protect a stretch of coast |
Cheaper method of construction Works to absorb wave energy from the base of cliffs and sea walls |
Boulders can be eroded or dislodged during heavy storms |
Gabions |
Wire cages filled with stone, concrete, sand etc |
Cheapest form of coastal defence Cages absorb wave energy Can be stacked at the base of a sea wall or cliffs |
Wire cages can break, and they need to be securely tied down Not as efficient as other coastal defences |
Revetments |
Sloping wooden or concrete fence with an open plank structure |
Work to break the force of the waves Traps beach material behind them Set at the base of cliffs or in front of the sea wall Cheaper than sea walls but not as effective |
Not effective in stormy conditions Can make beach inaccessible for people Regular maintenance is necessary Visually unattractive |
Off-shore barriers |
Large concrete blocks, rocks and boulders are sunk offshore to alter wave direction and dissipate wave energy |
Effective at breaking wave energy before reaching the shore Beach material is built up Low maintenance Maintains natural beach appearance |
Expensive to build Can be removed in heavy storms Can be unattractive Prevents surfing and sailing |
Prediction
- Early warning systems allow communities to prepare (evacuate or take shelter) before flooding occurs
- Two methods are used to help forecast coastal flooding:
- Past records (diaries, newspapers, government/council records etc)
- These will identify areas that are at high risk of flooding and their frequency
- Modern technology - GIS, satellite and computer monitoring, weather stations (local and national) etc
- These allow for forecasting and tracking potential hazard events i.e.
- Tropical storms - track the storm's path and associated storm surge
- Earthquakes - size and position if underwater and possible tsunami outcome
- These allow for forecasting and tracking potential hazard events i.e.
- Past records (diaries, newspapers, government/council records etc)
- Both these methods of forecasting help officials to say when and where the event will occur
- It indicates the possible strength and scale of the flooding, and the likelihood of damage and death
Prevention
- Prevention is about taking action that reduces or removes the risk of coastal flooding
- Actions include:
- Flood defences
- These are built along high-risk stretches of coast
- Emergency centres
- Centrally placed on higher ground where people can be safe from flooding
- Early warning systems
- Allows for preparation or evacuation of an area
- Education
- Informing local people on what to do if and when a flood occurs
- Planning
- Planning any new development away from high-risk-areas
- Designing buildings to cope with low levels of flooding
- Elevating buildings so that flood waters can pass underneath
- Flood proof buildings with raised foundations (fixed or mechanical)
- Reinforced barriers
- Dry flood proofing - sealing a property so that floodwater cannot enter
- Wet flood proofing - allows some flooding of the building
- Buffer zones
- Areas of land are allowed to flood before reaching settlements
- This allows the energy in the surge to dissipate slowing down the distance the floodwater will travel
- It can mean moving people away from the coast which could be controversial
- Areas of land are allowed to flood before reaching settlements
- Flood defences
Coastal strategies
- Management of coastal regions is performed by identifying coastal cells
- This breaks a long coastline into manageable sections and helps identify two related risks:
- The risk of erosion and land retreat
- The risk of flooding
- Identification allows resources to be allocated effectively to reduce the impacts of these risks
- The 'cost to benefit' is easier to calculate using coastal cells
Shoreline management plans
- Shoreline Management Plans (SMP) set out an approach to managing a coastline from flooding and erosional risk
- The plans aim to reduce the risk to people, settlements, agricultural land and natural environments (salt marshes etc.)
- There are four approaches available for coastal management, with differing costs and consequences:
- Hold the line
- Long term approach and the most costly
- Build and maintain coastal defences so the current position of the shoreline remains the same
- Hard engineering is the most dominant method used with soft engineering used to support
- Advance the line
- Build new defences to extend the existing shoreline
- Involves land reclamation
- Hard and soft engineering is used
- Managed realignment
- Coastline is allowed to move naturally
- Processes are monitored and directed when and where necessary
- Most natural approach to coastal defence
- Mostly soft engineering with some hard engineering to support
- Do nothing
- Cheapest method, but most controversial of the options
- The coast is allowed to erode and retreat landward
- No investment is made in protecting the coastline or defending against flooding, regardless of any previous intervention
- Decisions about which approach to apply are complex and depend on:
- Economic value of the resources that would be protected, e.g. land, homes etc
- Engineering solutions - it might not be possible to 'hold the line' for moving landforms such as spits, or unstable cliffs
- Cultural and ecological value of land - historic sites and areas of unusual diversity
- Community pressure - local campaigns to protect the region
- Social value of communities - long-standing, historic communities
Worked example
Explain how gabions protect the coast
[2]
- The command word here is 'explain', therefore, there needs to be development of the answer for the full marks
- Examples include:
- Gabions absorb/dissipates/reduces the wave's energy/power, [1] and this reduces the impact of the waves at the foot of cliffs and seawalls, which reduces/prevents coastal erosion [1]