The concept of coastal defence and zone management

Coastal defence focuses on protecting the coastline from erosion (often termed coast protection) and flooding caused by the sea.

Coastal zone management encompasses a broader perspective, addressing all activities in the coastal zone. It promotes integrated planning to manage these activities.

Hard engineering strategies for coastal protection

Hard engineering involves constructing physical structures to alter natural coastal processes, primarily to reduce erosion and flooding.

Types of hard engineering structures

• Sea walls - Massive concrete walls, often curved, designed to reflect wave energy back to the sea. They are effective in high-density areas but are expensive to build and maintain, with a typical lifespan of 30-40 years. Their foundations can also be undermined by wave action over time.
• Revetments - Porous structures that absorb wave energy, reducing erosion. They are simpler and less costly to construct than sea walls but have a shorter lifespan.
• Gabions - Wire cages filled with rocks that absorb wave energy. They are a cheaper option compared to sea walls and revetments but are small-scale.
• Groynes - Barriers built perpendicular to the shore to prevent longshore drift, trapping sediment. They are relatively inexpensive and easy to repair but can cause increased erosion on the downdrift side by interrupting natural sediment flow.
• Rock armour - Large boulders placed at the base of cliffs or along the shore to dissipate wave energy. This method is cost-effective but can be visually unappealing, small in scale, and vulnerable to displacement during major storms.
• Offshore breakwaters - Structures built parallel to the coast, offshore, to reduce wave power before it reaches the shore. They are relatively cheap to construct but can negatively impact local marine ecosystems.
• Rock strongpoints - Specific points along the coast reinforced with rocks to reduce longshore drift. They are low-cost and easy to maintain but disrupt sediment movement, leading to erosion in downdrift areas.

Soft engineering approaches to manage coastal erosion

Soft engineering focuses on working with natural processes to protect coastlines.

Techniques in soft engineering

• Preservation of natural coastal vegetation - Maintaining or restoring vegetation to mitigate storm impacts.
• Beach nourishment - Involves adding sediment, often dredged from offshore locations, to increase the size of a beach. It maintains a natural appearance but is expensive and needs frequent replenishment.
• Offshore reefs - Constructed from recycled materials and placed underwater to slow incoming waves. This is a low-tech, cost-effective solution, though the long-term environmental impacts are still under study.

Cliff face strategies to reduce erosion risks

Specific strategies are employed to stabilise cliffs and reduce the risk of collapse.

Methods to stabilise cliffs

• Cliff drainage - Involves removing water from within the cliff rocks. This is a cost-effective method, but the drainage systems can create new lines of weakness, and dry cliffs may still experience rockfalls.
• Cliff regrading - Reduces the slope angle of a cliff to make it more stable. This is particularly useful for cliffs made of clay, where other methods are less effective. However, it requires significant land area, making it impractical in densely populated regions.

Managed retreat and the "do nothing" approach in coastal management

Not all coastal management strategies involve active intervention.

Alternative management approaches

• Managed retreat - Involves allowing certain areas of the coastline to erode naturally while deposition occurs elsewhere. This approach saves money compared to building defences and can create valuable natural environments. However, it often results in the loss of residential or agricultural land.
• "Do nothing" approach - Accepts that natural coastal processes will dominate, with no intervention. This is the most cost-effective option as it involves no expenditure on defences, but it is politically unpopular.

Important consideration in coastal management

A common misconception is that management schemes provide guaranteed protection. Even robust structures like sea walls can fail during extreme events.

Most coastlines use a combination of strategies, blending hard and soft engineering techniques to address specific local needs.