2.10 - Management of Coastal Landscapes - notes

Introduction to coastal management

• Coastal management involves strategies to protect coastlines from erosion and flooding, while considering the broader impacts on nearby areas.
• This is important because actions in one location can affect sediment movement and processes in others, potentially causing unintended erosion elsewhere.
• Local authorities often weigh the risks of large investments in defences, ensuring there is evidence of their effectiveness before proceeding.
• Management approaches are divided into hard engineering, which uses built structures to resist natural processes, and soft engineering, which works alongside them.

Aims and challenges of hard engineering

Hard engineering focuses on constructing physical barriers to alter coastal processes, such as wave action and sediment transport. These defences aim to prevent erosion and flooding by directly opposing natural forces. They are typically installed as permanent solutions in specific locations.

Challenges of hard engineering

• Hard engineering often requires significant financial investment and ongoing maintenance.
• These structures can disrupt local ecosystems by altering habitats and sediment flow within a sediment cell – a coastal system where sediment is sourced, transported, and deposited.
• This interruption may protect one area but accelerate erosion in others.
• Hard engineering can reduce the visual appeal of the coastline and limit beach access.

Types of hard engineering structures

Various hard engineering methods are used to defend coastlines, each with specific functions, costs, and impacts on physical processes. The choice depends on local conditions, such as wave energy and geology.

Sea walls

Sea walls are vertical or curved concrete barriers built along the shore to reflect wave energy back to sea. This prevents direct erosion of the coast and acts as a flood barrier. Some designs include stepped or curved faces to better dissipate waves, and the top can serve as a promenade for public access.

Cost & impacts:

• Cost - Expensive to build and maintain due to the need for durable materials.
• Impacts - Creates strong backwash that can erode the base of the wall or remove beach sediment, potentially undermining the structure. They can appear visually unappealing and alter natural coastal aesthetics.

Revetments

Revetments are slanted structures positioned at the base of cliffs, constructed from materials like concrete, wood, or rocks. They absorb wave energy upon impact, reducing the force that reaches the cliff and preventing erosion.

Cost & impacts:

• Cost - High initial construction costs, but maintenance is relatively inexpensive.
• Impacts - Generate strong backwash leading to further erosion nearby. They have a lifespan of 25–60 years, after which replacement is needed.

Offshore breakwaters

Offshore breakwaters consist of concrete blocks or boulders placed in shallow waters parallel to the coast. They cause waves to break early, dissipating energy before it reaches the shore. Over time, sediment may deposit around them, enhancing protection and creating sheltered areas for activities like swimming or harbours.

Cost & impacts:

• Cost - Expensive to install, with frequent maintenance required due to storm damage.
• Impacts - Can lead to sediment deposition in one area, starving others of material and increasing erosion elsewhere. This alters natural sediment distribution within the coastal system.

Rip rap

Rip rap, also known as rock armour, involves piling large, irregularly shaped boulders along the coastline. The rough surfaces increase friction, absorbing wave energy and minimising erosion.

Cost & impacts:

• Cost - Relatively inexpensive compared to other methods.
• Impacts - Boulders can shift during severe storms, requiring repositioning. If sourced from non-local areas, they may look out of place and detract from the natural landscape.

Groynes

Groynes are fence-like structures extending perpendicular from the beach into the sea, made from wood, concrete, or rock.

They intercept sediment carried by longshore drift – the process where waves transport material along the coast at an angle. This builds up wider beaches, which act as buffers to slow waves and reduce erosion and flooding.

Cost & impacts:

• Cost - Moderately priced to construct.
• Impacts - By trapping sediment, they can deprive down-drift beaches of material, leading to increased erosion in those areas (known as the terminal groyne effect). Groynes may obstruct beach walking and be seen as visually intrusive.

Principles of soft engineering

Soft engineering emphasises working in harmony with natural coastal processes to manage erosion and flooding, rather than resisting them outright. These methods promote adaptation to changes like rising sea levels and aim for flexibility, allowing adjustments as conditions evolve. They often result in a more natural appearance that blends with the environment.

Types of soft engineering approaches

Soft engineering includes techniques that enhance or restore natural features to provide defence. These methods are often less visually intrusive but may require regular upkeep.

Beach nourishment

Beach nourishment involves adding sand and shingle to eroded beaches, sourced from offshore dredging. This replenishes material lost to erosion and longshore drift, creating wider beaches that absorb wave energy and protect cliffs.

Cost & impacts:

• Cost - High, due to the need for ongoing additions.
• Impacts - Longshore drift continues to remove material, requiring repeated nourishment. Dredging can harm marine organisms like corals and sponges, affecting biodiversity.

Dune stabilisation

Dune stabilisation reduces the slope of sand dunes and secures them with vegetation, stakes, or old tree trunks to prevent wind erosion. This forms wide, stable barriers that buffer against waves and flooding.

Cost & impacts:

• Cost - Inexpensive to implement.
• Impacts - Dunes naturally shift, so maintenance is essential to preserve their position and effectiveness.

Cliff regrading

Cliff regrading alters the cliff's profile to create a gentler slope, making it less prone to erosion. Vegetation is then planted on the reshaped surface to further stabilise the soil and support local ecosystems.

Cost & impacts:

• Cost - Expensive, involving significant earthworks.
• Impacts - The process can disrupt communities, potentially requiring temporary or permanent relocation of residents.

Cliff drainage

Cliff drainage installs channels within the rock to remove excess water, reducing internal pressure and the risk of landslides or collapse.

Cost & impacts:

• Cost - Moderately expensive to set up.
• Impacts - Effectiveness varies with cliff geology, as some rock types are harder to drain.

Sustainable coastal management

• Sustainable coastal management ensures that current needs for protection and resource use are met without hindering future generations.
• It addresses ongoing threats like rising sea levels – which may accelerate unpredictably – and more intense storms, leading to variable erosion and deposition patterns.
• Central to this is adaptation, which involves adjusting to current changes, alongside mitigation to reduce future risks.
• Strategies consider the entire coastal system, including physical features, human activities, and ecosystems, to minimise broader environmental harm.

Conflicts in sustainable coastal management

Implementing sustainable strategies can create tensions among stakeholders, as decisions affect livelihoods, economies, and access.

Key sources of conflict