The concept of coastal cells and risks of erosion and flooding

Coastal management revolves around understanding coastal cells, which are distinct sections of the coastline that operate as self-contained systems for sediment movement. These cells help in planning strategies to address conflicts between various coastal users and to protect the health of coastal ecosystems. Additionally, management focuses on tackling significant threats that impact long stretches of the coast, particularly the risks of erosion and flooding.

Coastal cells

Coastal cells are segments of the coast where sediment movement is largely contained within the area, forming mini-systems that influence local management strategies.

Risk of coastal erosion

Erosion is a natural process, but it can be severe in certain areas. For instance, some cliffs made of soft materials like sand and clay can retreat at rates of up to 3 metres annually, with historical records showing coastlines receding by multiple kilometres over hundreds of years.

Risk of coastal flooding

Flooding often results from erosion but can also occur due to unusually high sea levels, storm surges, or tsunamis. The most significant long-term threat is the rising sea levels due to global warming, which exacerbates flooding risks in low-lying areas.

Hard engineering techniques for coastal protection

Hard engineering involves constructing physical barriers or structures, typically made from concrete or rock, to shield the coast from erosion and flooding. These methods aim to resist the force of waves directly but come with specific advantages and drawbacks.

Common hard engineering methods

General limitations of hard engineering

• High costs - Building and maintaining these structures is often very expensive, with significant ongoing repair expenses.
• Impact on nearby areas - Defences in one location can worsen erosion or flooding in adjacent areas, especially downstream of longshore drift.
• Inability to adapt - These structures struggle to cope with rising sea levels caused by climate change.
• Aesthetic impact - Hard engineering solutions can detract from the natural beauty of the coastline, affecting tourism and local appeal.

Soft engineering approaches to coastal management

Soft engineering focuses on working alongside natural coastal processes, using elements like beaches and dunes to protect against erosion and flooding. These methods are generally more sustainable and visually appealing than hard engineering.

Key soft engineering techniques

• Beach replenishment - Adding sand or shingle to eroded beaches by pumping or dumping material, which helps to buffer against wave energy.
• Building offshore bars - Creating underwater barriers just off the coast to reduce the power of incoming waves before they reach the shore.
• Fencing, hedging, and vegetation replanting - Stabilising beaches and dunes by reducing sand loss to inland areas through barriers and planting, with broader ecosystem rehabilitation offering even greater benefits.
• Cliff regrading - Reducing the steepness of cliffs to lessen the risk of sudden mass movement or collapse due to water erosion.

Benefits of soft engineering

• Environmental harmony - These methods blend with the natural landscape, preserving the aesthetic value of the coast.
• Cost-effectiveness - Generally cheaper to implement and maintain compared to hard engineering solutions.
• Energy absorption - Soft engineering absorbs wave and tidal energy naturally, reducing the impact on the coastline without disrupting sediment flow.

The strategy of managed retreat as a response to coastal changes

Managed retreat is a distinctive approach to coastal management, often seen as a form of soft engineering or a separate strategy altogether. It involves deliberately allowing certain coastal areas to be flooded by the sea, creating new natural defences over time.

Features and implications of managed retreat

• Process of managed retreat - Existing coastal defences are abandoned, permitting the sea to advance inland until it reaches higher ground or a new defensive line is established.
• Creation of natural barriers - Flooded areas often develop into salt marshes, which act as effective buffers against storm surges and enhance biodiversity by expanding scarce ecosystems.
• Cost considerations - While relatively inexpensive compared to building hard defences, managed retreat involves significant compensation costs for lost homes, businesses, and farmland.
• Limitations in application - This strategy is less feasible in areas with dense urban development or valuable agricultural land due to the high economic and social costs of relocation.

Examples of coastal management in different countries

Coastal management strategies vary across the globe, reflecting different levels of economic development, environmental priorities, and local conditions. Examining specific cases highlights how these strategies are applied in practice.

Case studies of coastal management

• United Kingdom - In areas like the Holderness coast, a combination of hard engineering (such as sea walls and groynes) and soft engineering (beach replenishment) is used to combat rapid erosion rates. Managed retreat is also being trialled in some low-value areas to create salt marshes as natural defences.
• Netherlands - A highly developed nation with much of its land below sea level, the Netherlands employs advanced hard engineering, including massive sea walls and storm surge barriers. Soft engineering, such as dune reinforcement, complements these efforts to protect against flooding.
• Bangladesh - As a developing country with extensive low-lying coastal areas, Bangladesh faces severe flooding risks due to storm surges and rising sea levels. Managed retreat is often used, allowing flooding in less populated areas to form natural barriers, while limited resources restrict widespread hard engineering solutions.