Coastal Management: Managed Retreat

Definition of Managed Retreat

Managed retreat is a coastal management strategy where certain areas of the coastline are allowed to erode naturally. Instead of building or maintaining sea defences, these defences may be removed or not repaired, allowing the sea to flood low-lying land. This creates a buffer zone between the sea and inland areas, reducing the risk of flooding further inland.

The key idea is to work with natural coastal processes rather than against them. By allowing the coastline to move inland, managed retreat can reduce pressure on more valuable or vulnerable areas further inland.

Reasons for Managed Retreat

Cost-effectiveness: Maintaining hard defences like sea walls or groynes can be very expensive, especially in areas where erosion rates are high. Managed retreat avoids these ongoing costs by allowing natural erosion.

Environmental benefits: Managed retreat helps restore natural coastal habitats such as salt marshes and mudflats. These habitats support wildlife, improve biodiversity, and act as natural flood barriers. Salt marshes also help capture and store carbon, aiding climate change mitigation.

Sustainability: It is a long-term, sustainable approach that accepts the dynamic nature of coastlines. Instead of fighting against the sea, it adapts to changes like rising sea levels.

Adaptation to sea level rise: With climate change causing sea levels to rise, some coastal areas will become increasingly vulnerable. Managed retreat allows space for the coastline to move naturally inland, reducing the risk of catastrophic flooding in the future.

Processes and Implementation

Managed retreat involves several steps and careful planning:

• Identifying low-value land: Areas chosen for managed retreat are usually low-value farmland, salt marshes, or unpopulated land where the economic and social impacts of flooding are minimal.
• Relocation of people and infrastructure: If there are any buildings, roads, or utilities in the area, they may need to be moved or abandoned. This requires careful consultation with local communities.
• Removing or breaching sea defences: Existing sea walls or embankments may be deliberately removed or breached to allow tidal water to flood the land.
• Monitoring natural coastal processes: After managed retreat begins, scientists monitor erosion, sediment deposition, and habitat development to understand how the coastline is changing.
• Creating salt marshes and habitats: Flooded land often develops into salt marshes, mudflats, or lagoons, which provide important habitats for birds, fish, and other wildlife.

For instance, at the Medmerry managed retreat scheme in West Sussex, a new embankment was built inland and the old sea wall was breached. This allowed the sea to flood the land behind the old defences, creating new salt marshes and reducing flood risk to nearby towns. Other UK examples include managed retreat schemes along the Humber estuary and parts of the Essex coast.

Advantages and Disadvantages

Advantages:

• Restores natural habitats: Managed retreat creates valuable ecosystems such as salt marshes, which support biodiversity and act as natural flood defences.
• Reduces maintenance costs: Without the need to maintain expensive sea walls or groynes, local authorities save money in the long term.
• Allows natural coastal processes: The coastline can evolve naturally, which is more sustainable in the face of rising sea levels and increased storm frequency.

Disadvantages:

• Loss of land and property: Some farmland, homes, or infrastructure may be lost to the sea, which can cause economic losses.
• Social impacts: Communities may be displaced or lose access to land they value, leading to resistance or conflict.
• Economic impacts: Loss of agricultural land or tourism sites can affect local economies.

Learning Example: Cost-effectiveness of Managed Retreat

Imagine maintaining a sea wall costs $\text{£}100,000$ per year. If managed retreat costs $\text{£}500,000$ as a one-off cost to relocate infrastructure and create buffer zones, after 5 years the total cost of sea wall maintenance would be $\text{£}500,000$, equal to the managed retreat cost.

After 5 years, managed retreat becomes cheaper because there are no ongoing maintenance costs, while sea wall costs continue annually.

Example: For instance, if maintaining a sea wall costs $\text{£}50,000$ annually, and managed retreat costs $\text{£}300,000$ as a one-off, after 6 years managed retreat becomes more cost-effective.