Adapting to Coastal Change at Brownsea Island

An aerial view of Brownsea Island, Dorset. Brownsea Island sits in the middle of Poole Harbour. — An aerial view of Brownsea Island, Dorset. | © National Trust Images / John Miller

The coast is a constantly changing environment shaped by waves, wind and tides. Climate change will accelerate coastal change at Brownsea Island, making it essential to act now to understand future impacts and adapt in a thoughtful, sustainable way.

Living With Change: How Brownsea Island Is Adapting to Coastal Erosion.

Brownsea Island is a wildlife haven, a place of deep heritage, and a much‑loved destination for visitors. But like many UK coastal landscapes, Brownsea is already experiencing the effects of climate change. Rising sea levels, more frequent storms and natural erosion are gradually reshaping its shoreline.

To help protect the island for future generations, the National Trust has developed a long-term Coastal Adaptation Strategy. This plan sets out how we’ll respond to change in a way that keeps people safe, supports wildlife, and works with the natural processes that shape the island.

Importantly, these decisions are not made by the National Trust alone. Brownsea Island lies within the Environment Agency’s Poole Harbour Shoreline Management Plan (SMP), which directs how different parts of the coastline should be managed over the next 100 years. Our responsibility is to follow this guidance and manage the land safely and sustainably as the coast evolves.

The beach at South Shore Lodge, Brownsea Island — The south shore | © National Trust Images / Mike Henton

Why Brownsea’s coastline is changing

Although sheltered inside Poole Harbour, Brownsea’s soft cliffs, sandy shores and low-lying areas are naturally vulnerable to erosion. Climate change is accelerating these processes. By the end of the century, sea levels could be nearly a metre higher than they are today, meaning that storm surges and high tides will increasingly affect places like Town Quay, Castle Beach and the lagoon.

This change doesn’t happen overnight, but it is happening. Understanding how, where and when it occurs helps us plan ahead before risks become urgent.

Working within the Shoreline Management Plan

Shoreline Management Plans are developed by coastal scientists, engineers, councils and the Environment Agency. They guide how each section of coastline should be managed. The SMP covering Brownsea recommends:

Allowing natural processes to shape much of the coastline, rather than replacing old defences
Managing the retreat of certain structures when maintaining them is no longer viable
Planning ahead for the relocation of vulnerable buildings and facilities
Protecting people and wildlife by taking a long-term view

These policies apply to every landowner within the SMP area. The National Trust’s job is to follow them responsibly, not to set them.

A landscape rich in nature

Brownsea Island is famous for its wildlife. The lagoon is internationally important for overwintering birds like avocet and spoonbill, and in summer supports breeding Sandwich and common tern and gulls. Red squirrels thrive in the island’s woodland, and underwater surveys have revealed large areas of seagrass, a precious and rare habitat that supports fish, seahorses and carbon storage.

As the coastline changes, habitats will change too. Part of our role is to understand how to support both existing and emerging habitats in the decades ahead.

The lagoon behind Agent's House, Brownsea Island, Poole, Dorset — Brownsea lagoon | © National Trust / Mike Henton

How we’re planning for the island’s future

Managing Town Quay (High priority)

Town Quay is the island’s main access point and one of the areas most at risk from future flooding. As sea levels rise, it will not be feasible to protect the quay indefinitely.

We are:

Improving short‑term flood resilience
Closely monitoring the quay wall, slipways and buildings
Setting clear 'tipping points' for when change becomes essential
Beginning long‑term planning to relocate key visitor and operational facilities to safer ground

This early planning means we can move gradually, not react in crisis.

Brownsea Castle and Castle Beach

The shoreline here is also vulnerable to rising sea levels. The SMP advises that the existing beach defences should not be replaced once they fail.

We are working closely with John Lewis & Partners, who lease the Castle, to:

Improve flood resilience
Plan for the eventual return to a more natural shoreline
Protect the heritage and current use of the Castle for as long as possible

South Shore and Western Island

These wilder areas of the island are already shaped largely by natural processes. Old sea defences were removed over a decade ago to allow the coastline to evolve naturally, this was an early example of the National Trust’s Shifting Shores approach in action.

We will:

Continue monitoring erosion and visitor safety
Record vulnerable archaeological features
Support natural sediment movement that strengthens beach resilience

Brownsea Lagoon and Dorset Wildlife Trust Reserve

The lagoon is one of the island’s most valuable wildlife habitats. The seawall is in good condition today, but rising sea levels mean it will eventually overtop more frequently.

We’re working with Dorset Wildlife Trust, Natural England and BCP Council to:

Monitor wall condition and lagoon ecology
Understand when natural change becomes unavoidable
Plan future habitat creation if needed, elsewhere in the harbour

The aim is to preserve the lagoon’s ecological value for as long as possible and plan responsibly for the future.

Improving island access

Safe access for visitors, staff and residents is essential. With Town Quay becoming more vulnerable, we are investing in:

A new, more resilient jetty at Sandbanks

Better emergency plans
Long-term exploration of alternative access points

Understanding and protecting marine habitats

New discoveries of seagrass around Brownsea highlight the importance of its marine environment. In 2026, we’re partnering with the University of Southampton to map seagrass beds using underwater drones and support volunteer diver surveys.

This work will help guide how we protect and enhance marine life around the island.

Working with communities and partners

More than 300 local people, organisations and harbour groups contributed to early stages of coastal planning for Brownsea Island. Their insight continues to shape our approach.

We’ll keep working with:

Dorset Wildlife Trust
BCP Council’s Flood & Coastal team
Poole Harbour Commissioners
Local schools and cultural organisations
The Environment Agency
Marine and conservation partners

Together, we’re shaping a future that respects Brownsea’s past while ensuring it remains a vibrant, resilient island for generations to come.

A resilent future for Brownsea

Coastal change is natural and unavoidable. But by planning ahead, working within the guidance of the Shoreline Management Plan and collaborating with partners and communities, we can ensure Brownsea Island continues to thrive.

Our goal is simple: to keep people safe, protect wildlife, and allow this remarkable island to adapt naturally and beautifully as the coastline evolves.