Improving coastal resilience in Southsea, Portsmouth

The Southsea Coastal Scheme aims to reduce the risk of flooding and erosion along 4.5km of coast. It’s the UK’s largest local authority-led coastal defence project, worth more than £160 million, and will preserve heritage, and enhance recreational areas and the environment.

The challenge: protecting local communities against flooding and erosion while breathing new life into a dated seafront

The current coastal and flood defences in Southsea, Portsmouth have come to the end of their serviceable life. In 2015, they weren’t expected to last more than 10 years.

TThe defences were too low to provide sufficient protection to the 10,000 homes and 700 commercial properties at significant risk of coastal flooding and erosion, particularly with predicted sea level rise. To protect local residents and businesses, as well as preserve and improve the area’s unique heritage and amenities, the defences need to be replaced.

With sea levels set to rise by approximately 1m, and extreme weather events predicted to increase over the next century, Portsmouth City Council needed a solution that would provide effective protection against the impacts of climate change well into the future.

The solution: integrated coastal engineering balancing nature and architecture

The Southsea Coastal Scheme is a once-in-a-generation scheme to strengthen coastal defences, provide flood risk reduction, and enhance the seafront. It includes a mixture of seawalls, stepped revetments, raised promenades, embankments, rock structures and managed shingle beaches coupled with highway and public realm improvements. It is being completed by an integrated delivery team, with Royal HaskoningDHV as the lead detailed design engineer.

We were chosen for our extensive experience in detailed engineering for flood and coastal defences and are involved throughout various stages of the scheme – from scoping and initial design, through to detailed design and construction support, set to completed in 2028. Our approach emphasises regeneration, enhancing the public realm, and preserving the area’s historic and cultural features – without negatively impacting the natural environment.

Part of this is reducing material use and waste as much as possible. For example, the project team has optimised designs and developed a local waste processing site to process, store, and reuse materials including concrete, earth, and stone. And we’ve repurposed materials from the demolished sea defences as a temporary flood protection, then recycled them again. Nature-based solutions and biodiversity play a vital role, enhancing habitat creation and species preservation, and increasing the amount of green areas.

The project will progress over six phases, or frontages, each focusing on a different area of Southsea.

The 6 frontages

This once-in-a-generation project will preserve Southsea’s rich history and create sustainable recreational space, while reducing the flood risk for local residents and businesses 100 years into the future.

Thomas GreenSenior project manager at Royal HaskoningDHV

The result: enhanced flood resilience for the next 100 years

Once complete, the scheme will provide flood and erosion risk reduction for 10,000 residential and 700 commercial properties, three scheduled ancient monuments, four critical access roads, and more.

It will guard against the predicted 1m rise in sea levels, and provide a 1 in 200 year standard of protection over the next 100 years.

The scheme also ensures Southsea’s seafront will be regenerated, creating a more accessible and sustainable coastal environment with recreational spaces and increased biodiversity. It will help preserve a significant length of uncovered historical structures, like 17th-century city walls, tunnels, and defences.

The scheme will also contribute more than £12 million through local jobs, training, and investment. Almost three quarters of the workforce are local, and so far, the scheme has engaged with 40 local organisations, and volunteered 450 hours to community projects – ensuring Southsea is involved at every step.

Explore the Southsea Coastal Scheme

The zero-waste construction initiatives are predicted to save:

0of waste going to landfill

0in landfill costs

0lorry movements

0to move materials

0of CO2 being released

0of wood, recycled for use in other schemes

A widely recognised and multi-award-winning scheme

Frontage 1, Long Curtain Moat, received multiple awards for its engineering excellence and positive impact on society.

Winner – 2024 ICE South East England: Large Project, A grand scale project that demonstrates excellent engineering prowess

Winner – 2024 ICE South East England: Nature and People Positive, Recognised for prioritising sustainability and having a positive impact on communities

Winner – Flood and Coast 2024 Award: Climate Resilient Places, Recognised for project excellence, beating over 90 other submissions

It was also a finalist for several other awards including:

Runner up – 2023 Concrete Society Awards celebrating excellence in the use of concrete
Runner up – 2023 Construction Excellence SECBE Award for Sustainability
Shortlisted with “highly commended” – 2024 British Construction Industry Awards: Placemaking Project of the Year recognising initiatives that create quality public spaces for people to use and enjoy
Shortlisted – 2024 British Construction Industry Awards: Environmental Project of the Year recognising projects that mitigate the impact of extreme weather and climate change on people, businesses, and infrastructure