Portsmouth’s Southsea Coastal Scheme in full swing

The Southsea Coastal Scheme is the UK’s largest local authority-led coastal defences project – worth more than £100 million.

This capital coastal protection program will stretch for 4.5km, from Old Portsmouth to Eastney, and help to reduce the risk of flooding to more than 10,000 homes and 700 businesses.

The current defences are coming to the end of their lifespan, which increases the risk of flooding in Southsea.

The work is set to improve the seafront for future generations and stimulate regeneration, whilst protecting the community and preserving the area’s unique heritage.

There are 8,077 homes and 704 non-residential properties in Southsea at risk of flooding from the sea. Current defence levels only offer limited protection from coastal flooding and the existing structures have residual lives of less than 10 years, with two major failures in recent years.

If improvements are not undertaken, the current defences will continue to deteriorate with an increasing risk to property and lives. Sea level rise and the increase in extreme weather events predicted over the next 100 years will continue to put Southsea’s coastal defences under increasing pressure.

The project aims to mitigate increasing risks of flooding from the sea, and high tides & winter storms.

In 2020, the government awarded nearly £100m of funding to the project.

Funding from the Environment Agency was the final hurdle the Portsmouth City Council project had to overcome and work started on 7 September 2020.

Previously, Portsmouth City Council was allocated £6.5m of grant funding from central government to progress the design phase of the project. This came following approval of the scheme’s Outline Business Case by the Environment Agency, Defra and HM Treasury.

Following planning approval of the principal design, council presented a Full Business Case to government to apply for the funding for the construction works.

This project is being delivered through Coastal Partners, with backing from the Environment Agency and UK Government.

Leading the detailed engineering design stage is Royal HaskoningDHV, supported by Atkins and LDA Design for landscaping and public realm.

The contractor for the scheme is VSBW, a joint venture between VolkerStevin and Boskalis Westminster.

The partnership brings together two of the world’s leading maritime contractors; VolkerStevin focusing on marine civil engineering and Boskalis Westminster on dredging, land reclamation and marine construction.

“We continue to power ahead with preparing eight bays for the fitting of an apron revetment (sloped wall). With two bays now complete, we’ve moved on to not only bay three, but to excavation on bay four as well,” said Southsea Coastal Scheme in their latest project update.

The bay work involves attaching a waling beam (horizontal beam for extra stabilising the wall) to the front pile line and a toe beam (beam at the bottom of the pile wall to provide more stability) to the rear pile line.

“We’ll fit a granite apron revetment between these two walls later in the year. This will be sympathetically designed to match the walls in the surrounding area.”

“A caponier is a type of defensive structure in a fortification (originating from the French word caponniére meaning ‘chicken coop’) and we are working next to one at the east end of the defence wall at Long Curtain Moat.”

“Here, it is essential to work carefully so as not to damage the historic walls during construction, therefore we are creating a separate wall linking the pile line to the caponier.”

“Conservation Architect Giles came to site last week to collect samples of the mortar on the city walls that we revealed in the spring.  These samples will be analysed so that we can create a mortar mix that matches the original as closely as possible for use on repairs to the historic walls.”

Thousands of tonnes of armour rock arrived in Southsea by ship recently to form new primary sea defences.

The rock is Anorthosite, which has a density of more than 2.6t per m3. This makes it incredibly heavy and durable – both key characteristics for a rock armour defence.

The first shipment of 5600 tonnes of rock was discharged onto the shore at Frontage 1 (Long Curtain Moat).

A barge and tug transported the rock from ship to shore, where it will be temporarily stockpiled before being used to build the sea defences that will form both the east and west revetment at Frontage 1.

The west revetment construction is expected to begin in the following days and will last approximately six weeks.

The whole scheme is due to be finished by 2026.