Southsea Seafront Enhancements

Detail from the Collaborative Enhancements Plan related to the Southsea Coastal Scheme. Click the image to view the detail.

Solent Protection Society have been engaged as a public stakeholder in several of the Solent’s coastal sea defence enhancement schemes as part of our watching brief over the preparations to confront the inevitable impact of climate change on the region.

Low lying Portsea Island lies at the heart of the City of Portsmouth and with significant historical building assets and a population in excess of 200,000, the engineering effort required to protect the city is immense. The work has been driven by the Eastern Solent Coastal Partnership, recently rebranded as Coastal Partners , who have been managing an extensive programme of engagements with the wide variety of local stakeholder groups involved.

With our background in coastal engineering and marine sciences, the members of the SPS Council understand that on a rough 80:20 rule, the bulk of the work involved is coastal engineering. However at times some of the public stakeholders appear to expect the greater part of the focus to be on maintaining and enhancing the fabric of the historic assets. The Coastal Partners team have approached this stakeholder management task to good effect with notable effort and commendable patience. The decision whether to adopt a policy of managing natural re-alignment of the coastline or one of actively ‘holding the line’ is always going to court local controversy approaches’. However, when a hold the line policy is the only option, as in the case of Portsea Island, the need to literally raise the level of the sea defences inevitably leads to protests from groups who feel that the value of sea views and property is being compromised.

Coastal Partners have secured central government funding for the engineering side of the Southsea Coastal Scheme, with Historic England and Portsmouth City Council contributing to the funding and management of the more publicly visible assets. In parallel with the coastal engineering work, the city council’s Seafront Masterplan is available for public consultation until October 30.

Coastal Squeeze and Rollback

It is generally accepted that sea-levels are rising in Britain, although there are many opinions about the causes and the rates. Most scientists believe that the rate of sea-level rise has already accelerated and will continue to do so until levels of atmospheric carbon-dioxide start to be reduced.

Regardless of the cause or rate of sea-level rise the effects are the same, in a natural system land is “lost” and becomes sea. With a high coastline this manifests itself as erosion of the cliffs, but with a gently rising coastline the result is a slow movement of the shoreline inland – so over time a particular piece of land will change from dry land to shoreline shingle or mud, then foreshore and eventually to sea. The rate of change will depend on sea-level rise, but also on how “dynamic” the environment – how exposed it is to tide and waves.

In the case of a defended coastline if defences are maintained and increased to take into account the sea-level rise (Hold the Line in SMP’s etc) this results in the seaward side of the defence continuing to develop naturally – ie change from foreshore to sea, but the landward side remains the same. The result, known as “Coastal Squeeze” is that the foreshore (Sand, shingle or salt-marsh) is slowly lost together with the natural transition zone from land to sea.

The habitats of these ephemeral transition zones are both rare and important and as a result many are designated under international, European and National designations which require them to be protected.

We are very fortunate locally as the New Forest Coastline contains some of few areas where there is natural gently rising coastline. This is rare, particularly in Southern England, where most of coastline is heavily managed and defended to provide flood and erosion protection. These areas show a natural graduation from farmland, often to a narrow strip of woodland, then to a foreshore, often with the remains of fallen trees, to foreshore and salt-marsh.

The narrow strip of woodland provides a unique habitat, and the tree-roots will slow, and control the rate erosion. The fallen trees also provide a unique habitat and make the shoreline interesting and very different from most other places.

Within the Solent Protection Society we believe that these unique habitats should be maintained, by natural processes, and that they cannot be maintained by traditional engineering works. The most effective way to maintain the habitat is to allow natural roll-back. This should be done by allowing natural regeneration of indigenous vegetation, particularly woodland, along a margin between farmland and the coastal strip.

We would welcome members opinion of how these habitats should be managed and whether this should be funded by public authorities, or whether the landowner should be expected to manage appropriately.