Close
CareMoor

8-Why was a policy of limited intervention adopted following the ridge failure?

After the breach the Porlock Bay and Marsh Working Group, comprising officers from the Environment Agency, English Nature, West Somerset District Council, Exmoor National Park Authority, the two major landowners, the National Trust and the Porlock Manor Estate was convened.  Its brief was to make recommendations for the future management of the area to the various planning authorities, especially coastal district councils and in particular to a forthcoming meeting of the Environment Agency’s Somerset Local Flood Defence Committee on July 11th 1997.  A meeting was also called of all Interest Groups and a briefing paper was sent out to the local community, outlining the history of coastal processes at Porlock Bay, the current issues being faced and the various options for the future.  A public meeting was called by Porlock Parish Council at which a presentation was given by members of the Working Group.

The group took expert advice from Professor Pethick of the University of Newcastle’s Centre for Coastal Management who set out a series of options for it to consider with the following management objectives:

  1. Do nothing.  The responsible authorities would no longer take any interest in the site and there would be no management, monitoring or intervention of any kind either to the ridge or the low lying land behind as it became increasingly inundated by salt water.
  2. Restore the existing shingle ridge through artificial rebuilding with shingle and breach filling together with the creation of a more efficient drainage system, to re-establish the same level of sea defence that existed before the breach.  This would maintain the present land use behind the ridge using a combination of ridge restructuring and improved drainage. As a result the traditional system of agricultural land management including the existing SSSI would be retained and there would be no dislocation of the established footpath network.
  3. Limited intervention designed to help natural processes achieve a sustainable outcome.  This approach, referred to as managed retreat or realignment, emphasises local communities working with and adapting to changes resulting from natural processes as they occur.  It is also a management approach which accepts that from time to time some form of limited intervention may be appropriate to achieve the most sustainable outcomes for nature and people.  For example it was recognised that if a biodiversity rich inter-tidal salt marsh habitat was to establish itself behind the breached shingle ridge then it was very likely that the existing New Works sluice gate would need to be maintained and a deep artificial inter-tidal channel created through the ridge connecting to an artificial salt marsh creek system behind.  This would allow maximum sediment input since salt marsh vegetation will only become established once a layer of silt has been deposited.  In addition it was also felt that once such a channel system had been created regular maintenance would probably be necessary in order to keep the entrance clear of shingle.  It was considered also that intervention, in turn, could range from general site management (e.g. undertaking litter clearance, controlling visitor access and providing interpretation facilities) to the provision of basic structures to control water levels or retain a required water level across a particular part of the marsh.
  4. Major intervention through the complete removal of the existing ridge structures.  This would be preceded by a long period of re-modelling and its eventual replacement with a new re-profiled and aligned ridge, creating a larger area of brackish lagoon within the marsh (which Pethick considered to be the original environment behind the ridge) and a new system of associated drainage streams which would also help to control the salinity of the lagoon.  An important outcome of this approach would be to create a re-profiled continuous and permeable beach ridge with a crest lower than that which had existed before the breach.  This would allow wash over as well as seepage to supply saline water to the lagoon where it would mix with freshwater entering the lagoon via streams from the interior.  Ensuring the constant availability of a sufficient shingle supply to rapidly fill any future breaches in the ridge was crucial to this option.

The decision to recommend a strategy of limited intervention including allocating some funding for maintaining the outfall sluice at New Works, refurbishing groyne systems, monitoring and reviewing the ridge and to support the rerouting of the coast path, was informed by a number of important considerations including the following:

  • The 1996 breach being just one tiny and in terms of geomorphology, insignificant event, in the overall history of Porlock Bay stretching back tens of millions of years compared with the  infinitesimally short period of time (less than two hundred years) during which attempts had been made through human activity to protect the ridge and marsh from erosion and inundation by the sea.  Research shows that over the past 5000 years, the shingle ridge had breached and reformed naturally many times as it moved inland and that Porlock Marsh had been both a fresh water and saline environment on numerous occasions as a result.  For many geomorphologists such as Professor Pethick, the breach was seen as an inevitable stage in the long history of Porlock Ridge so that any attempt at repair would merely be to postpone the inevitable.
  • The storm of October 1996 was the latest in a series of storms that had breached the shingle ridge, the most recent in December 1981 and February 1990. During the 1980s schemes to strengthen the ridge had been prepared and rejected on the grounds of both a lack of financial viability and adverse ecological impacts.  In 1993 the Somerset Local Flood Defence Committee decided that the ridge should continue to be maintained for a year by moving shingle from the harbour to the weak point of the ridge at Porlockford, after which it recommended that when the shingle ridge next breached, it should not be prepared, but a salt marsh be allowed to develop behind it.
  • The ‘do nothing’ option was widely opposed and condemned locally with concern expressed over issues such as potential tidal litter problems at high water mark, dangerous and unattractive derelict structures remaining across the marsh, loss of access along the coast path and from Porlock village to the beach, exposed mud and potential resultant smell, the degradation of the duck decoy and possible pollution associated with the disruption of the sewage outfall from Porlock village due to submersion or regular inundation.
  • Given a scenario of likely rising sea levels, larger inshore waves, increased frequency of severe weather events and associated storm surges the option of restoring the existing shingle ridge to its pre-breach condition was considered both economically unviable and environmentally unsustainable, even though it would retain the traditional system of agricultural land management and the existing SSSI in its current state.    Assessment indicated only limited economic benefits would be derived from restoring or improving the shingle ridge and as a result the costs of any restoration scheme would far outweigh the financial benefits.  Over the previous sixteen years the ridge had already been rebuilt twice and a programme of low key maintenance had also been tried.  Regular and increasingly severe breaches would inevitably occur if the ridge was rebuilt and this option was seen as the ‘blank cheque’ scenario requiring a considerable financial commitment to constantly repair and rebuild the shingle ridge in perpetuity and in what would certainly prove to be an ultimately futile attempt to resist natural processes.  A 1992 report by Posford Duvivier for the Environment Agency estimated that over 1000 cubic metres more shingle would be required year on year to provide the same standard of defence and a further 2000 – 4000 cubic metres of shingle would be needed annually to compensate for the drift of shingle from the area at greatest risk of breaching at Porlockford.
  • The likely outcomes of a major intervention programme involving remodelling the entire coastal system after a long period of complex scientific study were considered to be far too uncertain to support.  This together with the very high financial cost of the scheme which was very unlikely to receive the support of government agencies meant that this possibility was never a viable option.
  • The then government department MAFF (Ministry of Agriculture, Fisheries and Food) which was merged into DEFRA in 2002 indicated that the area of Porlock Marsh would be suitable for their Countryside Stewardship Scheme.  Under this scheme landowners qualify for financial payments for work that they do to enhance biodiversity and the environment.  It was considered that such qualification would help compensate farmers on the marsh for lost income as low intensity grazing land with limited areas of arable cropping and reed bed production, notably in the low lying area behind the New Works outfall, were ‘lost’ over time to expanding salt marsh ecosystems.
  • An environmental assessment undertaken by Posford Duvivier of the existing SSSI behind the ridge ‘failed to identify any assets in the area of the marsh likely to be affected by flooding which are of more than local value’ and consequently no environmental reason could be found to justify maintaining or improving the standard of defence offered by the ridge.
  • By the 1990s and influenced by the pioneering work of geomorphologists such as Professor Bill Carter of the New University of Ulster, government policy was moving away from highly technocentric or ‘hard engineering’ approaches to coastal management such as sea walls, rip rap and gabions to seeking more sustainable options.  The political climate was now one of working with and adapting to coastal processes with interventionist approaches only being approved in exceptional economic and/or environmental circumstances.  Twenty years on this same policy still provides the steer for coastal managers as  reflected in the current Shoreline Management Plan for Porlock Bay which stresses the importance of ‘allowing natural coastal evolution to continue through no active intervention’ and ensuring that adaptation measures are implemented at the settlement of Porlock Weir to manage or adapt to the risk of flooding

Consolidate Your Thinking

Under the DEFRA Countryside Stewardship Scheme compensatory funding is available to land owners and farmers for environmental land management.  Farmers and land managers who choose options that support wild pollinators and wildlife and improve water quality or reduce flood risk are more likely to receive a grant.  There are a range of grants available under the Countryside Stewardship Scheme to support farmers and land managers who wish to adopt a variety of natural flood management techniques and help slow the flow of water with in a catchment and to reduce the impact of flooding downstream.  Referring to the infographic at https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/570105/cs-flood-reduction-infographic.pdf describe and explain which options would be most relevant to landowners at Porlock Bay and suggest the environmental benefits that could result.


Go to Question 9 - Twenty years on what have the cost and benefits of the limited intervention policy been?