Coastal Management on the Isle of Wight

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1 Coastal Management on the Isle of Wight Setting the scene The Isle of Wight has 65 miles of spectacular coastline, 28 miles of which are designated Heritage Coast. This varied coastline is one of the Island s main assets. Proper management of coastal development, including the planning of its defences, is necessary in order to sustain the beauty and variety of the coastline for future generations. Many piecemeal structural defences, such as revetments and groynes, have been haphazardly constructed to protect coastal property, by limiting the loss of sediment, without any thought of the consequences to adjacent stretches of coastline. There is greater understanding now that a structure on one section of coast may upset the balance of natural processes and cause erosion on an adjacent stretch. It is also now known that the coastline can be divided into sediment cells, lengths of coastline where the cycle of sediment erosion, transport and deposition are self-contained. Eleven major sediment cells have been identified around the coast of England and Wales. The Isle of Wight lies within a major cell that extends from Portland Bill to Selsey Bill. Regional Coastal Groups have been set up to ensure that liaison is made with all the local authorities and advisory bodies within each sediment cell. The Isle of Wight plays a leading part in the group that established a blueprint for other coastal groups - The Standing Committee on Problems Associated with the Coastline The Isle of Wight Shoreline Management Plan A Shoreline Management Plan is developed by the local council, the Environment Agency and a range of other consultees, including Natural England (the Government s advisory body on nature conservation). An SMP takes into account coastal processes, the natural environment, planning issues, coastal defence needs and current and future land-use, for the 168 kms (104 miles) of open coast, harbours, estuaries and headlands around the Island.

2 SMP 1 (2007): The Isle of Wight Council and the Environment Agency are the two operating authorities for the Isle of Wight s coast, and in 1997 published the first Shoreline Management Plan for the sub-cell that lies between Hurst Spit in the west and Selsey Bill to the east. SMP 2 (2011): The second SMP for the Isle of Wight was prepared by a Steering Group comprising representatives from: Coastal management, Isle of Wight Council Environment Agency Natural England English Heritage National Trust Isle of Wight Estuaries Project Planning Services, Isle of Wight Council Parks and Countryside Service, Isle of Wight Council Archaeological Centre, Isle of Wight Council Area of Outstanding Natural Beauty Funding is provided by the Department of Food and Rural Affairs (DEFRA) through the Environment Agency. The consultation phase was completed by the summer of 2010, and was adopted in January The Isle of Wight s coastline has been sub-divided into seven policy development zones (PDZs). Within each zone, the natural coastal processes are sufficiently independent of the stretch adjacent to it. The zones are as follows: 1. Cowes and East Cowes 2. North-east coast 3. Sandown Bay 4. The Undercliff 5. South-west coast 6. West Wight, Freshwater Bay to Yarmouth 7. Newtown estuary and Thorness Bay Coastal Defence Options There are four options for management of a stretch of coastline, based on guidelines drawn up by the Ministry responsible: 1. Hold the line. Retaining the existing line of defence through maintenance of existing defences or by constructing new defences where existing structures no longer provide sufficient protection.

3 Map 1. A map of the Isle of Wight showing where the 'Hold Line' option is being implemented. Hold the Line 2. Managed Realignment. Actively manage the rate and process by which the coast retreats (known as 'managed retreat'). This option has been used in one location in the Newtown to Thorness Bay PDZ Map 2. A map of the Isle of Wight showing where the 'Managed Retreat' option is being implemented Managed Retreat 3. No active intervention. The option chosen for stretches of coastline where it is not technically, economically or environmentally viable to undertake defence works. The value of the built environment along all the stretches of coastline shaded blue on the map below does not exceed the cost of installing coastal defences. Map 3. showing where the 'Do Nothing' option is being implemented. Do Nothing 4. Advance the line. Build new defences seaward of the existing line. This option has been carried out at one location along the Undercliff PDZ, at Wheelers Bay, Ventnor. Some examples of Coastal defence schemes on the Isle of Wight The advice given in the Shoreline Management Plan for the stretch of coast below Bonchurch and Ventnor between Monk s Bay and Steephill Cove, was to hold the line. The following examples (1 to 4 on map above) of coastal protection schemes completed since 1991 are all located along The Undercliff, a coastal zone reputed to form the largest built-up coastal landslide complex in north-west Europe.

4 Monk s Bay The cliff failure at Monk s Bay which resulted from a combination of high energy destructive waves and high rainfall associated with the severe storms over the winter of 1990/1991 gave additional impetus for the upgrading of the coastal defences at the eastern end of the Island s Undercliff.. The scheme involved the construction of an offshore breakwater, six rock groynes, beach nourishment using 17,000 cubic metres of sand and gravel and rock revetment to reinforce the existing sea wall. 25,000 tonnes of Swedish granite was off-loaded onto by barge. Re-profiling the slope and installing land drainage checked the active mass movement of the cliffs on the western side of the bay. Monk's Bay The collective value of the property stabilised by the upgraded coastal defences, including the East Dene Field Study Centre, far exceeded the 1.4 million cost of the scheme. Since completion in 1992 there has been a significant loss of placed sand and gravel to the east as the material has over-topped the rock groynes. Wheeler s Bay The danger of reactivating ancient landslides by a collapse of ageing sea walls at Wheelers Bay resulted in property on the cliff behind the bay becoming unsaleable. Government grant aid was awarded for a scheme to protect and stabilise the coastal slopes.15, 500 tonnes of Norwegian granite was placed seaward of the existing defences to form a rock revetment and the coastal slopes were regraded to make a shallower profile before installing land drainage. The scheme was completed in 2000 at a cost of 1.6 million. Property values of the houses immediately behind Wheeler s Bay have since recovered. Wheeler's Bay

5 Western Cliffs These cliffs below western Ventnor consist of blocks of chalk brought down by landslide activity over several thousand years and provide a natural protection from marine erosion to the scores of houses constructed on the ancient landslide complex inland. However, high-energy waves and sub-aerial processes have been removing the chalk and there has been a real danger that lateral unloading could reactivate the landslides. 1.2 million of Carboniferous limestone has been brought in from the Mendip Hills of Somerset to construct a 700 metre long rock revetment along the base of the cliffs, using blocks weighing 6 to 8 tonnes. The natural protection afforded to the chalk cliffs from boulders of Upper Greensand strewn on the shore has been reinforced by the construction of a series of Somerset limestone rock groynes at 100 metre intervals at the base of the cliffs. Western Cliffs Castle Cove Wooden revetment sea defences were being left progressively ineffective as the Gault cliffs retreated round Castle Cove. Property valued in excess of 10 million was becoming increasingly at risk as coastal processes reactivated ancient landslides. A scheme was drawn up to stabilise the environmentally sensitive cliffs by removing the topsoil, re-grading the slope, stabilising the slope with thousands of tonnes of chalk installing land drainage and reinstating the topsoil. The cliff toe has been protected with a rock revetment of Somerset limestone, a reinforced concrete walkway and a gabion wall. The scheme was completed in 1996 at a cost of 2.3 million. Castle Cove The following coastal protection scheme (7 on map above) is located on the north-east coast between St Helen's and Seaview, and was completed in the summer of 2000:

6 Seagrove Bay The advice given in the Shoreline Management Plan 2 for Seagrove Bay, with its unstable slopes and crumbling seawalls maintained by the residents themselves, was for the Isle of Wight Council to intervene and hold the line to protect the property along this stretch of the Island s north-east coast. For at least 100 years. The 900,000 scheme included a new concrete sea wall, with 200 metres of rock revetment placed in front of the wall to dissipate the energy of the waves. Rock groynes were constructed as a further layer of protection. Mass movement on the soft clay cliffs has significantly reduced by installing land drainage. The Military Road on Afton Down A mile east of Freshwater the A3055 passes over the chalk ridge and comes within eleven metres of the cliff edge. (6 on map above) Afton Down Sea defences would be economically unjustifiable and environmentally unacceptable and therefore a pioneering scheme was devised to stabilise the cliff top by anchoring the cliff face top solid chalk on the landward side of the road. The scheme was completed in the autumn of 2001 at a cost of 750,000. Castlehaven A 3.5 million scheme commenced in the autumn of 2003 to stabilise a section of Lower Greensand cliffs, just to the east of St Catherine s Point (5 on map above), where property valued at around 2 million was at risk from active coastal processes. The scheme was delayed because there were objections from conservationists about the impact of land drainage on part of the UK s soft cliff habitat that supports many nationally rare insects and plants. Following a public enquiry in August, 2001, a revised scheme was accepted by DEFRA and 70% funding was made available for the scheme to commence.

7 40,000 tons of Jurassic limestone was shipped over from France to construct a 550 metre long revetment. The sophisticated land drainage scheme was installed by French engineers using electro-magnetic wells and siphon wells to keep the winter groundwater levels at the average summer level. The whole coastal protection scheme was completed in Meanwhile, the coast road a short distance to the east of Castlehaven remains closed to commercial vehicles with a width restriction in place, due to a landslide that removed part of the road in Castlehaven For more information follow the link to