Coast protection in Purbeck

Purbeck District Council has a coastline of approximately 100km, which extends from Poole Harbour in the east to White Nothe in the west. The coastline includes the southern boundary of Poole Harbour and the islands within it.

Most of the coastline of the district is undeveloped and, in general, the council does not take any action to combat coast erosion. It is only where the coastline is developed that it is generally economic to carry out coast defence works.

There are two different types of coast defence works:

Works which protect against flooding of the land. These are called sea defence works and are carried out in accordance with the Land Drainage Act 1991.
Works which protect against erosion. This is where the land behind the works is higher than any tidal flooding level. These works are termed coast protection works and are carried out under the Coast Protection Act 1949.

The Government, by way of the Department for the Environment, Food and Rural Affairs, give maritime District Councils grant aid for carrying out works on the coastline provided that it can be shown that the works are technically sound and are environmentally, socially and economically justified.

Swanage

The only significant area of development, where coast defence works have been carried out, is at Swanage. Here there is a length of approximately 1.8km of coast defence works which principally involve concrete or stone sea walls and timber groynes.

Around the southern part of Swanage bay the coastline is protected by a stone wall and stone groynes to stabilise the beach. These were in place prior to 1900.

The second stage developed a generic management option for each specific length of coast. This could be:

to do nothing and allow erosion to continue
to control the amount of erosion by engineering techniques but retreat from the existing line of the coast
to prevent further erosion by maintaining existing or providing new defences on the existing line of the coast
to prevent further erosion by providing new defences in front of the existing line of the coast

The preferred options have been set out in the plans which have now been adopted by the relevant authorities and will provide the framework for the management of the coast in the future. Those plans are currently in the process of being reviewed with a second round of shoreline management plans. .

The purpose of the study at Swanage Bay was to appraise the effectiveness of the existing groynes, sea walls, and other coastal defences, as well as to look at where coastal defences were required in other locations around the bay. The report recommended a scheme to increase the width of the beach by recharging with sand to make it more effective in dissipating wave energy.

Consultations were carried out on this scheme and the council gave its approval to proceed with the design stage of this scheme in October 2004. Work on site started on installing the timber groynes at the end of October 2005 and approximately 90,000 cubic metres of sand were deposited on the beach. The works were completed at the beginning of June 2006. The final scheme cost was about £2.2 million.

Coastline protection history

Since the late 1990s there has been a significant change in the way that issues concerning the coast have been managed. This arose from the increased awareness of the need for a closer working relationship with those dealing with the coast and neighbouring Authorities.

Shoreline management plans were implemented which developed specific policies for dealing with issues on the coast. Purbeck District Council was involved with the neighbouring authorities in undertaking these plans.

The district's coastline falls within two separate plans:

The plan for the western length, defined as sediment sub-cell 5g, is for the length of coast from Durlston Head to Portland Bill
The eastern section, from Durlston Head to Hurst Spit, is defined as sediment sub-cell 5f.

Both these plans were completed in about 1999 and are available in Purbeck's office for inspection.The purpose of these plans is to provide a strategic framework for the long-term management of the coast. These plans were undertaken in two stages. The first stage involved gathering all existing data on the coastline and establishing what further data was required, as well as formulating a brief for the second stage.

Beach recharges

The scheme was designed to cater for a one in three hundred year storm and the performance of the beach and the near shore sea bed is monitored as part of the "Strategic Regional Coastal Monitoring Programme". This is a programme of monitoring along the whole of the south coast.

This provides measurement to assess the amount of movement of the sand and will provide the data to establish when the beach will need to be recharged. It is expected that there will be a loss of sand from the beach and that it will periodically need recharging. At the time of the design, it was estimated that there would be a need to recharge the beach with about 40,000 cubic metres of sand every 20 years.

A further study was being carried out to look at the possibility and impact of deepening the entrance to Poole Harbour and whether the dredged material could be used for re-charging the beaches at Bournemouth, Poole and Swanage. The study showed that there would be little impact to the harbour and therefore this material was used for the recharge of Swanage beach with the benefit of considerable cost savings.

The recharge contract was undertaken as a separate contract to the groynes contract as it involved partner authorities at Poole and Bournemouth as well as Poole Harbour Commissioners.

Further information

Purbeck District Council is a member of the Standing Conference on Problems Associated with the Coastline (SCOPAC) and you may be able to obtain more information from the SCOPAC website. (opens in a new window)

Part of the district's coastal boundary, running from the chalk stacks at Old Harry to the district's western boundary, forms part of the world heritage site. More information about the geology and geomorphology of this coast can be found on the Jurassic Coast website. (opens in a new window)

Shoreline management plan
A shoreline management plan (SMP) is a strategic document that sets out policies to assist decision-making on flooding from the sea and coastal erosion risk management over the next 20, 50 and 100 years.
Swanage Beach Recharge Scheme
During the winter of 2005/2006, 1.1 million cubic metres of sand was dredged from Poole Harbour channels and pumped on to the beaches of Swanage, Poole and Bournemouth to protect them from erosion as part of a £5 million coastal protection project.