Keeping the sea at bay
For over one hundred years, Poole has worked constantly to protect itself from the eroding effects of the waves, as Nick Wood recounts
Published in August ’10
‘By gradually carrying out the works recommended…a considerably greater improvement in the condition of the foreshore can be effected….To achieve this, however, as is indeed essential in all works on the sea coast, great care and constant vigilance are needed…’ This was the advice given by Professor L F Vernon-Harcourt in 1903 to the Poole Harbour Commissioners regarding erosion at Sandbanks and a proposal to construct an under-cliff drive at Bournemouth. If the narrow neck of land leading to Sandbanks had been breached, it would have changed the face and the history of Poole, jeopardising the operation of the Harbour and the development of the peninsula, which is now famed for its expensive property and celebrity residents. Seaside postcards from this time already show the developing use of the coast for leisure, the erosion of the cliffs and, in some cases, what seem to be early attempts at coast protection.
Professor Vernon-Harcourt found that the thirteen groynes built at Sandbanks between 1896 and 1898 were already in need of repairs and additions. He was able to make use of sea charts going back to 1785 and the results of ‘float experiments’ made in 1890 by John Elford, the Borough Surveyor, in connection with the Poole sewage outfall. The Borough’s engineers have been working on the cliffs and beaches ever since but now have the benefits of computer modelling and highly accurate surveying to assist them. The most recent works were the construction of rock groynes at the Borough boundary at Branksome Dene Chine in early 2009. Fifteen such groynes now protect Poole’s beaches, along with two earlier timber and rock groynes subsequently capped with concrete. The remains of earlier groynes are now buried beneath the beach itself.
The soft sands of the cliffs are inherently vulnerable to erosion and were probably eroding by around one metre per annum before coast protection works began. The construction of sea walls and promenades greatly reduces the rate of cliff erosion but also limits the supply of eroded cliff sand to the beach, resulting in beaches becoming lower and narrower. Eventually, the sea walls and promenades themselves are undermined.
The techniques used to protect the cliffs and beaches have shaped the character of the coast today. In many places the near-vertical cliffs have been re-graded and stabilised by planting. In 1962 the Borough’s Parks Superintendent, Ernie Gale, published a paper on the Borough’s experience, including an account of heather clotting: using heather turfs to restore the natural vegetation of the cliffs. Such work was carried out from at least the 1950s. It is estimated that work near Branksome Chine in the early 1970s used over 27,000 heather turfs, each a foot square and at least three inches thick. All the work was carried out by hand from a platform lowered down the cliffs, which, although re-graded, were still at a slope of around 42%. There was some concern about how quickly the platform could be returned to the top of the cliff should one of the workers need to answer an urgent call of nature.
A different technique was used at around this time at Canford Cliffs, where steel troughs where fastened to cables let down the cliff face, filled with an appropriate planting medium and then seeded with grass. However, further works were required in the mid 1990s when Cliff Drive, which runs close to the cliff edge, was threatened by erosion. The steepest part of the cliff was reinforced with steel soil nails driven horizontally into the cliff and the lower slopes were again covered with soil and re-seeded. The increasing recognition given to the wildlife interest of the cliffs meant that protected sand lizards had to be temporarily removed from the site whilst work was in progress.
Despite the inherent risk of building close to the shore or cliff edge, there seem to be few examples of properties actually being lost. However, a house built by a sea captain at Canford Cliffs in 1878 became known as Simpson’s Folly. It was so badly undermined by erosion that its demolition was eventually carried out with the aid of explosives, a technique not normally used by the Borough’s engineers today.
Sea-walls have been constructed for over half the length of Poole’s coastline in a dozen or so separate projects. The inclusion of promenades has allowed easy access to the beach and provided room for beach huts and other facilities for the growing tourism market. The Solarium, opened at Branksome Chine in November 1932, even included what was described as ‘England’s first indoor beach’, with dried sand and sun lamps to enable visitors to work on their tans whatever the weather.
Work in the earlier part of the last century relied on relatively primitive equipment, including steam traction engines and the construction of temporary rail lines along the bottom of the cliff to move materials. Modern machinery has increased the efficiency of such works but it is still an expensive business; the construction of four new rock groynes, the re-building of two existing groynes and ancillary works at Sandbanks in 2000/2001 cost just over £1 million, largely funded by central government. This scheme also included the creation of 2500 square metres of new sand dune designed to soften the appearance of the new coast protection structures by working with natural processes. Such work had begun a few years earlier with the experimental planting of marram, and the protection of the developing dunes from trampling by fencing. Marram can spread rapidly and grow up through accumulating sand. The success of the dunes and the increase in beach levels was soon evident as waist-high fences were reduced to knee-height by rising sand levels. If the dunes grow too high, the tops are removed and used to re-vegetate other eroded areas.
A supply of sand is necessary to create dunes and maintain beach levels, but this is limited if cliff erosion is controlled. The Borough’s engineers, working with the Poole Harbour Commissioners, have addressed this problem by beach replenishment: pumping sand, dredged from the shipping channels of Poole Harbour, onto the beaches from Sandbanks to the Borough boundary, with similar work being undertaken on beaches at Bournemouth and Swanage. The month-long project around Christmas 2005 resulted in over half a million tonnes of sand being pumped ashore and distributed along Poole’s beaches via a pipeline, which eventually extended to over two thousand metres in length. These works proved something of a tourist attraction in their own right, with large crowds watching the sand being moved by the tonne rather than the traditional bucketful.
Over one hundred years after Professor Vernon-Harcourt’s study, a new Shoreline Management Plan is being prepared for the coast between Durlston Head and Hurst Spit which will look forward for the next one hundred years. The plan will need to consider both local conditions and the impact of global factors such as climate change. This will present new challenges to the engineers, who are now responsible for exercising the ‘great care and constant vigilance’ advocated by Professor Vernon-Harcourt.
[The author would like to thank Dave Robson, Stuart Terry, Sarah Austin and John Lockwood for their help in the preparation of this article.]