SEPTEMBER 2000 Online 388 Geofile Neil Punnett Coastal erosion – Back to Nature What has caused the personal disaster Figure 1: Report in The Observer, 1 December 1996 for Sue Earle, described in Figure 1? On a quiet summer’s day the British GREAT BRITAIN GETS SMALLER BY THE DAY coastline can seem a peaceful place. Waves gently lap at the foot of the At twilight the burning remains of Sue evict-and-demolish policy of East beach while children play on the sand. Earle’s clifftop farmhouse at Cowden Yorkshire Council as almost contempt Yet this is also a battle zone, a front were reflected in the tide lapping for the land. "We’re losing the very soil between the land and the sea where Mappleton Sands below. It had taken and it’s probably being washed up on tremendous energy is exerted by the 10 hours on Friday to demolish the the Dutch coast." He has researched waves attacking the coast, and where building, set fire to the broken timbers the fate of his bit of coast. He found considerable sums of money are spent and clear the site. A pall of smoke that since 1786 the distance between protecting the cliffs and beaches. drifted over the North Sea, obscuring Mappleton church and the cliff edge the flashes from a lighthouse on had been reduced by 3.5 km. In Coastal erosion is caused in several distant Flamborough Head. 1990–91 the rot stopped. ways (Figure 2). The rate of erosion largely depends upon the type of rock The £250,000 house was destroyed, "We campaigned strongly and forming the coast. The Holderness by court order, because it was on the Holderness District Council came up coast of East Yorkshire where Sue edge of a clay cliff that had been badly with a scheme for sea defences, using Earle’s farmhouse was located is undermined by the sea. It was in giant rocks – 60,000 tonnes – and composed of weak glacial till, which is danger of sliding onto the beach groynes," says Mr Warrington. "By this easily eroded. below. Naturally the law couldn’t allow time a four hectare field of mine had that. So on Friday they pulled the been reduced to two hectares. house down and charged its Brussels promised to contribute, but Coastal protection strategies occupants £3,500 for the privilege. only if it was to promote leisure: a car ‘The best defence against coastal erosion is They now live in a caravan. park, picnic area etc., rather than just a good beach.’ sea defences. So we could spend only US Army Corps of Engineers This could have been prevented by part of the total £1.9 million on what spending money on coastal defences. we actually needed it for. The scheme Mappleton is the small village on the has saved Mappleton, but not enough Holderness coast whose fate is James Warrington, chairman of the money was spent and our farms are described in the newspaper article parish council, watched smoke rising still threatened." (Figure 1). It is threatened by coastal from the Earles’ ruin. He sees the erosion. This is the fastest-receding stretch of coastline in the world; since Roman times it has retreated by around 6 km. Dozens of villages and Figure 2: The processes of coastal erosion towns have been lost (Figure 3). The energy released by waves can cause great damage. Waves exert a pressure of up to 30 tonnes/m2. Weathered and weak rock is washed away from Why is such rapid erosion happening the cliffs. The waves can compress air into cracks and joints in the cliff face. The here? The plain of Holderness did not compressed air is released with explosive energy as the water retreats, exist before the Ice Age. It was once a loosening even the strongest rocks. This process of erosion is called hydraulic wide bay backed by chalk cliffs action. running from Flamborough Head to Hessle, west of the city of Hull. Today The sea erodes the land in three other ways: Holderness is made up of glacial tills – • Corrasion: the waves throw rocks and pebbles against the cliffs, wearing sands and clays deposited by ice sheets them away. This is often the most important method of coastal erosion. It during the Ice Age (Figure 4). The operates fastest on coasts that are exposed to storm waves. tills are soft and unstable and have • Attrition: the rocks and pebbles are worn away as they crash against each little resistance to erosion. The low other within the water. In the process they become smaller and more cliffs repeatedly slump down along rounded. rotational slip planes, lubricated by • Solution: the water itself is slightly acidic and can dissolve some minerals water which reduces friction and within rocks, such as calcium carbonate in limestones. Recent research makes the sands and clays slip easily. suggests that this form of erosion is not as important as previously thought, The sea washes the slumped material since there is a limit to the amount of calcium carbonate which seawater can away. This rapid coastal retreat will hold in solution. The evaporation of salts can produce salt crystals whose continue until the old buried cliff-line expansion can cause rock to break up. along the eastern edge of the Yorkshire Wolds is once again Often the most effective form of erosion operating on coasts is not the sea at all, exposed. This is composed of much but sub-aerial processes such as rain and frost. Surface run-off, or throughflow, more resistant chalk rock, which will can erode the cliff faces. Rainwater can provide the lubrication for slumping to again form impressive white cliffs occur. Frost action can cause blocks to fall. In such cases the action of the sea such as those north of Bridlington. is limited to transporting away the debris from the base of the cliff. Geofile Online © Stanley Thornes (Publishers) Ltd 2000 September 2000 no.388 Coastal erosion – back to nature Figure 3: The Holderness coast, showing its retreat since Roman times The sea defences constructed at Mappleton have contributed, unfortunately, to the destruction of N Flamborough Head Flamborough Sue Earle’s home, described in Figure Key Bridlington 1. The £1.9 million scheme, completed Wilsthorpe Lost towns in 1991, includes two large rock Roman Coastline groynes and a protective barrier of Auburn granite boulders laid along the beach Hartburn Great Driffield Barmston Present towns and villages Hyde close to the cliff base. Although it Ulrome Withow Area flooded in 1906 protects the area of cliff behind the Skipsea Cleton defences, the rate of erosion of the H Atwick unprotected cliff to the south has o Hornsea Burton Northorpe trebled. This is because the groynes l Hornsea Beck d Hornsea have destroyed the balance within the Soughorpe e Rowlston coastal system (see Figure 5) and have r Great Colden Mappleton stopped the supply of beach material n Colden Parva e by cutting off the longshore drift. The s Aldborough Old Aldborough Beverley s Monkwell narrower beach south of the defences Garton Ringbrough means that waves crash against the Grimston Garth cliff foot more often and with more Hilston Monkwike Tunstall Sand-le-mere energy. Hull Waxholme Owthorne or Sisterkirke Paull Hedon Withernsea Newsham H um b Keyingham Hollym Managed retreat e r e Old Withernsea R i v r Ottringham Holmpton Partington Welwick Out Newton Hard sea defences such as those at Frismersk Tharlesthorp Skeffling Dimlington Mappleton do not work in the long Penisthorpe Turmarr term. They have to be repaired East Somerte Northord Orwithfleet Hoton regularly, and they may exacerbate 0 10 km Sunthorpe Kilnsea Old Kinsea damage elsewhere, as has happened at Burstall Priory Ravenspurn Cowden. More than 10% of the British Ealington Ravenser Odd Spurn Head coastline is now protected by hard defences. Figure 4: The geology of the Holderness peninsula Geographers have tried to persuade Flamborough Head local authorities to adopt policies of N Boulder clay ‘managed retreat’, whereby natural Bridlington overlying processes are allowed to take their chalk cliffs course and people affected are paid Great Driffield compensation – this would often be cheaper than the cost of the massive Key ‘hard engineering’ defence schemes. Alluvium Hornsea Mappleton Boulder clay In August 1998 the House of (glacial tills) Commons Agriculture Committee Beverley Chalk gave its support to the managed 0 10 km retreat policy. Their report stated that Hull Withernsea continuing to build ever higher North Sea defences to keep out the rising sea is no longer an option, and retreat to Spurn new positions inland should begin R.Humber Head immediately in some places: Figure 5: The coastal system The coastline can be viewed as a system, with inputs and outputs. The inputs are sand, mud, gravel and rain wind frost beach other eroded materials forming the beach. The sea, spit through the process of longshore drift, transports this material along the coast until it is deposited mud somewhere else. Provided the amount of material flats coming into the coastal zone equals the amount of material leaving it, the section of coast is said to be in LONGSHORE EROSION sediment DEPOSITION balance, or in equilibrium. This equilibrium can be DRIFT upset by various natural events, such as rising or bar falling sea levels; however, nowadays the coastal equilibrium is usually upset by the actions of people, tombolo such as by the construction of groynes and other coastal defence works. offshore bar Geofile Online © Stanley Thornes (Publishers) Ltd 2000 September 2000 no.388 Coastal erosion – back to nature Figure 6: Report in the Daily ‘In spite of the introduction of Managed retreat is an example of ‘soft Telegraph, 6 August 1998 defensive measures, the engineering’.