Coastal Erosion: Back to Nature

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’. Other soft engineering underlying natural processes of strategies include beach replenishment If it goes on like this, erosion and deposition have and the construction of offshore reefs remained fundamentally that decrease wave height and absorb there won’t be any unaltered, albeit varying in their some of the energy, as well as altering farms left location, effects and intensity. the direction of the waves. The depredations of coastal Sue Earle lives on what is left of Grange erosion are particularly obvious Farm at Cowden, near Hornsea in East on the vulnerable eastern English Hard engineering – a case Yorkshire. Over the past eight years she coast, which is mostly composed study has lost eight acres to the sea, a third of of softer rocks and clay. Archival her arable land. In November 1996 East In some places too much property is and cartographic evidence threatened by coastal erosion to allow a Yorkshire council demolished her three- indicates that the East Riding of bedroomed Victorian farmhouse policy of managed retreat. Here the Yorkshire has suffered continual traditional approach is hard because it was just five metres from the loss of land to the sea since cliff edge and considered too engineering works, such as those at records began; a loss which at dangerous to live in. The same thing Mappleton. This policy is still happened to several of her neighbours. present amounts to 12 hectares of continuing at several locations today. Ms Earle and her uncle, who lives with land a year.’ her, received a bill for £3,500 that they At Sidmouth in Devon, a coastal have still not paid. Managed retreat, or ‘managed protection engineering strategy costing realignment’, involves dismantling They now live in a wooden hut built at many millions of pounds has been put any existing coastal defences and in place (Figure 7). Offshore rock their own expense and are suing the allowing the sea to encroach inland to council for compensation. On hearing barriers, groynes and seawalls have a predetermined ‘set back’ line. This been constructed. However, longshore yesterday’s announcement by the allows for the dissipation of the Agriculture Select Committee that more drift moved much of the beach energy of the waves and tides, as well farmland should be allowed to fall into westwards and reduced the protection the sea, Ms Earle said: "They want as the predicted sea level rise to the western part of Sidmouth’s shooting. Let them come and live in my resulting from global warming and seafront. Between January and May hut and I’ll go to their houses. Why did isostatic readjustment. Managed 2000 work took place on the third we fight two world wars? To protect our retreat is consistent with the natural phase of the project, which itself cost land. If it goes on like this, there won’t cycles of erosion and deposition. The over £600,000, partly funded by the be any farms left. I don’t think they formation of beaches, mudflats and should protect every inch of land, but Ministry of Agriculture, Forestry and sandbanks will enhance natural Fisheries. they should try to save as much as coastal defence. possible. I lost my farm, which was worth £250,000, and my loss of income This third phase, intended to reduce Opponents of managed coastal retreat for all this time has been huge." the movement of beach material from point out that wherever coastal land east to west, involved further major Ms Earle says that erosion of her is lost, the livelihood of individual engineering works: farmland accelerated after sea defences people is threatened. Certainly any were built to protect the village of policy should include proper • A new rock groyne, 64 m long and Mappleton, one mile north of Cowden, compensation for those who lose 4.6 m above beach level, has been in 1991. Two rock groynes were built their property – an issue that Sue constructed of boulders at Bedford and sediment was prevented from Earle had to fight for (Figure 6). Steps (Figure 8). The groyne is drifting along the coast to the beach. Managed retreat has been criticised made of 4,350 tonnes of primary "The cliff erodes faster because there is as simply a cost-cutting manoeuvre. no beach to protect it", she says. rock armour (6–10 tonne boulders, trucked in from Cornwall), 3,400 tonnes of medium armour and Figure 7: Sketch map of Sidmouth’s coastal protection works 2,100 tonnes of filler rock, trucked in from Somerset. • 2,500 cu m of new shingle has Cliffs been imported and placed between the York Steps and East Pier SIDMOUTH Beach groynes to increase the width of e nad the upper berm between those me pro East Pier locations. ng lyi East • Up to 20,000 cu m of beach ow L York Pier nourishment material has been steps Groyne Bedford moved from west of Bedford Steps steps to east of the new groyne, thereby Cliffs returning the material to its Beach English original location. Channel Offshore N Chit Rocks barriers These massive engineering works to wave-cut platform protect Sidmouth’s seafront appear rather unsightly and out of place at this 1 km attractive and elegant seaside resort.

Figure 8: Cross-section through the new A new factor in the choice of coastal Bibliography groyne at Bedford Steps, Sidmouth management strategy is the effect of global warming. The 20th century was Geofile No. 338 (September 1998) Primary Rock Medium Rock Armour the hottest for at least 500 years. Coastal management - Some Issues, Armour 3 to 6 tonne boulders Lynda Evans 6 to 10 tonne Global average temperatures have boulders increased by 1°C since AD1500; half Peter Webber and Neil Punnett (1999) 4.6 m of this increase has occurred since Physical Geography and People, Stanley Thornes, pp. 71–73 Beach 1900. One of the effects has been a rise in global sea levels of between 10 and 25 cm since 1900. The anticipated In addition to the usual sources, the 30 metres further increase in global following Internet sites were useful: Filter rock http://www.gov.uk up to 1 tonne temperatures this century presents those involved in coastal protection http://www.wwf- with a new challenge; sea levels are uk.org/news/news74.htm Soft engineering – a case predicted to rise by between half a http://www.rjcunningham.clara.net/ study metre and a full metre by 2100. The rule_britannia effects this would have on the British A different, soft engineering solution coastline are shown on Figure 9. has been adopted at Seaford in East Sussex, a small coastal resort whose sea-wall, built in 1881, had to be Conclusion regularly and expensively repaired There has been a dramatic change in following storm damage. Since 1987 a the way in which coastal protection is strategy of beach replenishment has viewed by the British authorities. The been adopted at Seaford. A broader traditional approach was to prevent beach was built using shingle dredged coastal erosion at all costs, through the from an offshore bank by a large use of hard engineering solutions suction dredger. Every year including sea walls, groynes and approximately 30,000 cu m of shingle breakwaters. This expensive policy are removed by longshore drift, and has, in some cases, caused more has to be replaced at an annual cost of problems than it has solved – as £60,000, but this is much less than allegedly has been the case at Cowden increased sea-wall defences would and Mappleton. New, soft engineering cost, and probably more effective too. solutions include the controversial Beaches dissipate wave energy by strategy of managed retreat, which was forcing the water to spread shallowly supported by the Agriculture Select across a broad area. The beach is also a Committee of the House of Commons valuable tourist resource. Several in 1998. Beach nourishment and the major resorts including Miami and construction of offshore reefs are more Rio de Janeiro replenish their beaches active forms of soft engineering. in this way every year. The issues concerning coastal erosion Figure 9: The effects of a one metre rise are likely to be of increasing in sea level on Britain’s coastline importance, should the predicted effects of global warming, such as the N Key consequent rise in sea levels, occur. Areas that would Whether a ‘back to nature’ strategy be flooded if sea- can be sustained in the face of level rose 1 metre potentially considerable loss of land is Areas of soft cliff a moot point. which will erode more quickly in future

0 100 km Focus Questions Holderness

N.E. 1. Why is Mappleton threatened by coastal erosion? Norfolk 2. How have human actions contributed to the erosion that destroyed Sue Earle’s home? Include in your answer mention of the effect human actions have had on the coastal system at Mappleton.

3. (a)What do you understand by the policies of ‘managed retreat’ and ‘beach feeding’? Norfolk & Suffolk (b) What do you consider to be the advantages and disadvantages of (i) hard Dorset, Isle of E.Devon Wight sea defences? (ii) managed retreat? (iii) beach feeding?