Disappearing coasts Understanding how our coasts are eroded is vital in a future of climate change and sea level rise, writes Catherine Poulton. ngland has some of the fastest retreating coastlines in Europe. At the British Geological Survey (BGS) we’ve been studying Along some of the coasts in the south and east, the cliffs are the process of coastal erosion and cliff retreat as part of our E made up of soft sediments that are easily eroded. Whole Stability of Cliffed Coasts project. By studying 12 study sites on villages have been lost to the sea over the years and many more the ‘soft rock’ coasts of Dorset, Kent, Sussex, Norfolk and North may be on the brink of joining them. Yorkshire, we’re trying to find out how the nature of the rocks and For local people, erosion is a serious issue. They have become climate change influence coastal erosion. accustomed to watching houses teeter dangerously on the cliff Standing on a specific point on the beach, we scan the cliffs edge. They have seen whole streets topple into the sea. The and beach with a low power laser to monitor and measure change consequences to the environment, and people’s assets and lives can along the coast. The laser measures the distance and relative be enormous – especially as home-owners do not usually receive position between our survey point and a set grid of points on the compensation for the loss of their homes and livelihoods. cliff face. We then feed our many thousands of measurements into How can people most effectively plan to live and work in such a computer to generate models of the shape of the cliff face. This a changeable environment? And how will climate change and sea shape changes constantly so we repeat the laser scan every year. level rise affect the rate of coastal erosion? What’s the best way to We can then analyse the results, calculate the rate of cliff retreat tackle the problem? and model the way the cliffs collapse. C Poulton .nerc.ac.uk The eroding coast and BGS test site at Planet Earth Summer 2004 — www Happisburgh, facing north. The relative strengths of different sediments in the cliff can be seen in 26 the slope angle - the stronger the sediment, the steeper the angle before it collapses. Mike Page The southern end of Happisburgh in 2003. On fast-retreating coasts it is not just the position of the cliff face that is important. The entire system of coastal erosion is complex. We must also look at the on- and offshore environment, the weather and climate, the strength and variability of the rocks and materials making up the coast and the influence of man-made structures such as groynes and sea walls. To do this we survey the coastal sections by geological mapping and aerial photograph analysis. We also test rock samples for strength to try to understand why the cliff is eroding so quickly. frequency and the influence of coastal Understanding how the offshore defences and offshore dredging. Through environment influences coastal erosion is the Stability of Cliffed Coastlines project, Environment Agency (Anglian Region) particularly important. These influences we are studying and comparing the include wave energy and wave direction, behaviour of different types of coastline to the distribution of sediments moved by gain a better and more accurate wave scouring and changing sea level. One understanding of the processes of coastal critical factor is the rate that sediment is erosion and landslides. moved away from the cliffs and beaches. One of the 12 sites in the project A 1992 aerial photograph with a line showing Coarse materials, such as gravels, may stay includes a section of cliffs next to the top of the cliff measured in 2003 by BGS. put in local beach systems, but finer Happisburgh (pronounced Haiz-borough) materials, such as clays and silts, are readily on Norfolk’s North Sea coast. This is a washed offshore and may end up on coasts pretty country village with a notable stone variable, weak and easily eroded. on the other side of the North Sea. church, an impressive manor house, listed There has also been considerable work One of the main interests in our buildings and a famous red and white done to defend parts of the Norfolk coast research is the mechanism by which the striped lighthouse. These assets may be against the sea. In 1983, about 70% of the cliffs collapse. Understanding this is threatened, as the receding cliff line claims East Anglian coastline was defended. essential in both predicting how coasts will the loss of a property every year or so. But these defences may have had a recede and how they will be affected by In the past, coastal defences built at detrimental effect on unprotected stretches climate change and sea level rise. Coastal Happisburgh slowed down the rate of of coast, such as at Happisburgh, where slopes fail in a number of retreat. Today, however, erosion rates are relatively high. This is ways. Steep-faced slopes England has some of the large sections are in because the defences trap sediments, can topple and fall once fastest retreating disrepair. Sea-level rise which would normally get washed along the sea has eroded the ‘ and climate change, the coast and replace those that are eroded. base of the cliff back far coastlines in Europe. including increased Therefore, in managing erosion, the entire enough. Other shallower storminess, are likely to coastal system must be taken into account slopes ooze their way down towards the sea increase the’ rate of erosion. in order to balance priorities. as part of a mud or debris flow or slumps. So far, we have monitored the rate of In a highly developed island nation Some coasts comprise very large landslides erosion at Happisburgh in 2001, 2002 and such as Great Britain, the coastal that slide along a deep spoon-shaped 2003, using the laser scan system. Where infrastructure and resources are critically surface and these are called ‘deep-seated there are defences, the surveys have shown important. We need to develop methods rotational’ slides. Many cliffs may fail in a an average erosion rate of approximately to accurately monitor and predict coastal .nerc.ac.uk combination of all these mechanisms, 2m per year, but elsewhere in more change to protect these assets and manage either as a domino effect where one failure exposed parts, the erosion rates are 8-10m them in the most cost-effective way. Our causes another, or as a constant cycle of per year, and about one house a year is research will improve everyone’s events involving over-steepened slopes and disappearing. understanding of the complexities of the erosive power of the sea. So, why is the coast retreating so fast? cliffed coast erosion and coastal retreat. We are trying to understand why It’s largely down to the composition and particular types of landslides occur in structure of the rocks and deposits that different geological settings and how fast make up the land. The exposed coast at coasts are likely to retreat given various Happisburgh is made up of sands and Catherine Poulton is a coastal sedimentologist and is part of the Coastal Geoscience and Global factors. These include the geology, the Planet Earth Summer 2004 — www clays, mostly deposited in glacial Change programme at the British Geological nature of the wave power along this conditions about 430,000 to 630,000 Survey, Keyworth, Nottingham NG12 5GG, section of coast, the climate and storm years ago. These deposits are highly tel: 0115 936 3100, email: [email protected] 27.