Defending the coast at Dawlish Warren

Transcription

1 Sólheimajökull: Defending the coast a retreating Dawlish Icelandic Warrenglacier By By Simon Hilary Edge Sampson Today, ice covers around 10% of the A case study about world s surface. But, for at least the last coastal 100 years, protection ice masses have been melting This case and study becoming looks at smaller. Dawlish Glacial Warren, retreat which has is a many spit in impacts southwest on the England. physical It is environment. facing similar issues These to include: many coastal areas of the UK today. The vegetation Warren needs patterns to be protected at great economic cost, or livelihoods allowed to return to its natural natural state. disasters The spit has been well protected in the past, for socioeconomic and environmental water and energy supply. This reasons. unit Many is about people Sólheimajökull. who live It is around a retreating the Exe outlet estuary glacier depend draining on the protection Mýrdalsjökull that ice the cap spit in provides. southern A new plan Iceland. is being It developed has reacted for to the changes future management in climate over of Dawlish the last 150 years. Warren. This The case study covers: The the development valley glacier of Sólheimajökull the spit over Glaciers time and climate Glacial coastal budget protection techniques Climate reasons for and protecting Sólheimajökull the area Implications the best methods of glacial to protect retreat the area in the future. Learning objectives Key vocabulary Through learning about glaciers in Iceland, longshore you drift, will have hard a engineering, better understanding soft engineering, of: sustainable, managed retreat, stakeholder how glaciers respond to changes Learning climate outcome In how this unit the implications you will: of climate change on ice masses worldwide find out how coastal areas are how protected to plan for future changes in the Earth s climate. study the physical geography of the area study the human responses evaluate maps and diagrams of the area. Key Relevance vocabulary to specifications Ice sheet, ablation, interglacial period, dynamic systems, Exam glacial Link to budget, specification accumulation zone, moraine, board glacial retreat AQA A Unit 1: Physical Geography, Section B, The Coastal Exam Link Zone, to page specification 15 board AQA-9030-W-SP-14.PDF AQA AB Unit 1: 1 GEOG1 Managing Physical Places and in the Human 21st Century, Geography, The The Coastal Physical Environment, Options, pages Cold 8 10 environments, page 7 aqa.org.uk/subjects/aqa-9035-w-sp-14.pdf Edexcel SP-14.PDF Unit 2: The Natural Environment, Section A, AQA A B Unit The Physical 2: Hostile World, world Topic and 1, Investigating Coastal Landscapes, the shrinking pages 19 and world, 20 Section A the Hostile World, The migrationdocuments/gcse%20new%20gcse/ challenge of extreme environments, page 15 Edexcel W-SP-14.PDF Unit 1: Dynamic Planet, Section B, Small-scale Edexcel B Unit Dynamic 1, Section Planet, B, Topic Challenges 5, Coastal for Change the Planet, and The A causes, Conflict, page effects 16 and responses to climate change, migrationdocuments/gcse%20new%20 see page 15 migrationdocuments/gcse%20new%20gcse/ GCSE/ _GCSE_Lin_Geog_B_ Accredited_spec_GCSE_2012_linear_inc_SPaG. Issue_5.pdf OCR B pdf Unit B563: Key Geographical Themes, Theme 1: Edexcel Unit Coastal 1, Dynamic Management, Planet, page Section 13 A, Changing B Climate, uk/images/82581-specification.pdf What challenges might our future WJEC A climate Unit 2: Options, present Physical us with?, Options, page 13 Theme 7, Our edexcel.com/migrationdocuments/gcse%20 Changing Coastline, page 18 New%20GCSE/UG GCSE-GeographyB- uploads/publications/16128.pdf WJEC B Spec-2012-Spagw.pdf Unit 1: Challenges and Interactions in Geography, OCR A Unit Theme A731: 2: Physical Contemporary Processes themes & Relationships in Geography, Extreme Between People Environments, and Environments, Mountain Coastal Environments, page Processes 12 and Coastal Management, page 19 specification.pdf pdf WJEC A Unit 1, The Core: Theme 2, Climate Change; CCEA Theme Unit 1: Understanding 3, Living an Our Active Natural Zone, World, page Theme 15 A: The Dynamic Landscape, page 9; a copy of the WJEC B Unit 1, Theme 2: Physical Processes & specification can be downloaded from: Relationships Between People and rewardinglearning.org.uk/microsites/geography/ Environments, page 16 gcse/index.asp uploads/publications/17213.pdf?language_id=1 Cambridge Theme 2: The Natural Environment, page 17 CCEA Theme B: Our Changing Weather and Climate, IGCSE The Causes and Consequences of Climate Edexcel Change Section A, The Natural Environment, Topic 2, Coastal IGCSE microsites/geography/gcse/index.asp Environments, page 7 migrationdocuments/igcse%20new%20igcse/ IGCSE Theme 2: The Natural Environment, page 13 IGCSE2009_Geography_(4GE0)_Specification.pdf syllabus.pdf 1

2 546 Defending the coast at Dawlish Warren In February 2014 the Dawlish area of Devon (Figure 1) hit national news when 150 km/hr (91 mph) winds hit the coastline. Waves up to 9 m high crashed onto the mainline railway which runs from London to the South West at Dawlish and washed away its foundations. This left the rails hanging in mid-air. Just along the coast from Dawlish the 2 km long sandspit of Dawlish Warren was also affected by this storm. Dawlish Warren spit Dawlish Warren spit grew up at the mouth of the River Exe (Figure 2). Longshore drift has moved material eroded from the Langstone Rock headland to the west of the spit, and the spit has built out Dawlish Warren resort shops, hotels, restaurants Old fixed sand dunes Golf course Visitor Centre Recreational area Amenity beach Mudflats and saltmarsh Middle section Cliffs at Langstone source of beach material Nature reserve Direction of longshore drift Neck Beach backed by sand dunes N m Exminster Marsh To Exeter N Figure 2 Dawlish Warren spit To London, Exeter Starcross Cockwood Dawlish Warren holiday camps Topsham Exton Exe estuary Lympstone Dawlish Warren sandspit To Plymouth Langstone Rock headland 0 2 km Key Railway and station Coastline at high tide Built-up areas Figure 1 Location of the Exe estuary Exmouth into the estuary. However, this source of material was cut off by the breakwater built at Langstone. Coastal management techniques In the mid-20th century, coastal protection (Figure 3) usually took the form of hard engineering, for example the construction of sea walls. However, these methods were expensive, short-term, and often had a serious impact on the landscape. More recently soft engineering, which does not involve the construction of expensive structures, has been favoured. It has less impact on the environment and is more sustainable in the longer term. Coastal protection in the 20th century Dawlish Warren has always been eroded by storms. The spit has been getting narrower at a rate of around 1 m a year. About 250 years ago it was 250 m wide but now it is only 50 m wide. Since 1962 the area has been protected (Figure 4). Groynes were built at 100 m intervals to try to trap the sand on the 2

3 Type Description Rank of cost 1 = high Rock armour (riprap) Revetment Sea wall Groynes Gabions Beach nourishment Managed retreat Very large blocks of hard rock such as granite, piled up An angled slope of concrete or rocks A curved concrete wall Barriers made of wood that stick out into the sea Wire cages with rocks and pebbles in them The beach is fed with material (sand, shingle or pebbles) from somewhere else to help build it up again Nothing is done except for safety reasons, natural processes operate Advantages 4 The spaces between the rocks weaken the power of the waves. 2 Prevents erosion at the base of the cliffs. 1 Withstands strong waves and reflects the energy of the waves away from the land. 3 Allow sand to build up on the beach. 5 Reduce the wave energy as the water drains through. 6 A natural beach is built up, which absorbs the energy of the waves. It protects the land behind the beach. 7 The beach or spit evolves into a stable position for the existing processes. Disadvantages Needs to be big enough so that the sea doesn t carry the rocks away. Costly to build and maintain. Flooding is possible behind the revetment. Expensive to build and maintain. Short lifespan and expensive to maintain. Short lifespan. After each storm, cages may need to be repaired. Older cages can rust and be dangerous. Needs constant maintenance as sand is constantly moving. Compensation has to be paid to local people for loss of land and property. Figure 3 Coastal management techniques N Old cliffs Beach Railway line 2014 flood defence embankment Breakwater Langstone Rock headland Sea wall Possible coastline in 2060 Exe estuary Gabions Nature Reserve Dunes Groynes Concrete revetment Rock armour revetment Rock platform at low tide Figure 4 Coastal protection methods at Dawlish Warren Exmouth Possible coastline in 2020 Coastline in 1787 Sea 0 1 km beach. Storm damage from the late 1980s led to the most recent management plan (1992), which cost 1.5 million. Now, 22 years later, the scheme needs updating in order to protect the spit for the next 50 years. Approximately a year is spent on maintaining the existing structures. The project needs 14 million from central government for the next stage. However, it is predicted that by about 2060 it will be too difficult and costly to defend the spit from the sea. This is partly due to the effects of climate change: 3

4 Sea levels are rising by 2 mm a year in the South West. By 2060 the sea level could be 400 mm higher. The railway line may also need to be moved but there is conflict between Network Rail and central government as to who is going to pay for this. Dawlish Warren has always been eroded by storms. Why should the spit be protected? Coastal protection is an expensive and continuous process. Experts now believe there should be less protection, because natural processes will always win in the end. But there are many very important reasons why this part of the UK coastline needs protecting. There are many stakeholders in this area that is, people who will be affected by any decision that is taken. The Exe estuary area, including the spit, is an important conservation area for plants and animals. For example, migratory birds, such as avocet, can be seen there in winter. There are 600 species of flowering plants, such as orchids. These are protected under UK and EU law. Around people live close to the estuary, and there is a railway line and main roads on both Figure 5 Aerial view of Dawlish Warren Source: Environment Agency sides of it. The spit acts as a natural breakwater, protecting homes and businesses including marinas and shellfisheries behind it from flooding. Waves on the seaward side can reach 3.4 m but in the estuary they are less than 1.1 m. If the spit were not there, 2300 properties in the estuary would be at risk of flooding. The railway line is also at risk and when the railway was out of action during spring 2014, there was a huge loss of income to businesses in Devon and Cornwall. Plymouth alone was estimated to be losing 5 million a day at that time. Dawlish Warren is an important tourist location. More than holiday-makers visit the Blue Flag beach there every year. This brings in approximately 5 million to the local economy. Local jobs are dependent on this income (Figure 5). The option of Managed retreat (see Figure 3) has not been a choice in this area, so a decision was made to continue to defend the coast with some defences being moved or altered. Sand dunes Beaches and sand dunes are well known to be one of the best ways of protecting a coastline, because they absorb the energy of the waves. The sand dunes and beach of the spit are being eroded by natural and human processes. In 1992, gabions were placed at the foot of the dunes to protect them from erosion by the sea. But visitors walking on the dunes can also cause the dunes to be eroded, by the wind. If nothing is done in the new management plan to protect the dunes, they could recede by up to 40 m, and 6 30 ha of sand dunes on the spit could be lost. The storm of February 2014 removed 5 m of sand from the base of the dunes (Figure 6). 4

5 Dawlish Warren Management Scheme, The Environment Agency must decide on the best way to manage the Dawlish Warren spit. The area nearest the mainland, where most visitors are found, has in the past been protected with hard engineering (rock armour and sea wall). The area at the end of the spit is a natural environment, but it is in danger of being washed away. The neck is becoming narrower and could be broken through by the sea. The people who created the new management plan had to decide whether to let the spit evolve naturally, or to continue to intervene in natural processes. Beach nourishment When sand is added to the beach it becomes higher, wider and less steep. This creates a larger dry beach which will be a source of sand for the dunes and also of recreational value. The sea will be further away from the top of the beach, so the sea wall, for example, will be less exposed to erosion. The project aims to add, in 2017, enough sand over the whole length of the spit to raise the height of the beach by 1 m. This may be repeated in Other plans The gabions in the middle section will be removed. They prevent natural sand Figure 6 Erosion at the base of the dunes Source: Environment Agency dune formation and look unattractive. The existing groynes will be repaired. A new hard defence will be buried under the sand at the neck. This will guard against the risk of a breach of the Warren during storms. A flood defence embankment was built in 2014 near the Visitor Centre. This should prevent any floodwater getting to Dawlish Warren village. The revetment and sea wall will be maintained to protect the recreational facilities. A sustainable future for Dawlish Warren? The new management plan considers the current and future impact of any management decisions. These decisions are looked at in the short, medium and long term. In the short term (up to 2020) the policy decision has been Managed retreat. In the next 100 years (medium to long term) less action will be taken as the spit adapts to changing climatic conditions. The aim is that by 2030 the spit will be functioning naturally. This means that the neck may have been breached and the end flattened, so it no longer protects the estuary. Other methods will then need to be considered. Is this a sustainable solution? A current decision that commits future generations to high costs or leads to environmental damage is unsustainable. 5

6 1 Why did Dawlish Warren grow up at the mouth of the River Exe? 2 On a sketch map, add the following labels. Use colour to show the movement of sediment. Breakwater at Langstone Rock headland stops material from reaching the spit Sand moves onshore from sandbanks Sediment moves down the river channel Sand moving along the shore is trapped by the groynes 3 a Make a copy of Figure 3. Use colours to distinguish between the hard and soft techniques (column 1). b Find images of these techniques on the internet and stick them next to your table. 4 Identify on Figure 5 the features shown on Figures 2 and 4. 5 a Add labels to a copy of Figure 5, using two colours: one to show the 1992 methods of protection and the other to show the 2015 methods. b Add more labels to show what might happen to the spit in the medium to long term that is, after Which option or combination of options did the Environment Agency choose: a in the short term b in the long term? 7 Complete a large copy of the following table to show the benefits of protecting Dawlish Warren. Economic benefits Activities Environmental benefits Social benefits 8 Imagine you are one of the following people. Write a letter to the Environment Agency explaining how you feel about the decision the Agency has taken. An owner of an amusement arcade on Dawlish Warren A local resident of Exton who has a house on the shoreline The RSPB warden of Exminster Marsh The owner of a marina at Lympstone A councillor of Teignbridge District Council, which owns part of the spit An official from Network Rail 9 a How will the defence of the spit change over the next 100 years? b How will this affect the estuary? c Is this management sustainable? Learning checkpoint Dawlish Warren is a spit in southwest England. It has been well protected in the past because: it gives shelter to the Exe estuary, thus protecting the economy and environment of the area it is an important tourist destination. The 2015 Management Plan has assessed how the spit should be managed in the short term and long term. It has looked at socioeconomic and environmental issues. Glossary task Write glossary definitions for these terms: hard engineering longshore drift managed retreat soft engineering stakeholder sustainable Remember this case study To help you remember this case study, make notes under the following headings. Why should Dawlish Warren be managed and protected? What methods have been used to protect it? What will happen to Dawlish Warren in the future? Try to make your notes fit a single sheet of A4 paper. 6