CASE STUDY Canvey Island, Topic: Changes in Relative Sea Level

Canvey Island

Canvey island, a low-lying area on the north side of the Thames Estuary was particularly badly affected by a devastating storm surge in 1953. At just 1 m. above average sea level, when spring tides occur it can be as much as 2 m. below high tide level, relying on the protection of 6 m. high sea walls. The eastern part of the island is densely populated and includes the town of Canvey, to the south there is a large oil storage facility and much of the western half of the island is marshland. The risk: while existing coastal defences are considered to be effective for current tidal and storm conditions, the forecast changes in relative sea level require additional measures to be considered. The isostatic rebound of the British Isles is unevenly experienced with the north west of Scotland (the region most ‘depressed’ by the greatest weight of ice in the last glacial advance) rising faster at a consistent rate of 1 mm. per year. However, in response to a geological axis the south east of is tilting down which, in the Thames Estuary, is at a rate of 1.5 mm per year. Up to 2100 that is likely to mean an isostatic submergence of 12 cm. In addition, eustatic changes to sea level as a result of thermal expansion and glacial/ice-sheet melt is believed to be causing sea level to rise at a rate of 3 mm per year. While it is difficult to forecast future rates, the combination of these factors means that by 2100, the sea level in the Thames Estuary is likely to be considerably higher compared to 1990 levels by between 53.1 cm. (high forecast) and 37.3 cm. (low forecast), in contrast with Edinburgh which may anticipate a of 39.2 cm. (high forecast) and 23.4 cm. (low forecast). The response: The Thames Estuary 2100 (TE2100) plan identifies that the 40,000 population is vulnerable to the overtopping of current defences by higher-than-present storm surges and proposes adaptation strategies. These include maintaining and improving the current defences and introducing community strategies such as safe havens on the highest land. Vulnerable low-storey developments such as mobile homes, single-storey buildings and camp sites should have escape or community refuge plans. If this is not possible they should be replaced with multi-storey buildings. The western marshlands may need to be remodelled for managed retreat if climate change mitigation strategies have not been successful in arresting sea level rise by 2050. With only two access roads off the island (making population evacuation difficult in the event of higher tidal surges) the main strategy is to prepare safe havens, high level building access and shelters.

Exam style questions: 1. To what extent should Canvey Island be considered a ‘high risk’ coastal area in experiencing the impact of changes to the relative level of sea and land? (9 marks) 2. Critically examine the range of strategies available to reduce the risks resulting from changes in relative sea level faced by communities such as those on Canvey Island. (12 marks)

tutor2u AQA A Level Geography Topic Case Studies (Volume 1) Specification 7037 For First Teaching from September 2016

CASE STUDY Canvey Island, Thames Estuary Topic: Changes in Relative Sea Level

1. To what extent should Canvey Island be considered a ‘high risk’ coastal area in experiencing the impact of changes to the relative of sea and land? (9 marks)

Arguments for ‘high risk’

• Low level of the land and large population means the number of people potentially affected is significant and the chance for wide scale inundation is high. • The large oil storage depot means flood water may become toxic with the potential for combustion adding to the threat in the event of flooding. • Isostatic change is consistent and gives a predictable fall in land relative to sea of at least 12 cm. irrespective of possible changes in actual sea level. This will put existing defences increasingly at risk of storm surges. This is one of the fastest rates of isostatic submergence around the coast of Britain. • Eustatic changes are less predictable but even the low forecast will intensify risk. Combined with isostatic change, the low-lying nature of the land and the large population and limited opportunities for evacuation, the risks of flooding and the likely consequences of any flooding make this a ‘high risk’ area compared with other areas of the British Isles.

Arguments against ‘high’ risk

• While there is risk, it may be considered less than ‘high’. With sea walls at 6 m. there is still considerable protection even if by 2100 sea level is half a metre higher on a 2 m. storm surge – that still gives considerable height protection 3.5 m. • The UK, as a globally affluent nation, has the capacity to install improved coastal defences and modify building height to accommodate the population above the level of flood waters. On a global scale, compared with less affluent coastal communities such as those in Bangladesh the likelihood of inundation and threat to life for people of Canvey Island is ‘moderate’ rather than ‘high’.

2. Critically examine the range of strategies available to reduce the risks resulting from changes in relative sea level faced by communities such as those on Canvey Island. (12 marks)

• Strategies can be classified as adaptation or mitigation strategies (plus definitions)

Adaptation strategies:

• Current coastal protection strategies appear effective as a result of the 1953 floods and have the capacity to cope with considerable sea level rise. • Investment will be in maintaining and strengthening current defences – a financially sustainable strategy compared with those that might suggest new expensive capital-investment. • Included in the plans is the possibility for additional low-cost sustainable strategies of managed retreat to manipulate future flood waters away from populated areas. • Plans for safeguarding life are in place with new refuges, safe havens and higher buildings.

tutor2u AQA A Level Geography Topic Case Studies (Volume 1) Specification 7037 For First Teaching from September 2016

CASE STUDY Canvey Island, Thames Estuary Topic: Changes in Relative Sea Level

However:

• There is no time-scale for new, higher buildings or a regulatory framework to ensure they will be built. • The cost of improvements will be borne by the local community – bringing into question whether they can afford them or be willing to construct them. • Plans are focused on safeguarding life, rather than guaranteeing protection from inundation. The long-term viability of the community and industrial base is at risk if chances of flooding bring destruction to the built environment. • The long-term viability of Canvey Island may be at risk given the unpredictability of climate change and its impacts on sea level. Long-term plans to move industry and people away from the island and onto higher land along the Thames valley might be considered.

Mitigation strategies

• There is no mitigation strategy that can influence isostatic causes of sea level rise for Canvey island, but there are for those affecting eustatic sea level rise related to climate change. • Attempts to limit atmospheric CO2 such that global temperature rise is limited to less than 1.5 C have been the aim of international agreements such as COP21. However, there are issues with these attempts: o It requires all nations to adhere to their stated agreements and implement effective carbon-reduction policies o It assumes the agreements are sufficient to limit atmospheric CO2 to 450 ppm or less – which many climate scientists suggest is unlikely. o It assumes current and almost-certain future CO2 increases are not going to go past a tipping-point at which reduced polar sea ice and melting tundra initiate further methane release and temperature rise. • It could be argued that the oil storage facility on Canvey Island is contributing to sea level rise through the burning of fossil fuels, and one practical mitigation action could be to move away from fossil-fuel dependency, which may result in the closure of this facility and reduce the need for some to live on Canvey Island.

tutor2u AQA A Level Geography Topic Case Studies (Volume 1) Specification 7037 For First Teaching from September 2016