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Home » Pilot Sites » Thames Pilot Site » Canvey Island

Canvey Island, shown in Figure 1, is an island in the Thames Estuary, covering an area of 18.5 km˛. The mean high water mark of the Thames Estuary at Canvey Island is higher than most of Canvey Island’s land. The first sea defences were constructed in 1623 and Dutch settlers formed the first Canvey Island communities of the modern era. The population did not expand rapidly until the 1920s, with 1,795 inhabitants in 1921 but over 6,000 in 1927 during which time the number of buildings rose from 300 to about 1,950 (Kelman, 20020). In 2001 its population was estimated to be approximately 37,000 (Office for National Statistics, 2002).

In 1953 the island was inundated by the “Great North Sea Flood”, shown in Figure 2 that breached flood defences and resulted in the deaths of 58 people and the destruction of several thousand houses. The age distribution for Canvey Island is shown in Figure 3. Approximately 8.6% of the population are aged over 70. There are a total of approximately 15,400 cars on the island. In 2001 there were a total of 15,490 residential properties on Canvey Island (Office for National Statistics, 2002).

The likelihood of flooding of the access routes to and from Canvey Island will increase following sea level rise. Access to Canvey Island is currently only possible by two roads (A130 and B1006), both of which are connected to the same roundabout. Any disruption to these routes would hamper evacuation and severely limit access to the industrial areas on Canvey Island, including potential disruption to gas terminals and oil storage depots. This could have significant implications for the national economy since Canvey Island is one of the main gas distribution centres for the UK.

Satellite image of Canvey Island

Figure 1: Satellite image of Canvey Island

Canvey island during the 1953 flood
(Source: Canvey Island Web site, 2007)

Figure 2: Canvey island during the 1953 flood

Age distribution for Canvey Island
(Source: Office for National Statistics, 2002)

Figure 3: Age distribution for Canvey Island

At present, Canvey Island is protected by a concrete sea wall that rises approximately 3 m to 4 m above the high tide level. A typical view of the Canvey Island flood defences is shown in Figure 4. It has been found that whilst substantial, these defences show signs of deterioration such as cracks in the concrete, and the degradation of seals between slabs. Metal access doors also represent a weak point with imperfect seals around them, bolts have to be manually placed to shut the gates and bolt holes are prone to get blocked with debris (Kelman, 2002). It is estimated that the current standard of protection at Canvey Island of 0.1% (1 in 1,000 years) will be reduced to 0.5% (1 in 200 years) by 2030 owing to the reasons detailed in Section 5.1.

On Canvey Island, it has been estimated that approximately 91% of dwellings are houses and 9% flats. Most properties have two storeys, and have a mean floor level 0.3 m above the surrounding ground levels. Thirty percent of properties are bungalows and 45% of flats are situated at ground floor level, there is thus a large risk to life and property with limited opportunities to temporarily move to a higher level (Kelman, 2002). Figure 5 shows some of the more vulnerable single storey housing that has recently been constructed on Canvey Island close to the flood defences. It is possible that a majority of the island would be inundated if a major storm surge occurred and led to major overtopping of defences. However, this is still considered to be a very rare event. The failure or breaching of a seawall is a more likely option and would involve more localised severe flooding depending on the exact breach scenario that occurred.

Canvey Island flood defences

Figure 4: Flood defences in the north of Canvey Island

New single storey housing on Canvey Island

Figure 5: New single storey housing on Canvey Island

The tools could be developed further so that they were used as tools in emergency planning exercises.

The end users agreed that the responsibility for evacuation modelling should be held b y the Environment Agency and their expertise should be used to inform local authority emergency plans.

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