HRPP367-Hydrodynamic and Loss... the 1953 Canvey Island Flood

Hydrodynamic and loss of life modelling for the 1953 Canvey Island ﬂ ood HRPP 368 Manuela Di Mauro & Darren Lumbroso Reproduced from: Flood Risk Management - Research and Practice Proceedings of FLOODrisk 2008 Keble College, Oxford, UK 30 September to 2 October 2008 Flood Risk Management: Research and Practice – Samuels et al. (eds) © 2009 Taylor & Francis Group, London, ISBN 978-0-415-48507-4 Hydrodynamic and loss of life modelling for the 1953 Canvey Island flood Manuela Di Mauro & Darren Lumbroso HR Wallingford Ltd, Wallingford, Oxfordshire, UK ABSTRACT: Canvey Island is located in the Thames Estuary. The island is a low-lying alluvial fan covering an area of 18.5 km2, with an average height of approximately 1 m below the mean high water level. Canvey Island is protected against inundation by a network of flood defences. In 1953, the island was inundated by the “Great North Sea Flood” that breached the island’s flood defences and resulted in the deaths of 58 people and the destruction of several hundred houses. As part of the EC funded research project FLOODsite, work was undertaken to set up both a hydrodynamic and an agent-based loss-of-life model of Canvey Island for the 1953 flood. The objective of the work was to obtain a better understanding of the 1953 flood event and to analyse the consequences of breaches in the island’s flood defences in terms of loss of life and injuries. The work undertaken indicates that the agent-based life safety model can provide a scientifically robust method to assess loss of life, injuries and evacuation times for areas that are at risk from flooding in the UK. 1 INTRODUCTION and 45% of flats are situated at ground floor level (Kelman, 2002). There is thus a large risk to life and Canvey Island is an island in the Thames Estuary, property with limited opportunities to temporarily covering an area of 18.5 km2. It is formed on a flat, move to a higher level. low-lying alluvial fan that has an average height of As part of the EC research project FLOODsite, approximately 1 m below the mean high water level. work was undertaken to set up a hydrodynamic and The location of Canvey Island is shown in Figure 1. a loss-of-life model of the 1953 flood for Canvey Canvey Island is protected from the sea by a network Island. The objectives of the work were: of flood defences. In 1953, the island was inundated − To obtain a better understanding of the 1953 flood by the “Great North Sea Flood” that breached the event; island’s flood defences and resulted in the deaths − To analyse the consequences of breaches in the of 58 people and the destruction of several hundred island’s flood defences in terms of loss of life and houses. The consequences of the 1953 floods led to injuries; the construction of new flood defences (Brown et al, 2007). A concrete wall rising approximately 3 m to 4 m above the mean high water mark currently surrounds Canvey Island. In 1953 Canvey Island was relatively Essex developed with some 5,200 houses on the island Canvey Island below the normal high tide level. The lowest part Canveypilot site Island GreaterThames London of the island lies at the centre of the island creating ThamesBarrier Barrier a bowl effect. All surface water drainage has to be Thames pumped over the sea wall. Access to Canvey Island Greater Estuary London is currently only possible by two roads both of which are connected to the same roundabout. Any disruption to these routes would hamper evacuation and severely Kent N limit access. The likelihood of flooding of the access routes to and from Canvey Island will increase as a 005101520a 5 10 15 20 km km Administrative result of the continuing rise in sea levels as a result boundary of climate change. Currently on Canvey Island, it has been estimated that 30% of properties are bungalows Figure 1. Location of Canvey Island. 1117 Chp_130.indd 1117 9/6/2008 6:29:09 PM − To assess the results provided by an agent-based − Information from HR Wallingford’s archives; loss of life model where the receptors dynamically − The Essex life in film archive; interact with the flood wave. − The results of physical modelling of the Thames Estuary carried out in 1954. This paper describes the results of the reconstruction of the 1953 flood event and the implementation This information was used to assist in assessing of loss-of-life model that dynamically simulates each the height and location of the 1953 flood defences, individual person at risk from flooding. to produce a digital terrain model, to reconstruct the tidal shape, to assess the incoming flood volume, and to establish the number and location of people on the 2 BACKGROUND TO THE 1953 FLOOD island when the flood occurred. The modelling of the 1953 flood was undertaken in The 1953 flood was caused by a storm surge, that has two stages as follows: been described as ‘the worst peacetime disaster that 1. Hydrodynamic modelling of the 1953 flood to the UK has known’. The tidal surge reached Canvey estimate the water depths and velocities as the Island at around 1.00 am in the morning on Sunday 1 event unfolded; February 1953 and around this time the first breach 2. Loss-of-life modelling using a dynamic agent- of the flood defences happened. In 1953 there was no based model. accurate tidal surge forecasting system in place and there was no single body responsible for flood warn- These two stages are described below. ings. Canvey Island archive web site states site that “whilst communities did have emergency plans, many telephone lines had been brought down by the gales 3.2 Hydrodynamic modelling of the 1953 and affected by the flooding, so large scale evacua- f lood event tions were not possible. As a consequence virtually 3.2.1 Background no warning of the impending disaster was received A two dimensional hydrodynamic model of Canvey at Canvey Island until it was too late. Under a plan Island was set up using the finite difference hydro- termed Operation King Canute the fire brigade were dynamic software TUFLOW. It was necessary to sent out to alert the people of Canvey. At the same use a two dimensional model to obtain the spatio- time the siren and fore maroons were sounded in temporal variation of the water depth and velocity such a way that it was hoped islanders would become as the 1953 event unfolded. The ground elevation curious enough to get out of bed to look outside. For- information used in the model was taken from a tunately some did and were evacuated; others were recently under-taken Light Detection and Ranging soundly sleep and did not hear anything above the (LIDAR) topographic survey data. Owing to the fact howling winds. They either woke up much later when the icy water lapped over them, or sadly never woke up at all. Many of the victims were in the holiday bungalows in the eastern Newlands part of the island and perished as the water reached ceiling level”. Fig- ure 2 shows a view of Canvey Island looking out to sea from the mainland taken a week after the flood occurred. 3 BACKGROUND TO THE MODELLING OF THE 1953 FLOOD 3.1 Introduction In order to model the 1953 Canvey Island flood a historical analysis was undertaken to establish the situa- tion, in terms of source, pathways and receptors that existed at that time. Important sources of in-formation included: − Historical maps of the island; − Articles from 1953 newspapers; Figure 2. Photograph of the Canvey Island flood taken on − Police reports; 8 February 1953. (Source: Canvey Island archive site, 2008). 1118 Chp_130.indd 1118 9/6/2008 6:29:09 PM that there was no topographic data readily available et al in 1954. This paper outlines the dimensions of for the island dating from 1953 work needed to be the breaches and indicates on a map the approxi- undertaken to establish if any significant changes had mate locations of the failures. Baxter states that 40 taken place in terms of the island’s network of flood breaches occurred in several places. Baxter also states embankments. that of the 58 that died during 1953, 53 of the fatalities occurred in the north-eastern part of the island where 3.2.2 Reconstruction of the 1953 source the first breaches occurred. This corresponds with the The shape of the tidal surge was available from data maps in Allen et al that show a number of breaches in in HR Wallingford’s archive. Newspaper and police the defences in the area adjacent to the South Benfleet reports from February 1953 indicated that the peak Creek, the channel that divides the island from the tidal surge level was reached at between 1.00 and 1.30 mainland Essex in the area of Sunken Marsh. a.m. and was 4.6 metres. The breaching of the flood Film from the Essex life in film archive proved a defences occurred shortly before the peak tidal surge useful source of information. Newsreels from 1953 was recorded. showed the aftermath of the Canvey Island flood. These newsreels were used to help provide more 3.2.3 Reconstruction of the 1953 pathways in-formation relating to the location and the size of One of the most useful sources of information was the main breach in the flood defences. The various the Bodleian Library in Oxford that had maps of Can- breaches in the flood defences were represented in the vey Island dating from 1939, 1961 and 1975.

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