North Sea storm surges

Storm surges in the southern North Sea pose a complex, persistent and perhaps growing threat to the surrounding coastline of NW Europe. In the UK, more than one million properties are at risk from sea and tidal flooding, corresponding to roughly five percent of the population (Jorissen et al., 2000). By comparison, two thirds of the Netherlands is at risk of flooding and over five million inhabitants actually live below sea level (Figure 1).

Figure 1 Flood prone areas around the North Sea (from: Jorissen et al., 2000). For the UK, the largest flood prone areas are found along and upstream of the Humber, The Wash and the Thames.

The momentum for the development of the Thames Barrier in the UK and the Delta Project in The Netherlands arose after the last great inundation from the North Sea on the evening of 31 January and the morning of 1 February 1953. Fifty years after that event, the Cambridge University Centre for Risk in the Built Environment (CURBE) of which the Cambridge Coastal Research Unit is a founder partner, organised an interdisciplinary science meeting at the Royal Society in London in 2003 to a) reflect on that event, b) review the technological advances, increases in scientific understanding of the physical processes, and developments in mathematical statistics relating to storm surge studies, and c) consider the implications of accelerated eustatic sea-level rise and possible changes in storminess as a result of near-future global environmental change (McRobie, Spencer and Gerritsen, 2005).

Within a broader project looking at 'Coastal Settlements at Risk' (Thomalla et al., 2000; Kelman et al., 2002; Thomalla et al., 2002) on the UK east coast, James Brown's (PhD 2004; now University of Amsterdam (brown@science.uva.nl)) research has focussed on the uncertainties associated with numerical modelling of extreme coastal flooding (Brown et al. (2007)). A storm surge model has been developed for predicting water levels at Canvey Island, Thames estuary in response to meteorological and tidal forcing of the North Sea. The storm surge model is based on four nested models, which provide a consistent increase in spatial resolution towards the case study site. The predicted water levels are then used to drive a flood inundation model of Canvey Island, which resolves the terrain and buildings of the study area with high-resolution topographic data. These models are then applied within an uncertainty framework where model sensitivities and uncertainties are evaluated for a range of both storm forcing conditions over the North Sea and sea defence failures at Canvey Island.

Figure 2 Output of water depths from a simulated 200-metre sea defence breach in the north of Canvey Island (J Brown, unpublished 2004)

Figure 3 Storm surge levels at Blakeney Quay, North Norfolk. The highest plaque records wave action on top of the 1953 storm surge (photograph: T. Spencer)

As past studies have shown (Steers et al., 1979; Figure 3), changes in storm surge magnitude and incidence are also likely to have consequences for coastal ecology and the population dynamics of littoral communities (e.g. Austin et al., 2001). Thus, for example, back-barrier marshes on the North Norfolk coast are likely to be threatened by the episodic landward migration of enclosing barriers (Figure 4).

Figure 4 (below) Salicornia Marsh, Scolt Head Island, a site instrumented for the study of tidal hydrodynamics and associated sediment and nutrient transports. The landward retreat of the enclosing sand and shingle barrier (foreground) will threaten the floristically diverse higher saltmarsh at this locality (photograph: T Spencer).

References

• Brown, J.D., Spencer, T., Möller, I. (2007) Modelling storm surge flooding of an urban area with particular reference to modelling uncertainties: a case study of Canvey Island, UK. Water Resources Research, 43, doi:10.1029/2005WR004597. 1-22.
• Austin GE, Rehfisch MM, Viles HA and Berry PM 2001 Impacts on coastal environments. In: Harrison PA, Berry PM and Dawson TE (eds) Climate change and nature conservation in Britain and Ireland: Modelling natural responses to climate change (The MONARCH Project). Oxford: UKCIP Technical Report, 177-228.
• Jorissen, R, Litjens J and Mendez Lorenzo A 2000 Flooding risk in coastal areas. Risks, safety levels and probabilistic techniques in five countries along the North Sea coast. The Hague, Ministry of Transport, Public Works and Water Management, 61pp.

Publications

• Kelman I, Thomalla F, Brown J, Möller I, Spence R and Spencer T 2000 Coastal settlements at risk: A study of England's east coast. Proceedings, International Symposium on River Flood Defence, Universität Gesamthochschule Kassel, Kassel, Germany. Kassel Reports of Hydraulic Engineering 9: F263-273.
• Kelman I, Thomalla F, Brown J, Möller I, Spence R and Spencer T 2002 Coastal flood-risk assessment in England. Philosophical Transactions, Royal Society of London A360: 1553-1554.
• McRobie A, Spencer T and Gerritsen H. (eds) 2005 The Big Flood: North Sea storm surge. Philosophical Transactions of the Royal Society of London A363: 1261 - 1491.
• Steers JA, Bayliss-Smith TP, Stoddart DR, Spencer T and Durbridge PM 1979 The storm surge of 11 January 1978 on the east coast of England. Geographical Journal 145(2): 192-205.
• Thomalla F, Brown J, Kelman I, Möller I, Spence R and Spencer T 2002 Towards an integrated approach for coastal flood impact assessment. Proceedings, Solutions to Coastal Disasters '02 L Ewing and L Wallendorf (eds) (ASCE : Reston Virginia) 142-158.

Collaboration

• Professor RJ Spence, Martin Centre for Architectural Research
• Allan McRobie, Department of Engineering
• Dr PJ Baxter, Institute of Public Health

Funding

'Coastal Settlements At Risk' was funded by Halifax General Insurance Services Limited (HGISL).