Storm Event

Significant coastal flooding along the UK south coast

Severity ? 4

Source

The storm developed off the east cost of the US on 13th December 1989 and moved eastwards towards the UK. Whilst over the central North Atlantic, the storm started moving northeastwards and crossed Scotland on 17th December and continued into the North Sea. The central pressure deepened to approximately 940 mbar. Along the south coast, winds were gusting to over 70 knots [36 m/s] (Davison et al. 1993).

The storm generated a skew surge of between 0.5 m and 1.25 in southwest England. Water levels exceeded the 1 in 5 year return level at one site: Newlyn. Here the return period water level was 1 in 5 years. The corresponding skew surge was 0.57 m. In Christchurch Bay, the sea level was reportedly the highest in recorded history (Davison et al. 1993). The event occurred a few days after peak spring tides. We know the event created much higher water levels along the south coast of the UK, but unfortunately none of the other UK national tide gauge sites were operational at the time between Newlyn and Dover. Interestingly, the storm may have generated a seiching event in the Channel which would have contributed to extreme water levels at the coast (Wells et al. 2001).

Wave heights in parts of the south coast were reportedly 20 ft. [6 m] high (Davison et al. 1993).

Pathway

Defences around the Solent, Hampshire are known to have suffered from serious overtopping during this event, and some breaches. Hurst Spit was seriously eroded.

Receptor and Consequence

This event, which occurred over several days, is considered to be the worst flood to hit areas of the south coast for the past 50 years (Ruocco et al. 2011). The most badly affected areas included Old Portsmouth, Fareham, Emsworth and Cowes. There was flooding of over 50 properties on the 14th – 17th December at Lymington (New Forest, Hampshire). Here, the railway was inundated along with some electricity substations (National Rivers Authority, 1990; Davison et al. 1993). At nearby Pennington, the sea broke through the embankment wall and caused widespread flooding of the grazing marsh and approximately 10 properties (National Rivers Authority, 1990). In total, this event is estimated to have flooded around 80 properties (Wadey, 2013). There was also flooding in Christchurch Bay, including total inundation of Mudeford Quay. The Hurst Spit shingle barrier at the western entrance of the Solent was flattened by the storm on 16th – 17th December (Stripling et al. 2008; West (2014)). Towns were also flooded on the Isle of Wight, including Yarmouth and Cowes, whilst at Seaview a 250 ft. [76 m] section of the sea wall was destroyed and the coastal road washed away (Davison et al. 1993). At Portsmouth, coastal floods occurred on 14th and 16th December, impacting the Old Portsmouth and Eastney areas of the city (Met Office, 1989; Davison et al. 1993; PCC, 2008; Ruocco et al. 2011). Worst affected areas included Old Portsmouth, Fareham, Emsworth and Cowes. Parts of Old Portsmouth experienced flooding to several ft. deep and residential properties were not left unaffected. Local roads and residential properties in and around Fareham were inundated to depths of several inches, and a caravan park near Selsey was flooded once a 25 ft. [7.6 m] gap appeared in a nearby shingle bank. In Hythe, the town centre was flooded to several ft. deep which undoubtedly affected non-residential properties there. Likewise, the central shopping area in Cowes reportedly “disappeared” under the waves. The 16th December also saw severe floods further to the southwest, in the Scilly Isles.

References

  1. Davison, M., Currie, I. & Ogley, B., 1993. The Hampshire and Isle of Wight Weather Book, Froglets Publications Ltd
  2. Wells, N.C. et al. 2001. Modelling of extreme storm surge events in the English Channel for the period 14-18 December 1989. The Global Atmosphere and Ocean System. Available at: http://eprints.soton.ac.uk/6078/ [Accessed March 31, 2015]
  3. Ruocco, A.C. et al. 2011. Reconstructing coastal flood occurrence combining sea level and media sources: a case study of the Solent, UK since 1935. Natural Hazards, 59(3), pp.1773–1796. Available at: http://link.springer.com/10.1007/s11069-011-9868-7 [Accessed March 27, 2015]
  4. National Rivers Authority, 1990. Lymington/Pennington flood investigation – interim report. Ref: IMP/SCH/008/5054
  5. Wadey, M.P., 2013. Understanding Defence Failures and Coastal Flood Events: a Case Study Approach. University of Southampton
  6. Stripling, S., Bradbury, A. P., Cope, S. N. & Brampton, A.H., 2008. Understanding Barrier Beaches. R&D Technical Report FD1925/TR. Published by the Joint Defra/EA Flood and Coastal Erosion Risk Management R&D Programme, Available at: http://sciencesearch.defra.gov.uk
  7. West, I.W., 2014. Chesil Beach -Hurricanes, Storms, and Storm Surges. Geology of the Wessex Coast of Southern England. Available at: http://www.southampton.ac.uk/~imw/chestorm.htm [Accessed March 8, 2015]
  8. Met Office, 1989. Monthly Weather Report of the Meteorological Office. Monthly Weather Report, 106(12). Available at: http://www.metoffice.gov.uk/learning/library/archive-hidden-treasures/monthly-weather-report-1980
  9. PCC, 2008. Flooding in Portsmouth; list of flood incidents. Unpublished email/report provided by Portsmouth City Council to M. Wadey