Updated Flood Defenses Can Make All the Difference

July 29, 2019

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Flood control methods are used throughout the world to prevent the detrimental effects of rising water levels. Permanent man-made flood defenses in the UK are dominated by four types:

 
  • Embankments
  • Floodwalls
  • Storage areas
  • Point structures

These four types are used singly or in combination throughout the UK to help defend against storm surge flooding. With increasing urbanization and rising sea levels, however, more areas become exposed to storm surge flooding every year. As major flood events occur, the UK continues to make improvements to its flood defenses.

One such major flood event was Winter Storm Xaver, which swept over the UK, the Benelux countries, northern Germany, and Denmark in early December 2013 with wind gusts exceeding 150 km/h (93 mph). Xaver downed trees over a wide area, causing severe damage to homes and vehicles. In addition, it generated a storm surge of 2.75 meters (9 feet) at many locations along the UK east coast. In Kingston upon Hull (Hull), the storm surge caused water levels to reach to an all-time high of 5.8 meters (19 feet), flooding 264 properties when the existing flood defenses were overtopped.

Since Storm Xaver, significant enhancements have been made to the flood defenses along the River Hull and the Humber Estuary. One recently completed GBP 5.2 million tidal defense project, for example, included a 1,700-foot-long glass-paneled floodwall—one of the longest of its kind in Britain—protecting Paull, 6 miles east of Hull on the north bank of the Humber Estuary. The flood defenses at Paull were raised to 6.8 m (22 ft.) above sea level. Additional improvements are being made to protect the city of Hull—90% of which lies below the regular high-tide level—from tidal flooding. In January 2018, for example, a GBP 42 million upgrade to 19 km of tidal flood defenses in the Humber Estuary was approved.

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Figure 1. The new glass-paneled floodwall at Paull. (Source: David Brown)

Taking into account the upgraded flood defense system, it’s easy to see that if Storm Xaver were to occur today, the impact to the City of Hull would be completely different. The estimated losses from a similar event could drop significantly from an 18-year return period down to a 13-year return period. In addition, the flood extent would be much less severe, as seen in Figure 2.

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Figure 2. The observed flood extent of Storm Xaver in Hull with the flood defenses at the time of the event (top) and the expected flood extent in Hull were Storm Xaver to occur with the flood defenses in place today (bottom). (Source: AIR)

Flood defenses can make an enormous difference when it comes to the extent of flooding and the resulting losses. In a 2009 study, for example, AIR estimated that had there been no inland flood defenses in place during the devastating UK floods of June and July 2007, insured losses would have been in excess of GBP 6.5 billion—more than double the actual reported loss of GBP 3 billion. The updated AIR Extratropical Cyclone Model for Europe now includes the updated storm surge components for England and Wales, including detailed coastal sea defenses such as levees and seawalls as well as their standards of protection. Using the updated model, clients are now able to realistically account for extratropical cyclones and their associated storm surge effects with today’s flood defenses.

View the webinar: The Addition of Great Britain Storm Surge to AIR’s Extratropical Cyclone Model for Europe

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