Mapping Flood Risk in the UK

Mapping Flood Risk in the UK
Written by Faith Clark

There are numerous types of floods and many ways of classifying them. According to Wikipedia floods are classified mainly by their source – areal, riverine, estuarine and coastal, urban and catastrophic and, although using different language, the UK’s Environmental Law Association’s website uses a similar, perhaps simpler, classification – coastal, river, flash, groundwater and sewer. What can’t be disputed, however, is the effect of floods and the realization that they are getting more common and more extreme.

Following the winter 2015/16 when storms Desmond, Eva and Frank battered the UK during December and into January, the Association of British Insurers (ABI) reported a headline figure of £1.3 billion paid by members to customers affected by flood damage.

In January 2017, gale force winds and higher than usual tides were predicted with many citing similarities with the events of 1953 when the North Sea floods, caused by a heavy storm combining with a high spring tide and severe winds, killed more than 2,500 people in the Netherlands, UK and at sea. The UK Environment Agency issued 17 warnings of danger to life, 80 flood warnings, 70 flood alerts, and tens of thousands of residents along the North Sea coast were advised to evacuate their properties.

Although flooding was less than expected, authorities maintained they did not ‘over react’ and defended warnings to residents saying they were ‘grounded in science and advice from the EA and Met Office’.

So science, particularly map science, has an integral part to play as floods become more of a concern. Rachel Tidmarsh, Managing Director of UK based aerial mapping company Bluesky, which has recently expanded its business into North America following the acquisition of Col-East Inc (www.col-east.com), commented “By making high resolution flood map data easily and affordably available we can arm those who prepare for and manage flood events with continuous and detailed information on which to base critical decisions.”

Bluesky has been working with hazard mapping specialist JBA to improve access to essential flood risk data for some time now. In 2015 JBA’s marketing leading GB Flood Map was launched on Bluesky’s on-line Mapshop. Detailing peril from six different types of flooding, the GB Flood Map is a leading tool for flood insurance underwriters and is used by the majority of the UK insurance industry.

The GB Flood Map, at 5 metre resolution, is a highly detailed flood map covering six flood perils – river, coastal (including wave overtopping), surface water, groundwater, canal failure and dam break, in Great Britain. The GB Flood Map is modelled using JFlow, JBA’s proprietary and highly acclaimed flood modelling software and has benefited from many years of updates, use, feedback and validation against actual flood claims.

More recently Bluesky published for the first time online a high resolution 5m groundwater flood risk map covering the whole of GB. Designed to help home owners, developers and risk management authorities understand the threat of groundwater flooding, the new color coded map is easy to use and complements other types of flood maps.

The new 5m Groundwater Flood Map was created by JBA and provides comprehensive coverage of all aquifers in England, Wales and Scotland. Created using a range of data, including known locations of past groundwater flooding events, rainfall measurements and aquifer properties, the new map provides classification of hazards on a 5-metre grid. A three-tiered methodology, used to create the map, allows for quick and efficient updates and refining of the map for local areas of interest.

“Groundwater flooding occurs when the groundwater table in permeable rock types rises to enter basements and cellars or presents as excess water emerging at the ground surface. Often overlooked or confused with other causes of flooding, it can pose considerable economic and social threat,” continued Tidmarsh. “As groundwater levels are generally highest following prolonged periods of rainfall, groundwater flooding is a growing threat as the UK is expected to experience considerably higher amounts of rainfall because of climate change.”

“These maps will support flood risk management activities at a national or local scale, and will assist risk management authorities in meeting their responsibilities under the Flood and Water Management Act,” added Dr Maxine Zaidman, Technical Director for Hydrology and Hydrometry at JBA.

Visitors to Bluesky’s online Mapshop can also access complete nationwide coverage of aerial photography from multiple epochs, 3D models, LiDAR data, Thermal Mapping and Bluesky’s National Tree Map™. Other flood related map layers also available include Susceptibility to Groundwater Flooding and Geological Indicators of Flooding from the British Geological Survey and a collection of flood data from the Environment Agency.

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