The Flood Mapping Problem

The original flood hazard maps from the EA and SEPA were called "indicative" floodplain maps (because they were not very accurate). These provided a general overview of areas that are within natural floodplains, and identified those properties which are potentially at risk from flooding from rivers or the sea. The maps were based upon historical flood records, survey records and computer models. Copies were provided to all local authorities in Britain .

In December 2000 the Environment Agency added indicative floodplain maps to its web site allowing anyone with access to the Internet to check out which areas of England and Wales are at potential risk of flooding from rivers or the sea. A feature called "What's in your backyard" means that users can enter the name of a town or a postcode to see what the flood risks are for their own properties. See http://www.environment-agency.gov.uk .

The Environment Agency service only applies to England and Wales , but there is a commercial web site that provides a free postcode search facility for the whole of Britain . It can be found at: www.home-envirosearch.com .

These indicative flood maps only give a rough indication of areas at risk of flooding. For example, they do not include the effects of flood defences, and because of this they may show areas to be at risk when they are not, and vice versa. In other words they may give a false sense of alarm or a false sense of security. Smaller insurance companies used them for underwriting, but the bigger insurers had their own, more accurate flood maps. Almost all insurers will have maps showing coastal flood hazard areas that take into account coastal flood defences. These maps also show which defences are likely to fail during a 50-year storm, and which areas would be inundated as a result.

Therefore if anyone is having difficulties obtaining flood insurance, it would pay them to shop around, trying a mixture of big and small insurers. The Environment Agency published "second generation" flood maps in October 2004, starting with river flood maps, based on the data commissioned by the Norwich Union, but extending this to include coastal flood and taking into account flood alleviation schemes. These maps may make insurance cheaper for some, but more expensive for others.  The Scottish Environment Protection Agency is due to publish similar maps in September 2005.

It will still pay to "shop around" as some insurers will still have more accurate and detailed maps than the government and its agencies can afford.

The Environment Agency has called for up to £200m more to be spent each year on flood defences, and it is also in the process of preparing a map of flood risks across the country in 2050, taking account of climate change.

If their property appears in the indicative flood map, they may still get a quote from one of the dozen or so bigger insurers which have more accurate and detailed maps than the government and its agencies can afford.

It should be emphasised however that insurers would generally try to maintain cover for existing long term clients, and those who change insurers frequently are more likely to have problems.

One of the problems of publishing flood maps is that this could have an adverse effect on property values, and possible legal consequences. In England this has been solved by classifying them as a "Statutory Public Register" which confers immunity from litigation as well as exemption from the Data Protection Act. (This step is apparently not necessary in Scot's Law.) The technology exists already to not only publish such maps on the internet, but to link them into existing gauging stations to give real time indications of the flood risk for flood warning dissemination purposes. Householders concerned about heavy rainfall and rising river levels could then check the danger directly themselves by keying their postcode into the internet and seeing the latest assessment "on line".

Future Mapping

The Environment Agency has commissioned work on an "extreme flood outline" to produce flood maps for the 1,000 year return period. In addition, flood hazard areas in England and Wales have been surveyed by the Environment Agency using an airborne laser instrument called "LiDAR". This instrument has the potential to produce much more accurate digital elevation models, essential for more accurate flood mapping. While the system has only recently been used in Scotland for the Scottish Executive on an experimental pilot study basis, a commercial operator, "Info Terra", has carried out independent LiDAR surveys in most urban centres in Britain , including Central Scotland .

(For more details see the panel and the glossary, or contact info@infoterra-global.com

Is flood mapping the answer?

Many insurers have spent large sums of money on improving their flood maps, but is this the whole story? Thanks to sewer overflows, and inadequate drainage infrastructure, it is clear that floods can occur almost anywhere. While mapping is adequate for commodity business like household insurance, insurers will need to be aware that avoiding such areas will not eliminate the flood risk.

For some years, the author has been encouraging Scottish local authorities to adopt a different approach when considering flood defence works. This is to use a zoning approach, to zone areas according to vulnerability, rather than hazard, and to concentrate on ensuring that locations such as hospitals, sheltered housing, social housing and evacuation routes are safe (more details appear later in this report). The EA are now looking into this concept with a view to improving the targeting of flood warnings, public education, and community involvement. An approach worth considering can be found in Sweden , where priorities vary depending on the "social tolerance" of flooding expressed in terms of impact. Thus inner city areas with a high level of people at risk and a high level of investment have the lowest tolerance.

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