Many maps and other desk-based products are available to assist insurers and brokers in assessing the risk of flooding on an individual property level. In the UK, maps produced by the Environment Agency in order to comply with the EU Flooding Directive, are available on-line. For major rivers the mapping is the result of a detailed study based on surveying the river and hydraulic structures and undertaking hydrological and hydraulic modelling. For small streams the mapping is the result of a countrywide methodology which is inaccurate and generally an over-estimate of the potential flood extents. In some areas the predicted flood extent does not even follow the stream channel because the mapping has assumed the path of the stream from a digital terrain model rather than using the actual mapped channel position.
Most insurance companies use mapping products which only have the less detailed maps resulting from the countrywide methodology and can be highly inaccurate. Likewise or site-search services to assist home owners only provide very general information in relation to flood risk, such as maps showing flood extent with a 50m grid-cell outline, which is of little use. To achieve a full assessment of the flood risk at a property level there is no substitute for a site-specific field-based survey. Even the most detailed flood risk maps do not provide information on the property of interest such as the height of the floor levels, points of ingress of water into the building, or alleviation measures such as pumps.
During 2016 and 2017 Hydro-GIS Ltd undertook a project for a major insurance company which involved surveying the top seven most at risk properties, as identified using off-the-shelf flood risk maps for insurance in the UK. The result was that out of the seven properties only one property was truly at high risk of flooding, three had significantly reduced the risk by incorporating flood alleviation measures, and three properties were incorrectly identified as high risk due to errors in the flood maps or the geo-referencing of the property.
Hydro-GIS Ltd has undertaken numerous site-specific flood surveys in the UK and internationally to assist with insuring, buying, selling a property or obtaining a mortgage.