Flood Risk Assessments

The Flood Risk Assessment forms the core of our water service offering. No matter how deceptively risk free a proposed development can seem there are always elements of risk relating to groundwater, surface water and sewer flooding.


Flood Zone 1

This flood zone is often interpreted as comprising land not at risk of flooding. In fact this zone is more properly defined as land having a less than 1 in 1,000 annual probability of river or sea flooding.

The modelling and mapping used to define these flood zones does not include every watercourse. Many ordinary watercourses are not modelled by the Environment Agency.


Flood Zone 2

Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding

Land having between a 1 in 200 and 1 in 1,000 annual probability of sea flooding

This flood zone represents the middle ground from a planning perspective. Most development can be accommodated in this flood zone with only highly vulnerable development requiring an exception test.


Flood Zone 3

Land having a 1 in 100 or greater annual probability of river flooding.

Land having a 1 in 200 or greater annual probability of sea flooding.

It can be difficult to develop in Flood Zone 3 although it is not impossible. Developments of a lower vulnerability classification can often be allowed if it can be shown that they can be made safe and will not increase flood risk elsewhere.


Flood Defences

This flood map shows a significant defence. Flood maps are generally prepared without consideration of the protection afforded by defences. Closer investigation often shows the actual flood risk to be significant only if the defence fails.

We can produce a Flood Risk Assessment (FRA) for any existing or proposed development in any flood zone. Click the buttons on the adjacent map for more information on flood zones and what they mean.

Current guidance requires an FRA for all sites, regardless of flood zone, when they are larger than 1 hectare. Typically, sites in Flood Zone 1 require less detail with respect to river based flood risk and the primary concern of the Local Authority will be with respect to surface water drainage, groundwater, sewer and pluvial flood risks. Our FRAs will investigate risk from all sources and generally include a separate surface water drainage statement or strategy as an appendix.

Even within Flood Zone 1 there may be some small watercourses that have not been modelled by the Environment Agency. Furthermore, the Environment Agency flood maps are not always correct.  Some areas of the UK have well defined floodplains that are accurately mapped by a combination of topography, flood history and detailed hydraulic modelling. However, in other areas the flood maps are poorly defined and based upon an inadequate understanding of topography or hydrology. In some places the flood maps are based upon historic records that may, or may not, reflect actual flood extents. In such circumstances Lumax can help you to challenge the flood maps with site specific hydraulic models. Whether the site is in Flood Zone 1,2 or 3, Lumax can identify the precise outline of the floodplain associated with features not included on the Environment Agency maps. Such modelling can be critical to identifying a solution that can facilitate a commercially viable development.

Whatever the unique flood risk circumstances of your site, Lumax can investigate the hazards, advise on appropriate mitigation and prepare an assessment which complies with the requirements of the National Planning Policy Framework.

Contact us for a site specific quotation …..