Flood Risk Assessment

What is a Flood Risk Assessment?

A Flood Risk Assessment, also known as a FRA, is a report that details the main flood risks to a development site.  The FRA is frequently needed as part of the planning application for a development. Your planning application may be refused by your local planning authority if you don’t include a flood risk assessment or if the FRA isn’t satisfactory. So it is essential to identify if your development site lies in a flood risk zone early in your planning application preparation.

Ideally, a FRA should be completed as part of your pre-planning process, so that architectural designs for the development can include any design changes to your scheme that mitigates flood water, allocates vulnerable users to the correct floor levels, and identifies the safest route in the event of a flood.

Your FRA should also take the surrounding area into account and whether the development poses a flood risk to areas nearby. At Earth Environmental & Geotechnical we also provide surface water drainage strategy SuDS for sites to ensure that the proposed development does not increase the flood risk to the local environment.

The scope and details of the Flood Risk Assessments will vary depending on the size and topography of the site, and which Flood Zone the site lies within.

The flood zone for a sites are obtained from the Environment Agency and Local Authority Strategic Flood Risk Assessment which are defined as Flood Zone 1 to Flood Zone 3, and the site areas being defined as more or less than 1 hectare.

(Flood Zone 1 is has 1 in 1000 (0.1%) or less annual probability of flooding, Flood Zone 2 has between 1 in 1000 (0.1%) to 1 in 100 (1%) annual probability of flooding, and Flood Zone 3 has more than a 1 in 100 (1%) annual probability of flooding).

The minimum FRA we provide that is required for most planning approvals is for sites that are less than 1 hectare in size and lie within Flood Zone 1.

In this circumstance, The Environment Agency Advice Note – April 2012 states that no flood risk assessment will be required, but a Flood Risk Statement and Surface Water Management of the site is required to demonstrate that the proposed development will not increase the risk of flooding to the site or surrounding areas.

• Details of each potential source of flood risks to the development site;
• Pre and post development surface water run-off rates and volumes for up to and including a 1 in 100 year storm event including climate change (analysis using industry recognised calculations obtained from XP Solutions WinDes computer software);
• Mitigation factors to be incorporated into the design of the development to minimise the risk of flooding

In some circumstances the development site may lie within Flood Zone 3 and is over 1 hectare in size. This will be the most detailed FRA required to obtain planning permission for a development, and the steps below are to be taken as minimum.

The National Planning Policy Framework guidelines and details are also to be adhered to in this circumstance. The full flood risk assessment for this will include:-

• Site sequential and exception test assessment for the development;
• Sources of flood risk within the vicinity of the development site;
• Flood risk mitigations design techniques;
• Flood compensation levels and volumes requirement within the development site boundary to maintain the functional flood plain;
• Pre and post development surface water run-off rates and volumes for up to and including a 1 in 100 year storm event including climate change (analysis using industry recognised calculations obtained from XP Solutions WinDes computer software);
• Safe egress assessment for evacuation off the post development site.

Do I need a Flood Risk Assessment?

If you are a property developer, planner, architect or property investor you need to understand the potential risk of flooding when designing and developing a new site. If your development site is over 1 hectare in size you automatically need to have a FRA and this should be completed early on in the pre planning process.

You also need a FRA for any new development, whether an extension or a new multiple home development is in a flood zone. You will also need an FRA if your development is within 20 meters of an Environment Agency main river
FRA’s are used by the planning industry to determine if a new development is sustainable in relation to flood risk.

The most important step you’ll need to understand is how you can use mitigation measures to manage these risks. With a robust FRA and mitigation strategies your potential development could get planning approval even if it is in a flood zone.
Every FRA is specific to the proposed development site as no two development sites will be exactly the same. Whether your planning a residential or commercial site, a FRA from Earth Environmental & Geotechnical will identify the risks, and where appropriate the mitigation steps you can take to make your development a success. Our expertise enables us to provides a detailed analysis of multiple sources of flood risk proving specific mitigation strategies that apply to your development. Our team is up to date on the latest legislation and flood modelling data to protect your development from flooding or impact it’s surrounding environment.

Contact us now to discuss your development