Flood Risk Assessment Survey

What you need to know

Flood risk assessments are complex, but don’t worry. We’ve got you covered with our most frequently asked questions below. If you have more, just ask!


What is a flood risk assessment?

A flood risk assessment gives you a detailed look into your development site and surrounding area, as well as recommendations for how to mitigate the impact of fooding. Developers need to take into account food risks when planning their new development to not only determine if the development is sustainable, but also understand how this afects the environment and if it increases food risk. It’s best
to carry out a food risk assessment early to avoid additional costs.

Site Investigation Checklist

The only Site Investigation Checklist you need

Download our Site Investigation Checklist, which covers the 13 Site Investigation surveys you need to complete on every site. This includes a rundown of why you need each of them and at what stage through the project lifecycle.

Download now

What is a preliminary flood risk assessment?

A preliminary flood risk assessment can be a rough assessment formed by looking back at past events. Models are created and used to identify sites that are at potential flood risk.

Why do you need a flood risk assessment survey?

If you are in flood zone 2 or 3, a food risk assessment is required for any development. If you are in flood zone 1, it might be required if the site is large enough, i.e. over 1 hectare, or has drainage problems.

What is the risk of not doing a flood risk assessment survey?

As we know, the risk of flooding is increasing and the number of properties and areas at risk of flooding is also increasing. To avoid possible delays, you’ll need to prove your development will not increase the risk of flood as part of your planning application.

When would a flood risk assessment be required?

You need to do a flood risk assessment for most developments within one of the flood zones.

This includes developments:

  • In flood zone 2 or 3 including minor development and change of use
  • Greater than 1 hectare (ha) in food zone 1
  • Less than 1 hectare in food zone 1, including a change of use in development type to a more vulnerable class (for example from commercial to residential), where they could be affected by sources of flooding other than rivers and the sea (for example surface water drains, reservoirs)
  • In an area within flood zone 1 which has critical drainage problems as notifed by the Environment Agency

How do you undertake a flood risk assessment?

Flood risk management plans (FRMs) can range from a short statement to a more detailed hydraulic model of the site. Flood risk will depend on the type of development, its size and the amount of surface water run of it discharges.

What should be included in a flood risk assessment?

The following information should be included in your flood risk assessment:

  • Your site address
  • A description of your development
  • An assessment of the flood risk from all sources of flooding for your development, plus an allowance for climate change
  • The estimated flood level for your development
  • Details of your flood resistance and resilience plans

How long does it typically take to complete a flood risk assessment survey?

The time to complete will depend on the size and complexity of the site, though typically, a flood assessment survey takes around 21 days to complete.


What does flood risk zone 1 mean?

Flood zone 1 is the lowest flood risk zone in the UK. This means a 1 in 1000 annual probability of any river or sea flooding.

When it comes to flood risk, there are very few restrictions in terms of the zone where development can occur. However, development over 1 hectare in size must have a flood risk assessment undertaken during a planning application process. Areas deemed to be at high risk from rainfall known as Critical Drainage Areas are excluded from this rule.

What is a level 2 flood risk assessment?

The level 2 flood risk assessment is a tool for understanding your flood risk and identifying the best ways to manage it. This report will help you make decisions on where to build, renovate or even relocate.

What is the difference between flood zone 3a and 3b?

Flood zone 3 is actually split into two separate zones; 3a and 3b. However, the local planning authorities do not split them and as such their maps only identify a general food zone 3. Areas within flood zone 3 have been shown to be in a 1% or greater probability of flooding from rivers or 0.5% or greater probability of flooding from the sea.

Flood zone 3b is a designation of areas that are at signifcant risk of flooding from rivers or the sea. This classifcation is usually classifed as land that had a 5% probability of flooding or a 1:20 chance. There are restrictions on what may be built in these areas, and it is imperative to know where this zone is.

How to identify competent flood risk surveyors?

[latest_post type=”boxes” image_size=”full” number_of_colums=”3″ number_of_rows=”1″ text_from_edge=”no” order_by=”date” order=”ASC” title_tag=”h4″ display_category=”0″ display_time=”0″ display_comments=”0″ display_like=”0″ display_share=”0″ text_length=”0″]
[button style=”white” target=”_self” hover_type=”default” text_transform=”none” text_align=”center” text=”View Blog” color=”#6c69f1″ background_color=”#ffffff” hover_color=”#ffffff” hover_background_color=”#444444″ border_color=”#6c69f1″ hover_border_color=”#444444″ link=”https://renkap.com/blog/”%5D