What is a flood risk assessment?

In Newsby Daniel Cook


What is a flood risk assessment?


If you’ve been told you need to include a flood risk assessment (or FRA) with your planning application, it can feel like just another expense to add to your long list of reports and assessments. This isn’t an uncommon situation to be in. We get calls every day from developers and architects who are near the end of their development planning stage and have been told by their local planning office that they require an FRA for planning. Without it, the application cannot be validated.

This is something we deal with on a daily basis so we wanted to write this article to explain what a flood risk assessment is, when they’re necessary so you can be prepared, and why it’s becoming more and more vital to get flood risk consultants involved earlier in the planning process if you want your development to get approved without blowing your budget.

Flooded front door of a red brick building

What is an FRA?

A flood risk assessment (FRA) is a document that reviews a development in its proposal form to assess it against the risk of flooding, whether that be from groundwater, river (fluvial), surface water (pluvial), estuary/coastal (tidal), or from sewer sources. It should also take the surrounding area into account and whether the development poses a flood risk to areas nearby.

It does this by using either 3rd party data sources, such as the Environmental Agency modelling, or independent data sets generated by our team of experts. More likely, companies will use a combination of both to get a full overview of a site. Ambiental are unique in that we use our own Flowroute-I flood modelling software which you can learn about here.

When do you need an FRA and when do you not?

An FRA is required under the National Planning Policy Framework (NPPF) and the Environment Agency (EA) guidance on development and flood risk when a development is located in Flood Zone 2 or 3,  a Critical Drainage Area, or the site is greater than  or equal to 1 hectare in size, for sites in Flood Zone 1.

You’ll also need an FRA if your development is taking place within 20 meters of an EA main river. EA activity permits will be required if the proposal includes temporary and permeant works within 8m of a EA river and 16m of a tidal EA river.

You can find out more about this on the UK government website here: https://www.gov.uk/guidance/flood-risk-activities-environmental-permits

legs covered in plastic against the flood water

What does an FRA have to include as a minimum?

The NPPF details what you need to include within a flood risk assessment in order to fully determine whether a development is viable in terms of flood risk.

The key part of the NPPF is paragraph 164. This is focused on the exception test parts A and B.

  • Part A determines whether what is proposed is safe for its lifetime.
  • Part B determines whether it provides sustainable benefits to the area.

What we mean by sustainable benefits is it’s not just about your specific development. You need to think about how people will be using the site and whether it benefits the general area.

For example, you could be unintentionally creating a greater risk of flooding in your neighbourhood by constructing an extension that impedes a flood route. The water could then move around your extension, into your neighbour’s garden and through their back door.  Although a hypothetical example, this could and does happen. It’s why the NPPF promotes development that does not increase flood risk elsewhere. This can be achieved through design of the structure, manipulating surfaces, or looking at wider river catchment solutions.

As the FRA evolves, another key area that an FRA addresses is when flooding does occur, how are humans then going to have to interact with the floodwater? Where do they go if flooding has already begun?

You could create the most flood-resilient building in the world where water will never enter, but if you don’t take into account what happens to the water immediately outside of it, you could create a situation where people can’t enter or leave the site because of the risks. Policy doesn’t only promote sustainable development in terms of construction, it further assesses the impact the development could have in a high-risk flood area and the potential demand for the emergency services. A robust FRA assessment would include how users would react and interact if flooding were to occur.

Contrary to the snippet from the NPPF which states developments need a simple FRA, we have only lightly touched one a selection of key areas that make up what an FRA is. There are other areas we would also need to include, the local policy of the planning authority, the NPPF and the EA, whilst most importantly working with you to provide a solution that is in line with your original development proposals.

You can read the full NPPF guidelines here: https://www.gov.uk/government/publications/national-planning-policy-framework–2

How to find out if your development is in a flood zone and therefore needs an FRA.

Fortunately, the government and the Environmental Agency provide a free service that you can use to check to see if your development is within a flood zone.

There are two different types of maps you should be checking. The first is the ‘Flood Map for Planning’.

Flood Map for Planning centred on Brighton

Screenshot of the Flood Map for Planning interface from the EA website

This map delineates between the different Flood Zones which then correlate back to the EA guidance and the NPPF as to what can and can’t be achieved.

You can find it on the Environmental Agency here: http://apps.environment-agency.gov.uk/wiyby/37837.aspx

The second is the ‘Long term flood risk map for England’ which details whether flood risk from rivers and seas is high and low. It further discusses whether a site is at risk of surface water flooding and if it’s affected by reservoir flooding.

These examples are focused to England only. There are alternative third party services provided by Scotland, Wales, and Northern Ireland. These services can be found on the relevant national governmental websites.

Long term flood risk map from government uk website

Screenshot of the Long term flood risk map from gov.uk website

You can find it on the gov.uk website here: https://flood-warning-information.service.gov.uk/long-term-flood-risk/map

Using these two together, you should get a good idea of what Flood Zone your development is in and whether policy states you need an FRA.

Helpful Tip: Where possible, it’s always worth checking these maps prior to purchasing any land to get an idea of how likely it is that planning would be approved or whether you should look elsewhere for your development.

Surface water in FRAs

We also wanted to talk about surface water here. Surface water is becoming more prevalent in terms of making decisions on planning applications than it ever has been in recent years. It is part of the Sequential Test to assess flood risk from all sources, yet the focus has traditionally been toward flooding from rivers and the sea. Surface Water can throw a spanner in the works. The main issue stems from the obstruction of overland flow pathways.

These are the natural pathways that water flows down when rainfall occurs. An example of this is a hill and rainfall. The rain will naturally flow downwards. Now expand this to everyday life. Villages, towns, cities etc. It will continue to flow until it finds the lowest topographical point.

The best case is it enters the river network.

The worst case is it pools in a low spot of topography that you are seeking to develop.

What Local Councils are now conscious of is that if you start constructing in an overland flow pathway without properly managing where that water is travelling, you could be increasing the flood risk elsewhere, as we discussed earlier. Due to this, we’re now seeing Councils requesting to see surface water models with specific depth calculations being produced alongside fluvial and tidal flood risk. This is important to keep in mind.

How to get a Flood Risk Assessment

There are a variety of businesses that can provide flood risk assessments. We would always recommend you go with a reputable, qualified environmental consultant to avoid any delays or extra cost.

Here are some things you should look out for when determining which environmental consultant you want to work with:

  • Do they have staff who are affiliated with ICE or CIWEM? Many local councils now require an FRA to be signed off by someone with this affiliation.
  • Does the person creating your FRA have a relevant background with a bachelors or masters level qualification?
  • Does the person creating your FRA sound credible and confident in what they’re saying?
flooded walkway outside of a professional building

What affects the cost of an FRA?

When pricing an FRA, every site is different. We can’t speak for other consultants, but all of our FRAs are bespoke to the site. This means we don’t have a standard price we could give you as an example. However, we can tell you what affects the cost and give you an idea of what to expect.

As a general rule, the price of a flood risk assessment is affected by the design of the project. This includes how complex it is, what Flood Zones is it located in, and how much third party data is readily available to conduct a robust assessment in accordance with policy.

If you’re building a development which is susceptible to flooding, or has a large number of receptors (users) which are susceptible to flooding, coupled with a high flood risk, then that’s going to make the work complex. This results in our experts working with you and with the policy to come to an agreed solution that best suits all.

Costs can accelerate if there is a lack of data available for the site. Most notably, topographic data or hydraulic modelling which provides Flood Levels for a range of return periods/flood events.

The NPPF identifies the importance of data.  Paragraph 43 of the NPPF discusses how you should be making informed decisions using the right data available. We always try to use as much data as is possible. On occasions, this could lead to us requesting the client to invest in sourcing more data (independent models/surveys etc.). To really understand a sites flood risk, you need to use multiple data sources which aren’t always easy and simple to come by, especially if you don’t have experience in finding it.

A key example of this happened just a couple of months ago. We were working on a new office building within a flood zone and we evidenced for months for the developer to invest in a topographic survey. There just wasn’t enough information available to us to make an informed decision on the site’s flood risk. In the end, we had to submit without this data and the planning got rejected due to a lack of information.

After this, the clients invested in a topographic survey and thanks to the additional information we were able to demonstrate how the floodwater interacted at the site. The data focused on where the flood water was likely to go across the site and how it could impact the future development. By having access to a site-specific survey, we were able to better evidence that the site and the future development had a low risk of surface water flooding.

By providing the additional data the planning was approved.

The more information you can give upfront to the environmental consultants, the quicker they’ll be able to understand the site and therefore the risk, the more affordable it will be. It also allows for the fee to be more accurate as they can advise upfront whether further investment is needed to acquire data.

We must stress that it’s okay to only have a crude plan of what you want to achieve, an ownership boundary, or even just an idea. Our team of consultants are well versed in being able to take ideas to reality or for a technical view – from concept to design.

Flooded picnic benches

When should you get an FRA for a development?

The final thing we want to talk about is the point at which you say yes to an FRA to be completed. Good planning can save you money.

Of the many developments we have supported, we are involved with so many at the end of the pre-planning process or the week before submission deadline. We so often see  ecology reports completed, designs drawn to the finest detail, Structural Engineer comments… and then the FRA is requested.

As you can imagine, getting us involved that late in the game is very likely to result in having to re-work the design.

The FRA is not there to cause problems. The FRA is there to better support you and advise on how to design a scheme that mitigates flood water, allocates vulnerable uses to the correct floor levels, and establishes the safest route in the event of flood.

As part of our work, our expert consultants may identify aspects that would need to change in order to make the project policy-compliant as they progress through the FRA. Our expert consultants work to policy, but they also work with you and your design team to find a solution that satisfies all.

On occasions, if any part of your design does not meet the criteria of national or local planning policies, you may need to re-view all those designs and surveys based on the updated scheme.

In our experience, we have seen projects where buildings have had to be relocated to a completely different area of the site in order to avoid any topographic low points, ecologically high-risk areas, high flood risk areas, or in order to make space for additional drainage infrastructure.

We hope this article has helped you understand what a Flood Risk Assessment does and how it can support your development.

If you have any questions about what you need to include in an FRA for your development, don’t hesitate to contact our Flood Risk Team on 0203 857 8540 or email us on [email protected] and we’ll answer all your questions.


Daniel Cook

Author: Daniel Cook

If you have any questions about Flood Risk Assessments for your development, don’t hesitate to contact Daniel and our Flood Risk Team on 0203 857 8540 or email us on [email protected] and we’ll answer all your questions. Alternatively, use the button below and fill out the form and we’ll call you back in the next 48 working hours.

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