Darren Frias-Robles, MD of Whitefox Chartered Surveyors looks at the topic of flooding and we learn about how staff member Lloyd Blyth is training for the Brighton Marathon

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By Darren Frias-Robles [email protected]

Published: January 24, 2024 | Updated: 24th January 2024



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The Risk of flooding can be increased by the development of land. Surface water drainage design is an important consideration in alleviating this. Rainwater runoff will need to be collected and discharged into soakaways or some form of attenuation or sustainable urban drainage system (SUDs) to prevent localised flooding.

Flood Risk Categorisation

One of the first steps in identifying whether a site is at risk of flooding is to commission a desktop environmental risk report (Groundsure, Landmark or similar). This will search various datasets relating to flooding and provide a flood risk categorisation for any given site.

The Environment Agency is the government body who manages flood risk in the UK. Land is divided into 4 flood zones which categorise the risk of flooding:

Flood Zone 1 (Low Probability)

“Land with a less than 1 in 1000 annual probability of river or sea flooding. (<0.1%)”.

In these flood zones, there are few restrictions to development.  An exception applies for development land over 1 hectare. In these instances, a flood risk assessment will be required as part of any planning application for development.

Flood Zone 2 (Medium Probability)

“Land identified as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% to 0.1%); or between a 1 in 200 and 1 in 1000 (0.5% to 0.1%) annual probability of sea flooding”.

Flood Zone 3a (High Probability)

“Land identified as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater (>0.5%) annual probability of sea flooding”.

Any development planned in flood zones 2 and 3a will require a flood risk assessment as part of any planning application. Applications in flood zone 3a will also need details of suitable mitigation measures to remove or reduce the risk of flooding.

Flood Zone 3b – ‘The Functional Floodplain’

“Land where water has to flow or be stored in times of flood. Identified as a flood zone having a 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood or at another probability determined by the local planning authority and the Environment Agency (including water conveyance routes).

Flood zone 3b development will require a flood risk assessment as part of any planning application & only ‘water compatible’ uses and essential infrastructure projects will be permitted in this zone”.

Source – The Environment Agency

Flood Risk Assessment (FRA)

A flood risk assessment will usually be prepared by an environmental engineer specialising in this field of work. As a minimum it should include the following:

  1. An assessment of the flood risk and estimated flood level for the site with contingency to allow for future climate change
  2. Details of all plans and designs clearly showing planned finished floor levels and their relation to maximum flood levels
  3. Details of flood defences and flood mitigation measures.

An FRA will set out the approach to mitigate the flood risk identified using the following approach:

1 – Avoidance

The site layout should be designed to protect the most vulnerable buildings by locating these within the areas of lowest flood risk on the site. Ground floor and basement areas should be designed so that these are the areas least likely to be affected by flooding e.g storage, garages etc.

2 – Control

Solutions can be deployed to control how flooding affects a site. Examples include localised flood defence works and water catchment zones, ponds etc.

3 – Mitigate

Buildings within a site can be designed to incorporate flood resistant construction to further mitigate the risk of damage occurring in the event of a flood event.

4 – Management of residual risks

Despite the deployment of flood mitigation works such as those described above, there will inevitably be residual risks remaining.  Further management of flood risk in those circumstances is necessary and will include solutions such as early warning systems and the creation of safe pedestrian flood escape routes.

Final Thoughts

As climate change continues to cause an increase in the number of flooding events in the UK, the careful design and management of rainwater drainage systems will become increasingly vital. It is important to be fully versed of the exact risk flooding presents to a site and expert advice should be sought in how best to control and mitigate that risk.

Darren Frias-Robles FRICS is a Chartered Surveyor (Fellow of the RICS) with over 25 years of experience in development and construction. Darren is owner and Managing Director of Whitefox – Chartered Surveyors


Name: Lloyd Blyth

Role: Quantity Surveyor

Time at Whitefox : 7 months

  1. Tell me about your background and how you ended up in this role?

I discovered the role of a Quantity Surveyor when I joined a Recruitment Consultancy specialising in Construction, previously I had no awareness of the job role.

Subsequently, I joined a Main Contractor as an apprentice quantity surveyor and began studying for a HNC in Quantity Surveying. By the end of my time in main contracting, I had been promoted to Quantity Surveyor, obtained a HNC and started a Chartered Surveyor Degree Apprenticeship.

I have since joined Whitefox as a Professional Quantity Surveyor and I am currently in Year 4 of my degree; at the end of my degree, I’ll have chartered membership status.

  1. What do you enjoy most about your work here?

I enjoy how each of the projects I am working on are completely different and all provide their own unique challenges.

  1. What’s the most interesting project you’ve worked on recently?

The most interesting would be the Bobby&Co project in Bournemouth.

  1. Do you have any hobbies or interests outside of work?

I play guitar and am a season ticket holder for Southampton FC. I’ve recently got back into fitness, and I am training to run the Brighton Marathon next year.

  1. Do you have any books or podcast recommendations that you listen too? Or if not this then any music?

I only ever listen to Joe Rogan’s or Steven Bartlett’s podcasts, both of which I listen to when commuting.

  1. What’s the one thing you’d like to do and/or achieve in the next 12 Months that you’ve never done before?

I’d like to be in a good position to sit my APC this same time next year. Running a marathon will also be a good achievement, considering how much I don’t enjoy running!

  1. If you could travel anywhere in the world, where would you go and why?

I’d like to go to Japan as culturally it is completely different to anywhere else in the world.

  1. Do you have an idol or someone who inspires you?

I would say Russ Cook who is currently running the entire length of Africa is pretty inspiring. If he can run 360 marathons in 240 days, then I can drag myself through one!

  1. What’s the first thing you bought with your first pay check?

No idea! My first job was a paperboy so likely a bag of sweets!

  1. If you weren’t doing this role, what might you be doing in an alternate reality?

Might have done something with music if I continued with it but I have no regrets!

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