Flood Zones – What you need to know

November 17, 20160 Comments

Some of the most frequently asked questions encountered by our consultancy team are ‘what flood zone is my house in?’, ‘what flood zone is my site in?’ and ‘how could it affect the proposed development?’

In this blog we’ll look into what a flood zone is, what they really mean in terms of flood risk and how this seemingly simple classification can affect what you can or can’t do on a site in terms of planning. 

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Background

Flood zones have been created by the Environment Agency to be used within the planning process as a starting point in determining how likely somewhere is to flood. However, they only refer to flood risk from rivers or the sea, and not all rivers are included. The most important thing to remember is a flood zone is predominantly a planning tool and doesn’t necessarily mean somewhere will or won’t flood.

Different types of development have been classified as being either acceptable or unacceptable for each of the flood zones based on the vulnerability classification it’s assigned. This is based on the National Planning Policy Framework (NPPF) and the technical guidance note can be found here  should you wish to review this further, or have a look at our development flow chart  which aims to demystify the requirements of a development based on flood zones and if specific uses are acceptable.

Flood Zones and what they mean for development

There are 3 flood zones as defined by the EA; Flood Zone 1, 2 and 3. These areas have been defined following a national scale modelling project for the EA and are regularly updated using recorded flood extents and local detailed modelling.

The flood zones are based on the likelihood of an area flooding, with flood zone 1 areas least likely to flood and flood zone 3 areas more likely to flood. Remember these flood zones don’t always take into account all the rivers in an area, and don’t take into account blocked drains or very heavy rainfall etc. so sites in a low risk flood zone 1 for example could still experience flooding.

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Flood Zone 1

Areas deemed to be in flood zone 1 have been shown to be at less than 0.1% chance of flooding in any year, this is sometimes known as having a 1:1000 year chance.

There are very few restrictions in terms of flood risk to development on flood zone 1 areas, the exception is for development over 1ha in size which must have a flood risk assessment undertaken as part of a planning application and areas deemed to be at high risk of flooding from rainfall known as Critical Drainage Areas.

Flood Zone 2

Areas deemed to be in flood zone 2 have been shown to have between 0.1% – 1% chance of flooding from rivers in any year (between 1:1000 and 1:100 chance) or between 0.1% – 0.5% chance of flooding from the sea in any year (between 1:1000 and 1:200 chance).

Flood zone 2 development needs to submit a flood risk assessment as part of its planning application which shows the risk of flooding to the site. As the probability of flooding within flood zone 2 sites can vary so much these reports are often the trickiest in terms of analysis and mitigation measures.

The types of development that can occur within flood zone 2 is controlled by the vulnerability of these usages. Our development flow chart aims to demystify the requirements of a development based on flood zones and if specific uses are acceptable.

Flood Zone 3

Flood zone 3 is actually split into 2 separate zones; 3a and 3b by the local planning authorities however the EA do not split the zone and as such their maps only identify a general flood zone 3. Areas within flood zone 3 have been shown to be at a 1% or greater probability of flooding from rivers or 0.5% or greater probability of flooding from the sea.

Flood zone 3 development needs to submit a flood risk assessment as part of its planning application which determines if the site is classified as flood zone 3a or 3b as well as reviewing flood risk on the site and proposing suitable mitigation.

The types of development that can occur within flood zone 3 is not only controlled by the vulnerability of these usages but also if the site is located within flood zone 3a or 3b. Our development flow chart aims to demystify the requirements of a development based on flood zones and if specific uses are acceptable

Flood Zone 3b

Flood zone 3b’s are classified as functional floodplain, and are deemed to be the most at risk land of flooding from rivers or the sea. Local planning authorities have classified areas at significant risk of flooding to be within flood zone 3b. This classification is usually classified as land which had a 5% probability of flooding also known as a 1:20 chance.

There are significant restrictions as to what can be developed on areas of flood zone 3b, our development flow chart aims to demystify the requirements of a development based on flood zones and if specific uses are acceptable, however if you are concerned please don’t hesitate to contact the consultancy team to discuss on 0203 857 8540 or fra@ambiental.co.uk.

Where can you go to see what flood zone somewhere is in?

To find out which flood zone an area resides in you will need to visit the Environment Agency’s Flood Map for Planning and enter the postcode in the box in the top left corner.

At Ambiental we generate flood risk assessments (FRA) to meet both basic planning application requirements and to help address complex flood risks that could stand in the way of you getting planning approval. If, you’d like us to assist you with determining the flood risk of an area taking into account other sources of flooding, including blocked sewers and extreme rainfall please do get in touch with the consultancy team on 0203 857 8540 or fra@ambiental.co.uk who can also produce due diligence flood risk assessments to allow for more informed decisions to be made surrounding flood risk on a site.

Filed in: FRA NewsPlanning & property

About the Author ()

Daniel Cook is a Senior Flood Risk Consultant at Ambiental and is involved in all aspects of FRA consultancy including account management, proposals, project management and producing the reports.

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