FRA Guidance Note 2: Minor Extensions
For the use where cumulative impact of development needs to be addressed

March 2007

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FRA Guidance Note 2:Minor Extensions - For the use where cumulative impact of development needs to be addressed

Environment Agency guidance on the requirements for undertaking a Flood Risk Assessment (FRA) for planning applications. This guidance note relates specifically to the commissioning and undertaking of Flood Risk Assessment studies for householder extensions and for minor non-domestic extensions (of less than 250m2) in Flood Zones 2 ¹ or 3 ² . This guidance note is applicable where local knowledge (Strategic Flood Risk Assessment, parish council etc.) has indicated that the cumulative impact of minor extensions may have a significant effect on flood risk as highlighted in Planning Policy Statement 25 (PPS) paragraph D16.

Where cumulative impact from this type of development in these locations is not a recognised problem, a simpler format of FRA should suffice as detailed in our Flood Risk Standing Advice standard comments on ‘Householder and other minor extensions’.

Why is a FRA required?

For minor extensions within Flood Zone 3 and 2 areas the proposed development itself could be at risk of flooding from either rivers or the sea. Where this is the case, a FRA will need to focus on mitigation measures such as setting suitable floor levels and incorporating flood proofing into the design of the extension in addition to including an assessment of residual risks on and off site. Developments immediately alongside watercourses classified as a Main River or in close proximity to flood defence structures may also affect the operation or maintenance of these, and we will expect to comment individually on these proposals ³. The FRA in these cases will need to consider these impacts and whether they might be acceptable or not.

What should be in the FRA?

The detail and technical complexity of a Flood Risk Assessment will reflect the scale and potential flood risk to and from the development. Flood Risk Assessments for this scale of development will be of a relatively minor nature and may even just take the form of a short written statement. In the cases covered here, the Strategic Flood Risk Assessment (if available) should highlight which elements of the section below will require particular attention.

Plans

• A location plan that includes geographical features, street names and identifies the catchment, watercourses or other bodies of water in the vicinity
• A plan of the site showing
• existing site;
• development proposals;
• proposed flood protection measures incorporated into the development to reduce flood risk to the development itself and to others.

Surveys

• Site levels related to Ordnance Datum, both existing and proposed.
• A cross-section of the site showing finished floor levels or road levels, or other relevant levels relative to the potential source of flooding.

Assessments

The Applicant should submit:

• Information about any other potential sources of flooding that may affect the site – streams, surface water run-off, sewers, groundwater, reservoirs, canals and other artificial sources or any combination of these
• Existing information on extent and depth of past flood events
• Details of flood mitigation measures proposed to reduce the impact of flooding
• Assessment of the residual risks after any necessary flood proofing measures or defences have been installed.
• The estimated standard of flood protection provided to the development when completed.
• Assessment of the off site impacts due to the effect on local flood storage and flood flow capacity.

What is the Environment Agency’s Role?

With the exception of developments immediately alongside Main Rivers and in close proximity to flood defences, we will not provide comments in terms of flood risk on these minor developments at the planning application stage due to their low-risk nature. We have two main interests:

• If the proposal is within the Byelaw Distance⁴ of a Main River ⁵ or flood defence structure, or includes the diversion or culverting of an Ordinary Watercourse⁶ then formal consent for the proposal may also be required from us.
• Prior to carrying out a FRA, developers should contact the Environment Agency and other operating authorities (including the engineering department of the local authority or Internal Drainage Board as appropriate) to establish whether any information is available relating to flood risk at the site they propose to develop. Our records of flooding are not exhaustive and the absence of information does not mean that a site will not flood. They should also take full account of the local knowledge of flooding in the community and account for this within the FRA.

Unless consent is required, our comments will be limited to the provision of flood level information where this is available.

Sources of information:

For information on flood resilience and resistance see

1. Draft Practice Guide to PPS25 Development and Flood Risk
2. Preparing for floods: interim guidance for improving the flood resistance of domestic and small business properties ODPM 2003.

¹ Flood Zone 2: This zone comprises land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1% – 0.1%) or between a 1 in 200 and 1 in 1000 annual probability of sea flooding (0.5% – 0.1%) in any year.

² Flood Zone 3: This zone comprises land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year.

³ The Town And Country Planning (General Development Procedure) (Amendment) (No. 2) (England) Order 2006, came into force 1st October 2006 and requires consultation be made with the Environment Agency for development involving —

1. the carrying out of works or operations in the bed of, or within 20 metres of the top of a bank of, a Main River which has been notified to the local planning authority by the Environment Agency as a main river for the purposes of this provision; or

2. the culverting or control of flow of any river or stream

⁴ Byelaw distance varies across the country. To find out what distance applies in your area call 08708 506 506 and ask to speak to a member of the Development Control team in the area where the development is proposed.

⁵ Main Rivers are watercourses designated as such on Main River maps and are generally the larger arterial watercourses. Main Rivers are indicated with a red line as part of the Flood Zones that have been provided to the Local Planning Authority and on maps held by the Environment Agency.

⁶ An Ordinary Watercourse is any watercourse that doesn’t form part of a Main River