Flood Risk Assessment – Bell Lane, Eton Wick

ACCON UK Limited (ACCON) was commissioned by W. M. Graham Associates to carry out a flood risk assessment for the proposed extension of an existing residential property in Eton Wick, Berkshire. The proposed extension involved the demolition of the current freestanding garage and coal bunker and constructing a two-storey extension to the east of the property in their place.

After contacting the Environment Agency it was established that the site is located within ‘Flood Zone 3’, which is an area which has a 1 in 100 chance of being flooded by a river each year.

The flood risk assessment was carried out in accord in accordance with the detailed guidance set out in the now revoked Planning Policy Statement 25 (PPS25) ‘Development and Flood Risk’ and also in line with the Technical Guidance to the National Planning Policy Framework (March, 2012).

Within Flood Zone 3, generally “more vulnerable” developments such as residential are discouraged, however, due to this being an extension to an existing property, the Sequential Test and Exception Test are somewhat redundant, as moving the proposed extension is not an option. However, similar development proposals for extensions to other properties in the street have previously been granted.

As part of this assessment a “Householder and other minor extensions in Flood Zones 2 and 3, Version 3.1, April 2012” form was included. The guidance applies to domestic extensions and non-domestic extensions where the additional footprint created by the development does not exceed 250 sq. metres. This form provides options of mitigation which is required to be included as part of the development. The options for the development were:

• Floor levels within the proposed development will be set no lower than existing levels AND, flood proofing of the proposed development has been incorporated where appropriate; OR
• Floor levels within the extension will be set 300mm above the known or modelled 1 in 100 annual probability river flood (1%) or 1 in 200 annual probability sea flood (0.5%) in any year. This flood level is the extent of the Flood Zones.

For this development the first option was recommended.