Appeal 3374167

The appeal is dismissed.

The main issue is the effect of the proposed development on flood risk.

The appeal site is an end of terrace two storey dwelling, with side and rear garden and driveway to the front. The surrounding area comprises dwellings of similar architectural style. The appeal site is proximate to the [name] and the [name], both of which are main rivers with intervening development in between. The proposed development is for a two-storey side extension which would provide a new kitchen/dining area and a bedroom at the ground floor level.

The National Planning Policy Framework states that local planning authorities should ensure that new development does not increase flood risk elsewhere and that any residual risk can be safely managed. The Planning Practice Guidance sets out the level of detail needed in a site-specific flood risk assessment. A guidance note also accompanies the Council’s Sustainable Drainage Proforma for [name] (the drainage proforma) on the content of such assessments.

The New Enfield Local Plan 2041: Level 1 Strategic Flood Risk Assessment (2021) (SFRA) states that in order to ensure that development is safe from fluvial flooding, finished floor levels should be raised 300mm above the 1 in 100 year plus climate change flood level. It notes that if this level of safety cannot be achieved, habitable rooms used for sleeping (such as bedrooms) should not be located at ground floor level as the onset of flooding can pose a risk to life. It also requires that the development has safe access routes that are either dry or within the very low hazard area.

The appeal site is within [name] 2 and subject to the 1 in 100 year plus 17% climate change flood event. A Flood Risk Assessment1 (FRA) was submitted with the planning application which concludes that based on mapping from the EA that the 1% [name] flood event plus appropriate climate change allowance would not inundate the site in either defended or undefended modelled scenarios. The appellant has confirmed that the finished floor level of the proposed development would be 300mm higher than the outside ground level in accordance with the conclusions of the FRA. However, the submitted plans do not include the 1 in 100 year plus climate change event flood depths and proposed finished floor levels in mAOD and therefore I cannot be satisfied that the proposal would provide sleeping arrangements safe from flooding.

The FRA states that the appeal site has direct connection to [address] which lies outside of the mapped flood extent and therefore would provide safe and dry access and egress for occupiers, during a flooding event. However, this does not demonstrate that the evacuation route is in the very low hazard level in accordance with FD23202 as required by the drainage proforma. Therefore, I cannot be satisfied that the proposal would provide adequate safety from flooding for occupiers.

The FRA states that the proposed sustainable drainage system (SuDS) led strategy would include a below ground attenuation tank of approximately 2m3 volume, which would discharge at a restricted rate of 0.90l/s into the existing surface water sewer in [address]. [name] is designed to accommodate the 1 in 100-year storm event plus 40% climate change uplift. In addition, a raised rain garden planter connected via a catchpit manhole would be installed in the front garden to receive runoff from part of the roof. However, the SFRA discourages the use of underground tanks and catchpits due to ongoing maintenance issues. Although the FRA includes a surface water maintenance strategy, a detailed SuDS maintenance plan has not been submitted to ensure an acceptable standard of operation of the SuDS for the lifetime of the development. Therefore, I cannot be satisfied that the proposed development would not increase flood risk elsewhere over the lifetime of the development.

I conclude that it has not been demonstrated that the proposed development would be safe from flooding and would not increase flood risk elsewhere over its lifetime. It thereby conflicts with [name] 12, SI 13 of the London Plan (2021), Policies CP21 and CP28 of the [name] 2010-2024 (2010) and Policies DMD59, DMD60, DMD61 and DMD62 of the Enfield Development Management Document (2014). Together, these policies seek to ensure that new development avoids and reduces the risks of flooding over its lifetime and does not increase the risks elsewhere.

The appellant has referred me to a concurrent appeal which has been submitted at [address], which was also refused on the grounds of flood risk. However, that case differs from this appeal in that it is for the change of use from a dwellinghouse to a House of [name]. [name] am the same Inspector for both appeals I have considered each scheme independently. 1 Prepared by [name] dated June 2025 2 As defined by the Hazard table from the Research and Development Technical Report FD2320 included as [name] of the SFRA

The proposal conflicts with the development plan when taken as a whole and the material considerations, including the Framework do not indicate that the appeal should be decided other than in accordance with it.

For the reasons given above the appeal should be dismissed.