Appeal 6001620

The appeal is dismissed.

This appeal relates to a timber decking platform at [site address] , positioned to the rear of this property and projecting riverward of the existing flood defence wall along the [name]. A similar structure has been installed at the neighbouring property [address], which is the subject of a separate appeal.

The development subject to this appeal has already been carried out. A number of drawings and technical documents were submitted with the application, including plans showing the position, extent and construction of the decking. For the avoidance of doubt, I have determined the appeal on the basis of the submitted drawings, flood risk assessment (‘FRA’) and the additional flood‐risk information submitted at appeal stage.

The main issue is whether the development is acceptable having regard to flood risk.

The appeal site lies within [name] 3b, the functional floodplain of the [name]. A concrete flood‐defence wall runs along the riverbank, and the decking is fixed directly over this structure.

The National Planning Policy Framework (‘the Framework’) requires development to be steered away from areas of highest flood risk. Where development is proposed in such locations, it must be demonstrated that it would be safe for its lifetime and would not increase flood risk elsewhere.

The Planning Practice Guidance (‘PPG’) explains that even small‐scale development can generate significant flood‐risk impacts where it affects a watercourse, the functional floodplain or flood‐defence infrastructure, or where it may impede access to such assets or contribute cumulatively to increased risk. It also emphasises that the functional floodplain must remain unobstructed so that water can flow and be stored during flood events. Development in [name] 3b therefore requires a proportionate, site‐specific Flood Risk Assessment (‘FRA’), and one has been submitted.

The appellant contends that the decking should be regarded as water‐compatible development. However, in practice it functions as private residential amenity space and operates as an extension of the domestic garden. Although it projects over the flood wall, its purpose remains wholly private and domestic, bearing limited resemblance to the open, water‐related recreational activities envisaged within the water‐compatible category. The Environment Agency’s classification of the proposal as “more vulnerable” is consistent with Annex 3 of the Framework, which identifies residential uses within that vulnerability class. Development of this nature is therefore not appropriate within [name] 3b, where national policy restricts new development to water‐compatible uses and essential flood‐risk management infrastructure.

Even if the decking were considered water‐compatible, it must still be shown that it would remain safe during flooding and would not impede flows, reduce floodplain storage or increase flood risk elsewhere.

The appellant relies on estimated levels and modelling from 2015 rather than the updated 2024 dataset. The EA disputes the accuracy of these assumptions and considers that the decking may not sit above the relevant design flood level. Without surveyed levels and modelling aligned with current data, I cannot be satisfied that the structure meets the required tests.

Behaviour‐based mitigation, such as avoiding use during flood alerts, does not address the physical presence of the structure within the channel. National policy requires demonstration of no increase in flood risk, not simply reduced exposure to it.

The decking lies riverward of the flood wall, within the active channel. Its supporting piles introduce a physical obstruction. [name] 3b, even small structures can influence flow conveyance, turbulence and debris movement, and the PPG confirms that development affecting a watercourse or flood‐defence asset can generate significant flood‐risk impacts.

The fact that the deck soffit sits above typical river levels is not determinative. [name] 3b is defined by design flood events, and EA evidence indicates that the pile shafts would be located within the active flow zone during flooding. Without reliable level data and up‐to‐date modelling, it cannot be demonstrated that the structure would avoid impeding flows or reducing floodplain storage.

Although the decking is slatted, debris accumulation and temporary blockage remain plausible during high‐energy flood events. Such effects can alter flow paths, raise local water levels or redirect hydraulic energy towards the flood‐defence wall. In the absence of hydraulic analysis addressing these risks, the potential for increased flood risk elsewhere cannot be ruled out.

The PPG encourages a pragmatic approach to minor development, but only where it does not affect a watercourse, floodplain or flood‐defence infrastructure. Here, the decking is located within the river channel itself and attached to a flood‐defence wall. In such circumstances, the PPG’s pragmatic approach does not override the strict policy requirements for development in [name] 3b.

For the above reasons, it has not been satisfactorily shown that the development is acceptable with regard to flood risk. As such, this fails to satisfy Policy LP12 of the Wandsworth Local Plan (Adopted 2023) (‘LP’), as it introduces built form within the functional floodplain without demonstrating that it would remain safe during flooding, avoid impeding flows, or ensure that flood risk would not be increased elsewhere. In addition, by being fixed directly to the flood defence wall, the decking does not accord with LP Policy LP59, which seeks to safeguard and maintain flood defence infrastructure.

I observed other similar platforms along this stretch of the river, and it is argued that refusing permission in this case would be inconsistent. However, there is no evidence that those structures were granted planning permission or assessed against current flood‐risk policy. As such, their presence does not justify permitting development that would otherwise be unacceptable.

For the above reasons, I conclude that the appeal should be dismissed.