Appeal 6004706

The appeal is dismissed.

The description of development has been amended since the original application submission. This revised description has been adopted by both main parties within their appeal submissions and, as it provides greater precision and clarity, I have also done the same.

The appellant has referred to a subsequently refused prior approval application on the appeal site1. However, as this decision post-dates the close of submissions for this appeal and no substantive details have been provided, I attach no meaningful weight to it.

Under Article 3(1) and Schedule 2, Class MA of the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended) (the GPDO), planning permission is granted for a change of use of a building from a use falling within Class E (commercial, business and service) to a use falling within Class C3 (dwellinghouses), subject to conditions. These include a requirement to apply to the local planning authority for a determination as to whether prior approval will be required in respect of various matters.

The Council determined that prior approval was required and was refused, for a single reason, this forms the basis for the main issue for this appeal - whether the proposed building would be safe from flooding. 1 RU.26/0228

The appeal site lies within [name] 2 and is therefore at risk of fluvial flooding associated with the [name]. The current use of the site is classified as ‘less vulnerable’, whereas the proposed change of use would increase this to a ‘more vulnerable’ residential use. Whilst the building itself is only predicted to experience shallow flooding during the design flood event, the surrounding area, including the local road network, is shown to be affected. As a result, the key issue is whether future occupants would be able to safely access and exit the site during flood conditions. The proposed access route in this case would run from the appeal site along [address] and the [address].

The SFRA sets out that a safe access/egress route should allow occupants to safely enter and exit buildings and be able to reach land outside of the flooded area, without the intervention of emergency services or others during flood conditions, including climate change allowances. It also sets out that it is acceptable for access/egress routes to be wet in Runnymede so long as the flood hazard is no greater than ‘[name] – Caution’ along the full length of the access/escape route. The route should also be along publicly accessible roads or paths.

The above policy context and mitigation expectations are broadly consistent with the Framework. This states that development should only be allowed in areas at risk of flooding where safe access and escape routes are included where appropriate, as part of an agreed emergency plan. National Planning Policy Guidance (NPPG) further guides that access routes should enable occupants to safely access and exit their dwellings during design flood conditions.

The appellant contends that the road is slightly higher than the EA flood model shows. Whilst the Council does not directly dispute this, it considers that it is not possible to adjust part of the model without recalculating the whole system, as doing so could generate unreliable results. In this regard, I am mindful that flood models operate as interconnected systems, and even small local changes in ground levels have the potential to affect flood depths, routes and velocities elsewhere.

The appellant’s approach compares updated survey data with the EA model and recalculates hazard ratings along the route, based on a relatively minor difference in land levels of around 100mm. I recognise the concern that the EA model does not fully reflect real-world conditions, including buildings and obstructions, which may overestimate flood velocities and create unrealistic flow paths. The appellant suggests floodwater would instead pond locally.

However, whilst I acknowledge the argument that more detailed modelling may be disproportionate for a development of this scale, this “real world” scenario has not been tested within a recalibrated model. As such, the extent to which flood behaviour may differ from the EA outputs remains uncertain. Although the Council has not fully engaged with the limited scale of the level differences or the short length of the route, I accept that unmodelled changes introduce uncertainty.

In any event, even if I were to accept the appellant’s methodology, both parties agree that part of the route would still exceed the “very low hazard” threshold. The access and egress route runs from the appeal site along [address] and then onto the [address], providing the only connection to land outside the flood extent. The route to safety is approximately 140m in length, and on the appellant’s own assessment a localised section of around 30m, just over 20% of the route, is subject to higher hazard ratings. This section corresponds with lower ground levels and is predicted to experience deeper flooding, with hazard levels reaching “moderate” to “significant” at peak conditions, indicating a potential risk to people.

National guidance expects access routes to remain safe, taking account of flood depth, speed and overall hazard. Similarly, the [name] advises that routes should avoid anything above “very low hazard – caution”. As this section exceeds that level, it suggests that people would need to pass through potentially unsafe conditions, which does not align with the expectations for a safe escape route.

I appreciate that the appellant considers these conditions to be manageable and notes that the route follows an urban street environment with footways and crossing points. These characteristics, together with the enclosed form of the street, may mean that conditions are less severe than those indicated by the model. Nevertheless, the route represents the only means of escape from the site to the [address] and beyond, and the presence of footways and urban features does not remove the potential for hazardous flooding where water depths or velocities are sufficient.

Importantly, the test is whether the route as a whole is safe, not whether the majority of it meets the relevant threshold. Although the section of concern is limited in extent and may, in reality, behave more like shallow, slow-moving or ponded water, it is unavoidable and represents the weakest part of the route. Given the absence of robust evidence confirming how floodwater would behave in this location, and the reliance on untested assumptions, I cannot conclude with sufficient certainty that a safe means of access and egress would be available during the design flood event.

I note that the appellant places reliance on a [name] and Evacuation Plan, with occupants expected to leave the site in advance of flooding. However, I am not persuaded that it provides a sufficient level of certainty in this case. Similar to the decisions at [address] (3360609) and [address], Chertsey (3365693), there is no guarantee that occupants would evacuate at an early stage, particularly where their own properties are not immediately at risk. As such, reliance on behavioural responses and management measures cannot replace the need for a clearly safe and reliable access and egress route.

Furthermore, even where adequate warning time may exist - the appellant indicates it would be passable for up to 11 days, the presence of a higher hazard section along the route remains. The existence of an evacuation strategy does not overcome concerns where occupants would still be required to pass through areas of elevated flood hazard, or where the route itself is not consistently safe. In this case, the effectiveness of the evacuation plan depends on assumptions about how occupiers would respond and does not remove the need to demonstrate that the route itself would remain safe during the design flood event.

The PPG states that proposals that are likely to increase the number of people living in areas of flood risk require particularly careful consideration, as they could increase the scale of any evacuation required. It would therefore be unreasonable to add to demands on the emergency services who would already be under pressure during a flood event.

My attention has been drawn to a number of approvals for schemes where there is reliance upon an evacuation plan and/or management measures. These include a number along [address], including Marchamont House2, The White Lion3 and [address] Road4. [name] note that these schemes also identified short sections of higher hazard along the route, and in some cases relied on evacuation plans and trigger points, the full circumstances of those decisions are not before me. I have limited information regarding the precise flood modelling, route conditions and the safeguards that were secured. As such, I cannot conclude that those schemes are directly comparable or that the same conclusions should apply in this case.

In relation to Lakeside East5, I note that this was a large-scale development, with on-site management and specific trigger mechanisms, including a flood gauge, forming part of the evacuation strategy. This differs materially from the current proposal in terms of scale and operational control, and it is not clear that the same level of management and coordination could be relied upon here. Similarly, [address] appears to have been accepted on the basis of active site management by the local authority itself, which again represents a materially different context.

Other examples, such as the [name] Station6, are said to have raised similar concerns about sections of the route exceeding “very low hazard”, but the outcome appears to have depended on site-specific evidence and judgement. Without the full detail of those cases, including how the hazard was assessed and what weight was given to it, they provide only limited assistance in determining the current appeal.

Overall, whilst these schemes indicate that similar issues have arisen elsewhere, they do not outweigh the specific evidence before me, which identifies a section of the route exceeding acceptable hazard thresholds and lacks sufficient certainty as to its safety.

I have also been referred to the [name] as a factor in reducing flood risk. However, this is a large-scale infrastructure project which does not currently have consent, as no formal application has been submitted through the [name] process, and works have not commenced. As such, there is no certainty as to its delivery, timing or the extent of flood risk reduction that would be achieved at the appeal site. Accordingly, this attracts very modest weight.

In light of the above, I am not satisfied that it has demonstrated that future occupants would be safe from flood risk, or that safe access and egress would be available during the design flood event. The proposal would therefore fail to satisfy condition MA.2(2)(c) of Class MA in respect of flooding risks in relation to the building, and prior approval should not be granted. 2 RU.20//0814 3 RU.18/1719 4 RU.21/0530 5 RU.21/0483 6 RU.15/1800

Insofar as they are relevant, the proposal would also conflict with Policy EE13 of the Local Plan, the related provisions of the SFRA, and the aims of the Framework in respect of managing flood risk for new development.

For the reasons set out above, the appeal is dismissed.