Planning Appeals and Flood Risk: Lessons from Recent Decisions

Planning appeals are where flood risk policy meets reality. When a local planning authority refuses permission on flood risk grounds, or when an applicant appeals a decision where flood risk was a determining factor, the Planning Inspectorate’s decision provides a window into how NPPF policy is being interpreted and applied in practice.

Over the past 18 months, we have reviewed dozens of appeal decisions where flood risk was a principal issue. Several clear trends have emerged — trends that developers, planning consultants, and flood risk practitioners need to understand to avoid refusal and succeed at appeal.

Trend 1: Sequential Test Rigour Is Increasing

The Sequential Test has always been a requirement for development in Flood Zones 2 and 3, but inspectors are now scrutinising the evidence base far more critically than in the past.

What Inspectors Are Looking For

• A clear, systematic methodology. Inspectors expect the Sequential Test to follow a defined methodology with a transparent search area, clear criteria for assessing alternative sites, and a reasoned conclusion. Ad hoc or cursory assessments are being rejected.
• Genuine consideration of alternatives. Simply listing sites and dismissing them on thin grounds is not sufficient. Inspectors are testing whether alternative sites were genuinely considered and whether the reasons for dismissal are reasonable. “The site was too small” needs to be backed by evidence of the minimum site area required for the proposed development.
• Consistency with the LPA’s own evidence. If the LPA’s Strategic Flood Risk Assessment identifies suitable alternative sites in lower-risk zones, the applicant must address those sites specifically and explain why they cannot accommodate the development.
• All flood sources considered. Following the September 2025 PPG update, inspectors are applying the Sequential Test to all sources of flooding, not just fluvial and tidal. Surface water risk is now a legitimate basis for sequential comparison between sites.

Lessons for Practitioners

Prepare the Sequential Test as a standalone, evidence-based document — not a paragraph in the planning statement. Engage with the LPA early to agree the search area and methodology. If the LPA’s housing land availability assessment identifies sites in lower-risk zones, address them directly.

Trend 2: Climate Change Allowances Are Non-Negotiable

The Environment Agency’s climate change allowances are now firmly embedded in appeal decisions. Inspectors consistently dismiss FRAs that do not properly account for climate change, and any attempt to use lower allowances without justification is treated sceptically.

What Inspectors Are Looking For

• Correct application of the current allowances. The EA’s climate change allowances are updated periodically, and using outdated allowances is a ground for refusal. Check the EA’s website for the current allowances at the time of submission.
• Upper end allowances for residential development. For residential development with a design life of 100 years, inspectors generally expect the upper end climate change allowance to be applied. Using the central estimate without clear justification is risky.
• Sensitivity testing. Where there is uncertainty about the appropriate climate change allowance, inspectors expect to see sensitivity testing showing how the flood risk and mitigation would change under different scenarios. This demonstrates that the assessment is robust rather than reliant on a single assumption.
• Credible mitigation at the design flood level plus climate change. Finished floor levels, access routes, and compensatory storage must all be assessed against the climate change-adjusted flood level, not the present-day level.

Lessons for Practitioners

Always use the most current EA climate change allowances. Apply the upper end allowance for residential development unless there is a compelling reason not to. Include sensitivity testing to demonstrate robustness. Do not allow climate change to become a ground for refusal — it is entirely avoidable.

Trend 3: Safe Access and Egress Is a Dealbreaker

Access and egress during a flood event has emerged as one of the most common grounds for refusal at appeal. If the flood risk assessment cannot demonstrate that a safe route to and from the site is available during the design flood event, inspectors will dismiss the appeal regardless of how well the other flood risk issues are addressed.

What Inspectors Are Looking For

• A defined access route assessed for flood depth, velocity, and hazard. It is not sufficient to assert that “access is available.” The FRA must identify the specific route, quantify the flood conditions along that route during the design event, and demonstrate that the hazard rating is acceptable.
• Hazard rating in accordance with Defra guidance. The Defra/EA hazard rating methodology (depth x velocity + a constant) is the accepted standard. Inspectors expect to see hazard maps and a clear assessment against the “danger to most” and “danger to all” thresholds.
• Consideration of the most vulnerable users. Access routes must be safe for all occupants, including the elderly, disabled, and children. A route that is passable by able-bodied adults but dangerous for wheelchair users or young children is not acceptable.
• Emergency service access. Inspectors are increasingly asking whether emergency vehicles can access the site during a flood event. If the primary access route is flooded, alternative routes must be identified.

Lessons for Practitioners

Map the access route and assess flood conditions along its full length during the 1 in 100 year plus climate change event. Produce hazard maps showing the route. If a completely dry route cannot be achieved, demonstrate that the route through shallow flooding has an acceptable hazard rating. Address emergency access explicitly.

Trend 4: Surface Water Drainage Must Be Evidenced, Not Assumed

LLFAs and inspectors are no longer accepting vague drainage strategies that promise to “manage surface water through SuDS.” Detailed, quantified drainage designs are expected even at outline planning stage.

What Inspectors Are Looking For

• Attenuation calculations for a range of storm events. MicroDrainage, InfoDrainage, or similar calculations showing that the drainage system can manage storms up to the 1 in 100 year plus climate change event without flooding.
• Discharge rate limitation to greenfield (or agreed) rates. Evidence that the proposed discharge rate has been agreed with the LLFA and that the drainage design achieves this rate.
• SuDS management train. A clear hierarchy of SuDS features from source control through site control to regional control. Underground storage alone is unlikely to satisfy inspectors, particularly in Wales where Schedule 3 applies.
• Exceedance flow paths. Evidence that the design accounts for storms that exceed the capacity of the drainage system, directing overland flow away from buildings and towards areas of low consequence.

Lessons for Practitioners

Provide detailed drainage calculations with the planning application, even at outline stage. Engage with the LLFA early to agree discharge rates and design criteria. Design the SuDS scheme using the management train hierarchy and demonstrate that above-ground features have been maximised.

Trend 5: Inadequate FRAs Are Being Called Out

Perhaps the most significant trend is that inspectors are increasingly willing to criticise the quality of flood risk assessments themselves — not just the conclusions, but the methodology, data sources, and assumptions.

Common Criticisms

• Reliance on outdated data. FRAs that use superseded EA mapping, old climate change allowances, or historical data without checking for updates are being criticised.
• Failure to consult the EA. FRAs that do not reference EA data or pre-application advice, or that contradict EA guidance without justification, are treated with suspicion.
• Inadequate consideration of all flood sources. FRAs that focus on fluvial risk and ignore surface water, groundwater, or sewer flood risk are being rejected as incomplete.
• Over-optimistic assumptions. FRAs that assume flood defences will always function, that blockage scenarios do not need to be considered, or that climate change will have minimal impact are being challenged by inspectors.

Lessons for Practitioners

Produce FRAs that are thorough, well-referenced, and based on current data. Engage with the EA before and during the assessment. Address all flood sources. Test assumptions through sensitivity analysis. If the EA has concerns, address them before submission — do not leave them for the inspector to discover.

What This Means for Your Project

The standard of flood risk evidence required to secure planning approval — whether at application stage or at appeal — has risen significantly over the past two years. The days of a cursory desktop FRA being sufficient for anything but the simplest sites are over.

If you are preparing a planning application for a flood-constrained site, invest in a robust flood risk assessment from the outset. Engage with the EA and LLFA early. Apply current climate change allowances. Evidence your drainage design with calculations, not promises. And if you are heading to appeal, ensure your flood risk evidence is watertight.

At Aegaea, we prepare FRAs with appeal resilience in mind. Our assessments are designed to withstand scrutiny by the EA, LLFA, LPA, and Planning Inspectorate. If you need an FRA that will stand up at appeal, get in touch.