Defining the search area for a flood sequential test

A flood sequential test succeeds or fails on the geography before it fails on the sites. Get the area of search agreed with the council in writing, and the rest of the exercise is a matter of diligence. Choose it yourself, tightly drawn around the site because that is the answer you want, and the council will reject the geography and everything resting on it, several weeks into determination.

The test asks whether there are reasonably available sites appropriate for the proposed development in areas with a lower probability of flooding. Three phrases in that sentence do the work: reasonably available, appropriate for the proposed development, and lower probability.

Agreeing the geography first

The default is the local planning authority area. That reflects the fact that the council applies the test within its own decision making area and holds the evidence about site availability there.

Departures need a reason grounded in the development rather than in the applicant's land holdings. A wider area can be right where the proposal serves a catchment that crosses the boundary, such as a distribution use serving a region or a facility with a defined service population. A narrower area can be right where the development has to serve a specific community, such as a replacement village hall or a school with a fixed catchment.

Put the proposed geography, with the reasons, in a pre-application enquiry and ask for a written response. Two paragraphs from a case officer confirming the search area is worth more than twenty pages of subsequent analysis.

Where the council will not engage, state the geography and the reasoning prominently in the submission so it is visible rather than buried in an appendix.

The Environment Agency will comment on flood matters but does not decide the search area, and it will say so. That is the council's job, and asking the Agency to bless the geography wastes a consultation response you may need later on the assessment itself.

What appropriate for the proposed development means

The comparison is against the development proposed, not against any development. A site is only a candidate if it could take what is being applied for, at a broadly comparable scale, delivering the same function.

That comparison has limits. An applicant cannot define the proposal so narrowly that only their site fits. A scheme described as 120 dwellings on this specific parcel with this specific access will be treated as a scheme for around 120 dwellings, and sites capable of that will be considered.

Equally, a council cannot compare a specialist use to a generic housing site. Where the proposal has real locational requirements, set them out plainly, with evidence, and expect them to be tested.

Timescale is part of appropriateness and it is often left out. A site that could deliver the same development in eight years is not a reasonable alternative to one deliverable in two, and saying so with reference to the site's status in the plan is a stronger argument than asserting that the alternative is unavailable.

Scale flexibility is worth addressing directly. If two smaller sites in Flood Zone 1 could together deliver the same number of homes, the council may treat them as a reasonable alternative, and the assessment should say why that does or does not work.

Reasonably available, and how to evidence it

The pool of candidate sites comes from documents the council already holds. Housing and employment land availability assessments. Site allocations in the local plan. The brownfield land register. Sites with unimplemented planning permission. Sites openly marketed.

Search each, list every site in the area of search that could take the development, and then explain the position on each. Ownership alone does not remove a site from the pool, because reasonably available is not the same as available to you. What removes a site is a constraint that means the development could not be delivered there in a comparable timescale.

Record the date of each source. An assessment relying on a land availability study that was superseded during determination will be attacked on exactly that point.

Objectors do this work too, and they do it well. A residents group with local knowledge will produce three sites the assessment missed, usually including one that has just come to the market. Refresh the search shortly before submission and again if determination runs long, and say in the document when the search was carried out.

Then set out the conclusion in a table showing each site, its flood zone, its capacity, its status and the reason it is or is not a reasonable alternative. Officers copy that table into the report.

The test within the site

The sequential approach applies inside the application boundary as well as across the area of search. Where a site spans more than one flood zone, more vulnerable uses should be located on the parts at lowest risk, with car parking, open space and less vulnerable uses taking the higher risk land.

Doing that visibly, on a plan, answers a question the case officer would otherwise ask. It also strengthens the case where the wider search is finely balanced, because it shows the risk has been minimised rather than accepted.

Allocated sites deserve a paragraph of their own. Where a site is allocated in an up to date development plan and the sequential test was applied through the plan making process, the position at application stage is different, and the council should not require the whole exercise again. Say so, cite the plan and the relevant evidence base document, and let the officer confirm it. That paragraph has saved many applicants a month.

Sequencing against the rest of the flood evidence

1. Establish the flood zone and any other source of flooding from the Environment Agency mapping and the council's strategic assessment.
2. Confirm whether the test applies at all, given the development type and any allocation.
3. Propose the area of search and agree it in writing.
4. Compile and assess candidate sites from the council's own evidence base.
5. Apply the sequential approach within the site and show it on a layout.
6. Only then commission the flood risk assessment and, where required, the exception test.

Commissioning the assessment before the search area is agreed is the common sequencing error on major applications. The assessment is the more expensive document and it is worthless if the gateway test fails.

Where the sequential test forms a standalone submission document, keep it short and evidenced. A twelve page document with a clear geography, a sourced site list and a reasoned conclusion carries further than sixty pages of policy recital.

Illustrative example: a 90 dwelling scheme in Flood Zone 2 on the edge of a market town. The applicant proposes a search area covering the district. Candidate sites are drawn from the housing land availability assessment and the brownfield register, producing eleven sites in Zone 1. Four are discounted on capacity, three have permission for other uses and are under construction, two are constrained by highway access, and two remain as arguable alternatives. The assessment addresses those two directly rather than ignoring them. This example is illustrative.

PlanScope checks a site against Environment Agency flood data and drafts flood documents structured to UK planning policy, with the site facts flagged where they need confirming. The judgement about which alternative sites are reasonably available stays with the applicant and the council.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.