Reviewing a drafted Flood Risk Assessment before you send it

Before you review a flood risk assessment draft, know what the reviewer will do. A lead local flood authority officer or an Environment Agency consultee opens the document and looks for four things in the first few minutes: which flood zone the site is in and where that came from, which climate change allowance was applied and for which epoch, what the proposed finished floor level is relative to the modelled flood level, and whether safe access and egress has been dealt with. Everything else can be fixed by condition. Those four cannot.

An AI-assisted draft will give you a correctly structured document with the right section headings, the right policy framework and the right method described. It cannot give you site levels, a modelled flood level or an agreed area of search, and a good draft says so rather than guessing. The review is where you supply what the draft flagged.

What the consultee reads first

Consultee time is short. The habit among drainage officers is to read the conclusion, then jump to the levels, then check whether the allowances match the current published guidance, then decide how much of the rest needs reading.

That tells you where to spend your effort. A clear summary table near the front, giving flood zone, sources of flooding considered, the design event, the allowance used, existing ground level, modelled flood level and proposed finished floor level, all with the datum stated, does more for the document than three extra pages of policy narrative.

It also tells you what gets a holding objection. A Flood Risk Assessment that reaches a conclusion the numbers in the body do not support is the fastest way to a consultee response asking for a revised assessment, and that costs three to six weeks on a minor application.

Flood zone and the currency of the data

Check three things about the flood zone statement.

First, the source. The flood zone must come from the Flood Map for Planning rather than from the long term flood risk service, which answers a different question and bands risk differently. State the date of the enquiry in the document. Flood zone data is revised, and a zone screenshot taken 18 months ago during a feasibility study is not evidence of current risk.

Second, whether the zone is the whole story. Flood zones describe risk from rivers and the sea. A site in Flood Zone 1 can still have a high surface water risk, a groundwater problem, a history of sewer surcharge or a culverted ordinary watercourse crossing it. The assessment should list all sources considered and say explicitly where each was ruled out, because the sentence "the site is in Flood Zone 1 and therefore no further assessment is required" is where self-build applications get stuck.

Third, whether modelled levels exist. For any site in Flood Zone 2 or 3, a detailed flood risk data enquiry to the Environment Agency gives modelled levels for the relevant return periods. A draft cannot have those. If the document quotes a flood level without naming the enquiry reference or the model it came from, the figure is not usable and should come out.

Drafts produced by PlanScope insert a [TO BE CONFIRMED] flag wherever site data is missing instead of inventing a number, and those flags are the review list. Work through every one.

Climate change allowances and where they come from

This is the single most common technical error in submitted assessments, and it is entirely avoidable.

The Environment Agency publishes climate change allowances for flood risk assessments covering peak river flow by river basin district and management catchment, peak rainfall intensity, and sea level rise, each split by epoch. The allowance you apply depends on the river basin district, the vulnerability of the development and its lifetime. Planning practice guidance treats residential development as having a lifetime that runs to the end of the century, which usually puts you in the later epoch, while a commercial building may be assessed over a shorter period.

Four checks on the draft:

• Does it name the river basin district and management catchment, or does it quote a national figure?
• Does it state the epoch and justify it against the development lifetime?
• Does it use the central, higher central or upper end allowance, and does it say why?
• Does it cite the version of the guidance it used, with the date?

The allowances are updated periodically, so check the current published schedule rather than reusing a figure from an earlier scheme. A draft written against a superseded allowance set reads as careless even where the conclusion would not change, and it invites the consultee to doubt the rest.

Finished floor levels and the survey a draft cannot supply

Finished floor level is where the assessment becomes a design decision rather than a desk study.

You need a topographic survey tied to Ordnance Datum, not a scaled level off a site plan. Existing ground levels, the level of the nearest road, threshold levels of neighbouring properties and the proposed finished floor level all have to sit on the same datum, and the assessment has to show the arithmetic: modelled flood level for the design event including the climate change allowance, plus freeboard, gives the proposed floor level.

Freeboard is a judgement. Many authorities look for 600mm above the design flood level, though the figure varies and should be checked with the lead local flood authority rather than assumed. Where raising the floor is not possible, for example in a conversion or an infill plot between existing houses, the assessment has to deal with flood resilient construction, and that discussion needs to be specific about materials and detailing rather than generic.

Watch for a draft that sets a finished floor level in metres above ground level. That is a construction note, not a flood risk statement. It has to be an absolute level.

External levels matter too. A raised floor reached by a driveway that dips below the flood level does not give safe access, and the two drawings need to agree. The levels drawing and the drainage layout should be checked against each other before either goes near a consultee, which is the same discipline that applies to any AI-assisted draft where structure is sound and site evidence is missing.

Sequential and exception test coverage

The sequential test is about whether the development could go somewhere at lower flood risk. It is not satisfied by a paragraph saying the applicant owns this site.

The draft should set out the area of search, which has to be agreed with the local planning authority rather than chosen by the applicant, the sites considered within it, and why each was discounted on reasonable grounds. Where the site is an allocation in an adopted local plan and the plan applied the sequential test at allocation stage, say so and reference the plan and the strategic flood risk assessment, because that shortens the argument considerably. A standalone Sequential Test is the document that carries this where the application site is not allocated.

The exception test only arises for certain combinations of flood zone and development vulnerability. Check that the draft has correctly identified the vulnerability classification of the proposed use before it starts arguing the test, because a misclassification makes the whole chapter irrelevant. Where the test applies, both limbs have to be addressed: wider sustainability benefits to the community, and development that will be safe for its lifetime without increasing flood risk elsewhere.

Reviewers notice when the exception test narrative is generic. Benefits have to be tied to this scheme on this site.

Residual risk, access and the evacuation plan

Residual risk is the chapter most often thin, and it is the one that decides whether a Flood Zone 3 application is defensible.

Deal with the failure cases: a breach or overtopping of a defence, a blockage of a culvert, a rainfall event exceeding the design standard, and the exceedance flow route across the site when the drainage system is full. Say where the water goes and what depth and velocity are predicted. Then address people: dry pedestrian access out of the site to land above the design flood level, or, where that cannot be achieved, safe refuge within the building at a stated level, along with registration for flood warnings and a flood evacuation plan the occupier can actually follow.

Be honest where access is not dry. Consultees respond better to a document that says access will be flooded to a stated depth for a stated duration and sets out the management response than to one that asserts safe access without analysis.

Drainage sits alongside this rather than inside it. Discharge rates, attenuation and infiltration belong in a Drainage Strategy, and the two documents must use the same areas and the same levels.

The checks to run before you send it

Work through this list with the drawings open beside the document.

1. Every [TO BE CONFIRMED] flag resolved or deliberately retained with an explanation.
2. Flood zone sourced from the Flood Map for Planning with the enquiry date stated.
3. All sources of flooding listed, each either assessed or ruled out with a reason.
4. Modelled flood levels referenced to an Environment Agency data enquiry, or their absence explained.
5. Climate change allowance named by river basin district, epoch and percentile, with the guidance version cited.
6. Development vulnerability classification stated and correct for the proposed use.
7. Finished floor level given as an absolute level to Ordnance Datum, with the freeboard shown.
8. Levels in the assessment matching the levels on the submitted drawings.
9. Sequential test area of search agreed with the authority, or plan allocation relied on and referenced.
10. Residual risk, access and egress, and the evacuation plan all addressed.
11. Conclusion consistent with the numbers in the body.
12. Author and reviewer named, with the version and date on the front page.

For specialist technical reports, qualified professional input may be required, and hydraulic modelling is specialist work by any measure. Where the assessment goes beyond a desk study, send the draft for review through the professional directory before it is submitted. This is general guidance rather than legal advice, so 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.