Flood risk assessment review, from the planning advisor’s side of the desk

In my experience the gaps that lead to objections are usually ordinary ones. The wrong climate allowance. An Environment Agency model used without checking that it suits the site. Nothing on how people get out when the road floods. Each is cheaper to fix before submission than after an objection.

I review for four kinds of client. The table shows what each one gets.

The sequential test asks whether a site at lower flood risk is reasonably available. It is the planning authority’s decision, informed by the assessment. The exception test, where it applies, has two parts: wider benefits to the community that outweigh the flood risk, and a development that is safe for its lifetime, taking account of who will use it, without increasing flood risk elsewhere.

The Environment Agency comments on the flood risk evidence. If a council is still minded to approve major development in Flood Zone 2 or 3 against a sustained Environment Agency objection, it must refer the application to the Secretary of State for possible call-in.

The allowances are set for each management catchment, so the same development needs a different uplift in different parts of the country. At Hamstall Ridware, in the Trent Valley Staffordshire catchment, the central allowances I used for peak river flow were +15% for the 2020s, +17% for the 2050s and +29% for the 2080s. The upper end for the 2080s is +61%.

The figure shows why the choice matters. In the same village, the 1-in-100-year flood reaches 14 buildings. With the 2080s allowance it reaches 21, and the deepest water at a building rises from 0.13 m to 0.34 m.

The Hamstall model shows what that test looks for. Raising the right bank keeps the village dry in every flood modelled, up to the 1-in-1,000-year event. But the water has to go somewhere. It spreads across the farmland opposite, typically 0.01–0.06 m deeper.

At Hamstall the extra water fell on farmland, so the farmers had to be part of any solution. In a planning application the same map is the evidence an assessor asks for: drag the handle and you can see exactly where the risk moves.

Read the objection as a checklist. Each reason names a missing piece of evidence. The response should answer them one for one, in the same order, so the officer can see that each has been dealt with.

If the objection is about modelling, first check whether the model can answer the question at all. GOV.UK puts that on the applicant: “It’s your responsibility to check the suitability of an existing model for your development.”

If the objection is about the sequential test, more modelling will not help. That test is about whether a site at lower risk is reasonably available, not about how well the flood is described.

Residents often know things an assessment does not: which road floods first, where water came over the bank, how deep it was last time. At Hamstall Ridware, residents’ records of the February 2020 flood were how I checked the model, because the village gauge is bypassed in big floods. The same kind of record can test a developer’s assessment.

Comments carry most weight when they are specific: the paragraph, the evidence that contradicts it, and what the parish asks the council to require. How residents’ records become evidence.

On duty I turned forecasts and overnight river-level alerts into flood alerts and warnings, as the risk level moved between yellow and red, and kept police and ambulance services involved. A plan for a development has to work for the people who will receive those messages: what each one means for them, where they go, and when.

The meanings are short. A Flood Alert means flooding is possible, so prepare now. A Flood Warning means flooding is expected, so act now. A Severe Flood Warning means flooding could be a risk to life and cause significant disruption to communities.

Reviews that include modelling take longer, because the model files (Environment Agency Products 5 to 7, or your consultant’s own) have to be obtained and checked.