Refusals on drainage and the sequential test

A refusal on flood grounds is usually one of two quite different things wearing the same coat. Either the council says you failed the sequential test, which is an argument about whether your site should be developed at all when others are available, or the lead local flood authority says your surface water drainage evidence is inadequate, which is a technical gap you can fill. The first is hard and sometimes unanswerable. The second is nearly always fixable, and a great many flood refusals on small residential schemes are the second dressed up as the first.

Work out which you have before you decide whether to appeal or resubmit.

Reading what the refusal reason actually says

Take the reason apart clause by clause. A sequential test reason will refer to development being directed to areas at lowest risk of flooding and to alternative sites being available. A drainage reason will refer to insufficient information, to runoff rates, to infiltration, to a discharge point, or to the absence of a maintenance regime.

A mixed reason covering both is common, and it needs two separate answers. Councils also sometimes refuse for want of a Flood Risk Assessment altogether, which is the easiest reason to cure and the most embarrassing to receive.

Then read the consultation responses on the file. The lead local flood authority's response tells you precisely what it wanted and in what form, and it is far more useful than the summarised refusal reason. Reading the reasons for refusal properly starts with that file rather than with the decision notice.

Sequential test refusals and the area of search

The sequential test asks whether there are reasonably available sites at lower flood risk that could accommodate the development. National guidance sets out the approach, and the burden of carrying it out sits with the applicant where the site is not allocated in the development plan.

Refusals on this ground almost always trace back to one of three failures. The test was not carried out at all. It was carried out over an area of search so narrow that the answer was predetermined. Or it dismissed alternative sites on grounds that are not about flood risk, such as the applicant not owning them.

The area of search is the battleground. The starting point is normally the local planning authority's area, and a smaller area needs justification tied to the nature of the development rather than to commercial preference. A test that searched only within one parish because that is where the client's land is will be given no weight.

What does work is a documented search: the area of search and its justification, the sources used including the authority's own housing land availability assessment and brownfield register, each site identified, and why each is not reasonably available on grounds that relate to flood risk and to the development's requirements. A properly prepared Sequential Test reads like a methodology, with a date on it.

Where the sequential test does not apply

This is the point that rescues a surprising number of refusals, and self-builders in particular should check it.

National guidance provides that the sequential test does not need to be applied to minor development or to changes of use, with a stated exception for changes of use to caravan, camping, chalet, mobile home and park home sites. Minor development, in this context, means householder development, small non-residential extensions and alterations that do not increase the size of the building.

Read that definition carefully, because a new dwelling on a garden plot is not minor development even though it feels small. A rear extension to an existing house is. If a council has applied the sequential test to a householder extension, that is a point worth making plainly and early, and it is often conceded without an appeal.

Surface water refusals and the discharge hierarchy

Drainage refusals are technical, and they follow a pattern. The lead local flood authority applies a hierarchy for surface water disposal, and it expects each step to be tested and ruled out in order before the next is accepted.

1. Infiltration to ground, evidenced by soakage testing at the right depth and season, not by an assumption from the geology map.
2. Discharge to a surface water body, with the consent of whoever controls it and evidence of capacity.
3. Discharge to a surface water sewer, with the undertaker's confirmation of a connection point and capacity.
4. Discharge to a combined sewer, which is the last resort and usually resisted.

Alongside the hierarchy, expect to be asked for the runoff rate, the storage volume for the design event with the current climate change allowance applied, exceedance routing for events above the design standard, water quality treatment where appropriate, and a long-term maintenance and adoption arrangement for every component.

Half of these refusals come down to missing infiltration testing. Commission it early, in a season when the result is meaningful, because a soakage test in a dry August on clay is not evidence of anything useful.

What the lead local flood authority asked for

The authority's consultation response is your specification for the resubmission or the appeal, and it is worth treating as a checklist.

Go through it line by line and produce a table in your Drainage Strategy showing the comment, the response and where in the document the answer sits. Officers and inspectors both find that format persuasive, because it demonstrates the objection has been engaged with rather than talked around.

Where you disagree with the authority on a technical point, say so explicitly and give the calculation. A polite disagreement supported by numbers reads very differently from silence on the point.

Offering betterment and conditions

On previously developed land, offering a reduction in the existing runoff rate is the strongest card you hold. Many authorities publish the betterment they expect on brownfield redevelopment, so check the local standard rather than guessing at a figure.

Conditions can resolve a great deal. A condition requiring a detailed drainage scheme to be submitted and approved before work above ground level, based on an approved strategy and stated runoff rates, is a normal outcome and one an inspector will readily impose. Offer the wording yourself.

Where the refusal is founded on flood risk to the development rather than on drainage, finished floor levels, safe access and egress, flood resilient construction and a flood warning and evacuation plan are the usual mitigation, and where the Exception Test is engaged the wider sustainability benefits have to be evidenced rather than asserted.

When the site cannot pass

Sometimes the honest advice is that the scheme fails and no amount of evidence changes it.

The clearest case is a site in the functional floodplain proposed for residential use, where policy directs the development elsewhere and the exception test cannot realistically be satisfied. Another is a site where the only available discharge is into a sewer with no capacity and no alternative, and no amount of on-site storage resolves it within the developable area.

In those cases the productive response is to change the proposal rather than the paperwork. A reduced footprint clear of the highest risk zone, a different use with a lower vulnerability classification, or a layout that puts the built form on the higher ground will sometimes get built where the original would not. And where a site has simply been refused on a sequential test carried out by the council rather than by you, carrying it out properly and resubmitting is faster than an appeal.

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.