If your site sits beside a river, brook, ditch or culvert, a flood risk assessment for a site near a watercourse is usually just the start. Proximity to flowing water in England brings in a second layer of control — buffer zones, byelaws and separate drainage consents — that catches many applicants by surprise. This guide explains what a nearby watercourse means for your planning application and what your FRA needs to show.
Note that this applies to England. Flood policy and the consenting regime differ in Scotland, Wales and Northern Ireland.
Main river or ordinary watercourse? The distinction that matters
Every watercourse in England is legally classified as either a main river or an ordinary watercourse, and that single fact changes who regulates work near it.
Main rivers are the larger, mapped rivers for which the Environment Agency has responsibility. If you want to build, dig or place a structure within 8 metres of a main river (or its flood defence), you will generally need a Flood Risk Activity Permit from the Environment Agency, on top of planning permission. The 8-metre strip is kept clear so the river can be maintained and so flood flows are not obstructed.
Ordinary watercourses are everything else — the smaller streams, brooks, ditches and culverts. Works that could affect the flow of an ordinary watercourse usually need consent under Section 23 of the Land Drainage Act 1991 from the Lead Local Flood Authority (LLFA), or from an Internal Drainage Board where one exists. Culverting or building a structure over one of these is exactly the kind of work that needs consent.
You can check which category applies using the Environment Agency’s flood-risk maps, but the classification is not always obvious on the ground — a modest ditch can still be an ordinary watercourse for consenting purposes.
Why a nearby watercourse raises your flood risk
A watercourse on or near your boundary usually means the site touches Flood Zone 2 or 3 for river (fluvial) flooding, and it can raise surface-water risk too. If your site is in Zone 2 or 3, the National Planning Policy Framework requires a site-specific FRA, and often the Sequential Test as well — the process we set out in our guide to Flood Zones 1, 2 and 3. Even a Zone 1 site can need an FRA if it is over one hectare or affected by other sources of flooding.
Your assessment should follow the Environment Agency’s FRA template (updated March 2025) and reflect its standing advice on floor levels and resilience. It also needs to allow for climate change, applying the latest allowances to peak river flow — something we explain in our post on climate change allowances.
Buffer zones and the case for a riverside setback
Beyond the legal 8-metre strip for main rivers, planners and the Environment Agency often push for a wider undeveloped buffer alongside a watercourse — frequently 8 metres, sometimes more — to protect the channel, support biodiversity and provide space for flood water. Designing that setback in from the outset is far easier than losing developable area later. A generous riverside margin can also become an asset: a landscaped buffer can double as a sustainable drainage feature.
Drainage: keep the watercourse working
Where a scheme discharges surface water to a nearby watercourse, the FRA and drainage strategy must show that runoff is controlled to greenfield or agreed rates and managed through sustainable drainage systems (SuDS) designed to CIRIA C753. Attenuation, permeable surfaces and flow controls all help — see our guide to choosing SuDS for small sites. Discharging to an ordinary watercourse will itself usually need LLFA consent.
Getting the sequence right
The common mistake is to treat the FRA, the drainage consent and the flood risk activity permit as one thing. They are separate approvals with separate decision-makers. The FRA supports your planning application; the permit or land drainage consent are obtained alongside or after it before you can lawfully start work near the water. Flagging all three early avoids a nasty surprise on site.
How Fortress Associates can help
Fortress Associates produces automated, site-specific flood risk assessments for planning applications in England, built on live Environment Agency data and following the March 2025 EA template, with a SuDS drainage strategy to CIRIA C753. The report is free and ready in minutes, so you can see whether a watercourse pulls your site into Flood Zone 2 or 3 straight away. Browse our services or contact us for a riverside site.
Sources & further reading
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