Building close to a flood defence: byelaws and clearances
Permanent works within eight metres of a main river bank or flood defence need an Environment Agency permit, sixteen metres on tidal defences. The maintenance strip usually decides the layout.
Build within eight metres of a main river bank or a raised flood defence in England and you need a flood risk activity permit from the Environment Agency, on top of planning permission. The distance rises to sixteen metres alongside tidal main rivers and sea defences. The permit regime sits in the Environmental Permitting (England and Wales) Regulations 2016, it is administered separately from the planning system, and it is the consent that most often turns a viable layout into an unviable one because the setback strip has to stay clear for maintenance plant.
Find out where the defence is and who owns it before the layout is fixed. The strip is not negotiable in the way a planning setback sometimes is.
Why a setback strip exists
A flood defence is an asset that has to be inspected, repaired and eventually replaced, and all of that needs plant on the bank. An excavator working on a revetment needs room to stand, room to swing and room to place material, and a tracked machine needs a route along the bank to reach the work.
The strip also protects the defence itself. Loading close to a raised embankment changes the stresses in it, foundations can create seepage paths, and trees planted on or near a defence destabilise it as they grow and when they fall.
There is a third reason that developers appreciate later. A defence with houses built up against it is far harder to raise when climate change allowances require it, and the Agency is protecting its own future options as much as its current access.
Which activities need a permit
A permit is needed for a flood risk activity, which covers works in, over, under or near a main river, works on or near a flood defence structure, and works in a floodplain that could affect flood flows.
The activities that catch development most often:
- Any permanent structure within eight metres of the top of the bank of a main river, or within eight metres of a flood defence structure or a culverted main river.
- Any structure within sixteen metres of a tidal main river, sea defence or tidal flood defence.
- Excavation within those distances, including foundations, drainage runs and service trenches.
- A new outfall or the alteration of an existing one.
- Raising ground levels or placing material in the floodplain.
- Temporary works, including site compounds, haul roads and craneage within the strip.
Some low risk activities are exempt or excluded and can be carried out without a permit provided the published conditions are met. Check the current exemption and exclusion lists rather than assuming, because they are revised and the consequences of getting it wrong include a criminal offence rather than merely a refusal.
Works to an ordinary watercourse, meaning one that is not a designated main river, fall outside this regime and need land drainage consent from the lead local flood authority instead. The two are regularly confused, and land drainage consent for works to an ordinary watercourse sets out that route.
What the distance is measured from
This is where layouts go wrong. The eight metres is measured from the landward toe of a raised defence, or from the top of the bank where there is no raised structure, and not from the water's edge or from the red line on a title plan.
On a channel with a berm and a set-back embankment the relevant point can be twenty metres from the water. On a culverted main river running under a car park there is no visible bank at all and the measurement is taken from the outside of the culvert structure, which needs the Agency's records to locate.
| Situation | Measure from | Distance |
|---|---|---|
| Main river, natural bank | Top of the bank | 8 m |
| Raised fluvial defence | Landward toe of the defence | 8 m |
| Culverted main river | Outer face of the culvert | 8 m |
| Tidal main river or sea defence | Toe of the defence or bank top | 16 m |
| Ordinary watercourse | Consent from the lead local flood authority | Set locally |
Ask the Agency for its asset records early and get the defence position confirmed in writing. A survey that picks up the visible bank but misses a buried sheet pile line is the kind of error that reaches the surface after foundations are designed.
Piling, excavation and loading restrictions
Where work is permitted close to a defence, the Agency's conditions bite on how it is done.
Piling is scrutinised most closely. Driven piling near an embankment or a sheet pile wall raises vibration and displacement concerns, and the Agency will normally want a method statement, a vibration monitoring regime with trigger levels, and a commitment to stop work and review if a trigger is exceeded. Bored or continuous flight auger piling is often preferred, and the choice affects cost.
Excavation below the level of the defence toe creates the risk of a seepage path or a slip, and a geotechnical assessment of the defence stability under the proposed works is usually required. That assessment needs the defence construction, which means asset records rather than assumptions.
Loading is the quiet one. A building, a retaining wall or an engineered platform placed near an embankment increases the load on ground that supports the defence. Structures are generally required to be designed so that the defence is not relied upon and is not loaded by the new works, which in practice means piled foundations taken below the zone of influence and a clear gap.
Maintenance access and vehicle turning
The strip has to work as a working area rather than exist on a drawing. A bank that is eight metres wide but reachable only through a locked residential courtyard with a three metre gate is not accessible.
Four things need showing on the layout: a continuous route along the defence at the required width, an access point from the public highway suitable for a low loader and a tracked machine, a turning or setting down area at a practical interval, and a surface capable of carrying plant rather than a lawn over a shallow attenuation crate.
Gates and bollards are acceptable where the Agency holds a key and the opening is wide enough. Level changes are not: a flight of steps across the access route defeats it.
Where the site relies on the strip for anything else, such as an emergency access route or part of a play space, say so and get it agreed. Dual use can work where the primary function is protected, and it fails where nobody has thought about the machine.
Landscaping and boundary treatment in the strip
Planting is where the Agency and the design team most often disagree. Trees on or near a defence are resisted because roots create seepage paths and windthrow can breach an embankment, so expect a requirement for grass or low planting only within the strip, with any tree planting set outside it.
Boundary treatment needs to be removable or gated. Close boarded fences across the route block it, and a fence along the route that leaves less than the required width is no better. Where plot boundaries reach the strip, the usual solution is a post and rail fence on the plot side with the strip held in common ownership and maintained by a management company.
That arrangement needs setting up properly in the legal documents. A strip in the ownership of individual plot owners will be fenced, planted and shedded within a few years, and the Agency will then have a problem that the developer created and cannot fix.
Design the strip as a considered piece of the layout instead. A mown route with a hedge outside it, used as a footpath and a green corridor, satisfies the access requirement and improves the scheme, and it supports the case made in residual flood risk and property flood resilience measures.
Application content and timescales
A permit application needs a location plan, detailed drawings showing the works against the defence and the measured distances, a design statement, a method statement covering construction sequence and plant, a flood risk assessment where flood flows are affected, and details of the maintenance access arrangement. Bespoke permits attract a charge under the published scheme, so check the current fees.
Allow real programme time. Determination takes considerably longer than a planning consultation response, pre-application discussion with the Agency's permitting team is a separate exercise from the planning consultation, and a permit refusal after planning permission is granted leaves you with an unbuildable consent.
Run the two in parallel and reference the permit position in the Flood Risk Assessment submitted with the application, along with the drainage arrangement set out in the Drainage Strategy. Where surface water risk is also present, describe it accurately rather than optimistically, as covered in reading the surface water flood risk map without overstating it.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required. This is general guidance, not legal advice; check the position with the Environment Agency, your lead local flood authority or a qualified professional before relying on it.
Frequently asked questions
How far from a flood defence can I build?
A flood risk activity permit is needed for permanent structures or excavation within eight metres of the top of the bank of a main river, of a flood defence structure or of a culverted main river, and within sixteen metres of a tidal main river or sea defence. Some low risk activities are exempt or excluded, so check the current lists.
Where is the distance measured from?
From the landward toe of a raised defence, or from the top of the bank where there is no raised structure, and from the outer face of the culvert where a main river is culverted. Not from the water's edge. On a channel with a berm and a set-back embankment the relevant point can be well back from the water.
Does a flood risk activity permit replace planning permission?
No. They are separate consents administered by different bodies, and both are needed. Planning permission does not authorise works near a defence and a permit does not authorise development. Run the two in parallel, because a permit refusal after permission is granted leaves an unbuildable consent.
What does the Environment Agency require in the maintenance strip?
A continuous route along the defence at the required width, an access point from the public highway suitable for a low loader and a tracked machine, a turning or setting down area, a surface able to carry plant, and no trees, permanent structures or level changes. Gates are acceptable where the Agency holds a key.
What if my site is on an ordinary watercourse rather than a main river?
Then the permit regime does not apply and you need land drainage consent from the lead local flood authority under the Land Drainage Act 1991 instead. Confirm which designation applies before designing, because the two regimes have different requirements, different timescales and different consenting bodies.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.