Flood defence byelaw margins and works near a bank

If your site touches a main river, there is a strip along the bank in which you need a permit from the Environment Agency before you build, excavate, plant or even store materials. It is eight metres wide on a non-tidal main river and sixteen metres on a tidal one, measured from the top of the bank or from the landward toe of a flood defence, and it applies whether or not your works go anywhere near the water.

Getting this wrong is expensive rather than fatal. The permit is obtainable on most schemes. What it is not is quick, and a layout drawn without the margin in mind usually has to change.

What the margin protects

The strip exists so that the Environment Agency can reach the river and its defences with plant. Dredging, bank repair, tree work, defence inspection and emergency response all need vehicular access along the bank, and a structure in that strip removes it permanently.

There is a second purpose. Loading the ground close to a bank affects its stability, excavation near it can undercut it, and a building hard against a defence makes future raising of that defence impossible. Flood defences are being raised as climate change allowances increase, so an obstruction that looks harmless today constrains a scheme the Agency has not designed yet.

The margin is not a flood zone and it is not a planning designation. A site can be entirely in Flood Zone 1 and still have a byelaw margin running through it.

The distances that apply

Those are the Environment Agency's byelaw distances in England. Ordinary watercourses are regulated separately by the lead local flood authority, or by an internal drainage board in its district, under the Land Drainage Act 1991, and the margins those bodies apply are set locally. Establishing which body regulates your watercourse is the first task, because the wrong application to the wrong regulator wastes weeks.

Culverted lengths catch people out. A main river that has been culverted is still a main river, and the margin runs on the surface above it even though there is nothing to see.

Activities caught even when you are not touching the river

The permitting regime covers a wider range of activity than most applicants expect. Within the margin, the following normally require a permit or a registered exemption:

1. Erecting any permanent structure, including a garden wall, a shed, a garage or an extension.
2. Excavation, including foundations, drainage runs and service trenches.
3. Raising ground levels or placing fill.
4. Planting trees or removing existing ones.
5. Storing materials or siting site accommodation during construction.
6. Forming a new hard surface that prevents plant access.
7. Any work to the bank itself, to a defence, or to a structure in or over the channel.

Temporary construction activity counts. A site compound in the margin for eight months is an obstruction for eight months, and the Agency treats it accordingly.

Permits, exemptions and exclusions

Flood risk activities are permitted under the Environmental Permitting (England and Wales) Regulations 2016. Three outcomes are possible for any given activity.

Some activities are excluded from the regime altogether, so nothing is needed. Some qualify as registered exemptions, which require you to register the activity with the Environment Agency but not to obtain a full permit. The rest need a permit, and permits come in standard rules and bespoke forms depending on what you are doing.

Check the current guidance for which category your activity falls into rather than assuming, because the exemption list has been revised. A registration is a short process. A bespoke permit is not, and it carries an application charge that varies with the activity.

The permit is separate from planning permission and neither one implies the other. A council can grant permission for a house whose foundations sit four metres from a main river bank, and the Agency can then refuse the permit that would let you build it. Officers will usually flag this in consultation, but the responsibility is yours.

Access for maintenance plant

The practical test the Agency applies is whether a tracked excavator and a support vehicle can still work along the bank after your scheme is built. That drives more decisions than any written policy.

Keep the margin clear and level. Avoid changes in level, fences across it, gates that lock, planting that will grow into the working width, and drainage features that cannot take a machine. Where the margin has to serve as part of your landscape scheme, grass and low planting are acceptable in a way that a hedge, a bund or a swale with steep sides is not.

Where existing access is already obstructed by older development, the Agency sometimes accepts an alternative access point in exchange for consent elsewhere. That is a negotiation worth opening early rather than proposing as a late fix.

Designing a layout that keeps the margin clear

The habit that saves money is to plot the margin on the constraints drawing at the same time as the flood zones, before the layout is drawn. It usually becomes the site's green edge, which is convenient because it also serves the biodiversity, drainage and amenity requirements the council will apply anyway.

Three design moves work repeatedly. Put the road, the parking and the open space in the margin side of the site and the built form beyond it. Run the site drainage away from the bank rather than along it, so that no manhole or outfall sits in the working width. And set finished levels so that the margin does not become the low point where surface water collects.

Where an outfall to the river is unavoidable, design it once and design it properly, because an outfall is itself a permitted activity and a poorly detailed headwall is a common reason for a permit to be returned. Bring the Drainage Strategy and the permit application into line before either is submitted.

The byelaw margin should also appear in the Flood Risk Assessment, with the distance stated, the datum explained and the layout shown against it. Councils increasingly ask for that as a validation item on riverside sites, and it is one of the constraints worth pinning down when checking a site for constraints before you make an offer.

Applying in good time

Determination periods for permits are published and vary by permit type, and the clock only starts when the application is complete. Incomplete applications are returned rather than held, which is why the practical lead time is longer than the published period.

The sequence that works is to establish the margin and the regulator at the feasibility stage, raise the proposal informally with the Agency's local team before the planning application is submitted, and apply for the permit once the layout is fixed but before you need it on site. Applying in parallel with the planning application is sensible where the layout is settled. Applying after permission is granted is normal, and applying after the contractor is mobilised is not.

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.

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