Ordinary watercourse consent or an environmental permit
One fact decides which regime applies: whether the channel is a designated main river. Planning permission authorises neither consent, and the sequence can trap you.
Whether you need ordinary watercourse consent or a permit depends on one fact you can check in five minutes: whether the watercourse beside your site is a designated main river. Works affecting a main river need a flood risk activity permit from the Environment Agency under the Environmental Permitting (England and Wales) Regulations 2016. Works affecting an ordinary watercourse, meaning everything that is not a main river, need land drainage consent from the lead local flood authority under section 23 of the Land Drainage Act 1991. Different regulator, different application, different timescale, different fee.
And neither is granted by planning permission. That is the point most self-builders discover late.
Which authority regulates which watercourse
Main rivers are designated by the Environment Agency and shown on the published Main River Map. Designation follows the significance of the channel for flood risk management rather than its size, so a modest brook can be a main river while a substantial drainage ditch is not. Do not judge by appearance.
Everything else is an ordinary watercourse: streams, ditches, drains, cuts, culverts, dykes, sewers other than public sewers, and passages through which water flows. The regulator is the lead local flood authority, which is the county council or unitary authority, unless the site sits inside an internal drainage board district, in which case the board consents instead.
A single channel can change status along its length, with a main river designation beginning at a defined point. Check the position at your site rather than at the nearest bridge.
What land drainage consent covers
Consent under section 23 of the Land Drainage Act 1991 is needed for a mill dam, weir or other like obstruction to the flow of an ordinary watercourse, and for any culvert or alteration to a culvert.
In practice that reaches most of what a small development does near a ditch: culverting a length to form an access, installing a headwall and pipe, putting in a flow control structure, building a crossing, or altering an existing culvert's size or alignment. Temporary works count if they obstruct flow.
Culverting an open watercourse attracts particular resistance. National policy and Environment Agency practice both favour keeping watercourses open, so an application to culvert needs to explain why an open channel with a clear span crossing is not achievable, and how the culvert is sized, protected from blockage and maintained.
Lead local flood authorities also make byelaws, and internal drainage boards almost always do, commonly controlling works or structures within a set distance of the bank top. Those byelaws bite even where section 23 consent is not required, so ask the authority what its byelaw distance is.
What the flood risk activity permit covers
For a main river the trigger is broader. A permit is required for work in, over, under or near a main river, with the proximity test generally reaching structures and works within eight metres of the bank top on a fluvial main river and sixteen metres where the river is tidal. Works in or affecting a flood defence structure or a floodplain also fall within the regime.
The permitting regime has three routes: exemptions for defined low risk activities that must still be registered where the rules require it, standard rules permits for activities matching a published rule set, and bespoke permits for everything else. Check the exemption list first, because a surprising amount of minor work near a main river falls within it.
| Point | Land drainage consent | Flood risk activity permit |
|---|---|---|
| Watercourse | Ordinary watercourse | Main river |
| Regulator | Lead local flood authority, or internal drainage board | Environment Agency |
| Legislation | Section 23, Land Drainage Act 1991 | Environmental Permitting (England and Wales) Regulations 2016 |
| Typical trigger | Obstruction to flow, culverting, altering a culvert | Works in, over, under or near the river, and works to defences |
| Proximity test | Set by local byelaws | Generally 8 metres fluvial, 16 metres tidal |
| Routes available | Consent or refusal | Exemption, standard rules permit, or bespoke permit |
| Fee | A statutory fee per structure, modest | Charged under the Environment Agency charging scheme, higher |
Main river designation and how to check
The Main River Map is published and searchable, and the Environment Agency's own data services carry the underlying layer. Check three things while you are there.
The designation at the point of your works, not along the reach. The bank top position, since the proximity test runs from bank top rather than from the water's edge, and on a shallow-sided channel those are far apart. And whether any flood defence structure, formal or informal, sits between your works and the channel.
Print the extract with the date visible and keep it. Where the answer is not obvious, the Environment Agency will confirm the designation on enquiry, and a written confirmation is worth having in the file.
Then check the flood zone separately, because the consent question and the planning flood risk question are different. A Flood Risk Assessment may be required for the planning application whether or not any consent is needed for the works themselves.
Application timescales and fees
Land drainage consent under section 23 carries a statutory determination period, commonly two months from a valid application, and a modest statutory fee per structure. Confirm both with the lead local flood authority, since the application form, the required drawings and the calculations expected vary between authorities.
Flood risk activity permits run on the Environment Agency's published determination periods, which differ between standard rules and bespoke applications, and they carry charges under the agency's current scheme. A bespoke permit for anything involving modelling or a defence structure should be programmed in months rather than weeks. The mechanics are covered further in flood risk activity permits for works near a main river.
Both regulators will ask for the same underlying material: a location plan, a cross section, hydraulic calculations showing no increase in flood risk, construction details and a maintenance proposal. Prepare it once.
Planning permission does not replace either
This is the expensive misunderstanding. A grant of planning permission does not authorise works to a watercourse, and a planning condition requiring a drainage scheme does not discharge the consent requirement. The regimes run in parallel and are enforced separately.
Worse, the sequence can trap you. A drainage design approved under a planning condition may be refused consent by the lead local flood authority, which then leaves a discharged condition that cannot be built. The way round it is to secure the consent or permit before, or alongside, the condition discharge, and to say in the planning submission which consents are being pursued. The same trap is set out in ordinary watercourse consent: when planning is not enough.
Riparian ownership adds a third layer. Where you own land adjoining a watercourse you have rights and duties at common law, including a duty to let water pass without obstruction, and those duties survive any consent you obtain.
Programming the consents
Work through this order before committing to a drainage strategy.
- Establish the designation at the works location from the Main River Map and record the date checked.
- Ask the lead local flood authority or internal drainage board for its byelaw distance and its application requirements.
- Check the Environment Agency exemption list if the channel is a main river.
- Prepare the hydraulic case once, to the standard the stricter regulator expects.
- Check ecology, because works in or near a watercourse engage protected species with fixed survey windows, as water vole survey season and works near a watercourse explains.
- Submit the consent or permit application in parallel with the planning application rather than after it.
- Align the construction programme with the determination periods, and with any seasonal restriction the consent imposes on in-channel work.
Where the scheme discharges surface water to the watercourse, the discharge rate and the outfall detail belong in the Drainage Strategy and in the consent application in identical terms. Regulators compare them.
Enter your postcode on PlanScope to see which flood and drainage documents a site is likely to need, then confirm the watercourse designation before designing the outfall.
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.
Frequently asked questions
How do I find out if a watercourse is a main river?
Check the published Main River Map and the Environment Agency's data services for the underlying layer, at the exact point of your works rather than along the reach, because designation can begin part way along a channel. Print the extract with the date visible. The Environment Agency will confirm designation on enquiry if the position is unclear.
What works need land drainage consent?
Under section 23 of the Land Drainage Act 1991, a mill dam, weir or other like obstruction to the flow of an ordinary watercourse, and any culvert or alteration to a culvert. In practice that covers access culverts, headwalls and pipes, flow control structures, crossings and temporary works that obstruct flow.
How close to a main river does a permit apply?
The proximity test generally reaches works and structures within eight metres of the bank top on a fluvial main river, and sixteen metres where the river is tidal. Works in or affecting a flood defence structure or a floodplain also fall within the regime. Measure from the bank top, not the water's edge.
Does planning permission authorise works to a watercourse?
No. The regimes run in parallel and are enforced separately, and a planning condition requiring a drainage scheme does not discharge the consent requirement. A design approved under a condition can still be refused consent by the lead local flood authority, leaving a discharged condition that cannot be built.
Who consents works inside an internal drainage board district?
The internal drainage board, rather than the lead local flood authority. Boards almost always have byelaws controlling works and structures within a set distance of the bank top, and those byelaws apply even where section 23 consent is not itself required. Ask the board for its byelaw distance early.
Why is culverting an open watercourse discouraged?
Because national policy and Environment Agency practice both favour keeping watercourses open, for flood risk, maintenance and ecological reasons. An application to culvert needs to explain why an open channel with a clear span crossing is not achievable, and to show how the culvert is sized, protected against blockage and maintained.
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.