Ordinary watercourse consent: when planning is not enough
Building a culvert or an outfall in a ditch needs consent under the Land Drainage Act 1991, from the lead local flood authority. Planning permission does not authorise it, and building first is an enforcement risk.
Ordinary watercourse consent is granted under section 23 of the Land Drainage Act 1991 by the lead local flood authority, and it is required before you erect or alter any structure that would obstruct or alter the flow of an ordinary watercourse. A planning permission does not authorise those works. Two separate bodies, two separate applications, and the drainage one is frequently discovered after the contractor has arrived on site with a culvert pipe.
An ordinary watercourse is any river, stream, ditch, drain, cut, dyke, sluice or passage through which water flows that is not designated as a main river. Most field ditches, most urban culverted streams and almost every roadside drain fall into that category.
What counts as an ordinary watercourse
The dividing line is the main river map. Watercourses designated as main river are the Environment Agency's responsibility, and works affecting them need a flood risk activity permit under the environmental permitting regime, plus consent for anything within 8 metres of the bank under the Agency's byelaws.
Everything else is an ordinary watercourse, and consent comes from the lead local flood authority, which is the county or unitary authority. Inside an internal drainage board district, the board takes that role instead.
Three practical points follow. A ditch that is dry for most of the year is still a watercourse if water flows through it. A watercourse that has already been culverted is still a watercourse, so altering the existing culvert needs consent. And a piped land drain crossing a field can qualify, which surprises people who assume the regime is only about open channels.
Check the main river map before you assume which regime applies. Getting this wrong means applying to the wrong body and losing weeks.
Works that need consent from the lead local flood authority
Consent is needed for a mill dam, weir or other like obstruction, for altering or repairing one, and for erecting or altering a culvert in a way that would affect the flow.
In development terms, that captures most of the things a site actually needs.
- A culverted crossing to provide an access to the site.
- A new outfall discharging attenuated surface water into the ditch.
- Headwalls, wingwalls, flow control devices and trash screens.
- Realigning or diverting a length of ditch around a plot.
- Infilling a length of watercourse, or building over one.
- Temporary works, including a construction access crossing or over-pumping.
Temporary works catch people out most. A crossing installed for the build and removed afterwards still needs consent, because during its life it is an obstruction to flow.
How consent differs from planning permission
The two regimes ask different questions, and neither answers for the other.
| Consent | Body | Question asked |
|---|---|---|
| Planning permission | Local planning authority | Is the development acceptable in planning terms |
| Ordinary watercourse consent | Lead local flood authority or drainage board | Will the works obstruct or alter flow to the detriment of others |
| Flood risk activity permit | Environment Agency | Works on or near a main river |
A drainage engineer looks at hydraulic capacity, the effect on flood levels upstream and downstream, maintenance access, structural adequacy and the ecological consequence. A planning officer looks at land use, design, amenity and policy. It is entirely possible to hold a permission for a scheme whose access crossing will not be consented as designed.
Because of that, the Drainage Strategy submitted with the planning application should describe the crossing and the outfall in enough detail that a drainage officer can see the intent, and should state that land drainage consent will be sought. Silence on the point invites a holding objection.
The presumption against culverting
Lead local flood authorities start from a position against culverting, and the reasoning is sound rather than obstructive.
A culvert reduces capacity relative to an open channel, blocks with debris, is far harder to maintain, cuts the watercourse off from light and from wildlife movement, and hides a problem that later owners will not know about. Once culverted, a watercourse is rarely opened up again.
So consent for culverting is normally limited to the minimum length needed for an access crossing, with conditions. Expect the authority to look for a clear span structure rather than a pipe where the channel is of any size, an invert set below bed level so that a natural bed can form, headwalls designed for maintenance access, and a trash screen only where it is really needed and can be maintained safely.
Culverting a length of ditch simply to gain developable area is very unlikely to be consented. If the layout depends on it, redesign the layout.
Where an open channel is retained, an easement strip either side for maintenance is normally required, usually shown on the layout and excluded from private curtilages so that access is not obstructed later.
Application content and typical timescales
A consent application that gets determined first time contains all of this.
- A location plan and a detailed plan showing the works, the watercourse and the extent of any easement.
- Long sections and cross-sections through the structure, with existing and proposed bed levels, soffit levels and channel dimensions.
- Hydraulic calculations demonstrating capacity and showing no increase in flood risk upstream or downstream, with the design event and climate change allowance stated.
- Structural details and the construction method statement, including how flow will be maintained during the works.
- Evidence of riparian ownership or the consent of the owners of the bed and banks.
- An ecological note covering the channel and its margins.
- Maintenance proposals, naming who will be responsible and how they will get access.
Authorities publish their own determination periods and fees, and two months is a common figure, so confirm with the authority rather than assuming. That period runs from a valid application, and an application missing hydraulic calculations is not valid in practice even if it is accepted.
Where the works could affect protected species or a designated site, a Preliminary Ecological Appraisal should come first, since water voles, otters and white-clawed crayfish all use ordinary watercourses and all carry survey seasons.
Enforcement and the risk of building first
The Land Drainage Act gives the authority power to require the removal or alteration of an unconsented obstruction, and to carry out the work itself and recover the cost if the notice is not complied with. There are also criminal penalties for carrying out works without consent.
That is the legal position. The commercial position is worse. A culvert installed without consent and later found to be undersized has to come out, which usually means the access road above it comes out too, and the site has no access while it happens.
Riparian responsibilities sit alongside all this. As a riparian owner you are presumed to own the bed up to the centre line, you must let water flow through without obstruction, you must accept flow from upstream and you must keep the channel clear of anything you have put there. Those duties do not depend on any consent and they pass to whoever buys the land.
Sequencing consent alongside the planning application
Run them in parallel, with the drainage design leading.
Fix the crossing and outfall design before the planning layout is frozen, because a change from a pipe to a clear span structure changes levels, gradients and the road alignment. Submit a pre-application enquiry to the lead local flood authority at the same time as any planning pre-application, and ask specifically whether the crossing principle is acceptable and what structure type will be expected.
Then submit the consent application either alongside the planning application or as soon as the layout is settled, so that consent is in hand before conditions are discharged. Where the planning permission contains a drainage condition, the consented details are what you submit to discharge it, which means the two documents have to describe the same structure.
Keep the Flood Risk Assessment consistent with the consent application. A modelled flood level in one document and a different one in the other is the fastest route to both being queried.
Illustrative example: a nine plot scheme reached across a 1.2 metre wide field ditch. The layout showed a 600 millimetre pipe with 20 metres of culvert to widen the entrance. The authority required a clear span crossing of 4 metres with the bed left in place, which raised the road by 300 millimetres and lost one plot. Discovering that at pre-application stage cost a fortnight. Discovering it after permission would have cost a redesign and a fresh application.
Include the works in the Construction Management Plan as well, since maintaining flow during construction, silt control and the timing of in-channel works are conditions the council and the drainage authority both care about.
This is general guidance, not legal advice. Consenting procedures, fees and determination periods vary between authorities, so confirm the position with the lead local flood authority and a qualified drainage engineer before relying on it.
Get the drainage evidence drafted while the crossing design is being agreed. Enter your postcode on PlanScope to see which reports a site with a watercourse is likely to need.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Who grants ordinary watercourse consent?
The lead local flood authority, which is the county or unitary council, under section 23 of the Land Drainage Act 1991. Inside an internal drainage board district the board takes that role. Works on or near a designated main river fall to the Environment Agency instead, under the environmental permitting regime and its byelaws.
Does planning permission cover works to a ditch?
No. The two consents ask different questions and are granted by different bodies. A planning permission for a scheme whose access crosses a ditch does not authorise the crossing itself, and it is entirely possible to hold permission for a layout whose culvert will not be consented as drawn.
Why are councils so resistant to culverting?
A culvert reduces capacity compared with an open channel, blocks with debris, is much harder to maintain, severs the watercourse from wildlife movement and hides the problem from future owners. Consent is normally limited to the shortest crossing needed for access, with a clear span structure preferred over a pipe.
How long does a consent application take?
Authorities publish their own determination periods and fees, and two months is a common figure, but confirm with the specific authority. The period runs from a valid application, and an application without hydraulic calculations or ownership evidence will stall regardless of when it was submitted.
What happens if I build a culvert without consent?
The authority can require it to be removed or altered, carry out the work itself and recover the cost, and there are criminal penalties. Practically, removing an undersized culvert usually means taking out the access road above it, leaving the site without access while the replacement is built.
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.