Ordinary watercourse consent from the flood authority

Works in, over or under an ordinary watercourse need written consent from the lead local flood authority before they start. That consent is separate from planning permission, separate from any Environment Agency permit, and a planning consent does not carry it. An ordinary watercourse consent application under the Land Drainage Act 1991 is the step that most often appears halfway through a build, after the groundworker has already ordered the pipe.

For a rural landowner the practical list is short. Piping a ditch, putting in a culvert for a field access, building a weir or a dam, installing a flow control structure, or raising a bank. All of those are likely to need consent. Clearing out a blockage usually does not.

What counts as an ordinary watercourse

An ordinary watercourse is any watercourse that is not designated a main river. Main rivers are the responsibility of the Environment Agency and appear on its main river map. Everything else, which is most ditches, brooks, streams, drains, dykes and some unexpectedly small channels, is an ordinary watercourse.

The definition in the legislation is wide. It covers rivers, streams, ditches, drains, cuts, culverts, dikes, sluices and sewers other than public sewers, together with passages through which water flows. A dry ditch that only carries water after rain is still a watercourse.

Who consents depends on where you are. In most of England the lead local flood authority, which is the county council or the unitary authority, grants consent. Inside an internal drainage board district the board does it instead, and the board's own byelaws may add requirements that go beyond the Act.

Check the main river map first. Getting this wrong costs weeks, because the two organisations will not process each other's applications.

Works that need consent and works that do not

Consent is required for works that would affect the flow of water in the watercourse. In practice that means:

1. Any culvert, pipe or bridge crossing the channel.
2. Any structure in the channel that controls flow, including weirs, dams, sluices, flow controls and trash screens.
3. Outfalls discharging into the watercourse, including a new surface water outfall from a drainage scheme.
4. Diverting the channel, infilling it or raising its banks.
5. Temporary works such as a construction haul crossing or a dam for dewatering.

Routine maintenance by the riparian owner is not consentable work. Clearing silt, removing a fallen tree, cutting bank vegetation and repairing an existing structure like for like generally sit outside the consent regime, though an internal drainage board's byelaws may still require notification.

The grey area is replacement. Replacing a collapsed culvert with the same size pipe in the same position is arguably maintenance. Replacing it with a larger or smaller pipe, or at a different level, is new work. Ask the authority in writing and keep the reply.

Outfall design is the item that most often comes back for revision, and our note on outfall design, bank stability and scour protection covers what the engineer will be asked for.

Who grants consent and the application process

Applications go to the lead local flood authority's flood risk team, not the planning department. Most publish a form, a fee schedule and a technical guidance note. A statutory fee applies for each structure, so a scheme with three culverts and an outfall is four fees.

The submission needs to tell a drainage engineer what the structure does to the channel:

• A location plan showing the watercourse and the works.
• Long sections and cross sections with invert levels, soffit levels and bed levels to Ordnance Datum.
• Hydraulic calculations showing the structure passes the design flow without raising upstream levels, usually for the 1 in 100 year event with a climate change allowance.
• Details of the headwall, bed protection, scour protection and any trash screen.
• A construction method statement, including how flow is maintained during the works.
• Maintenance arrangements and who will carry them out.

The climate change allowance is the item that dates fastest. Use the current Environment Agency peak river flow allowance for your management catchment and river basin district, and say which allowance you have applied. Our note on which rainfall dataset to cite in a drainage calculation explains the equivalent choice for surface water.

The presumption against culverting

National and Environment Agency policy resists culverting. The reasons are practical rather than ideological: culverts block, they are difficult to maintain, they remove habitat, they worsen flood risk when they fail, and they are expensive to reinstate.

Expect the authority to ask whether the length of culvert can be reduced, whether an open channel with a clear span bridge would work instead, and whether an existing culvert could be opened up as part of the scheme. For a field access, a clear span bridge or a bottomless arch is often consented where a pipe culvert is refused.

Where a culvert is unavoidable, the consentable design usually has a minimum diameter the authority will accept for maintenance access, a trash screen at the inlet with a safe means of clearing it, and a bed set below the channel invert so that natural substrate forms inside the pipe. Design it that way first rather than arguing about it later.

And if the scheme involves a flow control structure, model what happens when it partially blocks. That sensitivity test is standard, and our note on modelling a partially blocked flow control sets out the approach.

Timescales and the risk to a construction programme

The Act sets a two month determination period for a consent application. Many authorities state that if they fail to determine within that period, consent is deemed to be granted, but the position varies in how it is expressed and you should get your authority's view in writing rather than relying on a general statement.

Two months is the statutory maximum, not the normal turnaround. In practice an incomplete submission restarts the clock, and flood risk teams are small. Build three months into the programme and submit at the same time as the planning application, not after approval.

The programme risk is sequencing. Many drainage schemes cannot be built until the outfall is consented, and the outfall is often the last thing designed. Pull it forward.

Enforcement for works without consent

Carrying out consentable works without consent is an offence, and the authority has powers to require the works to be altered or removed and to recover its costs. An unconsented culvert discovered during a later property sale is a real problem, because the buyer's solicitor will ask for the consent and it cannot be issued retrospectively in the same form.

Retrospective applications are sometimes accepted, but the authority is then assessing a structure it cannot inspect during construction, and it may require opening up or hydraulic proof. That is slower and more expensive than applying first.

Where the works were done by a previous owner, the liability still attaches to the current riparian owner for maintenance. Riparian responsibilities include keeping the channel clear and accepting flow from upstream, and they pass with the land.

An illustrative example

Take an illustrative case: a landowner wants a new field access over a 1.2 metre wide ditch. The first design is a 450 mm concrete pipe culvert, 9 metres long. The authority asks for hydraulic calculations and these show a 90 mm upstream rise in the 1 in 100 year plus climate change event. The design changes to a 1.5 metre bottomless arch with a stone bed and rock scour protection at both ends. Consent issues in seven weeks. The figures are illustrative and not from a real consent.

Relationship with planning permission

Planning permission and watercourse consent run in parallel. A planning officer may condition a drainage scheme without checking whether the outfall is consentable, and a planning approval is no defence to an enforcement notice under the drainage legislation.

So state the consent position in the planning submission. A Drainage Strategy that names the receiving watercourse, identifies the consenting body and confirms whether a pre-application discussion has happened removes a round of consultee comments. Where the site also sits in Flood Zone 2 or 3, the same information belongs in the Flood Risk Assessment.

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. This is general guidance, not legal advice; check the position with your lead local flood authority or a qualified professional before relying on it.