Ordinary watercourse consent for farm ditches and outfalls

Ordinary watercourse consent farm works are governed by section 23 of the Land Drainage Act 1991. If you want to culvert a ditch, put in a new outfall, install a weir or build anything that obstructs the flow of a watercourse that is not a main river, you need written consent before the work starts. It is a separate permission from planning, granted by a different body, and doing the work without it is an offence that can end with a requirement to take the structure out again.

The application itself is short. The evidence behind it is where the time goes.

What needs consent under the Land Drainage Act 1991

Section 23 catches two categories. Erecting a mill dam, weir or other like obstruction to the flow of an ordinary watercourse, or altering or repairing one. And erecting or altering a culvert in an ordinary watercourse.

In practice that covers most of what happens on a farm:

• Piping a length of open ditch, whether for a field access, a yard extension or to gain cropped area.
• Replacing an existing pipe with a different size, length or invert level.
• Installing a headwall and outfall discharging into a ditch.
• Putting in a flow control, penstock, sluice or weir.
• Building a crossing that constricts the channel, including a bridge with abutments in the bed.

An ordinary watercourse is any river, stream, ditch, drain, cut, dyke, sluice, sewer other than a public sewer, or passage through which water flows, that does not form part of a main river. So a field ditch that is dry for half the year still counts. Check the Main River Map before you start, because if the channel is a main river the regime changes entirely.

Where an internal drainage board covers the land, its byelaws usually bite as well, commonly requiring consent for works within a stated distance of a watercourse, often around 9 metres. That catches buildings and hardstanding near a ditch even where the ditch itself is untouched.

Who grants it and how long it takes

For an ordinary watercourse outside an internal drainage board district, consent comes from the lead local flood authority, which is the county or unitary council. Inside an internal drainage board district, the board consents instead. For a main river, you need a flood risk activity permit from the Environment Agency, which is a longer and more expensive process.

The Act sets a two month period for determination, and an application that is not determined within it can in some circumstances be treated as consented. Do not build a programme on that. Authorities ask for further information, which resets the clock in practice, and a farmer relying on deemed consent who later faces an enforcement notice is in a poor position. A statutory application fee applies per structure, and the figure is set by regulation, so ask the authority for the current amount.

Allow three months from a complete application on a straightforward pipe, and longer where the authority wants hydraulic calculations or consults the Environment Agency.

Culverting and the presumption against it

Both national guidance and every lead local flood authority guidance note I have read start from the same position: watercourses should not be culverted unless there is no reasonable alternative. The reasons are practical rather than sentimental. A culvert blocks, it removes habitat, it cannot be inspected along its length, and it converts a visible maintenance problem into an invisible one.

So an application to culvert has to justify the need, not just describe the design. Length is the main battleground, and authorities will usually grant consent for the minimum length needed for an access crossing while refusing a longer run that exists to gain field area.

Where culverting is accepted, expect requirements on:

1. Pipe size calculated for the design flow with a blockage allowance, not sized to match the existing pipe.
2. Invert level set to the bed of the ditch so the channel does not perch or scour.
3. Headwalls at both ends, with erosion protection and a wing wall arrangement suited to the bank angle.
4. A manhole or access chamber at any change of direction and at intervals along the run.
5. No trash screen unless it is unavoidable, and where one is fitted, a written maintenance regime, because a blocked screen causes more flooding than no screen.
6. A maintenance responsibility recorded in writing, since the riparian owner keeps it whatever the authority consented.

Ditches and field boundaries often coincide, so check whether the hedgerow alongside is caught by the important hedgerow test before machinery arrives, because a ditch is one of the features that can matter to that assessment.

New outfalls and headwall design

A new outfall discharging farmyard, roof or field drainage into a ditch needs consent and needs to show it will not make flooding worse downstream.

The design points authorities look for are consistent. A headwall rather than a bare pipe end. The invert set above the normal water level so the pipe does not surcharge. Erosion protection to the bed and bank at the discharge point. A flow control where the discharge rate has been limited as a condition. And a non-return valve where the ditch can back up, though these need maintenance access and they fail closed as often as open.

Rate matters as much as design. An authority consenting an outfall from a new agricultural building will usually want the discharge limited, which means attenuation upstream, and that in turn means a Drainage Strategy sized for the design events rather than a pipe sized for the downpipe.

Illustrative example: a 900 square metre general purpose agricultural building with a new outfall to a roadside ditch. The authority consents the headwall on condition that discharge is restricted, so the design adds an attenuation pond at the low corner of the yard with a flow control at the outlet. The pond also takes the yard runoff, which solves a separate problem the farm had every winter.

Consent and planning permission are separate

Neither permission authorises the other, and the sequence trips people up.

A planning permission for a farm building does not authorise the outfall into the ditch. A land drainage consent does not authorise the building. An agricultural notification under permitted development rights says nothing about the watercourse. And on a site in a flood zone, the Flood Risk Assessment submitted with the planning application should be consistent with what the land drainage consent proposes, because the same authority often sees both.

Apply for both in parallel. Where the planning application depends on a drainage solution that needs consent, tell the planning officer that the consent application is in, and give them the reference. It costs nothing and removes a reason to hold the application.

What to submit with the application

A complete application typically contains a location plan at an identifiable scale, a detailed plan showing the works and the extent of the channel affected, longitudinal and cross sections with invert and bed levels, the design flow and the calculation behind the pipe size, a construction method statement including how flow will be maintained during the works, a maintenance plan with a named responsible party, photographs of the existing channel upstream and downstream, and confirmation of land ownership or the consent of the riparian owner where the works are not all on your land.

Riparian ownership deserves a check before anything else. Where a ditch runs along a boundary, ownership is often presumed to run to the centre line, which means the works affect a neighbour. Sorting that out first avoids an application being withdrawn.

Enforcement where work is done without consent

Unconsented works are an offence, and the enforcement powers are practical rather than merely punitive. The authority can require the works to be altered or removed, can carry out the work itself and recover the cost, and can prosecute. Separately, a notice can be served requiring a riparian owner to maintain the flow of a watercourse where a blockage is causing a problem.

Retrospective consent is sometimes granted where the works turn out to be acceptable, and the practical route is to approach the authority before it approaches you. A culvert installed twenty years ago without consent remains unconsented, and it becomes the buyer's problem on a sale, so it is worth resolving while the farm is not under offer.

This is general guidance rather than legal advice. Check the position with your lead local flood authority, internal drainage board or a qualified professional before relying on it.

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