Land drainage consent for works to an ordinary watercourse

Land drainage consent for an ordinary watercourse is a separate permission from planning permission, and having one does not give you the other. If you intend to culvert a ditch, install a headwall, build a bridge, divert a channel or put anything across a watercourse that is not a main river, you need written consent under section 23 of the Land Drainage Act 1991 before the works start. Doing the works first and applying afterwards is an offence.

Farmers and rural landowners meet this most often, because the ditches that cross agricultural holdings are almost all ordinary watercourses and almost none of them are shown on the drainage plans that came with the farm.

Ordinary watercourses and main rivers

Every watercourse in England falls into one of two categories, and the category decides which regulator you deal with.

A main river is one shown as such on the statutory main river map, and works in, over, under or near it need a flood risk activity permit from the Environment Agency under the environmental permitting regime. An ordinary watercourse is everything else: ditches, drains, cuts, culverts, dykes, sewers other than public sewers, and passages through which water flows that do not form part of a main river.

The main river map is published and worth checking before you assume anything. A channel can change status along its length, and the point where it becomes a main river is often nowhere near where you would expect.

Within an internal drainage board district, the board rather than the lead local flood authority exercises the consenting function for ordinary watercourses. Outside those districts it is the county council or unitary authority acting as lead local flood authority.

The works that need consent

Section 23 catches two things: erecting a mill dam, weir or other like obstruction to the flow, and erecting a culvert or altering a culvert in a way that affects the flow.

In practice that covers more than people expect.

• Piping or culverting any length of open ditch, including a short crossing for a field access.
• Installing a headwall, trash screen or outfall structure.
• Building a bridge with abutments in or beside the channel.
• Diverting or realigning a channel, even within your own land.
• Damming for irrigation storage or a fishing pond.
• Replacing an existing culvert with one of a different size or invert level.

Routine maintenance such as clearing silt, cutting vegetation or repairing a bank in the same line and level does not normally need consent, though an internal drainage board may have byelaws requiring notice. Check the byelaws for the district rather than assuming.

Ordinary discharge of surface water into a watercourse does not need section 23 consent in itself, but it is very often controlled through the drainage design and through the planning conditions attached to a drainage strategy.

Who grants it and how long it takes

Apply to the lead local flood authority, or to the internal drainage board where the site sits inside a district. Most publish an application form, a fee and a guidance note.

The application usually asks for a location plan, a cross-section and long-section of the proposed structure with invert levels, hydraulic calculations showing that the structure passes the design flow without increasing flood risk upstream or downstream, details of any trash screen and its maintenance arrangements, and the name of the riparian owner or owners affected.

Authorities normally state a determination period of around two months. Check the published procedure for the authority you are dealing with, because the fee and the timescale are set locally.

The hydraulic calculation is where applications fail. A 300mm pipe under a farm track may be adequate for the flow in the ditch today and wholly inadequate for a design storm with a climate change allowance applied. Size the structure for the design event and show the working.

Culverting and why it is resisted

National policy and drainage authority practice both start from a presumption against culverting an open watercourse.

The reasons are consistent. A culvert reduces channel capacity and creates a blockage point. It removes habitat and severs the connection between the channel and its banks. It is harder to inspect and maintain than an open channel. And a blocked culvert floods land upstream that an open ditch would have drained.

Expect to be asked to justify the length, to minimise it, to demonstrate that no reasonable alternative exists, and to provide a trash screen with a maintenance regime where the inlet is at risk of blockage. Screens introduce their own problems, and the design and access requirements are set out in trash screens, headwalls and maintenance access.

Where a scheme reduces flood risk overall, that is a material benefit in the planning balance and worth stating explicitly, as flood risk betterment as a planning benefit explains.

Riparian ownership and the duties that come with it

If a watercourse runs along or through your land you are a riparian owner, and where it forms a boundary you are presumed to own the bed up to the centre line unless the deeds say otherwise.

The duties are longstanding and are set out in government guidance on owning a watercourse. You must let water flow through your land without obstruction, pollution or diversion. You must accept flood flows through your land even where they are caused by natural events. You are responsible for maintaining the bed and banks, and for clearing debris from the channel, including debris that arrived from upstream. You must keep any structures clear and in good repair.

Two practical consequences for a rural owner. The maintenance duty is yours whether or not you created the problem, and the authority can require you to carry it out. And a buyer's solicitor will ask about it, so unconsented structures found during a sale become a price negotiation.

Sequencing the consent against planning permission

Run them in parallel, and design as if both regulators will read the same drawings.

The planning application should include the watercourse works on the layout, with the section and invert levels, and the flood risk assessment should address them directly rather than treating them as a detail for later. A council will often condition the development on land drainage consent being obtained, which is sensible, and it also means the consent sits on your critical path.

Do not assume that a planning condition discharging drainage details satisfies section 23. They are separate regimes with separate decision makers, and the drainage engineer at the lead local flood authority may be a different person from the drainage consultee on the planning application even within the same council.

Where the works involve raising ground in a floodplain, compensatory storage will be required, and the level for level method is covered in compensatory flood storage and level for level design.

Where works go ahead without consent

Carrying out section 23 works without consent is an offence, and the drainage authority can prosecute. It can also serve notice requiring the works to be removed or altered, and carry out the work itself and recover the cost if the notice is not complied with.

The more common outcome is a retrospective application. Authorities will usually accept one, and will assess it on the same hydraulic grounds as a prospective application, which means a structure that does not pass the design flow gets removed or replaced at your expense.

If you have inherited an unconsented culvert, the pragmatic route is to survey it, calculate its capacity, and approach the authority before somebody else does. A structure that performs adequately is usually regularised without much difficulty. One that does not was going to flood your neighbour eventually in any case.

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