Land drainage consent for discharging to a watercourse

If your drainage design ends at a ditch, stream or brook rather than at a sewer, you probably need land drainage consent for the watercourse before you build the outfall. Consent under section 23 of the Land Drainage Act 1991 is required for works that obstruct or alter the flow of an ordinary watercourse, including culverts, and most authorities treat a new outfall structure in the bank as falling within it. It is a separate consent from planning permission, it is granted by a different body, and a planning permission does not authorise the works.

Ordinary watercourse against main river

The first question is which watercourse you are discharging to, because it decides who you apply to. A main river is one shown as such on the Environment Agency's main river map. Everything else that carries water, including ditches, brooks, dykes, sewers other than public sewers and passages through which water flows, is an ordinary watercourse.

Works in, over or near a main river need a flood risk activity permit from the Environment Agency under the environmental permitting regime. Works in an ordinary watercourse need land drainage consent instead. The two regimes have different application forms, different fees and different timescales, and the boundary between them is a line on a map that does not always match what the channel looks like on the ground.

Check the map before you design the outfall. A stream that looks like a ditch for a kilometre can be designated main river along the stretch where your site sits.

Who grants the consent

For ordinary watercourses the consenting body is the lead local flood authority, which is the county council or the unitary authority, under powers that moved to it following the Flood and Water Management Act 2010. Inside an internal drainage district the internal drainage board consents instead, and its byelaws usually add requirements of their own.

The lead local flood authority is often also the statutory consultee on surface water drainage for major planning applications. Those are separate functions carried out by the same team, so a scheme that satisfies the drainage consultation can still be refused consent for the structure, and the reverse happens too.

Ask early which officer handles consents, because it is frequently not the person commenting on your application.

What works trigger a consent

The statutory trigger is the erection or alteration of a mill dam, weir or other like obstruction to the flow, or the erection or alteration of a culvert, in an ordinary watercourse. In practice authorities apply it to a list of works that is broader than those words suggest.

• A new piped outfall or headwall in the bank
• Culverting a length of open channel, including for an access crossing
• A bridge or crossing with abutments in the channel
• A flow control structure, penstock or trash screen
• Temporary works such as a dam or over-pumping arrangement during construction
• Realignment or regrading of the channel

Discharging water into the channel is not itself the thing being consented. The structure that delivers it is. But the discharge rate matters to the decision, because the authority will refuse a structure that passes more water than the channel can take, and it will look at whether the discharge would increase flood risk downstream.

Where the discharge could be polluting rather than clean surface water, a separate environmental permit may also be needed. That is a water quality question for the Environment Agency, distinct from both consents above.

Information the application needs

A consent application that goes through first time usually contains a location plan with the watercourse named and the structure positioned, a detailed drawing of the structure with invert levels, bed level and bank levels, the design discharge rates for the relevant return periods, the hydraulic calculations behind the flow control, and a construction method statement covering access, working in the channel and sediment control.

Add the maintenance arrangements. Who owns the structure, who clears the screen, and how is it reached. Authorities refuse outfalls with trash screens that nobody can get to, and they are right to.

The drainage case for the development sits alongside this in a Drainage Strategy, and where the site is in Flood Zone 2 or 3, or exceeds one hectare, a Flood Risk Assessment is also needed. Outfall detailing itself is a design exercise in its own right, as our note on outfall design, bank stability and scour protection sets out.

Timescales against the planning programme

The statutory determination period for a land drainage consent is two months from a valid application. Some authorities take the view that consent is deemed granted if they fail to determine within the period, but programming on that basis is unwise, and a deemed consent gives you nothing in writing to show a contractor or a funder.

The sequencing error that costs the most time is leaving the consent until after planning permission. If the authority will not consent the structure as designed, the drainage layout changes, and if the layout changes materially the planning permission may need a variation. Submit the consent application in parallel with the planning application, or at least share the outfall design with the consenting officer before the application goes in.

Construction works in the channel also have seasonal constraints for fish and for protected species such as water vole and otter, which can push a two-week job into the following spring. The consents that bite during construction are set out in our note on construction dewatering.

Easements where the outfall crosses other land

Consent from the drainage authority is a public law permission. It gives you no right to cross anybody's land, and this is where schemes stall.

If the pipe run from your site to the watercourse crosses a neighbour's land, you need an easement or a deed of grant from that owner, negotiated and registered. If the watercourse bank is in third party ownership, you need their consent to build the headwall. The general rule is that riparian ownership extends to the centre line of the channel where it forms a boundary, so an outfall in the bank usually sits on the neighbour's land as well as yours.

A riparian owner downstream also has rights. The general position is that an owner is entitled to receive the flow in its natural quantity and quality, so a materially increased discharge can give rise to a private claim even where the drainage authority has consented the structure. Attenuating to the agreed rate protects you here as well as satisfying policy.

Enforcement for unconsented works

Where works are carried out without consent, the drainage authority can require them to be altered or removed, and carrying out works without the necessary consent is an offence under the Act. Authorities do use these powers, particularly for culverts installed to gain more usable garden or yard space.

The practical consequence for a developer is worse than the penalty. An unconsented outfall is a defect on title that shows up on a sale, and retrospective consent is not always available if the structure would not have been approved in the first place. Removing and rebuilding an outfall after the surfacing is down is expensive and avoidable.

If you have inherited unconsented works, approach the authority and ask what it needs to regularise them. The usual outcome is a retrospective application with a survey of the as-built structure, and sometimes a requirement to improve the screen or the scour protection.

This is general guidance, not legal advice. Check the position with the lead local flood authority, the internal drainage board or a qualified professional before relying on it.

To see which drainage and flood documents your site is likely to need, enter your postcode on PlanScope and answer the questions about the watercourse and the constraints.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.