Ordinary Watercourse Consent (OWC) Explained

Ordinary Watercourse Consent (OWC) is the written permission you need under Section 23 of the Land Drainage Act 1991 before carrying out any work that could obstruct or alter the flow of an ordinary watercourse — a stream, ditch, culvert or other waterway that isn’t a designated Main River. The Flood and Water Management Act 2010 transferred responsibility for granting OWC to Lead Local Flood Authorities (LLFAs), so in most areas that means applying to your county or unitary council rather than the Environment Agency. Some LLFAs — Surrey County Council among them — call the same permission a “flood defence consent” rather than OWC; it’s the identical consent under the identical section of the Act, just different house terminology. The Act extends to England and Wales, so the same consenting principle applies there too, though day-to-day administration sits with the relevant Welsh unitary authority rather than an English LLFA.

Get it wrong and the risk isn’t just a fine — the LLFA can require unauthorised work to be removed entirely at your own expense, with no route to consent it retrospectively.

What does OWC stand for?

OWC stands for Ordinary Watercourse Consent. It’s the term used across UK planning, construction and civil engineering for the Land Drainage Act permission required before altering an ordinary watercourse — as distinct from a Flood Risk Activity Permit (FRAP), the equivalent permission the Environment Agency issues for work on a designated Main River. If a drawing or planning condition refers to “OWC”, it means this consent, not a FRAP.

Why is OWC needed?

OWC exists so that changes to a watercourse don’t create problems for people downstream or for the environment. In practice, it covers four things:

• Flood risk. Modifications must not increase flood risk to surrounding land or property.
• The environment. Protects habitats, aquatic ecosystems and water quality.
• Compliance. Avoids enforcement action, fines or a requirement to reverse unauthorised works.
• Infrastructure. Keeps roads, bridges and embankments stable by controlling water flow around them.

When do you need ordinary watercourse consent?

Section 23(1) of the Land Drainage Act is precise about what triggers consent. You need it before you:

• Erect an obstruction. A mill dam, weir or “other like obstruction” to the flow of an ordinary watercourse, or raising or otherwise altering one.
• Erect a culvert in an ordinary watercourse.
• Alter a culvert in a way that would be likely to affect the flow.

In practice, that covers the works most projects actually propose: a new culvert to carry water under a road or access track, a bridge, outfall or pipe crossing, realigning or widening a channel, and temporary works such as diversions or cofferdams during construction. Consent can be given subject to reasonable conditions — the LLFA isn’t limited to a straight yes or no.

Even where planning permission has already been granted, OWC is a separate approval that must be in place before work starts — one doesn’t imply the other, and a live planning permission is not a defence if the watercourse works go ahead unconsented.

Is a ditch or drain a watercourse?

Usually, yes. An ordinary watercourse is any channel through which water flows — a river, stream, brook, ditch, drain, leat or culvert — whether it’s natural or artificial, permanent or dry for long periods. Government guidance on owning a watercourse (updated February 2026) draws the line the same way: a channel that only fills during a flood, and is otherwise dry, is not a watercourse. If you’re not sure whether a feature on your site counts, check the Environment Agency’s Main River Map to rule out a Main River, then ask your LLFA — filling in or diverting what turns out to be a watercourse without consent is treated the same as any other unauthorised works.

How to apply for OWC

The process has five stages, and the third — preparing the application — is where most of the real work sits:

1. Confirm the watercourse is “ordinary”. Check the Environment Agency’s Main River Map. If it’s a Main River, you need a FRAP instead.
2. Contact the right authority — before you apply, not after. That’s usually your LLFA, though in some low-lying areas an Internal Drainage Board (IDB) holds the consenting role instead. Most LLFAs actively encourage a pre-application call: several publish a direct phone line specifically so they can tell you whether consent is needed at all, or flag problems before you’ve drawn anything up. It’s free, and it routinely saves a redesign later.
3. Prepare the application. This is the part that actually takes time, and it’s more than a form — see the document checklist below.
4. Submit and pay. The statutory default fee is £50 per structure, though the Act allows this to be varied by order, so it’s worth confirming the current figure with your LLFA — a scheme with three culverts needs three separate consents and three fees, though most authorities will process them under one application if they’re on the same watercourse.
5. Wait for a decision. The Act gives the LLFA up to two months to decide, but that clock starts from whichever is later: the day you submit the application, or the day your fee payment clears. If the LLFA doesn’t notify you of a decision within that window, consent is treated as automatically granted. It’s still worth chasing a written decision rather than relying on the default, particularly if a lender or building control inspector will want to see it.

A typical submission needs:

• A location plan based on an Ordnance Survey base, showing the site and the watercourse in its wider context.
• A site plan showing the existing watercourse, the proposed works, and any other structures affecting local hydraulics — bridges, pipes, culverts, screens, embankments, outfalls — plus any existing fish passes.
• Cross sections upstream and downstream of the works, and a longitudinal section along the watercourse’s centre line, showing existing and proposed bed and water levels referenced to Ordnance Datum.
• Hydraulic calculations comparing pre- and post-development flow, so the LLFA can see the works won’t increase flood risk upstream or downstream.
• A method statement covering construction technique, timing, and pollution-prevention measures — a separate consent may be needed for temporary works (cofferdams, temporary diversions) that don’t form part of the permanent structure.
• A maintenance statement setting out who is responsible for maintaining the structure, both during construction and once it’s finished.
• An environmental appraisal where the site is near a protected habitat — several LLFAs have a statutory duty under the Habitats Regulations to confirm the works won’t harm a Site of Special Scientific Interest, Special Area of Conservation, Special Protection Area, Ramsar site or Scheduled Ancient Monument before they can grant consent.

Timing matters too: if the watercourse supports salmonid fish or other protected species, expect a condition restricting when the in-channel work itself can happen, to avoid the spawning season.

In our experience, the £50 fee is rarely the real cost of an application. The hydraulic modelling, the cross sections and the method statement behind it are what take the time and the expertise — and what an LLFA actually scrutinises when deciding whether to grant, condition or refuse consent.

Does consent expire, and who maintains the structure afterwards?

Consent isn’t indefinite. Many LLFAs attach a standard condition — commonly around three years — requiring works to start within that window, after which the consent lapses and has to be reapplied for. The application itself has to name who is responsible for maintaining the structure both while it’s being built and once it’s finished, so this isn’t something to leave vague: an unmaintained culvert or headwall that later blocks and causes flooding is exactly the kind of problem OWC exists to prevent, and it can trigger enforcement long after the original works were signed off. If a site changes hands, check what the consent says about who inherits that maintenance duty — it sits alongside, not instead of, the riparian ownership responsibilities that come with the land.

What if the LLFA refuses, or won’t decide?

The Act is explicit that consent “is not to be unreasonably withheld.” If you think it has been — a flat refusal, or conditions that go beyond what’s reasonable — Section 23(5) gives you a specific route: the dispute is referred to a single arbitrator, agreed between you and the LLFA or, if you can’t agree, appointed by the President of the Institution of Civil Engineers. It’s arbitration, not a planning-style appeal, and it’s a mechanism most guidance on this topic — including some professional flood-risk sites — doesn’t mention at all. In most cases it’s faster and cheaper to revise the application to meet the LLFA’s stated concerns, but the arbitration route exists if a refusal genuinely looks unreasonable.

What happens if you don’t get consent?

Carrying out work on an ordinary watercourse without consent is treated as a nuisance under Section 24 of the Land Drainage Act, and the drainage board can serve a notice requiring you to put it right within a set period. In practice, LLFAs tend to escalate: an advice letter first, then a formal warning, then an enforcement notice, and — if that’s ignored — direct remedial action with the cost recharged to you, alongside possible prosecution.

Critically, there’s no route to consent retrospectively. Work already carried out can’t be regularised after the fact — the LLFA’s only tools are enforcement and remediation. If you’re regularising development more broadly through a retrospective planning application, unconsented watercourse works is one of the few problems planning permission alone cannot fix.

A small number of works are exempt from Section 23 altogether: anything under the control of a navigation, harbour or conservancy authority, and works carried out under another Act or an order with the force of one — nationally significant infrastructure projects are sometimes granted a Development Consent Order that specifically disapplies Section 23 for that scheme. These are edge cases; assume consent is needed unless your project falls squarely into one of them.

Which activities need consent — and which don’t?

Not every structure near a watercourse counts as an obstruction. As a general guide:

• A culvert — including extending or removing one.
• A trash screen fitted to a culvert that could restrict flow.
• A pipe crossing the watercourse within the channel.
• A weir or dam.
• A bridge or decking where the underside sits below the top of the bank, or where the supports narrow the flow width.

Usually doesn’t need consent:

• Bank protection works.
• A pipe crossing above the bank, or laid below the bed.
• A pipe outfall that protrudes into the channel without restricting flow.
• A clear-span bridge with no supports in the channel.

That split is a general guide, not a substitute for a site-specific check — some “usually doesn’t” items still need consent if they’re temporary works during construction, and several LLFAs, including Derbyshire County Council, publish detailed cross-section diagrams of consentable and non-consentable activities that are worth checking against your specific design before you assume either way.

OWC vs FRAP: what’s the difference?

Both regulate work on a watercourse, but which one applies depends entirely on how that watercourse is classified.

Other permissions to check

A few things sit alongside OWC and catch people out:

• Protected sites and species. Work within 2km of a Site of Special Scientific Interest may need input from Natural England, and protected species such as water voles, otters or nesting birds can trigger a separate wildlife licence.
• Landowner permission. Where land ownership is shared, get agreement from every owner before starting — this sits alongside, not instead of, riparian ownership responsibilities for the stretch you own.
• Culverting. Risk management authorities are reluctant to consent new culverts at all, because they tend to increase flood risk and damage the watercourse environment — don’t assume it’s a formality.

OWC and planning permission are two separate hurdles, and clearing one doesn’t clear the other. If your project touches a Main River rather than an ordinary watercourse, you’ll need a FRAP instead. For help working out which consent applies to your site, or with the flood risk assessment or drainage strategy that usually sits alongside it, Unda’s team can help — or start a quote for a free, no-obligation assessment of what your project needs.