Internal drainage board districts and drainage rates

If your land sits inside an internal drainage board district, internal drainage board consent is a separate permission from planning permission, and no planning condition can deliver it for you. The board controls works in, over, under or near the watercourses it maintains, it sets the rate at which you may discharge surface water into its system, and it raises money from the land through drainage rates or through a special levy collected by the district council. None of that shows up on a standard planning search unless you go looking.

Boards exist where drainage needs active management rather than gravity alone. The Fens, the Somerset Levels and Moors, the Humberhead Levels, the Lincolnshire and Norfolk marshes, the Kent and Sussex levels, parts of Shropshire and the Vale of York are the obvious clusters. Outside those districts the same statutory functions for ordinary watercourses sit with the lead local flood authority, usually the county or unitary council.

What a board does and how to find out whether you are in one

Boards are constituted under the Land Drainage Act 1991 and are risk management authorities under section 6 of the Flood and Water Management Act 2010. Within its district a board maintains a network of drains, channels, pumping stations, sluices and outfalls, and it holds the powers over ordinary watercourses that would otherwise sit with the lead local flood authority.

Two questions need answering at the start of a project.

1. Is the site inside a board district. District boundaries follow drainage catchments rather than parish or district council boundaries, and they are published by the boards and their consortia.
2. Is any watercourse on or near the site board-maintained. A board maintains some channels and not others, and the ones it does not maintain are still ordinary watercourses subject to consent, just with a different consenting body and no byelaw distance.

Ask the board directly, in writing, and keep the reply. A one-line email confirming that the ditch along the northern boundary is a board-maintained drain saves an argument later.

Consent for works affecting a board maintained watercourse

Section 23 of the Land Drainage Act 1991 makes it an offence to erect a mill dam, weir or other obstruction in an ordinary watercourse, or to alter or replace a culvert, without consent. Inside a district, the board grants that consent instead of the lead local flood authority, and the position is otherwise similar to the one set out in our note on land drainage consent for works to an ordinary watercourse.

The works that need consent are wider than most applicants assume:

• Piping or culverting a ditch to create an access or to gain developable width.
• A new or replaced headwall, outfall or flap valve.
• A bridge or vehicle crossing, including a temporary construction crossing.
• Diverting a channel, even a few metres.
• A new surface water discharge into a board drain.

Boards resist culverting as a matter of policy, because a piped length is harder to maintain and reduces conveyance. If the scheme depends on culverting 40 metres of ditch for a farm access, expect to justify the length, the pipe diameter, the hydraulic capacity and how the pipe will be cleaned.

Byelaw distances and access

Byelaws made under section 66 of the 1991 Act give boards a further layer of control near their channels. Most boards apply a byelaw requiring their consent for any works, structure, planting or excavation within a set distance of the top of the bank of a board-maintained watercourse. Nine metres is the common figure, but it is set board by board, so read the byelaws that apply to your district rather than assuming.

Inside that strip the board is protecting maintenance access. It wants a working width for a long-reach excavator, somewhere to place the spoil that comes out of the channel, and a route for plant to reach the length being cleaned. A boundary fence, a row of new trees, a soakaway or a foundation inside the strip all interfere with that, and a board will refuse rather than negotiate where the alternative is available on the applicant's own land.

This is where site layout and the planning application collide. If you draw a housing layout or a farm building hard against a board drain and only discover the byelaw distance after the permission is granted, you lose plots or you redesign. Establish the strip first and draw the development behind it. Then the Drainage Strategy submitted with the application can show the maintenance strip as a constraint, which is exactly what a lead local flood authority consultee wants to see.

Drainage rates and the special levy

A board's income comes from the land it drains, in two streams set by the Land Drainage Act 1991.

The consequence for a rural owner is that developing agricultural land changes which stream applies. Land that leaves agricultural occupation usually drops out of drainage rates and falls into the levy pool instead. Do not assume the annual cost simply disappears. Boards also commonly seek a one-off surface water development contribution where a new or increased discharge is made into their system, calculated from the additional impermeable area or the additional volume. Rates and contribution formulas are set annually, so ask the board for the current schedule rather than working from a figure quoted in an old report.

Discharge rates and what a board will accept

Boards are usually stricter than the national position on surface water discharge, because their systems are pumped and every extra litre costs electricity and capacity downstream.

In practice that means a greenfield or better discharge rate, attenuation storage sized for the appropriate return period with a climate change allowance applied, and a restriction device the board can inspect. Some boards set a maximum discharge per hectare for their district and publish it. Some require a betterment against the existing rate where the site already drains to their system.

Before committing to an outfall, test whether the site can drain any other way. Infiltration is often impossible in fen and levels soils with a high water table, and that finding belongs in the submitted evidence rather than in a consultant's memory. A Flood Risk Assessment on a site inside a board district should describe the board's system, its design standard and its residual risk, and should avoid overstating the mapped surface water picture in the way our piece on reading the surface water flood risk map describes.

Getting the consent in the programme

Board consent is not a planning matter, so the planning authority will grant permission without it and a condition will not create it. That splits the programme into two tracks that have to be managed together.

Start the board conversation at the same time as the pre-application discussion with the planning authority. Boards are small organisations whose members meet periodically, and an application that misses one meeting waits for the next, so ask the board at the outset how often it determines applications and what it needs to see. Expect to supply a plan showing the watercourse and the byelaw strip, a section through any proposed crossing or outfall, the hydraulic calculations behind the discharge rate, and a maintenance proposal naming who will be responsible in 20 years.

One honest uncertainty. Boards vary a great deal in how they operate, what they charge and how quickly they respond, far more than lead local flood authorities do, and there is no single national procedure to point you at. The board's own published byelaws, policy statement and fee schedule are the authority on its own district, and any article that tells you the answer without naming your board is guessing.

Illustrative example

A landowner in a fen district wants a general purpose agricultural building on the corner of a field bounded on two sides by board-maintained drains. The byelaw strip removes the corner. Moving the building 12 metres into the field puts it outside both strips, keeps the existing field access, and lets roof water discharge to a shallow swale rather than straight to the drain, which avoids a new outfall and the consent that goes with it. The board confirms in writing that no consent is needed for the revised position. This example is illustrative, and the distances and the board's response on any real site depend on that board's byelaws.

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

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