Who can write a drainage strategy a council will accept

There is no statutory licence for the author of a drainage strategy. Nobody holds a register, and no regulation says who can write one. Working out who can write drainage strategy documents that a lead local flood authority will accept is therefore a question about competence and evidence rather than about a qualification you can look up, which is why self-builders get caught out when a document they paid for comes back unaccepted.

What the lead local flood authority actually tests is whether the person who wrote it has done the calculations properly and stood behind them.

What the lead local flood authority checks

The lead local flood authority is the county council or unitary authority for your area, and it is a statutory consultee on surface water drainage for major development. On a single house or a small scheme it may not be formally consulted at all, in which case the planning officer or the drainage engineer in the council's own team reads the document.

Either way the same things get checked. Whether the drainage hierarchy has been followed, starting with infiltration, then discharge to a watercourse, then a surface water sewer, then a combined sewer as a last resort. Whether the discharge rate has been justified against greenfield run-off rates for the site. Whether storage has been sized for the right return period with the right climate change allowance. Whether exceedance flows have somewhere to go. And whether anyone has confirmed that the outfall exists and can be used.

The last of those fails more strategies than the hydraulics do. A storage volume calculated to three decimal places means nothing if the pipe it discharges into belongs to a neighbour who has not agreed to it.

Civil engineering and hydrology competence

What a competent author looks like in practice is a civil or water engineer who does drainage design regularly. The institutional markers to look for are chartered status with the Institution of Civil Engineers or the Chartered Institution of Water and Environmental Management, which carries the Chartered Water and Environmental Manager designation.

Those are indicators rather than requirements. A chartered engineer who has not designed a soakaway in fifteen years is worse value than an experienced drainage designer who is not chartered. Ask directly about recent work. How many strategies has this person submitted to this particular lead local flood authority, and were any returned?

The documents to ask for before appointing are the professional indemnity certificate with its limit of indemnity, a named author rather than a company, and two recent examples of strategies accepted by a comparable authority. Our note on briefing a specialist so the fee stays fixed sets out how to scope the appointment so the quote covers the queries as well as the first draft.

Infiltration testing and the calculations behind it

The design standard most authorities work to for SuDS is the Defra non-statutory technical standards, read alongside the industry design guidance in the SuDS Manual. For soakaways, infiltration testing follows the method in the relevant BRE digest, and the test matters more than the model.

A strategy that assumes an infiltration rate without testing is a strategy that will be queried. Proper testing means trial pits at the depth and position of the proposed soakaway, three fillings of each pit, the rate taken from the slowest, and groundwater level recorded. On a clay site the honest result is often that infiltration does not work, and saying so early saves a wasted redesign.

For climate change, use the Environment Agency's current allowances for peak rainfall intensity, selecting the figure for the right management catchment, the right epoch and the development's design life. Those allowances have been revised, so a figure copied from an older report is a reason for rejection on its own. State the allowance used and where it came from.

Where the site sits in flood zone 2 or 3, or is a hectare or more, the drainage work sits inside a Flood Risk Assessment rather than standing alone, and the two documents have to agree on levels and on run-off destinations.

Who takes responsibility for the outfall

The outfall is where responsibility becomes personal. Three positions come up.

Discharge to a watercourse usually needs land drainage consent from the lead local flood authority, or an environmental permit from the Environment Agency where the watercourse is a main river. That consent is separate from planning permission and takes its own time.

Discharge to a public sewer engages the right to connect under section 106 of the Water Industry Act 1991, exercised through the undertaker's own process. The undertaker can impose conditions about the point and manner of connection, and on a constrained network it may require attenuation or refuse a surface water connection outright.

Discharge across third-party land needs an easement, and that is a conveyancing matter your engineer cannot solve. Flag it the moment the strategy proposes it.

A competent author will say in the document which of these applies, what evidence exists that the route is available, and what has not yet been confirmed. A drafting that leaves the outfall vague is a drafting that transfers the risk to you.

Working with the sewerage undertaker

Submit a pre-development enquiry to the water and sewerage undertaker before the strategy is finalised, not after. The response tells you whether capacity exists, what the undertaker will accept, and whether a foul connection needs upgrading.

Foul drainage is a separate question from surface water and is frequently forgotten on small schemes. A Foul Sewage Assessment deals with it, and on sites with no sewer connection it has to address a package treatment plant or septic tank against the general binding rules, which is a regulatory regime in its own right.

Keep the correspondence. An undertaker's written response is the strongest evidence you can put in front of a drainage officer, and it is far more persuasive than an engineer's assumption about capacity.

Adoption, maintenance and what happens in year 20

A lead local flood authority will ask who maintains the system for its design life and how that is funded. On a single self-build the answer is the householder, and a short maintenance schedule in the strategy is enough. On anything larger the question is real.

Options are adoption by the sewerage undertaker under section 104 of the Water Industry Act 1991 for elements that meet the sector's design and construction requirements, adoption by the highway authority for highway drainage, a management company funded by estate charges, or a planning obligation securing maintenance. Schedule 3 to the Flood and Water Management Act 2010, which would create a SuDS approving body and a separate approval regime, has not been brought into force in England, so adoption still runs through these existing routes. Check whether that has changed before relying on either position.

The practical test of a good strategy is whether a maintenance contractor could follow it in twenty years. Named components, access points, inspection frequencies and expected tasks, with a drawing.

Getting the scope of works right

Most disputes about a drainage strategy are disputes about scope. Write the scope so it includes the parts that generate the arguments.

• Infiltration testing to the relevant BRE method, with the number and depth of trial pits stated
• A pre-development enquiry to the sewerage undertaker, and the cost of it
• Greenfield run-off calculation with the method named
• Storage sizing for the stated return periods and the current climate change allowance
• Exceedance routing and a plan showing where water goes when the system is full
• A maintenance schedule and, where relevant, an adoption strategy
• Response to the first round of lead local flood authority queries included in the fee
• A named author, their professional indemnity limit and the reliance position

That last point matters when a buyer's solicitor asks for a reliance letter. Our piece on reliance letters and collateral warranties for planning reports explains what you can reasonably ask for.

You can draft the surrounding planning documents and a first-pass Drainage Strategy structure on PlanScope, then hand it to your engineer to complete with the tested figures and send for professional review through the professional directory. Councils expect a suitably qualified author for drainage work, so treat the draft as the frame rather than the finished document. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

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