Discharging a drainage strategy condition

A surface water drainage condition is normally a condition precedent, which means no development may start until the details have been approved in writing. Starting anyway does not simply risk enforcement. Works carried out in breach of a condition precedent may not count as lawful implementation at all, so a permission approaching the end of its three year life can expire while the site looks busy.

Allow ten to twelve weeks from submission to approval, and build that into the programme rather than discovering it when the groundworker is mobilised.

What the condition usually asks for

Read the condition word for word before assembling anything, because the wording controls the scope.

Most surface water conditions require a detailed design, prepared in accordance with the approved strategy, to be submitted to and approved in writing by the local planning authority before development starts, with the works then carried out as approved. Many add a second limb requiring a maintenance and management plan, and a third requiring a verification report before occupation.

Three drafting details change the work. Whether the condition says "in accordance with the approved Drainage Strategy" and names it, because that document then sets the parameters you must meet. Whether it is phrased by phase or for the whole site, since a whole-site condition means phase one cannot start until phase four is designed. And whether the condition requires consultation with the lead local flood authority, which affects both the timescale and whether the deemed discharge provisions are available.

The document set that answers it

Submit one complete package rather than sending material in instalments. Officers process a complete submission far faster than a growing pile.

• Detailed drainage layout drawings showing pipe runs, sizes, gradients, invert and cover levels, manhole schedule, flow control location and the outfall.
• The hydraulic model output for the design events, normally the 1 in 1, the 1 in 30 and the 1 in 100 annual probability events with the climate change allowance applied, together with the model input file if the authority asks for it.
• The discharge rate calculation, showing the method, the site area used and any minimum rate applied.
• Infiltration testing results with trial pit logs and groundwater observations where infiltration forms part of the design.
• An exceedance flow routing plan showing where water goes when the design event is exceeded, with finished floor levels and site levels annotated.
• Flow control device details, including the manufacturer's data and the design orifice or outlet size.
• The treatment train for water quality, with the components and the indices used.
• A maintenance and management plan with responsibilities, frequencies and access arrangements.
• Copies of third-party consents or applications in progress.

Cross-reference each item to the part of the condition it answers. A one-page covering schedule that maps document to requirement saves a round of correspondence and signals that the submission is complete.

The calculations the authority will re-run

Lead local flood authority engineers check a predictable list, and knowing it lets you pre-empt every query.

They will check that the discharge rate matches the one approved at application stage, and that the derivation is stated rather than asserted. They will check the climate change allowance against the current Environment Agency figures for the river basin district and the relevant epoch. They will check that an urban creep allowance has been applied to private curtilage areas on residential schemes. They will check the storage volume against the critical duration rather than against a single assumed storm. They will check half drain down time, since a system that does not empty in good time has no capacity for the next event. And they will check freeboard to finished floor levels and to the top of any basin.

Where any of these differs from the strategy approved with the permission, say so openly and explain why. A change made because the infiltration testing came back differently is a reasonable change. The same change discovered by the engineer in a spreadsheet is a refusal.

Keep the numbers consistent with everything else in the file. Officers compare the submission against the Drainage Strategy and against the Flood Risk Assessment, and inconsistent climate change allowances between the two are one of the commonest reasons for a holding response.

Maintenance, adoption and third party consents

The maintenance answer is the part most likely to be treated as an afterthought and the part the authority cares about most, because it is the one that determines whether the system still works in 30 years.

State who owns each component, who maintains it, at what frequency, and how the funding works. Where a management company is responsible, say how it is funded and whether the obligation is secured in the transfer documents. Where the sewerage undertaker will adopt, provide the agreement reference or the current status of the application. Where the highway authority adopts part of the network, set out the boundary.

Third-party consents are the other frequent gap. A connection to a public sewer needs the undertaker's agreement. A discharge to an ordinary watercourse needs consent from the lead local flood authority under section 23 of the Land Drainage Act 1991. A discharge to a main river or works in its vicinity engages the Environment Agency's permitting regime. And an outfall crossing third-party land needs an easement.

You do not always need the consent in hand to discharge the planning condition, but you do need to show the position, because an approved design that cannot be built is no use to anybody.

Why submissions get refused

Five reasons account for most refusals and holding responses.

Where a submission is refused, the authority is not required to grant you a second attempt within the same fee. A resubmission is a fresh application with a fresh fee and a fresh determination period, which is the real cost of an incomplete first go.

Timing against the start on site

The determination period for an application to approve details reserved by condition is normally eight weeks, and authorities consult the lead local flood authority within that window. In practice the consultee response arrives late in the period, so a first-time approval at eight weeks is a good outcome and ten to twelve weeks is more realistic.

There is a deemed discharge mechanism in section 74A of the Town and Country Planning Act 1990 for certain conditions, operated by serving a notice, but the exclusions are wide and conditions requiring consultation with a statutory consultee are often outside it. Check whether the route is available for your condition before relying on it.

The consequence of starting early is the one to keep in front of the client. Works carried out in breach of a condition precedent may not amount to a lawful start, which can mean the permission was never implemented and can expire. Site clearance and ground investigation are usually safe, but anything that constitutes a material operation is not. Where the programme is tight, ask the authority for a partial discharge covering the first phase rather than starting on hope.

Verification after construction

The verification condition is the one people forget until a purchaser's solicitor asks about it at the point of sale.

Build the evidence as you construct rather than reconstructing it afterwards. Photograph each stage of the attenuation installation with a scale and a date. Record the flow control device installed, with its serial number and the orifice size, and keep the delivery documentation. Survey the as-built invert and cover levels rather than assuming the design levels were achieved. Carry out CCTV survey of the adoptable network and keep the report. Where infiltration features were built, record the ground conditions actually encountered.

The verification report then states what was built, confirms it matches the approved design, explains any departure and includes the handover pack for whoever will maintain it. Where the design relied on assumptions about groundwater, the notes on groundwater flooding evidence and how to assess it set out what a reviewer will expect to see confirmed. And where storage credit was claimed for reuse, the question of whether rainwater harvesting counts as attenuation has to be answered again at verification, with the installed volumes.

Enter your postcode on PlanScope to see which reports a site with drainage conditions is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority and lead local flood authority before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.