Checklist: submission for discharging a drainage condition

Most applications to discharge drainage condition requirements fail on the same thing: the submission answers the drainage question rather than the condition. The condition is a legal document with specific limbs, and the lead local flood authority will check each one. If the condition asks for a maintenance schedule and you send calculations, it does not matter how good the calculations are.

Start by printing the condition and marking each requirement in the margin. Everything below hangs off that list.

Reading what the condition actually requires

Take the wording apart and produce a list of deliverables, each mapped to a document in your submission.

A typical surface water condition asks for a detailed scheme, calculations demonstrating a stated discharge rate, details of any attenuation, evidence of the outfall agreement, a maintenance and management regime for the lifetime of the development, and confirmation that the scheme is implemented before occupation. That is six deliverables, and a covering letter that addresses them in the order the condition lists them makes the consultee's job trivial.

Note the trigger point as well. A condition requiring approval before development starts is different from one requiring approval before above-ground works, and the first one catches site clearance. Where the trigger is already past, say so and explain the position rather than hoping nobody checks the commencement date.

Check whether the condition names a standard or a document. Conditions frequently require the scheme to accord with a specific drainage strategy submitted with the application, or with the non-statutory technical standards for sustainable drainage, and a scheme that departs from the referenced document needs that departure explained.

Calculations and model outputs

The calculations are the core, and they need to be readable by somebody who did not build the model.

Provide the greenfield runoff rate with its derivation, the proposed discharge rate and the justification for it, the storage volume required, and the results for the design events the condition or the strategy requires, normally including the one in 100 year event with the appropriate climate change allowance applied. State the climate change allowance you have used, the river basin district and epoch it comes from, and the date you checked it, because the Environment Agency allowances are revised and an out-of-date figure invalidates the whole model.

Include the model inputs, not just the summary. Catchment areas with a plan showing how they were derived, impermeability factors, infiltration test results with the method and the location of each test, time of entry, and any half-drain-down assumptions.

Where infiltration has been assumed, the test results have to support it. Tests carried out in summer in a dry year, at depths above the winter water table, are the most common reason a soakaway design is rejected. Give the groundwater monitoring data if you have it.

Drawings and levels

Drawings carry more weight than the report, because they are what gets built.

The set normally needs a drainage layout at a scale where pipe runs, manholes and structures are legible, with invert and cover levels on every node. A longitudinal section through the main run. Details of the attenuation structure, the flow control device with its make, type and design flow, and the outfall arrangement including any headwall or non-return valve. Finished floor levels and external levels shown against existing ground. And a plan showing the exceedance routes.

Two frequent omissions. The flow control device is often shown as a generic symbol with no type or setting, which means the consultee cannot check that the discharge rate is achievable. And levels are often given for the new works but not tied to the existing outfall, leaving no evidence that the system will drain by gravity.

Maintenance and adoption arrangements

This is the limb most often left thin, and it is the one lead local flood authorities examine hardest, because a system nobody maintains stops working within a decade.

The submission should name who will own each element, who will maintain it, what each maintenance task is, how often it is done, and how the arrangement is funded for the lifetime of the development. Set it out as a table by component: gullies, filter drains, permeable paving, swales, basins, tanks, flow controls, headwalls and outfalls each have different regimes.

Then evidence the mechanism. Adoption by the sewerage undertaker under the current design and construction guidance requires the design to meet that guidance from the outset, so retro-fitting adoptability at discharge stage rarely works. A management company needs to exist, with a deed, a service charge and a sinking fund. Highway adoption of any element within the highway needs a section 38 agreement in progress.

Bear in mind that Schedule 3 to the Flood and Water Management Act 2010, which would introduce a separate SuDS approval body in England, has not been brought into force, so approval still runs through planning. Check the current position, because the government has kept it under review.

Exceedance routing evidence

Exceedance is what happens when the design event is exceeded or the system blocks, and it is assessed increasingly often as a discharge requirement rather than a design nicety.

What the consultee wants to see: a plan with arrows showing where water goes once the system is full, evidence that flow is directed away from buildings and towards a safe area, finished floor levels set above the exceedance flood level with a stated freeboard, and confirmation that exceedance flow does not pass onto third party land or into a neighbouring property.

Where the site slopes towards existing houses, this is the limb that will hold up the discharge. Deal with it through level design and landscape features rather than a note saying that exceedance has been considered. The wider flood context sits in the Flood Risk Assessment submitted with the application, and the two documents should agree on levels.

Consultee sign-off expected

Work out who has to say yes before you submit.

On most sites the lead local flood authority is the technical consultee, and it is a county or unitary authority function rather than a district one. The sewerage undertaker comments where the discharge is to a public sewer and will want to see the connection agreement or at least the application for one under section 106 of the Water Industry Act 1991. The Environment Agency comments where the outfall is to a main river or where groundwater is a concern. The highway authority comments on anything draining or discharging within the highway.

Send the package to the technical consultee at the same time as you submit to the council, with a short note. The statutory clock runs against the council, and the council is usually waiting for the consultee.

Timing against commencement

Build the discharge into the programme as a critical path item, not an administrative task.

The determination period for a discharge application is eight weeks, and a consultee round inside that leaves little margin. Section 74A of the Town and Country Planning Act 1990 provides a deemed discharge procedure for certain conditions where the authority does not respond in time, but drainage conditions are frequently outside its scope and it requires its own notice procedure, so do not plan around it.

Submit at least twelve weeks before you need to start, and expect at least one round of comments. A Drainage Strategy prepared to discharge standard at application stage, rather than to outline standard, is what compresses this period, and it is usually worth the extra fee at the front end.

Where partial discharge is possible

Conditions with multiple limbs can sometimes be discharged in part, and authorities will often confirm that limbs (a) to (c) are satisfied while (d) remains outstanding.

Ask for it explicitly. A letter saying which limbs you consider satisfied, with the evidence for each, gives the officer something to confirm in writing. That partial confirmation is what lets you start groundworks while the maintenance deed is being finalised by solicitors.

What does not work is treating silence as approval, or starting on the basis that the outstanding limb is minor. A breach of a pre-commencement condition can render the whole development unauthorised, and the enforcement exposure is long. Keep the written trail, including the officer's email confirming partial discharge, with the rest of the construction environmental management documentation. You can see the full set of 66 report types by category when scoping what else the site needs.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional 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.