Croydon drainage strategy and SuDS requirements
When Croydon expects a drainage strategy, which forms to use and what the calculations and drawings need to cover.
The short version
A major scheme with surface-water drainage implications needs a drainage strategy for Croydon's Lead Local Flood Authority. Submit the council's drainage checklist and the London SuDS Proforma with it. For a minor or unusual scheme, check the validation list or ask the council to confirm the scope.
- Planning trigger
- Major development with drainage implications
- Required forms
- Croydon checklist and London SuDS Proforma
- Design focus
- Hierarchy, storage, exceedance and maintenance
Use this as a starting point. Check the current validation list and the particular flood and drainage constraints on your site before submitting.
Start by confirming what the council asks for and which flood-risk tests apply to the site. Then use the document list and technical checks to set the scope. Further down, we look at the drainage conditions and refusal reasons found in the borough's decision notices.
When is a drainage strategy or FRA needed?
| Project situation | What to do | Status |
|---|---|---|
| Major development with surface-water implications | Submit a surface-water drainage strategy for Lead Local Flood Authority review. | Required |
| Major planning application | Submit Croydon’s drainage checklist and the London SuDS Proforma with the strategy. | Required |
| Flood Zone 2 or 3, or another national FRA trigger | Add a site-specific flood risk assessment to the drainage submission. | Usually required |
| Infiltration proposed | Undertake BRE 365 testing and address groundwater, geology and source-protection constraints. | Usually required |
| Minor development or unusual site constraint | Check Croydon’s current validation list or ask the LLFA to confirm what is needed. | Check for this site |
What to send with the application
Prepare these first
- Surface-water drainage strategy, Croydon checklist and London SuDS Proforma
- Existing and proposed drainage layouts with levels, dimensions, storage and controls
- Runoff-rate and attenuation-storage calculations for the stated design events
- Drainage-hierarchy assessment, exceedance plan, water-quality treatment and maintenance plan
Add these if relevant
- Flood risk assessment where national or site-specific triggers apply
- BRE 365 results, groundwater and source-protection evidence where infiltration is proposed
- In-principle connection evidence for a proposed sewer or watercourse discharge
- An alternative drainage arrangement if site investigation is incomplete at application stage
What the drawings and calculations need to show
Check every source of flood risk
Use the strategic flood risk assessment and current flood maps. Set out each risk that affects the site and how the design deals with it.
Target greenfield runoff
Follow the London drainage hierarchy, calculate storage and justify clearly if greenfield runoff rates cannot be achieved.
Test infiltration and extreme events
Use BRE 365 infiltration testing where infiltration is proposed. Show exceedance routes above the design event. Croydon’s published checklist uses the 1-in-100-year event plus 40% climate change and says the allowance must align with the latest Environment Agency guidance.
Provide a buildable, maintainable layout
Show storage, dimensions, levels, gradients, pipes, flow controls and connections, with water-quality measures and a long-term maintenance plan.
Major brownfield housing scheme with uncertain infiltration
A residential redevelopment increases roof area, the geology varies across the site and the final connection has not yet been agreed.
- Check every source of flood risk and reserve space for surface SuDS before the site layout is fixed.
- Complete infiltration testing early. If results are not available, say so and show an alternative instead of assuming a sewer connection.
- Use the same impermeable-area schedule and climate allowance in the proforma, checklist and calculations.
- Show exceedance routes, water-quality treatment, access and maintenance responsibility on the drawings.
This example shows how the submission might be assembled. It is not a drainage design. The final scope depends on the site and the proposal.
Official forms and guidance
- Croydon Council: drainage advice for planning applicants
- Croydon Council: technical drainage submission guidance
- GLA: London Sustainable Drainage Proforma
- GOV.UK: when a flood risk assessment is required
- GOV.UK: national standards for sustainable drainage systems
These links were checked 3 September 2026. Forms and validation requirements do change, so check the council website again before issuing the application.
Observed planning-condition data
What the drainage conditions actually ask for
The theme breakdown appears once enough drainage-conditioned approvals have been read to report it reliably.
Allow for discharge before agreeing a start date
There are not yet enough records to publish a reliable borough figure. Check the exact wording on the permission before agreeing the programme.
- Copy the condition into a schedule and list the evidence that answers each clause.
- Check that the calculations, drawings, specifications and maintenance plan use the same assumptions and references.
- For a pre-commencement condition, secure the written discharge before starting any work covered by the restriction.
- Where the condition asks for verification, keep site photographs, installation records and as-built information.
Understand the programme effect of a pre-commencement condition .
Reasons drainage submissions are refused
We have not read enough refusals in Croydon to publish a useful local breakdown. The London-wide analysis is available for wider context.
Projects attracting these conditions
There are not yet enough records to publish a reliable project-type breakdown.
About the data
The observed figures are computed from the planning decision notices from Croydon and are recalculated as we read more. We do not publish a rate when its sample is too small. This is not a complete record of every decision made by the authority, and it cannot tell you whether a document will be accepted for a particular site. Only aggregate figures appear here. See the full methodology or the London-wide picture.
Working in another borough? Compare drainage conditions and refusal patterns across London, then look at the individual schemes and project teams behind the figures.
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