How to Get Drainage Approval: Step-by-Step Guide
Table of Contents
- What You’ll Need Before You Apply for Drainage Approval
- Step 1: Conduct a Site Survey and Topographical Assessment
- Step 2: Prepare Your Drainage Design for Planning Permission
- Step 3: Meet SuDS Drainage Strategy Requirements
- Step 4: Determine If You Need a Flood Risk Assessment for Planning
- Step 5: Submit Your Application and Understand How Long Drainage Approval Takes
- Common Reasons for Rejection and How to Avoid Them
- Post-Approval Maintenance Obligations and Next Steps
- Frequently Asked Questions
Last Updated: September 11, 2026
What You’ll Need Before You Apply for Drainage Approval
Getting drainage approval in the UK means satisfying your local planning authority and the Lead Local Flood Authority that your surface water drainage strategy is compliant, buildable and maintainable. This guide walks through each stage, from the first site survey to the maintenance plan you’ll need after consent is granted.
Applications with a complete drainage strategy, accurate runoff calculations and a clear SuDS hierarchy justification move through the system far more smoothly than those submitted piecemeal.
Essential Documents and Surveys
A drainage approval submission typically rests on four core documents:
- A topographical survey showing existing levels, boundaries and any watercourse
- A drainage strategy drawing set, including proposed pipe runs, discharge points and attenuation
- Runoff rate and volume calculations for the developed site
- A SuDS hierarchy statement explaining why your chosen drainage methods were selected
For larger or more complex sites, expect to add a flood risk assessment and, in some cases, a hydrological assessment of the receiving watercourse.
When to Bring in a Qualified Professional
A qualified person is someone with the engineering competence to certify drainage design, typically a chartered or incorporated civil engineer. If your scheme involves attenuation, hydraulic modelling or discharge to a watercourse, you’ll almost certainly need one.
Engage a drainage engineer at concept stage; bringing them in after the layout is fixed often means redesigning levels or losing garden space to a storage tank.
Ask your engineer for the runoff calculation assumptions in writing at the outset. If the local authority queries the discharge rate later, you’ll have the reasoning ready rather than scrambling to reconstruct it.
Step 1: Conduct a Site Survey and Topographical Assessment
A site survey is the foundation of every compliant drainage design. Without accurate levels and a clear picture of where water currently goes, case officers will spot guesswork quickly.
What a Site Survey Should Cover
Your survey should record:
- Existing ground levels across the whole site, not just the building footprint
- The location and invert level of any existing drains, sewers or soakaways
- Any watercourse, ditch or ordinary watercourse within or bordering the site
- Hardstanding areas and how they currently drain
- Soil conditions, from trial pits or boreholes, to assess infiltration potential
Infiltration testing is critical. If the ground won’t accept water at a usable rate, permeable surfaces and soakaways come off the table, and your SuDS strategy must lean on attenuation and controlled discharge.
Step 2: Prepare Your Drainage Design for Planning Permission
Drainage design for planning permission must demonstrate that surface water can be managed without increasing flood risk on or off site.
Calculating Runoff Rates and Attenuation Requirements
Runoff rates describe how much water leaves your site per second before and after development. The goal is to match or reduce the existing greenfield rate to avoid adding downstream flood risk.
Attenuation is storage that holds back the difference between rainfall and permitted discharge. This means underground tanks, oversized pipes, ponds or basins that fill during a storm and release slowly. Accurate hydraulic modelling is essential to size it correctly.
| Design Element | What It Does | Typical Trigger |
|---|---|---|
| Runoff rate calculation | Sets the permitted discharge | Every application |
| Attenuation volume | Stores peak flows temporarily | Most new builds |
| Permeable surfaces | Lets water infiltrate where ground allows | Driveways, parking |
| Flow control device | Limits discharge to agreed rate | Sites with attenuation |
Step 3: Meet SuDS Drainage Strategy Requirements
SuDS drainage strategy requirements flow from the sustainable drainage hierarchy, a sequence of preferred options case officers expect you to work through in order. A sustainable drainage system (SuDS) manages surface water by mimicking natural processes, using infiltration, storage and controlled release.
The Sustainable Drainage Hierarchy Explained
The hierarchy runs from most to least preferred:
- Discharge to ground via infiltration
- Discharge to a surface water body such as a watercourse or pond
- Discharge to a surface water sewer
- Discharge to a combined sewer, as a last resort
Your drainage strategy should walk through each level and explain, with evidence, why you stopped where you did. “The ground didn’t infiltrate” is not enough on its own; you need the trial pit data to back it up. UK Government guidance on sustainable drainage systems sets out the policy context that local authorities apply when assessing these strategies.
Step 4: Determine If You Need a Flood Risk Assessment for Planning
A flood risk assessment for planning is required when your site sits in a flood zone, exceeds one hectare, or falls within a critical drainage area. For smaller domestic projects outside flood zones, a simple drainage statement often suffices.
The assessment identifies flood sources, evaluates the risk to and from your development, and shows how you’ll manage it. If your site drains to a watercourse, the assessment should also address whether your discharge could affect flood risk downstream.
Submitting a drainage strategy without checking whether a flood risk assessment is required is one of the most common causes of delay. Case officers will pause the application rather than advise you informally, and that pause can add weeks.
Step 5: Submit Your Application and Understand How Long Drainage Approval Takes
How long drainage approval takes depends on which consent route your works trigger. A householder planning application typically runs for around eight weeks from validation, while major applications can take thirteen weeks or more (gov.uk). Land drainage consent usually takes around eight weeks once a complete application is received. Run both in parallel rather than sequentially, as the planning determination will often be conditioned on land drainage consent being in place.
Land Drainage Consent Criteria and When It Applies
Land drainage consent is required when your works affect an ordinary watercourse (gov.uk). An ordinary watercourse is any river, stream, ditch or culvert not designated a main river. Main rivers fall under the Environment Agency; ordinary watercourses fall under the Lead Local Flood Authority. The Environment Agency’s flood map for planning shows main river extents.
The consenting body assesses your application against three tests:
- Flood risk – will the works increase flood risk upstream, downstream or on site? Culverting a ditch removes storage and speeds flow, which is why it is rarely consented without compensatory attenuation.
- Flow capacity – does the proposal preserve or improve the watercourse’s capacity to convey the ordinary flood?
- Ecology and morphology – does the works harm the watercourse’s ecological function or natural form?
Your application must include a location plan, topographical survey, scaled cross-sections of the watercourse, a method statement and a maintenance plan for any new structure. Check the LLFA’s validation checklist before submission.
What Drainage Approval Costs
Application fees are set nationally for planning applications, and land drainage consent fees are set by each LLFA. Budget for topographical survey, infiltration testing (BRE 365), hydraulic modelling and drainage strategy, and flood risk assessment where required. Get fixed-fee quotes for the survey and engineering work before you commit, and confirm whether the fee includes responding to case officer queries.
Submission Mechanics
Planning applications go through the Planning Portal. Land drainage consent applications go directly to the LLFA. Keep a dated record of everything you submit, as validation queries are common.
If your scheme touches a watercourse, submit the land drainage consent application at the same time as the planning application. Case officers will often validate the planning application but hold determination until consent is confirmed, so running them together saves weeks.
Common Reasons for Rejection and How to Avoid Them
Rejections rarely come from bad engineering. They come from incomplete evidence, mismatched calculations and strategies that skip the hierarchy without justification.
| Problem | Why It Fails | Fix |
|---|---|---|
| No infiltration testing | Hierarchy not evidenced | Commission trial pits early |
| Runoff rate mismatch | Calculations don’t tie to drawings | Cross-check before submission |
| Missing maintenance plan | Long-term viability unclear | Include schedule and responsible party |
| Discharge point unclear | Case officer can’t verify consent | Mark on drawings with invert levels |
| Flood risk assessment omitted | Statutory requirement unmet | Confirm requirement at pre-app stage |
The single highest-value habit is a pre-application enquiry. It costs little, confirms exactly what your local authority expects, and removes most of the guesswork that leads to rejection.
Post-Approval Maintenance Obligations and Next Steps
Approval is not the finish line. Most consents carry conditions requiring you to maintain the drainage system for the life of the development, with a formal maintenance schedule naming who is responsible.
How Maintenance Obligations Are Imposed
Maintenance duties reach you through one of four routes:
- Planning conditions – the most common route. A condition will require a maintenance plan to be submitted and approved before occupation.
- Land drainage consent conditions – where works affect an ordinary watercourse, the LLFA can attach conditions requiring ongoing maintenance.
- Adoption agreements – if a water company or the local authority adopts the drainage, responsibility transfers to them, but only if the system is built to their specification.
- Management companies – on shared SuDS serving multiple properties, a management company is often set up to hold and discharge the maintenance duty.
If you sell the property, the maintenance obligation usually transfers with the land. Buyers’ solicitors will ask for the maintenance plan and evidence that it has been followed, so keep records.
What Maintenance Actually Involves
A typical SuDS maintenance schedule covers:
- Gullies, channel drains and flow controls – inspected and cleared at least twice a year and after significant storms.
- Attenuation tanks and oversized pipes – inspected annually for silt build-up; silt removal usually needed every five to ten years.
- Ponds, basins and swales – vegetation managed to keep storage volume clear; inlet and outlet structures checked for blockage.
- Permeable paving – swept and vacuum-cleaned to maintain infiltration rates.
- Flow control devices – checked to confirm they are still limiting discharge to the consented rate.
Record every inspection with a date, what was found and what was done. A documented maintenance history is essential if a system fails and causes flooding.
When to Reapply or Vary Consent
Approval covers the scheme as designed. If you later want to change the discharge point, increase impermeable area, or alter the attenuation arrangement, you will usually need to vary the consent or submit a new application. Check with your LLFA before assuming a change is covered.
Submission Readiness Checklist
Before you submit, run through this checklist:
- Topographical survey complete and dated
- Infiltration testing results attached (BRE 365 where infiltration is proposed)
- Runoff rate calculations cross-checked against drawings
- SuDS hierarchy statement written with evidence for each level ruled out
- Flood risk assessment requirement confirmed with the local planning authority
- Land drainage consent applied for if an ordinary watercourse is affected
- Maintenance schedule drafted with named responsible party
- Fee schedule checked for both planning and land drainage consent
- Pre-application enquiry response on file
If that list looks long, it is because drainage approval genuinely rewards completeness. Pulling the package together properly the first time is faster than answering queries for months.
The single highest-value habit is a pre-application enquiry. It costs little, confirms exactly what your local authority expects, and removes most of the guesswork that leads to rejection. Pair it with a maintenance plan you can actually follow, and your approval will stand up long after the certificate is issued.
Frequently Asked Questions
Do I need planning permission for drainage?
Drainage works often form part of a broader planning application, but separate land drainage consent may be required if you plan to discharge into an ordinary watercourse. For new builds and extensions, drainage details are typically submitted as part of the planning application. If your project involves connecting to a public sewer, you will also need approval from the sewerage undertaker. Always check with your local authority’s planning department before starting work.
What information must be included in a drainage strategy for planning?
A drainage strategy typically includes a topographical survey, calculated runoff rates and volumes, details of discharge points, attenuation requirements, and how the scheme follows the sustainable drainage hierarchy. You will also need technical drawings showing pipe layouts, permeable surfaces, and any SuDS features. The strategy must demonstrate that surface water drainage will not increase flood risk elsewhere and that maintenance arrangements are realistic.
How long does drainage approval take?
How long drainage approval takes depends on the type of consent and the local authority’s workload. Planning applications that include drainage details often take eight to thirteen weeks. Land drainage consent applications are typically decided within two months. If your application is incomplete or raises technical queries, it will take longer. Submitting a thorough, well-documented drainage strategy upfront helps avoid delays.
Who is responsible for maintaining private drainage systems?
The property owner is responsible for maintaining private drainage systems that serve their property, including any SuDS features like attenuation tanks or permeable paving. If you share a system with neighbours, maintenance responsibilities should be set out in a legal agreement. Some SuDS features may be adopted by the local authority or a management company, so confirm this before construction begins.