How to Prepare for Drainage Planning Site Visits

Table of Contents

• What Happens During a Drainage Planning Site Visit
• LLFA Drainage Strategy Requirements You Must Meet
  • Key Documents the LLFA Expects to See
• Your Flood Risk Assessment Site Visit Checklist
  • Before the Visit
  • During the Visit
  • After the Visit
  • Common Pitfalls to Avoid
• How to Respond to LLFA Planning Objections
  • Step-by-Step Resolution Workflow
• Common Pitfalls in Technical Drainage Reports
• Cost-Benefit Analysis of Professional Intervention
• Post-Objection Communication Etiquette
• Frequently Asked Questions

Last Updated: September 17, 2026

What Happens During a Drainage Planning Site Visit

A drainage planning site visit is a physical inspection of your development plot to assess how surface water and foul drainage will be managed before a planning application is submitted. A drainage planning site visit is the foundation of a compliant drainage strategy, not a box-ticking exercise.

Here is what typically happens on the day:

• The engineer walks the full site boundary and records levels and fall
• Existing drains, manholes and watercourses are located and photographed
• Ground conditions and any signs of flooding are noted
• Access points for future maintenance are checked
• Soil and infiltration test locations are agreed

LLFA Drainage Strategy Requirements You Must Meet

The Lead Local Flood Authority (LLFA) is the statutory consultee for surface water drainage on major planning applications. For minor applications, the Local Planning Authority (LPA) may still seek LLFA advice. LLFA drainage strategy requirements focus on how your site manages runoff, not just where water goes.

• Peak flow control: For greenfield sites, the discharge rate must not exceed the pre-development runoff rate for the same return period. For brownfield sites, it should be as close to greenfield as reasonably practicable.
• Volume control: The drainage system must ensure that post-development runoff volumes do not exceed pre-development volumes for rainfall events up to the 1 in 100 year plus climate change allowance.
• Flood risk within the site: Surface water must not increase flood risk elsewhere. Attenuation storage must be designed to contain the 1 in 100 year plus climate change event without flooding buildings or exceeding the capacity of the drainage network.
• Maintenance and adoption: A clear maintenance schedule must be provided, naming the responsible party for each element of the drainage system.

Key Documents the LLFA Expects to See

A complete submission for a major application typically includes:

• A surface water drainage strategy report with calculations for peak flow, volume, and attenuation storage.
• A flood risk assessment (FRA) where the site is in Flood Zone 2 or 3, or where the site area exceeds one hectare in Flood Zone 1.
• A hydraulic model showing the network performance for the 1 in 1, 1 in 30, and 1 in 100 year plus climate change events.
• A maintenance schedule for any attenuation, permeable paving, or other SuDS features, including inspection frequencies and responsible parties.
• Site layout drawings with drainage routes, manhole locations, and outfall positions clearly marked.
• Infiltration test results (BRE 365) if infiltration is proposed as the discharge method.

If your site is in an area where the LLFA has published a local standards document, such as a supplementary planning document, you must also meet those additional requirements. Check your local council’s website for any such guidance before finalising your strategy.

Your Flood Risk Assessment Site Visit Checklist

A flood risk assessment site visit is not just about walking the site. Proper preparation before the visit and a structured approach during it will save you time and reduce the risk of a holding objection. Use this checklist to prepare, conduct, and follow up on your site visit.

Before the Visit

• Download the Environment Agency flood map for planning and confirm the site’s flood zone. Note the map’s limitations: it does not account for surface water flooding or smaller watercourses.
• Check the LLFA’s local flood risk management strategy for any known surface water flooding hotspots or critical drainage areas.
• Obtain a copy of the site’s topographical survey if available. If not, arrange for a surveyor to attend or use a GPS device to record levels.
• Review any previous planning applications for the site or nearby plots to see if drainage objections were raised.
• Prepare a site plan showing the proposed development layout, existing drainage features, and any watercourses within 20 metres.
• Contact the LLFA case officer (if known) to ask if there are any specific concerns they want addressed during the visit.

During the Visit

• Confirm the site’s flood zone using the Environment Agency maps. Take screenshots or printouts to annotate.
• Record existing ground levels at key points, especially at proposed outfall locations and along the drainage route.
• Identify any ordinary watercourses within 20 metres. Note their width, depth, and flow direction. If the watercourse is main river, the Environment Agency is the relevant authority.
• Note any historic flooding evidence on site, such as silt lines, debris, or water damage to structures.
• Check for existing drainage connections and their condition. Lift manhole covers and photograph the interior, noting pipe sizes and invert levels.
• Photograph all manholes, gullies, and outfalls. Include a scale reference (e.g., a tape measure) in the photos.
• Locate any public sewers crossing the plot. You can obtain sewer records from the local water authority. If a public sewer crosses the site, you may need a build-over agreement.
• Agree infiltration test positions with the engineer. The test must follow BRE 365 methodology and be conducted in the correct location relative to the proposed infiltration feature.

After the Visit

• Compile a site survey record that includes all photographs, level data, and notes.
• Cross-check the recorded levels against the topographical survey. Any discrepancies should be resolved before design begins.
• If infiltration testing was not possible on the day, schedule it promptly. Results are needed to confirm the discharge method.
• Update the flood risk assessment with the site-specific data collected.
• Share the survey record with your drainage designer and, if applicable, the LLFA case officer.

The Environment Agency flood risk mapping service should be checked before the visit, not after. For sites in Flood Zone 2 or 3, you will also need to complete the Environment Agency’s flood risk assessment template and may need to apply for a flood risk activity permit if works are within 8 metres of a main river.

Common Pitfalls to Avoid

• Relying solely on the Environment Agency flood map without checking for surface water flooding.
• Failing to record invert levels of existing manholes, which are essential for designing a gravity-fed drainage system.
• Not checking for public sewers, which can derail a layout if a build-over agreement is needed.
• Conducting infiltration tests in the wrong location or at the wrong depth, leading to invalid results.

By following this checklist, you will have the evidence needed to prepare a robust drainage strategy and flood risk assessment, reducing the likelihood of an LLFA holding objection.

How to Respond to LLFA Planning Objections

Knowing how to respond to LLFA planning objections starts with understanding what a holding objection actually is.

The most common triggers are:

• No discharge rate stated in the strategy
• Missing or unclear hydraulic calculations
• No evidence of infiltration testing
• Insufficient detail on maintenance and adoption

Step-by-Step Resolution Workflow

1. Read the objection letter carefully and list every point raised
2. Match each point to a document in your submission
3. Identify what is missing or unclear
4. Commission any additional survey or testing needed
5. Revise the drainage strategy to answer each point directly
6. Submit the revised documents to the case officer
7. Request confirmation that the objection is withdrawn

Common Pitfalls in Technical Drainage Reports

The biggest pitfall in technical drainage reports is a discharge rate that does not match the site’s actual greenfield runoff. Reviewers spot this quickly.

Other frequent problems:

• Hydraulic models run with the wrong rainfall data
• Attenuation volumes calculated without allowing for climate change
• Maintenance schedules that name no responsible party
• Drawings that do not match the written strategy

Cost-Benefit Analysis of Professional Intervention

Professional intervention can help mitigate the costs associated with a failed application, such as resubmission fees, lost time, and extended holding costs.

A simple way to weigh it up:

Scenario	What It Costs You	What You Gain
Submit without a site visit	Higher risk of holding objection	Lower upfront spend
Commission a full strategy	Design and survey fees	Fewer objections, faster decision
Respond to an objection alone	Weeks of delay, repeat fees	No design cost
Use a drainage specialist	One clear fee	Evidence-based submission first time

Post-Objection Communication Etiquette

• Reply to the case officer, not the whole consultation list
• Reference each objection point by its exact wording
• Attach only the documents that answer the points raised
• Avoid chasing more than once a week
• Copy the LLFA only when the case officer asks

The Planning Inspectorate guidance on appeals is worth reading if an objection is not withdrawn and you need to appeal.

Frequently Asked Questions

What documents should I have ready for a drainage site visit?

You should prepare a site location plan, existing and proposed drainage layouts, a topographical survey, and any previous correspondence with the Local Planning Authority. If a flood risk assessment has been completed, have that available too. The case officer or LLFA may also request ground investigation reports, hydraulic modelling outputs, and details of any sustainable drainage systems (SuDS) features you plan to use. Having these ready speeds up the visit and reduces the chance of a holding objection.

Do I need to be present during a drainage planning site visit?

It is not mandatory, but your presence helps. You can answer questions about site constraints, access, and existing drainage connections immediately. If you cannot attend, ensure your drainage designer or architect is there with full authority to discuss the design. The LLFA or case officer may ask for clarifications on discharge rates, attenuation, or maintenance arrangements. A knowledgeable representative on site prevents delays caused by unanswered queries.

How can I demonstrate sustainable drainage compliance during a site visit?

Show how your drainage strategy follows the drainage hierarchy: rainwater harvesting, infiltration, attenuation to a watercourse, and finally surface water sewers. Have calculations for surface water discharge rates, evidence of permeable paving or attenuation tanks, and a maintenance plan ready. The LLFA will want to see that you have considered site-specific constraints like ground conditions and flood risk. Clear, labelled drawings and a short summary sheet make compliance easy to verify on the day.

What role does the Environment Agency play in drainage site assessments?

The Environment Agency is a statutory consultee for flood risk assessments in certain areas, particularly where development is proposed in Flood Zones 2 or 3. They may comment on flood defence, biodiversity, and water quality. During a site visit, their input is usually separate from the LLFA, but their requirements can affect your drainage design. If your site is near a main river or in a flood zone, check whether an environmental permit is needed alongside planning permission.

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Drainage objections can stall a project for months, and most come down to missing evidence rather than bad design. The Drainage Designers handle the full process, from the initial site visit and flood risk assessment through to securing Local Authority and Lead Local Flood Authority approval, with nationwide coverage and a transparent customer charter. Get in touch to book a site visit and keep your project on schedule.