The 6 Most Common LLFA Drainage Objections — and How to Fix Them

Why Do LLFAs Object to Planning Applications?

Lead Local Flood Authorities are statutory consultees on planning applications. They are responsible for scrutinising surface water drainage proposals and can object if a development fails to demonstrate adequate drainage provision. LLFA objections must be resolved before planning permission can be granted.

Here are the six most common LLFA drainage objection reasons we deal with, and what resolves each one:

1. No Surface Water Drainage Strategy Submitted

The most common objection of all. Many planning applications are submitted without any drainage strategy, or with only a brief mention of drainage in the design and access statement.

Fix: A properly prepared SuDS drainage strategy addressing greenfield runoff rates, SuDS hierarchy, infiltration assessment and attenuation sizing. In most cases, this can be submitted as additional information during the application.

2. SuDS Hierarchy Not Addressed

CIRIA C753 requires applicants to work through the SuDS hierarchy in order: infiltration first, then attenuation, then discharge to watercourse, then sewer. Many drainage strategies jump straight to connecting to a sewer without demonstrating that higher-priority options have been considered and ruled out.

Fix: A structured SuDS hierarchy assessment demonstrating why each higher-priority option is not viable for the site, supported by evidence (geology, infiltration test results, site constraints).

3. Infiltration Not Assessed

LLFAs require evidence that infiltration has been properly assessed and ruled out before allowing a discharge to sewer. Simply stating that the ground "doesn't drain" is not acceptable without supporting evidence.

Fix: BRE 365 infiltration test results (from a site investigation), or reference to mapped geology and soils data demonstrating that ground conditions are unsuitable for infiltration. Many sites can use published BGS geological data as supporting evidence without commissioning a full site investigation.

4. Greenfield Runoff Rates Not Demonstrated

The drainage strategy proposes a discharge rate but doesn't demonstrate that this rate corresponds to the greenfield runoff rate for the site. LLFAs require this to confirm the development isn't increasing flood risk downstream.

Fix: FEH or IH124 greenfield runoff rate calculations, showing QBAR and 1 in 1 and 1 in 100 year runoff rates. Attenuation sizing must then be demonstrated to control post-development flows to these rates.

5. No Maintenance and Management Plan

LLFAs increasingly require a SuDS Maintenance and Management Plan (MMP) to be approved before granting drainage consent. Without one, the LLFA cannot confirm that the SuDS features will be maintained effectively over the long term.

Fix: A SuDS MMP identifying who is responsible for maintaining each drainage feature, the maintenance activities required, their frequency, and how maintenance access will be achieved. Often simple to prepare once the drainage scheme is designed.

6. LLFA SuDS Proforma Incomplete

Many LLFAs have their own SuDS proforma that must be submitted alongside planning applications. Incomplete or incorrectly completed proformas are a common reason for objections, even where a good drainage strategy has been prepared.

Fix: Careful completion of the LLFA's specific proforma, cross-referenced to the drainage strategy calculations and drawings. We complete LLFA proformas for all LLFA areas across England and Wales.

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