Drainage Tools • Guide

SuDS Guidance: susdrain, CIRIA & The SuDS Manual

The resources every drainage strategy is built on — susdrain, CIRIA's SuDS Manual (C753) and the government's technical standards — and what they mean for your scheme.

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A sustainable drainage system
A sustainable drainage system (SuDS) · Photo: Alan Hughes (CC BY-SA 2.0)

The key SuDS resources

Sustainable drainage systems (SuDS) manage rainfall close to where it falls, mimicking natural drainage instead of piping everything to a sewer. Good SuDS design draws on a small number of authoritative resources — and knowing them helps you understand what a Lead Local Flood Authority will expect from your drainage strategy.

The cornerstone is CIRIA's SuDS Manual (C753), the industry-standard design guidance. susdrain — run by CIRIA — is the free online community that puts that guidance, plus components, case studies and tools, in one place. Alongside them sit the government's non-statutory technical standards, which LLFAs use to judge a scheme.

Visit susdrain (the UK SuDS site) →

How to use it — step by step

Four quick steps to get what you need from the tool.

1. Start with susdrain

susdrain is the best free starting point — an overview of SuDS components (swales, basins, permeable paving, green roofs), how they work and real case studies.

2. Design to the SuDS Manual (C753)

CIRIA C753 is the design bible. It sets out the SuDS management train, treatment and attenuation design, and the criteria a drainage strategy must meet.

3. Check the technical standards

The government's non-statutory technical standards define the run-off rate and volume requirements LLFAs apply — the numbers your strategy has to hit.

4. Follow the discharge hierarchy

SuDS should discharge in priority order: infiltration first, then watercourse, then surface water sewer, then combined sewer — at greenfield run-off rates.

How this shapes your strategy

On any development that needs a drainage strategy, the LLFA (a statutory consultee on major schemes) will judge it against C753 and the technical standards — greenfield run-off rates, attenuation for events up to the 1% plus climate change, and treatment. We design SuDS-led strategies to exactly these standards. Send us your site for a fixed-fee quote.

Related: SuDS Drainage Strategies  •  Greenfield Runoff Rate  •  Soakaway Testing (BRE 365)

Frequently Asked Questions

What is the SuDS hierarchy?
The order in which surface water should be discharged: infiltration into the ground first, then to a watercourse or surface water body, then to a surface water sewer, and only lastly to a combined sewer. LLFAs expect the drainage strategy to justify moving down the hierarchy.
Is the CIRIA SuDS Manual (C753) free to access?
Yes — CIRIA makes The SuDS Manual available free online, and susdrain provides free supporting guidance, case studies and tools alongside it.
Do I have to use SuDS on a small site?
In most cases yes. National policy and the National SuDS Standards expect all new development to manage surface water sustainably where practicable, and LLFAs apply this to single dwellings and extensions as well as major schemes — proportionately to the site.

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