Sustainable Drainage Systems (SuDS) are no longer optional — they’re a planning requirement for many new developments across the UK. But the rules aren’t always straightforward. Local authorities interpret guidance differently, and expectations can vary depending on site size, flood zone, and location.

In this article, Nimbus Engineering explains what planners and Lead Local Flood Authorities (LLFAs) expect to see in a SuDS report — and how to stay compliant no matter where you’re building.

Why SuDS Are a National Requirement

SuDS exist to manage surface water runoff sustainably while reducing flood risk, improving water quality, and promoting biodiversity. The regulatory push comes from the Flood and Water Management Act 2010, Planning Policy Guidance on Flood Risk and Coastal Change, and local Strategic Flood Risk Assessments.

Many councils now require SuDS reports as part of planning submissions — even for modest developments.

When Are SuDS Reports Required?

While the level of detail required in each SuDS report varies by the specific council area, the general requirements are as follows:

• For major developments (10+ dwellings or equivalent non-residential projects), these are usually accompanied by a Flood Risk Assessment report.
• In areas with known flooding issues.
• Where new surfaces could increase impermeability (roofs, driveways, roads, paved courtyards).

What Local Authorities Expect to See

Rainwater Re-use

Due to drought concerns, rainwater re-use is now at the top of the SuDS Hierarchy. Therefore, rainwater harvesting for non-potable use is a must on all new developments.

BRE 365 Infiltration Testing

We always provide a desktop geological assessment to include in your SuDS report to assess the feasibility of infiltration. Should infiltration be viable, we will inform you of this at the quote stage. The local authority will request this to be carried out as part of your planning application, ensuring there are no unnecessary delays.

Tests must be carried out in accordance with BRE365 Percolation testing guidance, and all our in-house testing is fully compliant with this standard.

Surface Water Runoff Calculations

Councils want to see pre- and post-development runoff rates, with peak runoff modelled for 1-in-1, 1-in-30, and 1-in-100-year storm events. A climate change allowance is standard, as well as a 10% allowance for urban creep added in areas where required.

Most planning validation forms also ask for the percentage reduction in surface water runoff post-development, and these calculations allow us to provide you with that exact figure.

SuDS Management and Maintenance Plan

Local Authorities need to know who will be responsible for the short and long-term maintenance of your proposed SuDS assets. This ensures there are no blockages in the system, which could eventually lead to a backup of flow and flooding on your site. Therefore, we provide the necessary cleaning intervals, instructions, and guidance to allow the system to work effectively for the lifetime of your development.

How Nimbus Engineering Ensures Compliance

We stay ahead of evolving national and local requirements to deliver fully compliant SuDS reports. Our team carries out in-house BRE 365 testing, models drainage systems using approved software, and liaises directly with LLFAs and SABs. The result? Clear, submission-ready reports tailored to your site.

Knowing what your local authority expects in a SuDS report can mean the difference between smooth approval and costly delays. With expert guidance from Nimbus Engineering, your report will meet every technical requirement — and more.