Using the BGS Viewer to inform SuDS design at concept stage
When developing a new residential, commercial or industrial site, understanding the ground conditions is one of the most important early-stage considerations for effective SuDS drainage design.
Fortunately, there is a wealth of publicly available information that can help architects, developers, and contractors make informed decisions before appointing a SuDS civil engineer or commissioning site investigations. The British Geological Survey (BGS) provides several free tools that give valuable insights into the likely infiltration potential of a site during the concept stage.
In this article, we explore how the BGS Geology Viewer can be used to inform SuDS design and reduce planning risk.
Why infiltration matters in SuDS design
Sustainable Drainage Systems (SuDS) are a sequence of water management practices designed to manage surface water runoff by mimicking natural drainage processes. Instead of collecting rainwater and relying on traditional underground pipes transporting it to sewers, SuDS drainage slows down the flow of rainwater before releasing it into systems nearby.
Under the UK drainage hierarchy, infiltration is the preferred method of managing surface water after rainwater reuse. The principle is simple: if rainwater can be safely absorbed into the ground, it should be.
Infiltration-based systems such as soakaways, permeable paving and infiltration basins offer several benefits, including reducing runoff into public sewers, lowering flood risk downstream, supporting groundwater recharge, and creating more sustainable developments.
However, not every site is suitable for infiltration. Ground conditions, groundwater levels and geological hazards can all influence whether infiltration-based SuDS drainage design is feasible.
This is where BGS data becomes incredibly useful.
What is the BGS Geology Viewer?
The BGS Geology Viewer is a free online mapping tool developed by the British Geological Survey. It allows users to explore the geology beneath any site in Great Britain and provides a useful starting point when assessing infiltration potential.
The platform displays bedrock geology, superficial deposits, geological descriptions and classifications and three-dimensional visualisations of geological layers.
For anyone involved in SuDS design, these maps can provide an early indication of whether infiltration is likely to be successful.
High permeability ground
If the BGS Geology Viewer shows deposits such as sand, gravel, or river terrace deposits, there is a reasonable chance that soakaway systems could be viable.
Low permeability ground
Conversely, geology such as London Clay, mudstone, or clay-rich soils may indicate that the ground is relatively impermeable, meaning infiltration is unlikely to work and the project may need to progress further down the drainage hierarchy.
Although this information cannot replace on-site testing, it can significantly improve decision-making during RIBA Stages 0 – 2.
Using the BGS Borehole Viewer for greater confidence
While the BGS Viewer provides an overview of geological conditions, the BGS Borehole Viewer offers more detailed information.
The BGS Borehole Viewer contains records of previous ground investigations and boreholes that have been undertaken nearby. These records can provide valuable information on soil profiles, depth to bedrock, groundwater conditions and historic ground investigations.
For developers and design teams, reviewing nearby borehole records can help identify whether neighbouring sites encountered favourable or challenging ground conditions.
Understanding the limitations of BGS data
While BGS resources are extremely useful, they should always be considered as an early-stage desktop assessment rather than definitive evidence.
Geology can vary across a site
Ground conditions can change significantly over short distances. A geological map provides an indication of likely conditions rather than exact site-specific information.
Groundwater conditions can change
Seasonal groundwater levels are not always visible through mapping data and can significantly affect infiltration feasibility.
Planning authorities require evidence
Most Local Planning Authorities (LPA) and Lead Local Flood Authorities (LLFA) require formal testing to demonstrate infiltration suitability.
A desktop review using BGS data should therefore be seen as a tool to inform early decisions and guide the next steps in site investigation.
The role of BRE 365 testing
Even if the BGS data suggests favourable infiltration conditions, a formal BRE 365 infiltration test is usually required.
A BRE 365 Infiltration Test (based on BRE Digest 365) is the UK’s industry-standard field test used to determine if the ground can absorb enough water to support a soakaway or other infiltration-based SuDS.
If infiltration proves unsuitable, the BRE 365 report often becomes the evidence needed to justify moving down the drainage hierarchy to a watercourse or sewer connection.
Why assess infiltration at concept stage?
Early understanding of infiltration potential can have a significant impact on the success of a development.
By reviewing BGS data at concept stage, project teams can reduce planning risk, inform site layouts and landscaping strategies, identify potential constraints early, avoid costly redesigns, and better brief a SuDS engineer when detailed design work begins.
In many cases, a simple desktop review using the BGS Geology Viewer and BGS Borehole Viewer can save weeks of redesign and avoid unforeseen costs.
Final thoughts
Sustainable drainage should never be an afterthought. Understanding whether infiltration is likely to work from the outset enables architects, developers and contractors to make better-informed decisions and develop more robust drainage strategies.
The BGS Geology Viewer and BGS Borehole Viewer are powerful, freely available tools that provide valuable early insights into site conditions and can significantly improve the quality of SuDS design and SuDS drainage design.
While these tools do not replace site investigations or the expertise of a SuDS engineer, they are an excellent starting point for de-risking projects and creating a more informed and sustainable approach to drainage design.
Need help understanding SuDS requirements?
If you’re in the early stages of a project and want to understand the resources available to inform your drainage strategy, download our practical guide to Sustainable Drainage Systems.
The guide explains the key principles of SuDS, the drainage hierarchy and the free tools available to aid conversations when engaging with a civil engineer consultant.