Sustainable urban Drainage Systems (SuDS) and Permeability Testing

Sustainable urban Drainage Systems (SuDS) are an alternative way to dispose of surface water from buildings and paved areas. Instead of using traditional methods of channelling water through the sewer network, they more closely mimic natural drainage regimes through infiltration to the ground.

SuDS provide cost savings to projects, reduce surface water flooding risk, improve water quality, ecological environments, contribute to Biodiversity Net Gain (BNG), and have the added benefit of bringing nature closer to communities, increasing the natural capital value, and supporting health and wellbeing of site occupants.

Examples of SuDS include permeable paving, green roofs, ponds, basins, swales, wetlands, and rain gardens.

Testing is required to determine whether the ground conditions at a development site are suitable for SuDS which involve ground infiltration. According to the Flood and Water Management Act 2010 local planning authorities are required to adopt and maintain approved SuDS which are functioning properly and serve more than one property. It is also compulsory for all planning applications relating to developments of ten dwellings or more (or the equivalent non-residential developments) to assess a site for the suitability of SuDS.

How to Determine if Infiltration SuDS are Suitable for Your Site?

In order to determine if permeability characteristics are suitable for the development of SuDS, Roberts Environmental conduct soakaway testing either as part of a wider ground investigation or as a standalone service.

Trial pits are excavated and filled rapidly with water several times. The time taken for the pit to drain is recorded, providing the infiltration characteristics for use in future drainage design. This testing is carried out in accordance with BRE Digest 365 and Soakaway Design.

Sustainability Outcomes

As previously mentioned, SuDS have a number of ecological, environmental, social, and cost benefits when implemented during development, in addition to ensuring regulatory compliance. We set out below some of the many ways that incorporating SuDS into development proposals results in positive impacts on climate resilience and sustainable development.

Responsible Consumption and Production Contributing to SDG 12

Implementing or increasing the amount of SuDS within a development project will reduce the amount of traditional drainage infrastructure required to be installed (e.g., PVC piping), in turn reducing the need to excavate trenches to allow installation.

Increasing the provision of SuDS, in conjunction with replacing construction materials with sustainable alternatives, for example swapping asphalt and pavements for permeable paving can lead to a significant impact on both Embodied Carbon and cost saving.

One study carried out by the UK Green Building Council demonstrated that by replacing traditional drainage methods and maximising the use of SuDS through the methods described above Embodied Carbon emissions could be reduced by circa 17%.

Where such methods are considered, effective ground investigation and thorough permeability testing are highly important to determine feasibility and development options at the earliest possible opportunity.

Reduce Flood Risk Contributing to SDG 11

It is well understood that climate change will result in increased extreme weather events and rising sea levels, resulting in higher flood risk. Lack of flood resilience can undermine or even undo progress towards the SDGs. SuDS enable more sustainable ways to manage surface water run-off and reduce flood risk. Without this, development gains are at risk of being lost in future disaster events.

In addition to flooding posing a threat to developments by increasing the risk of damage, properties without suitable mitigation measures may also suffer from increases in insurance premiums, resulting in higher cost to protect developments, assets and infrastructure against damage during future disaster events.

Failing to take account of changing climate patterns and flood risk will also result in knock on effects, such as loss of crops, slowing economic growth and limiting investment. Damage to infrastructure will not only impact the physical asset but the people who work or live within them. Any associated loss of income will trickle into the local economy and have additional impacts, reducing the ability to provide sustainable growth.

Protecting Environments Contributing to SGD 6, 14 and 15

The biodiversity aspects of the Environment Act 2021 include the target to halt species decline by 2030 through measures such as requiring new developments to deliver a 10% increase in biodiversity. SuDS can contribute considerably to BNG requirements through water-enriched habitat. Wetland habitats often provide significant value to development within a BNG context, potentially enabling BNG to be achieved in a smaller area. In addition, by increasing soil moisture content and the recharging of groundwater SuDS have the potential to mitigate problems of low river flow, bringing back levels of biodiversity for both wildlife and plants.

Furthermore, through reducing the amount of surface water discharged to watercourses SuDS promote water quality and biodiversity of off-site habitats.

For example, where proposed developments are in the catchment of Special Areas of Conservation (SAC), Ramsar sites, Special Protection Areas (SPA) and potential SPA sites it is required to demonstrate Nutrient Neutrality. I.e., The nutrients (specifically nitrogen and/or phosphorus) from all surface water run-off and wastewater generated by the development will be less than or equal to the nutrients generated by the existing land use. Often mitigation measures are required to ensure an increase in nutrient loads are not caused by development resulting in algal blooms, starving the water of oxygen, smothering plant life, and causing fish and other water-based species to die. In doing so, removing a vital food source for birds and other wildlife.

SuDS are efficient sediment traps and reduce the amount of nutrients entering main watercourses and therefore can provide mitigation against nutrient run off. However, the type of SuDS employed will determine efficiency in achieving reduction.

Natural Capital and Health and Wellbeing – SDG 3

Biodiversity is a crucial part of human health and wellbeing. Nature supports good mental health by reducing stress anxiety and depressive symptoms, improving general mood, enabling better cognitive functioning, and improving mindfulness and creativity.

Furthermore, healthy natural habitats that support biodiversity and improve air, soil and water quality are fundamental to climate resilience and risk mitigation.

Following COVID19, there has been increasing awareness of the importance of the impact of the places we live and work and how these affect the health and wellbeing of the occupiers. Organisations in the built environment industry are under increasing pressure to evidence how they improve the wellbeing of workers, building users and communities. The demand for this is emerging across the value chain, from investors and local authorities through to tenants and communities.

Testing areas to see if SuDS would work in an area is important because by implementing SuDS, this allows for places to maintain their biodiversity and enhances communities’ well-being, human health, and protected areas.


In summary, implementation of SuDS results in:

  • Reduced surface water run-offs rates and volumes, reducing flood risk and nutrient loads to aquatic environments and habitats;
  • Increase biodiversity, proving added capital value and improving the health and wellbeing of occupants;
  • Resilient development, reducing transition risks; and
  • Lower development costs and embodied carbon associated with installation of traditional pipework, excavation and upgrading sewers.

Roberts Environmental provide Permeability Testing which is required as part of the regulatory requirements for planning and also feeds into feasibility assessments for development of SuDS. The results of the permeability testing can be taken into future drainage design and allow consideration of sustainable development at the earliest possible opportunity.

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For further information about this service on any other aspect of ground investigations please contact a member of the team on 0191 230 4521 or email:

1 Croft Stairs
Newcastle Upon Tyne

55 Whitfield Street

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0191 230 4521