Sustainable Urban Drainage Systems: Soakaway and Permeability Testing


Sustainable Urban Drainage Systems: Soakaway and Permeability Testing

At Roberts Environmental we have a wealth of experience in undertaking Soakaway & Permeability Assessments, which are often carried out as part of the broader scope of site investigation works.

Sustainable Urban Drainage Systems or SUDS are an alternative means of disposing of surface water from buildings and paved areas to the more conventional piped means. SUDS aim to mimic the way rainfall drains in natural system.

As of April 2015, planning applications relating to developments of 10 dwellings or more; or equivalent non-residential or mixed development will now have to assess a site for the suitability of the use of sustainable drainage systems.

The Environment Agency identified that an increased uptake of SUDS would have positive environmental benefits, through improved water quality and resource, decreased flood risk and improved water based amenity features.

Soakaways are a particular type of SUDS and in recent years have been used to limit the impact on discharge of new building works and to avoid costs of sewer up-grading outside a development.

Urban Drainage Systems

The Process

Soakaways should be designed in accordance with BRE Digest 365, Soakaway Design, they can be constructed in many different forms.

Soakaways store the immediate surface water run-off and allow for its efficient infiltration into the soil.  They must discharge their stored water sufficiently quickly to provide the necessary capacity to receive run-off from a subsequent storm.

As part of the design process, the soil infiltration characteristics must be determined.

We provide an in-house service undertaking trial soakaway tests during which a trial pit is excavated, to represent a section of the design soakaway. The pit is rapidly filled with water (under Northumbria Water licensing) from a 500 gallon water bowser and the soil infiltration rate is closely monitored and recorded. The process is repeated several times in quick succession to mimic storm events.

The data is used to establish the coefficient of permeability of the soils, which is used by the drainage design team.

Soakaway & Permeability Assessments


SUDS deliver high quality drainage while supporting urban areas to cope better with severe rainfall both now and in the future.

SUDS also help counteract the impacts on our water cycle caused by the increased urbanisation, such as reduced infiltration, which in turn can result in diminished groundwater supplies.

Where SUDS are designed to make efficient use of the space available, they can often cost less to implement than underground piped systems.

For further information about how we can help you with Soakaway and Permeability Testing please contact a member of the team on 0191 230 4521