Soil and Ground Conditions 

Healthy, uncompacted soil is essential to the performance of rain gardens, SuDS-enabled tree pits and other vegetated Sustainable Drainage Systems. Soil should be considered from the earliest stages of design and protected throughout construction. 

Why soil matters 

Soil helps SuDS features to store and filter rainfall, support planting and slow the movement of surface water. When soil becomes compacted, pore spaces are reduced and water cannot move through the soil as intended. This can increase surface runoff, contribute to standing water and prevent planting from establishing successfully. 

Protect soil from compaction 

Applicants should identify areas intended for vegetated SuDS early and explain how these areas will be protected during construction. Good site practice includes: 

  • keeping heavy machinery and repeated traffic away from future SuDS and planting areas 

  • using designated access and haul routes where practicable 

  • storing and handling soil appropriately to avoid compaction or contamination 

  • protecting prepared soil profiles and installed SuDS layers 

  • using an appropriate remediation method where compaction has occurred 

SuDS soil 

Rain gardens and SuDS-enabled tree pits rely on appropriately specified soil to support both drainage and healthy planting. The soil specification should be suitable for the intended feature and consistent with the approved landscape and drainage design.

Rain gardens 

Rain gardens receive, temporarily store and filter runoff from roofs and paved areas. They can be incorporated within plots, streets and communal landscapes, providing drainage, biodiversity and placemaking benefits within the same space. 

Rain gardens should have an uncompacted soil profile, suitable planting and a clear connection to the wider SuDS train. Their location and design should be coordinated with levels, utilities, landscape proposals and the source of incoming runoff. 

SuDS-enabled tree pits 

SuDS-enabled tree pits capture and manage surface water within the tree rooting area. They require sufficient uncompacted soil, an appropriate soil specification and careful coordination with utilities and other below-ground infrastructure. 

Tree pits should be integrated into the street and landscape design rather than treated as isolated drainage components.  

Key principle

Treat soil as part of the SuDS design. Protecting soil structure is essential to delivering the drainage, planting and placemaking benefits shown in the approved proposals.