SuDS-Enabled Street Trees

(Sources: CIRIA C753 Ch 19.8.3, Susdrain Tree Pit Guidance)

Key Benefits

Water Management: Enhanced Runoff Volume Reduction (infiltration/storage); Peak Flow Attenuation; Water Quality Improvement (filtration/uptake); Passive Irrigation for tree. (C753 S19.8.3)
Climate Regulation: Benefits as per standard street trees, potentially enhanced by better water availability.
Air Quality: As per standard street trees.
Biodiversity: As per standard street trees, potentially enhanced habitat.
Amenity & Well-being: As per standard street trees.
Resilience: Improved tree health and drought tolerance due to passive watering.

Technical Guidance

Design Principles (C753 S19.8.3)

Integrate SuDS functionality into standard tree pit design. Aim to capture runoff from adjacent pavements/roads. Calculate contributing catchment area and runoff volume to size pit appropriately. Design requires hydraulic, structural, and horticultural considerations.

Pit Construction & Inlet

Typically larger pit volume than standard tree pit to provide storage. Use structural soil or suspended pavement systems for load bearing under paving. Incorporate inlet (e.g., permeable paving edge, trench drain, weir inlet, grated inlet) allowing water entry without clogging. Ensure appropriate overflow mechanism.

Filtration & Drainage

Use filter layers (geotextile, sand/gravel) to prevent soil fines washing out. Include drainage layer at base (aggregate, drainage board) connected to underdrain or allowed to infiltrate (if ground conditions suitable - C753 Ch 25). Underdrain connects to downstream drainage system.

Soil & Planting

Use specified structural/engineered soil media capable of supporting load, allowing root growth, filtration, and water retention. Select tree species tolerant of occasional waterlogging and urban conditions.

Maintenance (C753 S19.12)

Monitor tree health and water levels. Manage surface vegetation/weeds. Check structural integrity of grilles/guards. Potential need for periodic flushing or removal of accumulated pollutants/sediment from pre-treatment zones or substrate surface. More complex and potentially costly than standard tree maintenance.