Public Realm Regeneration with Permeable Paving

A new case study explores recent regeneration projects in Tottenham, London exemplifying the synergy of concrete block permeable paving and street trees to address climate change while delivering SuDS. It demonstrates important new techniques that will prove invaluable in delivering the street trees now demanded by planning policies.

Completed in 2018, the regeneration of White Hart Lane in north Tottenham, by muf architecture/art, was a pilot designed using ‘Healthy Streets’ principles. But it also applies innovative sustainable drainage (SuDS) techniques introduced by design collaborators Robert Bray Associates. This approach reduces flooding and pollution of the hidden Moselle River through the integration of bioretention raingardens to collect and treat polluted road runoff.

Multifunctional Permeable Paving

In addition, extensive concrete block permeable paving (CBPP) surfaces not only act as SuDS elements – attenuating and treating rainwater runoff – but also enable essential air/CO₂ exchange and optimised water supply for tree roots, using a range of techniques. A focal point of the scheme is a new Pocket Park, enabled by relocation of a bus stop and removal of extensive asphalt paving. This allowed de-paving around a mature but suffocated Plane tree, now sustained by CBPP areas between the raingardens.

Nearby Love Lane is now a concrete block permeable paved, adopted highway accepting runoff from White Hart Lane and other impermeable surfaces as well. At two points, structural tree pits span the full width below the road surface connecting road-narrowing tree planters on each side, in readiness for future planting. Based on the ‘Stockholm Solution’ for urban tree planting, the deep structural soil zones form sumps which are hydraulically connected to the coarse graded aggregate sub-base of the permeable paving.

Healthier Resilient Street Trees

This means that in heavy or prolonged rain, once percolated runoff begins to move laterally along the interface between the sub-base and subgrade, it moves toward the structural tree pits where it begins to be attenuated. Once the pits fill to the level of the base of the road sub-base, the attenuation and infiltration spread out over the whole road zone. So, the trees benefit from rainwater collected from an extended catchment, making them healthier and more resilient to drought.

At the renovation of Broad Lane Square in south Tottenham, the same designers take forward these principles with further innovations. In particular, ‘inverted raingardens’ protect existing trees and new green infrastructure, supplied with a gradual supply of clean water from extensive CBPP catchments.

Permeable Paving in Harmony with Trees

Concrete block permeable paving and street trees have been proven to work together in synergy. CBPP – whether full-construction with sub-base or applied as an overlay on an existing impermeable road base – can collect rainfall away from the canopy and convey it to the tree. It can then simply discharge horizontally into a raingarden, with overflow into existing adapted gulleys. The raingarden stores water during heavy rain for SuDS, retains soil moisture during dry weather and provides additional water quality ‘polishing’, as well as irrigation.

Alternatively, CBPP can be used over standard tree pits, proprietary tree planters, Stockholm System or other structural soil installations, enabling irrigation and simple air/carbon dioxide exchange essential to trees – without additional reservoirs or pipes. CBPP also avoids tree root disruption common with other paved surfaces.

More information and case studies on permeable paving and SuDS, visit: www.paving.org.uk