Structural tree pits connect roadnarrowing tree planters on each side , based on the ‘ Stockholm Solution ’.
In particular , ‘ inverted raingardens ’ protect existing trees and new green infrastructure , supplied with a gradual supply of clean water from extensive CBPP catchments . by bioretention raingardens , intercepting runoff from the whole width of the ‘ side-hung ’ carriageway which acts as a catchment . It also includes long planters to accommodate mature and new trees , and other green infrastructure , incorporating seating . This also enabled de-paving around a mature but suffocated and asphalt-locked Plane tree .
Love Lane , which runs perpendicular to White Hart Lane in front of the new landmark Underground station , is now a concrete block permeable paved , adopted highway . CBPP can also accept runoff from White Hart Lane and other impermeable surfaces . At two points , structural tree pits span the full width below the road surface connecting roadnarrowing 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 subbase 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 subbase 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 .
This pattern of flow and attenuation means that trees benefit from rainwater collected from an extended catchment , making them healthier and more resilient to drought . Although initially unfamiliar with the structural tree pits , with support and advice the installation contractors soon became comfortable and are now installing them elsewhere .
At the renovation of Broad Lane Square in south Tottenham , the same designers take forward these principles with further innovations .
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 . Concrete block permeable paving technology will prove invaluable in delivering the street trees now demanded by planning policies for new developments as well as regeneration .
More information and case studies are available via : www . paving . org . uk
Images courtesy of Robert Bray Associates
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