DRAINAGE & LANDSCAPING
MODULAR CONCRETE PERMEABLE PAVING AND TREES IN SYNERGY Street tree planting and retention of existing trees in developments, with provision for long-term maintenance, are now embedded in planning policy.
The 2021 ‘National Planning Policy Framework’ (NPPF) for England lays out what local planning authorities (LPAs) will require, when setting local policies and also considering planning applications for all developments. The NPPF states that: “Planning policies and decisions should ensure that new streets are tree-lined and that opportunities are taken to incorporate trees elsewhere in developments.” This is backed up by other recent Government and local guidance such as the ‘National Model Design Code’ which says: “All schemes will be expected to follow national policy by achieving a 10% net gain in biodiversity. All new streets should include street trees.”
Maintenance requirement
However, measures need to be put in place to nurture and allow trees to mature, generally for decades, enabling them to actually deliver their real potential – including net-carbon
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storage, urban cooling through shading and evapotranspiration, biodiversity and public wellbeing. So, the NPPF also requires that “appropriate measures are in place to secure the long-term maintenance of newly-planted trees, and that existing trees are retained wherever possible”. Local planning authorities now need to incorporate long-term tree maintenance measures in their planning consents and a straightforward spatial solution, such as permeable paving, offers a holistic multifunctional solution. Urban trees and paving have traditionally been seen as in conflict. But this is not the case with concrete block permeable paving, a key sustainable drainage (SuDS) technique to reduce flood risk and make cities more liveable. CBPP offers unique opportunities to collect, attenuate and treat rainwater runoff, removing pollutants for a gradual supply of clean water irrigating green infrastructure.
Irrigation and gaseous exchange
Unlike conventional impermeable hard landscape materials, CBPP allows the same pattern of runoff transfer to the ground as natural vegetation, allowing water to reach tree and shrub roots, despite providing an attractive hard surface above. In addition to irrigation directly from rain, with CBPP there is scope for water storage and rainwater capture away from trees and their umbrella canopies for gradual conveyance laterally to trees – essential during the summer. In addition, CBPP enables air to reach roots and poisonous CO 2 to escape from them. The favourable environment created for tree roots avoids pavement surface disruption from upward root growth and facilitates natural growth into lower levels for stability in high winds and longevity. CBPP can be used within new-build or regeneration schemes with new tree planting and also for ‘rescuing’ mature trees. It can be used in conjunction with raingardens/ bioretention, tree-pits or proprietary systems avoiding air pipes, reservoirs or other structures for irrigation and gaseous exchange.
Beneficial relationship
A recent Interpave case study (available via www.paving.org.uk) explored the 20-year beneficial relationship between CBPP and trees at the Martlesham Park and Ride scheme. Here, concrete block permeable paving has operated efficiently with minimal maintenance amongst extensive tree planting without root disruption or other issues.
