Permeable external surfaces provide the starting point for sustainable surface water drainage (also known as SuDS), but concrete block permeable paving offers far more than flood prevention, explains Chris Hodson of Interpave
It’s over three years since the Government chose to abandon dedicated requirements for SuDS on new developments in England using the Flood and Water Management Act. Instead, the latest National Planning Policy Framework calls for SuDS on developments of 10 or more dwellings or similar scale non-housing schemes, and for it to provide multifunctional benefits where possible.
These measures are now being applied and enforced with increasing effectiveness by local planning authorities, through local policies and guidelines. Even the 2019 National Design Guide for developments considers that: “Well-designed places have sustainable drainage systems to manage surface water, flood risk and significant changes in rainfall.”
Dedicated SuDS requirements
However, last year the Welsh Government did implement Schedule 3 of the Act. New measures include the establishment of a SuDS Approving Body (SAB) within each local/unitary authority. SAB approval is required for drainage systems on new and redeveloped sites, and the SAB will be required to adopt and maintain approved SuDS that serve more than one property. In Scotland, 2011 regulations simply require surface water drainage systems from new developments to discharge water to the environment through SuDS.
In addition, other – often forgotten – changes to ‘permitted development’ rights for new or replacement paving around existing properties are now being more effectively enforced. They apply to homes and also industrial, warehouse, office and shop premises, unless permeable paving or a permeable area within the property is used. Otherwise planning permission will be needed, and this should be refused – with local policies requiring SuDS now appearing. For example, the Draft London Plan states “Development proposals for impermeable paving should be refused where appropriate, including on small surfaces such as front gardens and driveways.”
As the new Welsh National Standards explain: “The SuDS approach mimics natural drainage, managing surface runoff at or close to the surface and as close to its source as practicable.” By its very nature, concrete block permeable paving is uniquely placed as an essential, attractive, surface-based, multifunctional SuDS technique.
Of course, all developments need paving, whether for pedestrians, vehicles or other uses. CBPP simply combines well-drained, safe and attractive surfaces for a wide range of applications with attenuation, storage, treatment and conveyance of rainwater – by its very nature requiring no additional land-take. Fundamentally, CBPP captures the rainwater that falls upon it (which is immediately removed from the surface) and can also handle runoff from roofs and other impermeable surfaces.
CBPP attenuates and treats this water before infiltrating gradually into the ground or, where ground conditions preclude complete infiltration, discharges a delayed, gradual flow of clean water, either at the head of a SuDS management train or to a conventional drain system or watercourse, so improving water quality and reducing downstream flooding. CBPP is therefore an essential part of any development, irrespective of the drainage regime.
Defining urban character
Of course, paved surfaces help to define the character of any development. The growing choice of CBPP products available from Interpave manufacturers – with numerous shapes, styles, finishes and colours – allows real design freedom. At the same time, CBPP can provide a completely level, well-drained, firm and slip-resistance surface accessible to all, without the need for cross-falls, channels, gulleys or other interruptions. Rainwater ‘ponding’ is eliminated, reducing the risk of ice forming on the surface and preventing splashing from standing water.
As a result of its unique capabilities, CBPP offers designers the exciting potential of a gradual supply of treated water for safe, open SuDS features downstream. This can be integrated with landscape design and promotes biodiversity. The challenge for architects is to fully integrate SuDS and CBPP into their schemes from the very start. As the RIBA’s 2014 report ‘Building a Better Britain’ pointed out: “For too long, we have been designing water out of our towns and cities when we should have been designing it in,” and stresses the need to: “start putting water at the heart of discussions about what makes places great to live in.”
Chris Hodson is architect and consultant at Interpave