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PERMEABLE PAVING FOR REGENERATION & SUDS

Low-intervention permeable paving overlays can transform worn-out paving and also deliver multifunctional sustainable drainage (SuDS), trees and numerous other benefits. To understand how, it’s worth reminding ourselves of the unique characteristics and attributes of modular concrete paving generally – as the trade body Interpave explains.

Concrete Block Paving technology is based on high-strength, interlocking units installed with granular material filled joints and laying course. It enables small displacements between blocks, while retaining interlock, to create a particularly durable, very long-life surface over structural layers below. Decades of use internationally have demonstrated its suitability for the most taxing applications. A wide choice of shapes, styles, colours and finishes – including natural aggregates – add a richness, diversity, visual interest and a human scale to the urban environment.

Re-usable Block Paving - Concrete Block Paving is slip-resistant, durable, strong and sustainable. Modular concrete paving delivers fast, low-cost installation and replacement, using weatherindependent, ‘dry’ construction. There are no curing, hot-work or noxious fume problems and only small plant and equipment is needed, with noise and disturbance minimised. With an extremely long lifespan, blocks can be taken up and re-used without processing for repairs, changing layouts, or new schemes – saving carbon and meeting ‘circular’ economy’ criteria.

Concrete Block Permeable Paving (CBPP) enhances this technology as a well-established, multi-functional SuDS technique. It simply combines self-drained, safe and attractive surfaces for a wide range of applications with attenuation, storage, pollution treatment and conveyance of rainwater runoff. The difference with CBPP is angular aggregate – not sand – used to fill enlarged joints and as a laying course.

Then, pavement layers of voided material below accommodate water, whilst still providing structural performance. CBPP can also accept additional runoff from adjacent impermeable paving and roofs. The Key to Successful SuDS - By its very nature, CBPP requires no additional land-take for water storage or management, and no gulleys with related pipework. Its unique capabilities include source control and delivering a gradual flow of clean water, for example to open SuDS features, for amenity or biodiversity, to drainage systems or into the ground. More than 25-years usage has proven its adaptability on projects ranging from footpaths to container terminals.

Both construction and wholeof-life costs of CBPP have been shown to be lower than for conventional paving and drainage, and it requires only limited, straightforward maintenance without clogging problems. It’s important to remember that CBPP is unlike – and not to be confused with – permeable materials, which behave very differently.

Innovative Overlays - Concrete Block Permeable Paving Overlay is a deceptively simple, innovative approach to retrofitted CBPP, delivering SuDS as part of low-intervention repair, maintenance or regeneration.

The CBPP upper layer is applied as an overlay onto the original structural road or paving base. In many cases, it can simply run kerb-to-kerb to form a shared surface level with the footway and flush kerb top. This approach also enables low-cost improvement works – perhaps as part of creating traffic calming, Low Traffic Neighbourhoods or Homezones. The same blocks and grit bedding layer and jointing material as for permeable pavements generally are used. Water is attenuated, treated and conveyed within the laying course, enabling filtration of silt and retention/treatment of pollutants without clogging. A gradual flow of clean water can then be released near the surface, meeting SuDS requirements. This approach provides numerous benefits including:

• Interception losses, managing runoff during regular rainfall events • Attractive, popular surfaces with no puddles or potholes, for user safety • Maximising re-use of existing roadbase and its embodied carbon • Optimising the original drainage regime, but below the surface • Low-intervention, low carbon, no-heat retrofit installation • Long-life with minimal maintenance and low whole-of-life cost • No open gulleys – wildlife-safe • Integral water filtration, with debris/litter remaining on the surface • Straightforward access to below-ground services • Sustainable re-use of blocks for reinstatement or changed layouts.

Refurbishment and Green Infrastructure - CBPP and trees, and other planting, have been proven to work together in synergy. CBPP – whether full-construction or in overlay form – can collect rainfall away from the canopy and convey it to the tree. It can then simply discharge horizontally into a raingarden, perhaps with overflow into an existing gulley. The raingarden stores water during heavy rain for SuDS, retains soil moisture during dry weather and provides additional water quality, 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 gas (oxygen/carbon dioxide) exchange essential to trees – without additional reservoir units or pipes requiring maintenance. CBPP also avoids tree root disruption common with other paved surfaces.

This approach is exemplified in Bridget Joyce Square, London, where a typical, adopted asphalt street and adjacent parking areas were transformed for community use, with CBPP overlay shared surfaces discharging to tree-planted raingarden basins. The basins provide water storage for SuDS to reduce overloading existing drains as well as for irrigation. Interpave revisited the project around 5 years after completion and noted that the permeable paving was performing well and experienced no problems during recent extreme summer storms.

Tests were also carried out demonstrating that infiltration rates of the permeable paving were more than double those recommended by ‘The SuDS Manual’ (CIRIA, 2015). The trees and other green infrastructure were healthy, substantial and particularly wellestablished. A case study exploring Bridget Joyce Square is available on Interpave’s website and other innovative project case studies will be published shortly. www.paving.org.uk

HOW TO SPECIFY OUTDOOR POWER DISTRIBUTION UNITS TO MEET ANTICIPATED DEMAND

Adding a power supply infrastructure to an outdoor public space, such as a courtyard or enclosed garden, is an excellent way to unlock the potential for holding events and creating more revenue-generating space. But how can you ensure that the proposed power supply will meet the demands and needs of the site given the versatility that comes when an outdoor space is power-connected?

Over-specifying the services infrastructure and distribution units could be a costly mistake. But under-specifying could result in the need to hire temporary generators or run lengthy trailing cables from adjacent buildings, creating avoidable trip hazards.

Whether you are a site owner or an architect or landscape architect working to enhance an outdoor space, the starting point is to ask three basic questions about demand and needs: 1) How do you envisage that your proposed power unit or power distribution system will be used? 2) How many power sockets will be needed? 3) Would the location also benefit from a supply of water or data connectivity?

Designing-in versatility - Equipping any outdoor space with a power infrastructure is going to add a great degree of flexibility of use to the location. But when designing the power supply, it is important to have a picture of the typical and maximum usage that will be required.

Going back to basics, why is the site going to benefit from a power infrastructure? For a business such as a restaurant, bar, café or hotel, the outdoor space could add additional areas for eating and drinking primarily. Such uses would typically require the power distribution to provide access to sockets for lighting, till points, AV equipment or outdoor serving

points such as mobile counters or drinks dispensers. But is that the limit to such a site’s potential? Could it also be used as a stage are for outdoor music performances and other entertainment, for example. And if so, would your proposed power supply solution accommodate these requirements too? Also think about the location of the power units in relation to how they will be used.

If the site is to be used for market stalls, where will the stalls be set up on site and where will the main pedestrian routes be? Installing power units in the correct locations will help reduce the risk of trip hazards as cables trailing across the main footfall areas can be minimised or avoided completely.

Once you have a picture of how the site could be used, it is time to consider how you feed power to the locations across the space. This can be achieved with the installation of a Pop Up Power Supplies® power distribution unit in one of three forms: 1) Pop up, retractable power unit – this is submerged in the group until it is needed, and raised/lowered using a turning handle. 2) Flip-lid, in ground power unit – this is permanently submerged in the ground with access provided via a flip-lid which can be used while the lid is locked down. 3) Power bollard – a street furniture element which has power sockets integrated, accessible as required behind a lockable cover. The type of power unit you choose will depend on how the site will need to look or be used when the space is not being used for events, catering, etc. Both the pop-up and in-ground units can be hidden away when they are not in use, with the only evidence being a cover which can be designed to match surrounding surface materials.

A power bollard has a permanent presence, but the designs available from Pop Up Power Supplies® are elegant to avoid the utilitarian appearance that would be expected with a typical feeder pillar.

What should each power unit provide? - Consider what the electricity demand will be for the equipment that is to be connected to ensure the power supply units can handle the load. This is an area where Pop Up Power Supplies® has a wealth of expertise to help, given our experience of providing power units for a diverse range of sites across the UK, from Caerphilly Castle visitor centre to Chelsea FC’s Stamford Bridge pitch.

The retractable power units available from Pop Up Power Supplies® can be specified to provide a total power supply from as little as 63 amps right up to 600 amps. In ground units offer the option of 63 amps or 125 amps and power bollards provide up to 125 amps. The sockets in all can be configured to suit usage requirements.

These units can also be designed to provide a water supply or data connectivity. Access to water can be particularly useful for ground maintenance and cleaning purposes, so consider that too and the units can become extremely useful assets. www.popuppower.co.uk