RAINWATER MANAGEMENT
Left: Marshalls are increasingly seeing SuDs and planting schemes used together. Right: Brett Martin systems, installed beneath roads, car parks and landscaped areas, create large underground voids capable of storing significant volumes of stormwater following heavy rainfalls.
UNDERGROUND MOVEMENT
As the UK experiences increasingly extreme weather patterns, from prolonged droughts to more frequent and intense rainfall events, the challenges associated with water management continue to grow, as BMJ finds out.
T
he UK may have had its hottest, driest Summer for many years, but one of the consequences of this is that when it does rain, there will be flooding. The need to effectively manage surface water runoff and reduce flood risk has never been greater.
New developments, whether housing or commercial, inevitably reduce the amount of permeable ground available to absorb rainfall naturally, which places increasing pressure on drainage infrastructure, particularly the existing combined sewer network. The result is both localised and widespread flooding. At the same time, more stringent environmental regulations and planning requirements mean builders are expected to show how surface water will be managed throughout the lifetime of a scheme. Traditional drainage approaches that simply take water away are no longer enough on their own. The news has been full of examples where heavy storm events have triggered the safety mechanism in combined sewers, discharging both polluted water and surface water in to natural watercourses. Sustainable Drainage Systems (SuDS), on the other hand, manage rainfall close to where it falls, helping to reduce flood risk, improve water quality and create more resilient developments. Among the various solutions available, concrete block permeable paving has emerged
as one of the most effective and versatile SuDS techniques available to developers, engineers and planners. Combining drainage, water treatment and structural performance within a single system, it offers a practical solution for both residential and commercial developments. Crucially, it is specifically engineered to differ from standard concrete block paving Jamie Gledhill, engineering technical manager at Brett Landscaping and Building Products, says that one of the most common misconceptions surrounding permeable paving is that rainwater passes directly through the blocks themselves.
Interlocking design
“At Brett Landscaping and Building Products, our permeable paving incorporates a unique male-and-female interlocking nib design that maximises structural integrity while creating wider joints between the paving units. This delivers a superior elastic modulus, enabling the blocks to interlock securely under heavy traffic loads while maintaining excellent water conveyance through the joints.” Gledhill explains that, because the blocks themselves remain impermeable, they retain the strength and durability associated with traditional concrete paving products. Water is directed through the joints and into the engineered layers beneath the surface, allowing the pavement to function as an efficient
September 2026
www.buildersmerchantsjournal.net
drainage system without compromising structural performance.
“A core principle of SuDS is source control, managing rainfall at or near the point where it lands before it enters the wider drainage network,” he says. “Instead of rapidly directing runoff into pipes and sewers, the system captures water immediately and stores it temporarily within the pavement structure.” Beneath the paving surface sits a specially designed sub-base formed from open-graded aggregate. Unlike conventional pavement foundations, this aggregate contains significant void space, typically around 30%, allowing it to act as a storage reservoir for rainwater. This means the pavement functions as an attenuation system, holding rainfall and releasing it gradually over time. Gledhill adds: “Depending on site conditions, the stored water can then be managed in a number of ways. On suitable sites, water can infiltrate directly into the underlying ground, replenishing groundwater and maintaining natural drainage patterns. Where infiltration is not possible due to poor permeability, high groundwater levels or specific geological constraints, the system can be lined and connected to SuDS features such as swales, detention basins, attenuation
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