GREEN & BLUE INFRASTRUCTURE
MANAGING RAINFALL AT SOURCE:
WHY A CONNECTED SUDS APPROACH HELPS MEET THE REQUIREMENT TO RETAIN THE FIRST 5MM OF RAINFALL ON SITE
Why the first 5mm? With new housing developments expected to retain the first 5mm of rainfall on site, developers and landscape professionals face a growing challenge: how do you manage everyday rainfall when space is already under pressure?
The first 5mm matters because it represents the frequent, light rainfall that often creates the“ first flush” of urban runoff. As rain washes across roofs, roads and hard surfaces, it can pick up oils, microplastics, metals and other pollutants before carrying them into drains, sewers and local waterways. Capturing this rainfall at source helps reduce pollution, ease pressure on sewer networks and better mimic natural greenfield conditions, where much of this water would be intercepted by vegetation, absorbed by soil or lost through evaporation.
Small steps to successful solutions The answer is unlikely to be one larger tank, one deeper excavation or one standalone drainage product. Increasingly, effective SuDS design depends on using a connected network of complementary features that slow, store, filter and reuse water close to where it falls.
This is where the UK can learn from countries such as the Netherlands, where water-sensitive urban design has been embedded into public realm and development thinking for many years. Dutch cities have demonstrated that rainwater management does not need to be hidden underground. It can be visible, multifunctional and integrated into streets, buildings, landscapes and community spaces.
The way forward for constrained UK sites For UK projects, particularly on constrained sites, this means thinking beyond traditional drainage infrastructure. A more workable approach is to spread storage and treatment across the scheme, using a network of smaller, integrated interventions that manage water within a tighter footprint.
Green and blue walls can intercept rainfall and direct surplus to storage, while smart water butts capture roof runoff for reuse. SuDS planters and rain gardens add further capacity, supporting attenuation, filtration, habitat and amenity in compact spaces. When combined with green roofs, specialist soils, intelligent controls and materials such as Hydrorock, these elements form a coordinated, site-wide system that holds water and releases it gradually back into the ground.
One approach, multiple benefits This approach is not only about flood risk. Recent years have shown how quickly the UK can move from intense rainfall to drought conditions and hosepipe bans. For homeowners, schools, community gardens and developments with biodiverse planting, retaining water on site will become increasingly important. Captured rainwater can be reused to irrigate trees, living walls, planters, edible gardens and productive landscapes, reducing reliance on mains water during dry periods.
A connected SuDS strategy therefore supports both flood resilience and drought resilience. It helps meet planning and drainage requirements while also contributing to biodiversity, urban cooling, water quality and place quality.
The strongest schemes use a management train of smaller, integrated interventions, each performing a clear role within the wider system. Together, they create landscapes that absorb rainfall, reuse water, support planting and reduce pressure on drainage networks.
At BioScapes Group, this joinedup thinking sits at the heart of how landscapes are planned and delivered. It reflects an integrated approach to landscaping that considers water alongside biodiversity, soil health and longterm performance. By designing systems where these elements work together, it becomes possible to create places that respond to everyday rainfall, support thriving ecosystems and remain resilient as conditions change.
www. bioscapes. co. uk
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