groundworks Storm-proof rainwater harvesting
Combining rainwater harvesting with sustainable urban drainage systems (SuDS) enables architects to provide an efficient, space-saving water management solution that’s resilient against the future. Kevin Reed of Graf UK explains how.
T
he effects of climate change are making headlines almost daily – often in relation to serious flooding, which is becoming increasingly commonplace in the
UK. On the flipside, the threat of droughts is also a growing concern for the future. This has created the need for effective water management solutions that can handle both weather extremes. In response to this, rainwater harvesting (RWH) systems that can be combined with stormwater management to create an effective, dual-capability solution (often using just one tank) are emerging as market frontrunners. These systems reduce pressure on the potable mains supply
by collecting water for reuse elsewhere when rainfall levels are low. This makes both environmental and economic sense, particularly given that a third of domestic water doesn’t need to be drinking water quality and instead is used for flushing toilets, washing clothes and cars, and watering gardens. Combined systems also deliver effective, controlled protection against floods when rainfall levels are at their highest – providing valuable peace of mind when it’s needed most. Against this backdrop, there is clear and growing commercial
opportunity for architects and specifiers in the sector. However, to maximise this, it’s crucial that they familiarise themselves with the latest developments in this evolving market.
Joining forces
Alongside the changing climate, one of the key factors driving demand for combinable RWH and stormwater management is the fact that all new developments are now legally required to assess their flood risk, and incorporate SuDS to minimise it. While RWH cannot replace an entire SuDS system, when com- bined with a stormwater management solution, you essentially get two systems in one – making both more cost-effective. With this in mind, architects who can advise customers on how to bolster their RWH tanks to include stormwater management capabilities are putting themselves at a competitive advantage. So what do these architects need to know? There are two methods of stormwater management:
attenuation (where water is retained and then slowly discharged into the surface water drainage system or water courses) and infiltration (where water is gradually released back into natural groundwater reserves). However, due to the clay-heavy soil in many areas of the country not being suitable for infiltration, attenuation is the most common approach in the UK.
Attenuation can usually be incorporated into the same tank as the RWH system, allowing for a one-tank solution – while infiltration generally requires a separate system. An overview of the best options for different applications are listed in the following paragraphs.
Small-scale attenuation
With individual domestic properties, it is possible to opt for an oversized RWH tank that also incorporates attenuation. This tank is designed with an outlet which is placed high enough to provide enough water for reuse in the bottom of the tank, but low enough to ensure sufficient space for surplus water to collect at the top (see picture). In the event of storms, the surplus is then released at a con-
trolled rate, and is distributed over a much longer period – reducing pressure on the surface water drains and water courses. The submersible pump at the bottom of the tank feeds the remainder of the water either directly to the point of use (in the
RWH system with a tunnel system for storm water filtration
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