As the UK targets 1.5 million new homes, sustainable drainage must be part of the plan, says Ben Puddy of Hydro International; he explains how blending blue, green and grey systems can build the perfect drainage mixture to support climate-resilient communities.
The Government has put housing at the heart of unlocking growth in the UK, committing to deliver the biggest housebuilding programme in two generations.
The deliverability of building 1.5 million homes, the overhaul of the UK’s planning system, and the impact on the green belt have so far dominated the debate.
What receives considerably less airtime is climate resilience: the question of how, in a time when extreme weather events are becoming commonplace, we can deliver new settlements and towns with the drainage systems that are suitable for a changing climate.
Blending nature & engineered solutions
With targets in place for Biodiversity Net Gain (BNG) and a greater focus in the development community on creating green and biodiverse spaces that promote community wellbeing, there is a drive to embed nature-based drainage solutions.
Green and blue – nature-based solutions on the surface – are increasingly being seen as the prime solution to alleviate the burden on our wastewater infrastructure. The reality is that on many sites it is often more efficient for these solutions to be integrated with below ground ‘grey’ systems.
There are a number of reasons why this blend of drainage engineering is likely to be more successful. For many new housing sites, a solely natural green and blue SuDS solution that returns surface water into the environment is often not feasible due to limitations including soil types and ground conditions.
In these scenarios, grey flow attenuation systems are vital to effectively manage surface water runoff.
Selecting the right flow control solution is an essential element of a successful SuDS system. A better performing flow control passes a higher volume of flows earlier during rainfall and means that less capacity on site is needed to store excess flows. This approach not only reduces the land take of storage ponds or detention basins where needed, but also cuts construction costs.
SuDS installations must be resilient to increased run-off from urban creep, new developments and a changing climate. Flow controls that have the option for future adjustment will be key, as changes in flow rate can be accommodated through modifications to the unit, rather than requiring total replacement.
Blended grey, green and blue solutions can make best use of the land available and provide housebuilders and developers with an optimal combination of effective surface water storage and public amenity space. Sitting beneath swales, detention basins or ponds, storage and infiltration tanks add capacity while reducing the surface-level impact of the drainage solution.
Adding smart flow and sediment level monitoring within these below ground stormwater drainage systems provides asset owners with a greater understanding of performance over time. This enables proactive maintenance and optimises environmental protection.
The grey advantage
Ponds and swales have the ability to treat water sufficiently to meet water quality legislation (as outlined in the CIRIA SuDS Manual (C753) Simple Index Approach). However, an additional proprietary, below-ground grey solution can boost performance and bring additional benefits.
A stormwater treatment system, incorporated upstream of a pond can provide efficient pre-treatment and remove sediments, litter and hydrocarbons while reducing the footprint of the wider solution.
The resulting benefits are significant and wide ranging: firstly, reducing the size of the pond required if necessary due to a smaller sediment forebay requirement. Further benefits are simplifying maintenance and the associated reduction in costs through automated maintenance alerts; protecting the biodiversity of the pond by removing the majority of pollutants upstream; and reducing the chance of shock loadings of pollutants if pond sediment needs to be dug out.
Early engagement for long term benefits
To construct the most effective sustainable drainage systems, land take, long-term performance and maintenance must all be considered at the earliest stage of the planning and development lifecycle.
Forward thinking and early engagement with specialist providers can help the developer community to consider the options and integrate grey solutions while ensuring that green and blue SuDS are embedded across a scheme.
While the delay to the adoption of Schedule 3 of the Flood and Water Management Act 2010 means that the use of SuDS is not yet mandated in England, it does not need to hold back the developer community. With Wales having already adopted the schedule in 2019 and decades of tried-and-tested engineering expertise within the supply chain, there is already a wealth of knowledge available to housebuilders and developers.
Nature-based and grey underground systems are not an ‘either or’ decision for housebuilders. With early engagement they are complementary solutions which can be combined to deliver effective sustainable drainage, while reducing land take and supporting biodiversity and public amenity goals.
Ben Puddy is product manager at Hydro International