Designers of new developments must start to factor in government requirements for sustainable drainage systems which are due to come into effect soon.

With legislation mandating sustainable drainage systems (SuDS) and their adoption for new developments on the horizon, developers and designers must upskill to ensure future designs meet tough new standards.

The government’s recent announcement that it intends to implement Schedule 3 of the Flood and Water Management Act 2010, is a game changer for SuDS.

It means that SuDS adoption is expected to be mandatory in England, as it has been in Wales since 2019.

In Scotland, Schedule 3 has not been implemented, but SuDS are generally a requirement within planning legislation.

“While developers currently have the right to connect drainage systems into sewers, that is unlikely to be the case anymore,” explains Advanced Drainage Systems (ADS) UK manager Stuart Crisp.

“Instead, they will have to show that they have included SuDS in their schemes and demonstrate how that SuDS system can be maintained over the lifetime of a development.”

Subject to a consultation later this year, implementation of Schedule 3, which includes SuDS approval and adoption, is expected in late 2024.

That means that engineers have less than two years to get up to speed with the range of possible solutions above and below ground and the implications those bring.

“Designers will have to think about more than just hydraulic design, to include whole life maintenance and treatment to deal with water quality issues and specific pollutants,” says Crisp. “There will probably be a transition period as Schedule 3 comes in, but it makes sense to upskill now in order to future proof designs.”

Currently, SuDS can be adopted by water companies as long as systems comply with requirements in the Design and Construction Guidance (DCG) document which sets out how SuDS should be delivered. However, it is not compulsory for a developer to jump through the adoption hoops, leading to the use of some assets which are not a prescribed, consistent standard of quality and performance or which are not properly maintained and monitored, leading to problems down the line.

The DCG was updated last year to include arch-shaped, below-ground attenuation structures, such as ADS’s StormTech. StormTech offers a flexible and cost-efficient alternative to other below- ground attenuation structures such as crates or large diameter pipes. It has built-in pollution treatment, reducing the extent of additional treatment required elsewhere in the SuDS system.

It is expected that Schedule 3 will change the adopters of SuDS to become SuDS approving bodies (SABs), in line with the Welsh approach, which will be within unitary councils or county councils.

The change will bring in new statutory guidance, taking over from the DCG to cover design, construction and operation over an asset’s lifetime.

“The statutory requirements in England are likely to be more onerous than the DCG and the current non-statutory standards in terms of what will be acceptable for planning approval and adoption after construction,” warns Crisp. “SuDS adoption becoming mandatory, with few exceptions, will raise the bar. Happily, poor quality products and poorly executed designs are likely to disappear from the market.”

For anyone looking to start the upskilling process now, manufacturer training and continuing professional development, such as those on below-ground attenuation offered by ADS, are already available and should include information on legislation, best practice and comparable systems.

StormTech chambers can be an integral part of a green infrastructure project by offering additional scope for the designer to enhance performance and resolve technical issues.

StormTech has previously been used in a variety of GI applications including, pavements that allow the movement of water through the surfacing

material. The StormTech system can be installed below the pavement or used in combination with other SuDS systems to enhance the water storage capacity and pollutant removal performance.

In Francisco Park 372 StormTech chambers were installed in the existing reservoir to provide a total storage capacity of 2,000m³ of water. This has enabled the reservoir to be transformed into a sustainable and cost-effective community space with a stormwater capture and reuse system that will perpetually provide water for the park’s irrigation and toilets.

StormTech was chosen for this project as they provided the best ratio of storage volume to footprint area.

StormTech is manufactured by Advanced Drainage Systems (ADS). ADS is America’s largest manufacturer of corrugated thermoplastic drainage pipes and a specialist in water management systems. To read the full story click here.

ADS StormTech below ground SuDS attenuation has been used within over 50,000 projects worldwide. Eurocode modelling demonstrates that the standard StormTech Construction Guidelines for minimum and maximum cover depths can be used for both shallow and deep applications.

This enables the SuDS attenuation system to be installed under roads with HGV traffic loading with a cover depth as shallow as 350mm. StormTech’s arch-shaped chambers are designed and manufactured to codes and standards published by the American Association of State Highway & Transportation Officials (AASHTO) and the ASTM international.

Thanks to the wide range of StormTech chamber sizes available design can be adapted to meet many site configurations. All sizes of the StormTech chamber have been analysed using a finite element analysis (FEA) model to Eurocode design principles. In the most demanding loading scenarios and the calculations proved that all StormTech chambers are structurally adequate for each of the four Eurocode load model cases.

StormTech is now available in the UK and other European countries. With no “equivalent” standard to the AASHTO or ASTM available in the UK, ADS commissioned a modelling study to demonstrate their performance under the Eurocode design methodology.

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