Sustainable Urban Drainage Systems

Published by Housebuilder Magazine

Sustainable drainage systems have been a planning requirement since 2015. Chris Windle reports on the various forms of SuDS, which combat the problem of surface water flooding in new schemes.

Hydro WMS’ attenuation tank installed under a small block of apartments due to limited space on site.

Sustainable drainage systems – SuDS to those in the know – your time has come. Changes to the planning regime have made them mandatory on many developments. Not only that, these days they need to offer more than just water management.

Back in 2015 SuDS became a requirement on developments of more than ten homes and earlier this year the government made clear there was no room for one trick rainwater ponies – SuDS today must provide multifunctional benefits.

This, says Tobermore sales manager Brian Wilson, is a “turning point” for the industry. “It’s a very important milestone in a long journey towards full acceptance of the importance of SuDS in the UK.” Which is obviously good news for suppliers who will hope to see increased demand for water management products and services such as  “Tobermore’s Hydropave permeable paving range which is manufactured with a 6mm drainage joint that has been proven to have a permeability rate of approximately 30,000 litres/sec/hectare in tests carried out at The University of Newcastle.”

Aesthetics

Wilson adds: “In terms of aesthetics, the Hydropave permeable paving range is certainly one of the most attractive hard landscaping options for housebuilders. A variety of styles are available including granite aggregate, textured and smooth surface finishes, which provide the same striking aesthetics as Tobermore’s non-permeable products. So housebuilders don’t have to compromise on aesthetics when complying with planning requirements for a SuDS system.

It has to be said, housebuilders may be less excited about the extra planning burden. But they should see it as an opportunity, says Mark Manning, business development manager at SDS Limited. “They’re likely to face increasing demands to design above-ground features that double-up as amenities like pocket parks, recreation spaces or wildlife areas. But, every drainage design has to be achievable, commercially-viable and capable of being built to time and to budget. Some developers may, therefore, perceive the SuDS requirement to be a commercial hindrance, where others see an opportunity to create attractive surroundings for residents. With pragmatic, common-sense engineering, it is possible to achieve the best of both worlds. There will be very few cases where cost, land-take or ground conditions cannot be overcome with sound engineering.”

Tobemore says that with its products, housebuilders do not have to compromise on aesthetics when complying with planning requirements for a SuDS system

But Chris Daws of Hydro WMS points out that a preference for brownfield sites, combined with more rigorous SuDS planning requirements, brings further complications. “Brownfield sites present challenges such as the space available for soft SuDS, sloping sites, contaminated land, shallow bedrock and high water tables. While the developer wants to maximise the return on the land, the local authority has a duty to ensure that legislation is adhered to and water runoff is controlled to prevent flooding.”

The key to making sure planning goes as smoothly as possible given the stretched state of many local planning authorities is, alongside working closely with them, finding a solution that meets the specific needs of each site. “It’s important to ensure that any sustainable urban drainage systems decided upon are fit for purpose, not just initially but over their lifecycle. The solutions need to be carefully considered to be best suited for the environment that they are located within,” says Simon Thomas, managing director at Asset International.

He adds: “While green SuDS such as ponds and swales can be great additions, generally speaking, these options in housing developments cannot cope with rainfall alone and need to be combined with engineered SuDS. Housebuilders need to look for solutions that offer low maintenance and the best value. It’s tempting to opt for cost savings, but housebuilders need to avoid price driven installations and instead focus on the best value to ensure the success of SuDS within developments. With this in mind, our products, made from high-density polyethylene (HDPE), have superior abrasion resistance compared to traditional methods, making them extremely long lasting, with a 120-year design life and very low maintenance.”

SuDS should be fit for purpose over their lifecycle, says Asset International. Pictured: Asset International’s Weholite system at Lovell’s Eversley Road project

Combining drainage devices with natural water management processes, while overcoming ground conditions or commercial constraints, is also a focus for SDS, says Manning. “In the past, there has been a tendency to polarise SuDS as either ‘hard’ or ‘soft’ to distinguish between manufactured and vegetative devices. Now, there is growing acceptance that a broad and expanding SuDS toolbox is available and above and below ground components can be combined to achieve the best results.”

He explains that the company’s geocellular SDS GEOlight, installed below a pond or detention basin, makes it possible to incorporate above-ground features while still achieving the required hydraulic capacity and performance in the space available. “With below-ground attenuation, a public amenity such as a playing field can be used for most of the time, and designed to flood only infrequently during severe storm events.  Alternatively, an underground tank can serve as an overflow, so that a pond or wetland continues to operate efficiently and the resident wildlife is protected.”

Controlling the quality of such overflow water is an issue that is sometimes overlooked, adds Daws of Hydro WMS. “The design of SuDS is heavily dictated by the rainfall intensity, storm return periods and agreed rate of discharge. But this increased volume of water still makes its way back into the watercourses and there is little legislation or guidance to control the quality for the site runoff. As we develop more brownfield sites we’ve identified the need to control the quality of stormwater runoff and believe this is an important part of the planning process, particularly in environmentally sensitive areas. Our X-ceptor OSR, for example, is an advanced hydrodynamic vortex separator designed to protect waterways from hazardous material spills and stormwater pollution.”

As requirements have tightened, innovation has followed. There are an array of products available – much more than can be mentioned here – capable of meeting every kind of development’s needs. And there are bound to be more hitting the market soon.

SuDS deal with water when it hits the ground, but housebuilders also need to specify systems that protect the home from above.

This is especially true since severe rainfall events are on the rise, says Steve Skeldon, above ground project manager at Wavin. The challenge on a new home is to match guttering efficiency with aesthetics.

Efficiency comes down to a number of factors, says Skeldon, “including the gutter capacity itself – the flow of water through the gutter in litres per second – how the gutter is laid and the number of drainage outlets it has. The style of a building can also have an impact. For example, the system’s overall capacity will be less if the gutter is level or includes an angle. By contrast, a straight run gutter can help maximise the functionality of a system.”

High capacity gutters are becoming increasingly popular even in areas where there is less rainfall, because of the increased efficiency and longevity they offer. But, adds Skeldon, the aesthetic needs to be right. “With our products, aesthetics are part of the innovative engineering in our design. For example, our StormLine technology offers a classic ogee shape and features for optimum performance, as well as visual appeal. The high-fronted gutter profile conceals the edge of roof tiles and hanging brackets, helping to limit visibility from the road or driveway below. Similarly, features such as our Flexiclip make it easier and neater to connect gutters to fittings, ensuring a clean, permanently water-tight joint guaranteed to perform when installed correctly.”

All of which prevents guttering distracting from the main event, the building design.