Outdoor Engineering Effective Water Management
Ian Geeson, Technical Manager at Charcon, the commercial hard landscaping division at Aggregate Industries, considers how integrating Sustainable Urban Drainage systems (SUDS) into every future urban design project could play an essential part in effective water management. Advice is also provided on designing and planning SUDS for effective delivery and visual appeal.
In Winter 2015/16, we saw widespread flooding, with 16,000* homes in Yorkshire, Lancashire, Cumbria and parts of central and north east Scotland affected. Damage to roads, bridges, public rights of way and drainage systems totalled £250m* and the insurance bill topped £1.3bn*. But the problem did not just arise from rivers breaking their banks.
In the natural environment, a high proportion of rainfall soaks into the ground and filters its way into rivers and is carried away. However, in the urban environment, due to the extensive use of hard surfaces, water is unable to soak away and results in high volumes of surface water run-off. This water enters drainage systems that were never designed to have the capacity to cope with such high volumes of water.
There are a number of high performance and cost effective SUDS solutions readily available to manage the issue of surface water runoff. However, too often during the design process, the role SUDS can play in urban design and effective water management is misunderstood, an afterthought - or perhaps forgotten entirely.
URBAN DESIGN & EFFECTIVE WATER MANAGEMENT
There is a common misconception that SUDS can only be used in certain applications. But in fact, they can be applied to any residential, commercial or urban project, in towns or built up city centres. And whilst they can’t prevent flooding, by introducing permeable surfaces coupled with water storage and infiltration systems, surface water-run-off will decrease, relieving pressure on damage and sewer networks. This will ultimately help reduce potential flooding. The use of these techniques is well proven and documented.
While SUDS technology is not a new concept in the UK, architects, designers and engineers often forget that there is much more to SUDS than water storage. Certainly, it should help reduce water run-off and the risk of flooding but it can also help remove pollutants and create societal and biodiversity benefits. This means that water run-off that is treated within the SUD system can then be harvested for irrigation, biodiversity or amenity use within a development - or can simply be recycled. If you look at SUDS this way, as an architect, the design opportunities are countless!
The Government’s change in approach to implementing SUDS through the planning system is a very clear call for architects, designers and engineers to lead the way, developing multi-functional SUDS as part of the design process. With a holistic, design-led approach, the issue of damage should just become an integral part of the process, and not an end in itself. Indeed, by integrating SUDS with urban design, the architects, designers and engineers will be able to better deliver amenity and community value as well as improving the character of the landscape and townscape.
However, to achieve this, surface water management needs to be linked to development planning from the very start of a project. This will allow space to be used more effectively and in a multi-functional way, enabling water storage and conveyance zones to form part of the development’s character.
It will also maximise the drainage system’s capacity for delivering multiple planning and environmental benefits. Wherever possible, the 2013 Code of Practice BS 85823
suggests incorporating permeable surfaces and
surface-based conveyance. This could be porous concrete and asphalt - or when aesthetics is high on the agenda, concrete block permeable paving.
Whereas traditional drainage systems are constrained by capacity, SUDS solutions have no such constraints. SUDS solutions incorporating permeable paving allow water to soak naturally where it falls into the pavement below. Such systems can be designed to address a number of key issues such as water quantity, water quality, trafficking and biodiversity. By considering these key issues in the design you can develop drainage systems that reduce the impact of high levels of rainfall on communities and wildlife.
DESIGNING AND PLANNING FOR SUDS The Code of Practice3
advises that permeable surfaces and surface-based
conveyance and storage systems should be used in conceptual designs wherever practical. It also highlights the importance of linking multi- functional SUDS design to other development infrastructure, such as car parking and public open space. Indeed, a recent SUDS paper presented at the Building Centre looked at clever design responses to flood risks and considered the innovative design that leading architects are proposing, which seek to live with water, rather than just defend against it.
The permeable pavement can be designed to treat the water as it passes through the system, removing water-borne pollution, meaning it can be used in landscape design, harvesting and ecology. This also supports the ethos of ‘living with water, rather than defending against it’. The Building Centre’s ‘designing for flood risk’ presentation outlined the reality of flooding on home owners and the importance of designing for flooding. As water filtrates through the system, many of the pollutants are treated
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