Ian Geeson of Charcon considers how integrating Sustainable Urban Drainage systems (SuDS) into every future urban design project would make a step change in ensuring effective water management
In winter 2015/16, we saw widespread flooding, with 16,000 homes in north England 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. But in urban environments with the extensive use of hard surfaces, water percolation is impeded and results in high volumes of surface water run-off. This water enters drainage systems that were never designed 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.
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 while 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 drainage and sewer networks and reducing flooding potential. 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. It can help remove pollutants and offer wider societal and biodiversity benefits. This means that water run-off that is treated within the SuDS installation can then be harvested for irrigation, biodiversity or amenity use within a development – or can simply be recycled. The Government’s change in approach to implementing SuDS through the planning system is a very clear call for designers to lead the way, developing multi-functional SuDS as part of the design process. With a holistic, design-led approach, drainage issues should become an integral part of the process – and not an end in itself. However, to achieve this effectively, 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 8582 suggests incorporating permeable surfaces and surface-based conveyance. This could be porous concrete and asphalt – or for alternative aesthetics, concrete block permeable paving. While traditional drainage systems are constrained by capacity, SuDS solutions are not. Incorporating permeable paving allows water to soak naturally into the pavement below. Such systems can be designed to address a number of key issues such as water volume and quality, trafficking and biodiversity.
Designing and planning for SuDS
The Code of Practice advises that permeable surfaces and surface-based conveyance and storage systems should be used in concept 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. A recent SuDS paper presented at the Building Centre in London looked at innovative designs that leading architects are proposing, which seek to live with water, rather than defend against it. One example was ‘Permeable pavements’ which can be designed to treat the water as it passes through the system, removing water-borne pollution. This also supports the ethos of ‘living with water, rather than defending against it’. The ‘Designing for Flood Risk’ presentation at the Building Centre outlined the reality of flooding for home owners and the importance of designing for flooding. Concrete block paving can be used in almost all circumstances – full infiltration to the ground, partial infiltration with excess water directed to the next SuDS stage, or full containment and controlled release to the next SuDS stage. Concrete block permeable paving is ideally placed to meet the Code of Practice requirements and is a good choice for architects looking for a truly holistic, design-led solution. There’s an extensive range of permeable paving options now available and the styles, finishes and colours available mean architects have real freedom when making design choices. Also, the performance of these products is comparable to standard pre-cast concrete paving products. Permeable paving not only provides a level, firm and slip-resistant surface, it removes the needs for cross-falls, channels and gulleys. Furthermore, correctly designed, concrete block permeable paving can support heavy trafficking and loads, making it ideal for all shared surfaces and residential roads, as well as car parks and hard landscaping. A real benefit to the client, of course, is that very little maintenance of a permeable paving system is required – and as there’s no need to install below-ground drainage, ongoing cost and maintenance is kept to a minimum, if SuDS is designed in from the start of the project. The industry needs to grab the opportunities that SuDS present with both hands. Earlier engagement with landscape architects and SuDS manufacturers will help ensure the right SuDS solution is identified for the project – whether that’s permeable hard landscaping systems of soft SuDS, such as ponds, filter drains, or artificial concrete streams. In doing so, designers will be able to effective delivery a visually appealing and sustainable solution for the future.
Ian Geeson is technical manager at Charcon, the commercial hard landscaping division of Aggregate Industries