Page 4

evolutionwinter2012

WATER Evolving our approach to opportunity across a large area to create aSurface water management plans offer an manage surface water However, this requires all departmentsstrategic approach that can lead to greaterco-ordination when opportunities arise. within the local authority and other Managing surface water differently provides an opportunity key stakeholders such as water and to improve urban areas, says Dr Chris Digman, MWH, sewerage companies to recognise these Jonathan Glerum and Paul Shaffer, CIRIA. opportunities. Ideally these approaches should use a selection of SWMM that combine both Retrofitting urban areas, whether it is such a street to manage surface water above and below ground solutions, to replace ageing infrastructure, major resulting in the use of both green and blue and ideally SuDS. Where possible, any regeneration work or minor improvements, infrastructure (Figure 3) and retaining work should be aligned with other is not new. Even in times of austerity the below ground infrastructure for an urban improvement works, providing far there is a need to continually improve and enhanced level of performance. greater benefits to the community and enhance urban areas. Given the current environment. economic climate it is more important than ever to realise the opportunities available Creating benefits beyond drainage and maximise the benefits when retrofitting Selecting the correct SWMM will depend urban areas. This should include how on the local conditions and context where surface water is managed. retrofitting is taking place. For example, if it is possible to infiltrate water into the Out of sight, is out of mind ground, and this does not create other Managing surface water has traditionally consequences, then this should be done. taken place below ground, using pipes, Figure 1 A typical UK suburban street, in This has successfully been carried out in the culverts and tanks to convey and attenuate need of local enhancement United States in places such as Portland, surface water. However, points in the Oregon (see Figure 4). In places where drainage network such as combined sewer this is not possible then there are many overflows can pollute watercourses and other measures that can be used that will if, and when, this infrastructure fails it attenuate water, slow it down, and convey can lead to flooding. Retrofitting surface it to another place. Where possible, this water management measures (SWMM) should be done on the surface. However, still recognises the need to use traditional even in areas with low permeability, approaches where appropriate. However, some infiltration will still be possible, as these measures should be considered demonstrated by the retrofit rain garden at with a new suite of alternative measures Ashby Grove, Islington, London (Figure 5). to manage surface water both above Figure 2 The same street where recent and below ground, such as sustainable resurfacing works have taken place and drainage systems (SuDS). Adopting a a missed opportunity to manage the “mix and match” approach with a wider surface water range of SWMM will be vital for successful retrofitting and creating multiple benefits. Realising the opportunities for change Current regulation and legislation, including the Flood and Water Management Act (2010) and the EU Water Framework Directive (2000) will continue to create the need for improvements to the drainage Figure 3 A sketch of the same street showing network. The recent extended dry and wet how opportunities to retrofit could be realised weather periods causing the extremes of drought and flooding demonstrate that the There are two key approaches to UK should carefully consider how to make retrofitting SWMM in urban areas: best use of and manage surface water. 1 In an opportunistic way, where gradual Work to address these needs is likely to improvements to the urban realm are continue for many years and should create carried out step-by-step, picking off opportunities for surface water to be opportunities as and when they occur. managed using a range of measures. For 2 By taking a more strategic approach example, Figure 1 shows a typical suburban where a specific need is addressed, such semi-detached housing estate. Recent as reducing combined sewer overflow work replaced many of the grassed verges spills, pollution from surface water with hard-standing for parking (Figure 2). outfalls or risk of flooding. This will look Figure 4 A recently constructed stormwater This was a missed opportunity to retrofit for and create the opportunities to planter taking highway and footpath surface retrofit measures. water on a street in Portland, Oregon 2


evolutionwinter2012
To see the actual publication please follow the link above