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Sustainable drainage system

The central role of SuDS in blue-green infrastructure.
Centuries of simplistic views on urban water management are slowly but inevitably being replaced by modern, sustainable methods – often centred around the blue-green infrastructure (BGI) approach. New methods are inevitable not least due to greater population densities and expanding impervious surfaces in urban areas, which intensify pressure on water drainage systems.

Sustainable urban drainage systems, abbreviated SuDS, are an integral part of the BGI approach to water management, aimed at making urban drainage systems compatible with the natural water cycle. SuDS may consist of “natural” measures, such as green roofs, planters or green belts – combined with “artificial” measures, such as underground infiltration, retention tanks and many other solutions.

Here, we will summarise a number of insights from the Sweco Urban Insight report “From threat to opportunity – revaluating storm water management in urban areas”. As the name indicates, this report looks at the management of storm water in particular, and how value can be produced out of what once was merely a problem to be managed.


Background: Purpose and advantages of blue-green infrastructure

The blue-green infrastructure approach can perhaps best be summarised as building with nature, as opposed to only reacting to it, to solve urban challenges. It aims to secure a sustainable future while also generating multiple benefits in the environmental, ecological, social and cultural spheres.

It requires a coordinated interdisciplinary approach to water resource and green space management from institutional organisations, industry and academia, as well as local communities and stakeholders.

There are several terms and acronyms associated with this type of solution in various parts of the world, for example: Sustainable Drainage Systems (SuDS), Water-sensitive Urban Design (WSUD) in Australia, and Low impact Development (LID) or Best Management Practice (BMP) in the United States, as well as blue-green cities and blue-green infrastructure.

Some of the characteristics and benefits of this type of solution are:

  • Pollution control, improved air and water quality
  • Cost savings compared to operations and maintenance of traditional drainage systems
  • Community amenities – attractive green areas, health and well-being benefits
  • Improved habitats for wildlife
  • Flood prevention and reduction
  • Encouraging natural groundwater recharge
  • Adaptation to climate change
  • Innovative uses of SuDS in traffic management


Storm water as an asset to create sponge cities

Illustration: RSPB Wildfowl and Wetlands Trust

Without storm water management of our urban areas, flooding would affect the lives of citizens living, working and moving through these areas, and prevent the movement of goods and information. Storm water should not be considered a threat, however, but rather as a positive landscape element. Together with vegetation, it constitutes protective temperature islands in cities. Also, in daily speech this approach is called sponge city.

In recent years, conventional “hard engineering” approaches (sewers etc.) have been complemented – and in some cases replaced – with more natural approaches using blue-green infrastructure. This can involve, for example, a system of measures such as green belts, grassed dry retention ponds or raingardens. Integrated master planning and modelling has also become a key part of storm water management in urban areas.

Sustainable storm water management schemes must be integrated design solutions, involving a set of measures suitable to specific local conditions. Such an integrated storm water system has not only to consider and manage storm water in present climatic conditions, but also all potential future climate change scenarios (e.g. more intense rain events, less rain, rising temperatures etc.).

Comprehensive long-term planning for storm water is crucial and should involve integrated designs utilising various innovative technical solutions, including blue-green infrastructure.

There are three basic recommended stages to be taken when managing storm water in urbanised areas:

  • The first step is based on the idea of keeping storm water where if falls and retaining it locally.
  • If the amount of water is too great for local retention, then in the second step it is necessary to store storm water in extra storage capacity – either naturally or artificially created.
  • Excess storm water that cannot be retained or stored has to be, in a third step, slowly drained through available or created waterways.

From the point of view of key stakeholders including states, communities, business/industry groups, academia and non-governmental organisations, the overall process should rely on adopting a long-term approach to planning. Communities can also elaborate plans that allow for the integration of selected projects within other community development plans, including master plans.

With an effective participation strategy, guidance and public education, local communities have the opportunity to learn, ask questions, raise issues, and ultimately ensure Sustainable Drainage System (SuDS) implementation benefits communities in the best possible manner.


The financial case for suds and blue-green infrastructure

SuDS are sometimes incorrectly viewed as being more expensive than conventional storm water management. This misconception comes from too narrow a focus on investment costs for projects in city centres.

On the contrary, they are usually more cost effective than conventional methods, and they also bring additional multiple benefits. Experiences from the United States can give us some useful perspectives in this respect, when considering the financial costs of green infrastructure in general.

  • A study carried out in the United States of 479 green infrastructure projects found that 44 per cent of green infrastructure projects reduce total costs compared to the 25 per cent that increased the costs.
  • A green infrastructure project in Philadelphia is due to cost $1.2 billion compared to over $6 billion for “grey” infrastructure over 25 years. It is estimated that: 250 people will be employed annually in green jobs; property values will increase by up to $390 million near parks and green areas over 45 years; reduction of up to 140 deaths caused excessive heat over 45 years; visits to parks and recreation sites will increase.
  • It was estimated that a green infrastructure plan in New York City will cost $1.5 billion less than investments needed for grey infrastructure. It was also estimated that sustainability benefits over a 20-year period would range from $139–418 million. The plan estimates that “every fully vegetated acre of green infrastructure would provide total annual benefits of $8.522 in reduced energy demand, $166 in reduced COemissions, $1,044 in improved air quality, and $4,725 in increased property value.”

Experience from many European countries also suggests that maintenance costs and responsibility for maintenance of Sustainable Drainage Systems (SuDS) is usually more challenging than the cost of implementing SuDS in new developments. Consequently, arrangements for maintenance of SuDS systems should be considered during the early stages of design, or there is a risk of turning a good SuDS implementation into a non-functional set of facilities.

For additional information, conclusions, citations, and a wealth of examples, please refer to the full report: FROM THREAT TO OPPORTUNITY – REVALUATING STORM WATER MANAGEMENT IN URBAN AREAS

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