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Innovative rainwater solution for new urban district

Photo: cowi

​An innovative rainwater solution will save approx. 30 million litres of groundwater annually in a new urban district. COWI has developed the concept and design for the comprehensive solution.


Why use a resource such as clean drinking water for toilets and washing machines? Wouldn’t it be an idea to collect rainwater and use that instead?

Yes, says Jørn Tækker, CEO of the Tækker Group, which is working at full blast to develop a new urban district in a gently sloping 140 hectare agricultural area near Aarhus in Denmark. The ambition is that residents of the area should use cleaned rainwater for e.g. flushing toilets and washing clothes, thereby limiting the discharge of rainwater into watercourses and coastal areas while also protecting underground water reservoirs.

Rainwater as a ressource

More specifically, in the first phase of the urban development project, comprising 600 dwellings, approx. 30 million litres less water will be discharged from surfaced areas into the local stream every year, and likewise discharges of nitrogen and phosphorous into the Bay of Aarhus will be reduced. COWI has developed the concept and design for the comprehensive water solution, in which rainwater from roofs, roads and parking areas will be collected in canals and lakes adding a recreational value to the area.

The rainwater system represents a brand new approach to water management in urban development projects, says Carsten Fjorback, Development Director at COWI.

“Traditionally, rainwater is seen as a problem to be solved and led away as fast as possible. In an age of urbanisation and climate change, this has proved to create problems in the form of increased flooding. In the Town of Nye, we have taken another perspective and see rainwater as a resource to be managed where it falls,” says Carsten Fjorback.

Think several years ahead – it pays off

Water is incorporated into all solutions in the Town of Nye, including infrastructure such as roads and paths, parking spaces and green spaces. For example, multifunctional roads are being laid out, which not only meet the residents’ transport needs, but also have drains for collecting water and channelling it into catchment basins in the area. The drains also function as flow corridors, thereby helping to protect Nye against major rainwater incidents such as those experienced in Copenhagen in July 2011, when flooding caused damage in excess of DKK 5 billion.

“Existing towns and cities were founded in another age, when disciplines and functionalities were not necessarily coordinated. That increases the risk of serious flooding and water damage,” says Carsten Fjorback.

He admits that coordination may result in more expensive solutions for individual subcomponents.  

“But if we think several years ahead – and that makes good sense in connection with urban development – this is usually the most inexpensive and sustainable solution because later on less money will need to be spent on finding solutions to problems that could have been predicted from the beginning,” says Carsten Fjorback.

With shared cars, energy-efficient housing and collection and reuse of rainwater, Nye will generally have strong focus on sustainable use of resources, and Jørn Tækker makes it quite clear that he did not get involved in this project with a view to making a quick buck.

“Profit that leaves a bad taste in your mouth is worthless. Instead, it is about doing something that will benefit us all and help us look after the resources we have,” he says.

Climate change calls for better utilisation of rainwater

The ambition is that rainwater should be cleaned to a level where it can also be approved as drinking water. Ultimately, that would mean that not a single drop of groundwater will be required when Nye has been fully developed for around 20,000 residents. The cleaned rainwater will be enough to meet the whole district’s water consumption requirement.
Carsten Fjorback sees a huge potential for this solution in other parts of the world.

“Access – or lack of access – to water is a source of conflict and inequality in many parts of the world, and these issues will not become less prominent as the climate changes. So in that context optimisation of rainwater management could also be part of the solution,” he concludes.


Background & Facts

There is a strong need for innovative solutions for managing rainwater due to:

  • Climate change causing higher water levels in the oceans and more frequent and stronger cloudbursts. Other countries can anticipate more and longer spells of drought.
  • Water crises, including lack of and rights to water, are now on the DAVOS top 10 list of crises threatening world security and our future. 

In the urban development project Nye north of Aarhus, COWI – working with the Tækker Group and relevant authorities from the City of Aarhus and Aarhus Vand – has been responsible for development and design of roads and all water management, including innovative and sustainable use of rainwater and protection against cloudbursts. 

The solution is initially intended to ensure sufficient and clean secondary water for washing clothes, flushing toilets and extinguishing fires etc. for some 2,000 residents from 2017.

Adantages include:

  • A reduced load on local sewer systems – especially in connection with extreme rainfalls. 
  • A reduced need to supply the residential area with clean drinking water, which will reduce use of groundwater resources by approx. 30 million litres of water annually. 
  • The system for water management increases the variety of animals and plants in the area (biodiversity).

The solutions are based on well-known technologies, but they are used in an entirely new context: 

  • A treatment plant that cleans the rainwater and drainage water collected to give the water a suitable quality. 
  • A catchment basin that combines an efficient storage volume with a favourable environment for increasing biodiversity. 
  • A cleaning biotope that keeps the water in the lake clear. 
  • An intake of water from the lake to the treatment plant that has a gentle impact on the biology of the lake. 
  • A two-track distribution network. 
  • Fire extinguishing using secondary water in a system with a small pipe dimension. 
  • Operational routines and monitoring systems to ensure optimum security.

LAST UPDATED: 17.11.2017