Sustainable stormwater system – let nature do the work

Stockholm Royal Seaport is one of the City of Stockholm’s designated sustainability flagship districts. A clear stormwater strategy is in place to help prepare the area for future climate change threats such as increased flooding and drought. The district’s stormwater system is made up of an integrated structure of green roofs and rooftop gardens that interacts with water flow in courtyards, greenery in streets, grassy areas, rain gardens, ponds, and stormwater drains. Vegetation in courtyards and on walls and roofs and in streets strengthens park ecosystems and contributes to a robust ecosystem throughout the area.

Background

In 2008, the Stockholm City Council decided that Stockholm Royal Seaport should be an attractive, resource-effective, and fossil fuel-free district and an international model for sustainable urban development. New innovative tools, methods, and ways of working were to be developed and tested, and experiences shared with similar projects in cities nationally and internationally.

Changes to the climate that are already underway will alter conditions for the city’s green structures and stormwater management. Vegetation will be put under greater stress, winters will be warmer, and there will be longer periods during which we can be outside.

The Programme for Sustainable Urban Development in Stockholm Royal Seaport states that the outdoor environment shall be verdant and climate-smart and incorporate a variety of functions. Stockholm Royal Seaport has been designed to withstand higher sea levels of the future, more intense rainfall, and an elevated risk of flooding, as well as offering attractive outdoor environments in hot and dry periods.

Programme for Sustainable Urban Development (pdf, 3 MB, new window) >

Stormwater strategy 

The stormwater strategy, which considers stormwater as a resource, establishes guidelines for stormwater management in Stockholm Royal Seaport. Stormwater is rain- and meltwater from roofs and other hard areas in urban environments.

The goal of Stockholm Royal Seaport’s stormwater system is three-fold: withstand flooding; purify stormwater; and turn stormwater into a resource for irrigation and other ecosystem services.

The district is designed in such a way as to allow stormwater to drain from surfaces when the drainage system is overloaded and in the first instance be directed to plant beds to retain and purify water. The aim is that at least 75 per cent of stormwater on streets and squares is channelled to plant beds.

The stormwater system in Stockholm Royal Seaport is made up of an integrated structure of green roofs and rooftop gardens that interact with water flow in courtyards, greenery in streets, grassy areas, rain gardens, ponds, and stormwater drains. Vegetation in courtyards and on walls and roofs strengthens park ecosystems and contributes to a robust ecosystem throughout the district.

Vegetation, stormwater ponds, urban wetlands and waterways retain and purify stormwater that is ultimately channelled to Husarviken or Värtan on the Baltic Sea.

Public areas, i.e. squares, streets, and parks, have been designed to incorporate local drainage in plant beds to achieve more efficient stormwater management. Plant beds are of a size and storage capacity to withstand both extended periods of drought without being watered, and sustained water flow during periods of heavy rain.

In 2018, Hjorthagsparken, which forms part of the spreading zone, was completed. The park’s location, design and content strengthens the local ecosystem and with a special focus on oak and amphibian connections.

Good examples from Hjorthagen

The examples outlined below are from Hjorthagen, the first phase of Stockholm Royal Seaport. A number of parks, streets, and neighbourhoods have been completed in the district and significant numbers of new residents have moved into their properties.

  • A system of waterways and ponds has been put in place in Hjorthagsparken. These receive large amounts of water from the area’s hilly terrain and form part of a distribution area for aquatic animals and plants. It has also been possible to expand space available for frogs with the newly constructed “frog tunnel” under the main street of the new district.
  • Lawns have been designed to retain drainage water from the district and surrounding streets.
  • Co-ordinated greenways in the form of so-called ditches have been built on local streets with recessed planting areas that receive all water from the street and pavements. Pedestrian crossings and car rampways to garages have been placed over the ditches to avoid standing water in the event of heavy rain. Water is captured, retained, and used to support the growth of trees and other vegetation in these green areas.
  • On the main street, Bobergsgatan, trees have been planted in traditional avenues in pits with grates that are designed as concrete boxes with specially designed drains. All water from the street is channelled to the trees via drains for each tree.
  • To make it possible to handle large quantities of water, to retain it and purify it, and to ensure that conditions for plants are favourable, biochar-infused soil has been used. This is a mixture of gravel and charcoal that provides excellent conditions for growth while carbon dioxide binds into the charcoal.