Let nature do the work

Water and vegetation play a key role in Stockholm Royal Seaport. With well-thought-through design, blue and green structures fulfil several functions, contribute to synergy effects and deliver ecosystem services. This provides opportunities for recreation that contributes to better health and well-being.

Multifunctional green structures in which water and vegetation are actively used

Sweden’s climate has changed and become more unpredictable. Rising sea levels, heat waves and more extreme weather events increase the risk of flooding and drought, and need to be considered in urban planning. In Stockholm Royal Seaport, conventional stormwater systems have been replaced with innovative solutions, where rainwater is used as a vital resource.

Vegetation is used strategically, meets several social values and contributes to pleasant environments for people to live in. In public areas, the vegetation consists of parks and courtyards, green play areas and plant beds with a wide variety of plants. To manage more intense rainfall and drier periods, ponds and wetlands retain and store rainwater. Parklands such as the bowl-shaped Jaktparken and other green spaces are designed to balance large water flows during periods of heavy rain. Vegetation also provides shade and lowers temperatures on hot days. Almost 600 trees have been planted in Stockholm Royal Seaport. The variety of plant species builds resilience to disease and rot, making vegetation more robust.

To make it easier for developers to plan high-quality vegetation solutions in courtyards and on roofs, the Green Space Index (GSI) planning tool has been further developed. The size and shape of courtyards, as well as how many walls and roofs can be used for vegetation, determine the size of eco-efficient areas that can be created.

The below diagram shows the GSI for each phase. The GSI has been met and social aspects are shown to be playing an increasingly important role.

Innovation projects linked to Let nature do the work

One challenge is to ensure the long-term operation and maintenance of green spaces. Sensors have been set up in various green structures to investigate whether digitalisation can facilitate management of these areas. This has taken place within the framework of the Connected Stockholm Royal Seaport and Smarter Greener Cities research projects.

A well-planned and species-rich green structure develops and strengthens ecosystem services and biodiversity. That was the key finding of the C/O City innovation project, which started in Stockholm Royal Seaport. The purpose of C/O City was to demonstrate the value of ecosystem services created on public land and development sites.

Stormwater as resource

Every year, Stockholm is hit by intense rainfall, resulting in flooding that threatens infrastructure that is important to society. Early in the project, an overall stormwater strategy was developed that set out principles for stormwater management. It assumed that stormwater could be managed locally with plant beds, drainage and piping to adjacent watercourses, as well as a retention and discharge requirement for development sites. Heavy and torrential rain meant that the district’s elevations had to be such that stormwater could be directed to the nearest recipients on ground level. Following heavy rainfall in Copenhagen in 2011, elevation requirements were further tightened.

Stormwater is managed in an integrated system consisting of green roofs combined with courtyards, parks and green spaces. All stormwater from public open spaces is led via inlet drainage to plant beds, some with pumice- and others with biochar soil that stores and retains water before releasing it to recipients. In the event of heavy rain, ponds and wetlands help capture water that would otherwise cause flooding. Parks and other green spaces can also store large amounts of water, such as the bowl-shaped Jaktparken.

Two areas have been identified in Stockholm Royal Seaport where stormwater management is a challenging: Gasverket and Värtahamnen. These are flat, low-lying areas with buildings of cultural and historical interest. Here, too, the project has worked with elevations, plant beds, wetlands and ditches. Some changes were made to the structure to further adapt to new downpours requirements, including a ditch that would receive water and lead it through the area’s green spaces. Downpour models showed that the existing structure was sufficiently robust and flexibly planned with many open rain beds and green spaces.

Natural values and dispersal zones

In line with increased urbanisation and densification, green footways and green spaces have important ecological functions as distribution zones that strengthen natural values. Stockholm Royal Seaport’s location between the northern and southern areas of the Royal National City Park plays a key role in connecting the two. The Royal National City Park has one of the Nordic region’s largest contiguous connections of oak trees and research has shown high natural values and trees that are particularly worth protecting.

The area is home to plants, animals and insects that constitute conservation species, some of which are “red-listed” or protected under Swedish law. A previous ecological survey found that protected larger and smaller water salamanders lived in a pond near the oil tanks in Loudden. Prior to soil remediation , the salamanders were captured and moved to a new pond.

Green structures play a major role as part of a dispersal network for oak species and amphibians. Environments are protected and strengthened by planting and creating wetlands and wintering sites. New green spaces are strategically positioned to create dispersal zones. Old oaks are saved and new ones are planted on dispersal zones. A total of 120 new oaks have been planted. Nests for pollinating insects, birds and bats are also being placed in courtyards and on roofs. A frog tunnel has been dug under one of the pathways to connect wetlands and ponds.

An insect survey was conducted to see how the movement of insects has been affected by buildings in Stockholm Royal Seaport and how efficient dispersal zones between the Royal National City Park and Hjorthagsberget are. The study shows that Hästhagsparken is used by beetles and bees to some extent, and that it is likely to attract more individuals and species as tree growth increases.

The large oaks that have been preserved are important for dispersal, while flowers and wetlands are essential for flower-seeking species. Green roofs attract insects to some extent, but only marginally more than ordinary metal roofs. The survey provides valuable information for planning in the future phases of Stockholm Royal Seaport and elsewhere in the city. Swedish Television reported on the emptying of the study’s insect traps on rooftops and in Hästhagsparken and took part of the results.

Improved water quality and bottom sediment

Lilla Värtan is located between Stockholm and Lidingö and forms Stockholm Royal Seaport’s waterline from Husarviken to Loudden. Levels of phosphorus and nitrogen in the area are high, as are amounts of metals in bottom sediments due to previous historical industrial activity.

An early investigation of Husarviken’s contaminated bottom sediment determined that the sediment would not be remediated to avoid the release of dangerous heavy metals. Access to the water is limited by jetties from which it is not possible to swim.

In conjunction with the detailed development plans for Kolkajen and Ropsten, marine biological investigations have been conducted in Lilla Värtan. These show that the presence of benthic animals, plants and fish is very limited.

The environmental impact assessment states that remediation in the water area due to urban development in the long term contributes to reduced pollution and improved surface water quality in Husarviken and Lilla Värtan. Among other things, the goals of living coast and archipelago and a rich flora and fauna will be achieved. Improvement of water quality is also made through, for example, discharge requirements for drainage-pump water.

Investigations in Saltkajen in Värtahamnen show that soil, sediment and groundwater are polluted, but the concentrations are moderate and lower than in the nearby areas. The overall assessment is that there is no need to implement follow-up measures to alleviate environmental and health risks.

Key events in 2021

• The Green Space Index planning tool was updated and revised in 2021. The work of producing a Green Space Index for industrial port operations in Energihamnen was completed.
• The development of the northern part of Värtahamnen began with the construction of a stormwater tunnel and street work.
• Recycled woodchip from aspen trees felled near Gasholder 3 and 4 was mixed in new soil for the playground built at the site. Valuable trees are saved, more new trees are planted and the sowing of meadows continues in 2022.
• A nature value survey for oak connections was conducted in Hjorthagskransen.
• An analysis was made of how insects move in the first phases of the project. The purpose is to follow up and evaluate how green structures function as dispersal zones for insects.
• 44 new trees were planted.