Nature-Based Solutions for Water Management in the Peri-Urban

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Blue-Green infrastructure as nature-based solution in an urbanizing project in Stockholm: The case of Årstafältet, Sweden

Author: Lina Suleiman

Årstafältet (the Årsta farm) is a large open grass field area situated in a suburb that is located 5 km south from the city center of Stockholm. In 2000, the city decided to renovate the green space and develop it into Landscape Park focusing on ecological and cultural values. As part of the plan, the development office at the municipality construed Nature-Based Solutions (NBS) facilities that include a stormwater pond/dam “Valladammen” in order to clean the water running from the neighboring residential and industrial area, a small stream “Valla”, a distribution ditch, surface screens, vegetated soil beds and water steps.However, the demand of housing in Stockholm altered the original plan. A new plan “New Årstafältet” was developed with the aim of urbanizing the area and building urban settlements in which the existing NBS are to be enlarged and redesigned.Thus, the New Årstafältet is a planned project to develop the suburb on Årstafältet into an urban district in which NBS in the form of blue-green infrastructures are integrated for sustainable management of water, improving biodiversity, recreation and social interaction.

In the new project, NBS in the developed area are planned in form of blue-green infrastructure. In phase one, part of the field, where the existing NBS facilities are placed, will be transformed to City Park at the centre of Årstafältet in which the existing stormwater pond will be enlarged from three to seventeen hectares for sedimentation and water treatment through plants and plant islands and merge into one watercourse. The small stream “Valla” will be redesigned into three stormwater ponds and merge into one watercourse. Two stormwater parks to handle stormwater through infiltration and for delaying the water flow of stormwater are also to be constructed. Trees planting along streets to deal with runoffs; raingardens, green rooves and courtyards for local water infiltration and treatment alongside housing blocks; ditches that connect the housing blocks and the water ponds, allotment gardens for small-scale farming with meadow landscapes for biodiversity, and elevated forest area next to the highway are other types of planned green structure. Click here to see a video on NBS for stormwater management in Årstafältet.

NBS in the urban development project aim to:
- Counteract the adverse impacts of urbanizing the green space and the loss of biodiversity
- Manage water quantity and climate change impacts, mainly flooding and water overflow and load on the existing water treatment plants but also droughts for a time span of 100 years
- Infiltrate the treated polluted water, recharge and refill groundwater levels, purify and safeguard/or improve the water quality of the receiving water bodies (Årstaviken)
- Additionally, contribute to the restoration of the water flow in the dry stream Valla å that has been laid in pipes and rock tunnels and originally flows into Årstaviken.

In addition, NBS are designed as public spaces for people meetings and social interaction that improve social cohesion and equality and improve the urban quality and social identity. The development project is divided into five phases. The implementation of phase one of the project that integrates the construction of NBS commenced in 2018. The project is to be finalized in 2033.

The case study shows two compelling interlinked evidences. The first is that NBS, in principle, have a huge potential to respond to a plethora of socio-environmental challenges, including urbanisation and loss of biodiversity, management of climate change impacts, cleaning and maintaining if not improving the water quality and flow. The second, due to its spatial requirements and the common character of services and goods NBS provide, they can act as multifunctional landscape, accommodating more land-use interests and values and enhancing social resilience and adaptability.The title photo depicts NBS in form of Blue-Green infrastructure in the New Årstafältet Plan.

Årstafältet as a large open grass field area located south from the city center of Stockholm.

A satellite image showing the location of Årstafältet south of Stockholm (left) and
an aerial view over Årsta (right) (Photo courtesy: Overview Årstafältet)

The agricultural landscape character of Årstafältet

Årstafältet (Årsta Field or Farm) is a large, open grass field of more than 50 hectares and a suburb located 5 km south of the city centre of Stockholm.The field is a part of an originally agriculture area situated in a valley that extends in the east-west direction and a part of an important natural connection that extends from Årstaskogen via Årstafältet, Hemskogen and further south. Årstafältet has agricultural landscape character, covered by grass with isolated trees and shrubs, providing values for birds and insects, bears witness of Stockholm’s historical agricultural landscape, and thus has high ecological functions and cultural values. For this reason, the city decided to maintain the field despite the need for urban expansion in the southern suburbs. It is also because Årsta field is located in a wet and muddy valley with soil conditions that make development of this area costly and risky.

An aerial view over Årstafältet showing the large open grass field (top), the suburb located on the field (middle) and the water dam “Valladammen” (bottom) (Photo courtesy: Flying day in Årsta)

In 2000, the city decided to renovate Årstafältet by developing it into Landscape Park focusing on ecological and cultural values. In that time, planners were also concerned about stormwater issue and interested in open spatial systems as Nature-Based Solutions to manage stormwater in a more sustainable approach. A plan proposal by Stockholm Water Company to implement facilities that deals with stormwater in the Landscape Park plan was approved and financed. Together with the Stockholm Water Company and between 2005 and 2008, the land development office of the city, based on a proposal from the company, constructed NBS-based facilities as part of the Landscape Park plan. The system consists mainly of a stormwater pond/dam “Valladammen” as the main facility for the treatment of stormwater, a small stream “Valla”, a distribution ditch, surface screens, vegetated soil beds and water steps/stairs. The aim was to reduce the water load and the risk of overflows on water treatment plants, clean the polluted water flowing from the surrounding residential areas and part of the industrial area east of the field and runoffs from the roads that have high levels of traffic. It also aims to restore the dry and drained stream “bäckravin” that was originally Valla River’s natural outlet into Årstaviken (Årsta bay) of which large parts of the Valla River are now laid in pipes and rock tunnels. In addition, the NBS aim to provide other benefits and improve the biodiversity, cultural and pedagogic values of the area.

A new plan for Årstafältet as an urban district, capitalizing on the existing NBS

The Landscape Park plan could not stand the increasing socio-economic pressures and thus not fully materialised. In 2006, the city decided to alter the Landscape Park plan, urbanise the area and build residential settlements. Stockholm has been one of Europe’s fastest the fasting growing cities, increasing the demand for housing and residential areas, and thus pushing the city to consider space that was originally not thought of for urban development. A new plan of Årstafältet as a new urban district replaced the Landscape Park plan.

A civil society network demanding the city to implement the original detailed plan for Årstafältet (DP 93045) and develop Årstafältet into a Landscape Park

The alteration of the original plan was faced opposition by civil society network, "Nätverket Årstafältet" , that demanded the city to fulfill the Landscape Park plan (dp 93045). The network argued that the area is hydrologically sensitive and risky to build on. Also, the field functions as large open lung and the most important recreational area and reserve of arable land in Southern Stockholm, calling for preserving the last remnants of Stockholm's agricultural landscape but without success. The lack of space and the need to develop challenging areas like Årstafältet has become a municipal reality that pushed the new plan forward. Årstafältet sits in a valley of poor geology, which is wet, clayish, muddy, and with soil conditions that have made development of this area technically challenging, costly and risky.

The existing water pond will be enlarged and the Valla Stream will be redesigned and merge into one watercourse

In the new plan, a City Park integrating the existing water pond and the Valla Stream will be located and replace the Landscape Park

A new vision for the area was formulated that focused on sociotope and biotope values. NBS are assumed of playing a key role in attaining the vision. Over time of planning and designing the NBS, various socio-environmental pressures including the rising of water challenges, mainly flooding due to climate change impacts , decreasing groundwater levels but also the risk of quality deterioration of water receiving bodies have become municipal concerns that influence the process . It is therefore, the city decided to capitalize on the existing NBS, enlarge, and redesign them for high environmental and social quality objectives.In the new plan, the landscape park is replaced by a city park in which the existing water pond will be enlarged (from 3 to 17 hectares) and the Valla Stream will be redesigned from being a straight drainage ditch to get a more meandering course and flatter slopes and divided into three water ponds. Both, the large water pond and the three water ponds will merge into one watercourse.

Key policy documents and guidelines that acted a driving force of and influenced the planning of NBS in Årstafältet

Key policy documents and guidelines that shaped a driving force of and influenced the planning of NBS are:
- The updated Stockholm City's stormwater strategy in 2015 (Stockholms stads dagvattenstrategi)
- The guidelines for Stormwater management - The level of action for new and major renovations in 2016 (Dagvattenhantering -Åtgärdsnivå vid ny-och större ombyggnation).

The Stockholm stormwater strategy that was updated in 2015 and stresses the locally managed stormwater (LOD) approach and mimicking a natural runoff in the urban environment for achieving a number of benefits that promotes sustainability has been a legislative force that pushed planners to extend NBS facilities and types. The guidelines for stormwater management in 2016 aims also at achieving the set environmental goals and reduce the pollution load from the city's stormwater by 70–80%. This requires the planning of facilities for delaying and purifying approximately 90% of the stormwater's annual volume, capable of storing 20 mm of precipitation and have a more far-reaching purification than sedimentation functions. In addition to other instruments and impetus, these key policy documents and guidelines influenced the planning process of Årstafälttet towards the integration of a variety and ambitious NBS in term of scale and socio-environmental quality norms and objectives.

NBS in Årstafältet, designed in form of blue-green infrastructure

The NBS in Årstafältet are planned and designed in the form of a mixed of blue-green infrastructure and to be implemented in the first phase of the development project. Part of the field will be transformed to a City Park of 25 hectare size, located at the centre of Årstafältet and institutes the key green infrastructure. The blue component, which covers approximately 19,600 sq.m., constitutes mainly the enlarged stormwater dam and the redesigned “Valla” steam that will be impeded in the City Park. To fulfill the requirements for Stormwater management, the city planners have to develop, standardize and apply a green area factor “Grönytefaktor”, as a tool to decide on how much greenery should be planned for delaying and purifying stormwater that can be capable of storing 20 mm of precipitation. Within this frame, other green interventions are integrated in the plan that approximately includes planting 22 000 trees in streets and the forest area, two stormwater parks, raingardens, green rooves and courtyards; allotment gardens (20,000 sq.m.)and forest area (33,200 sqm).

The development project is divided into phases, in which phase one integrates the construction of NBS

The implementation of phase one of the project including the NBS commenced in 2018 and is ongoing

In overall, the designed blue-green infrastructure aims at cleaning, purifying and improving water quality; dealing with climate change impacts and managing mainly flooding but also drought; buffering and counteracting the negative environmental and ecological impacts on water flow, loss of biodiversity and urban ecosystem and protecting and improving the status of water receiving bodies. These challenges are not context specific but have been articulated in the international development agenda and particularly in the UN Sustainable Development Goals 6, 11, 13 and 14. The development project is divided into five phases, started in 2018 and to be finalized in 2033. Watch a related video here: A flying tour over Årstafältet and the working area on May 2021.

The sustainability of NBS projects that perform according to what they are assumed for faces significant challenges in overcoming future uncertainties is an issue that raises some questions and concerns. Examples of these include:
- How to manage the water flow in the ponds considering future uncertainties? Would the water flow in the water ponds be adequate to maintain a certain water level for not to cause overflow and flooding or drain? Would the clayish soil prevents water infiltration into groundwater aquifers?
- Would the plant islands in the water ponds be technically efficient to treat and clean the stormwater and runoffs?
- How to secure expertise for marinating the water dam?

The big question however raise concern on the maintenance organisation. It is still unclear who will be responsible for what and who should pay for the cost of maintenance? The multifunctionaliy of NBS (trees, water ponds, parks and green areas, forests) has resulted in divided ownership of NBS and unclear division and grey zones of responsibilities among the public organisations involved (The municipal administrations, the water company, district administration) and concerns and questions rise.
- Should the water company be responsible for maintaining the small water ponds designed for recreation purposes when it is, in principle, not liable for providing these services and does not have the budget for the task?
- Similarly, will the maintenance responsibility of the stormwater parks be the responsibility of the district administration that by regulation is responsible for or the water company that is responsible for management of stormwater by law?

These questions are discussed but have remained unresolved. The future will inform us more on the challenges and opportunities of the NBS projects for moving towards sustainable water cycle and management, societies, and cities.