Designing with and for vital soil in urban areas
Vital soil is one that is an integral part of the ecosystem, possessing regenerative properties that can provide ecosystem services for years to come. Vital soil acts as a sponge, creating conditions for water infiltration, buffering, and long-term water storage. It supports biodiversity, working in harmony with natural processes and providing space for nature. Furthermore, it accommodates a well-organized subsurface infrastructural system designed to serve multiple purposes while minimizing negative impacts.
When designing with and for soil, it is important to begin by understanding the existing soil conditions and the ambitions for the site, taking into account the various stakeholders involved. In our research, we focused on three components that interface with soil: water, organic material, and infrastructure.
To anchor our research within the practical constraints of the real world, we used the transformation of Westblaak as our test case. Rotterdam is currently developing eight city projects that are part of its plans to become climate adaptive and effectively address extreme heat and rainfall. These projects emphasize nature-based approaches, and the transformation of Westblaak is one of these initiatives.
The future ambition for Westblaak is to transform it into ‘Blaakpark’, a recreational space that also serves as a climate mitigation measure. Currently, the area is mostly paved, with only 12.5% of green space. The existing vegetation does not significantly contribute to mitigating heat stress, and there is surface flooding during extreme precipitation. The subsurface of Westblaak is also occupied by numerous cables and pipes.
In addition, there are various competing ambitions and goals at both the city and the project levels that need to be negotiated. In order to elucidate these differing ambitions and to get a holistic understanding of the optimal conditions required for the different ecosystem services provided by the soil, we framed three extreme scenarios.
Scenario 1: Maximizing climate adaptation
To withstand heavy rainfall and heat due to the changing climate, Westblaak gets more permeable surfaces, a water buffer, and underground water storage. In this scenario,
it becomes a typical Rotterdam “singelpark”, with one side accommodating recreational and sports activities and the other side preserved as a natural area with water-tolerant vegetation and restricted access to maintain soil porosity. Fluctuations in surface water levels can be observed along the edges, and the urban water buffer becomes a local landmark accompanied by a water square that cools the public space in summer. At night, surplus water from the surface buffer is used to irrigate plants and gradually infiltrates into the aquifer, reducing the need for large sewage pipe
Scenario 2: Maximizing biodiversity
This scenario focuses on increasing biodiversity below and above ground. More space is created in the most lively top soil layer by moving underground infrastructure deeper. Various complementary soil types are introduced alongside the existing soil, and vegetation is chosen accordingly. Priority is given to plants that support a wide range of species and facilitate beneficial fungal interactions. Trees of different ages are mixed, and separate patches of green are clustered into a wide green verge to provide optimal growth conditions. Façade gardens are connected to the verge under the sidewalk, and green façades establish a link between roofs, forming a cohesive ecosystem. Westblaak evolves into an urban forest where public space and buildings mutually enrich each other.
Scenario 3: Maximizing circularity
Design explorations in this scenario focus on growing the ecosystem of Westblaak over time while preserving existing elements. The design allows vegetation to develop through natural successions with minimal interventions. In the first stage, part of the Westblaak is unpaved, and nutrients are added to make the soil more fertile. Pioneer species are planted to prepare the soil for the eventual introduction of late succession trees. Based on the prevailing soil conditions at that time, public space designers determine the suitable locations for tree planting (and preservation). This way, Westblaak becomes an ever evolving public space. Obsolete infrastructure elements find new purposes, such as repurposing a car tunnel for water storage, transforming it into a vibrant meeting place, and reusing removed sewage pipes to connect underground green patches.
The role of urban designers
As stated before, the perspective of modern urban designers towards soil has been unidimensional. The subsurface is seen as a space for engineers, where the technical services that keep the city running are given a place, out of sight. In recent years, the role of urban designers is evolving towards one of integration: integrating conflicting spatial claims, building consensus, and designing livable spaces for all. Understanding how to design with and for soil requires a collaborative and interdisciplinary approach that involves working closely with experts from relevant fields such as soil science, hydrology, ecology, and landscape architecture. This approach ensures that soil considerations are integrated into all aspects of the design process and that the solutions developed are socially and environmentally equitable. Together, we can create cities that are not only beautiful and functional but also sustainable and resilient, for the benefit of both people and the planet.