Published in April 2021.
Historical city centres in Europe are densely built up. This density is actually a favourable design feature in terms of supporting the low ecological footprint of city residents: it enables cities to be more energy efficient compared to their peri-urban and rural counterparts. The small distances between everyday amenities mean lower transport use - they enable walking, cycling and efficient public transport modes to flourish. Living in compact apartment houses requires less energy for heating each apartment - and fewer square metres are taken up per resident. This high density is, however, also a challenge. Public and, in particular, green space is limited. This reduces the availability and quality of 'pleasant' outdoor environments. This lack of green correspondingly fuels the urban heat island effect.
The Green-Blue Development of the City of Breda: A Brief Background
The city of Breda in the Netherlands, a country with a very urban population density, faces many challenges when it comes to compact, sustainable urban development. In the 1950's and 60's, it filled parts of the inner city canals so much that the river Mark was no longer able to flow through the centre. This was done in order to establish a four-lane road and a carpark in the densely built-up centre. However, in the 90's, the mindset in the city changed: residents called for more nature and the city started to uncover parts of the river, a process that is still ongoing. Despite this positive development, the river stills runs between steep city walls, leaving very little space for nature to grow and thrive.
Nature-Inclusive Quays (NIQs): a new concept born in Breda
When local planners presented the rather grey design for the river opening sections to the citizens of Breda, their response was clear: "we want something greener". This prompted planners to reconsider the design and brainstorm innovative ideas to make the quays greener. While green walls are now well-known, Breda’s planners wanted to be even more nature-inclusive. Thus, the idea of Nature-Inclusive Quays (NIQ) was born. It takes its inspiration in observations of older, little used and/or poorly maintained quays and other walls, where nature (mosses and herbs, even small trees) invades the vertical surfaces on its own. The question for the design team was: could this natural phenomenon be mimicked by deliberately nature-inclusve quays (NIQs)?
To develop the NIQ, Breda sent an application to the innovative nature-based solutions call launched by the Urban Innovative Actions initiative. The proposal was selected, and in 2019, the GreenQuays project began.
The GreenQuays project: a test bed for nature-inclusive quays
The main output of the Green Quays project will be a real-life pilot nature-inclusive quay wall spanning a 175m stretch of the future river, to be launched probably in Autumn 2021. The pilot will then serve as a source of inspiration, data and experience to upscale the concept to other sections of the larger redevelopment project of the river Mark.
Before building the pilot, different types of bricks, mortar, and joint patterns are being tested at a small-scale test site, where small wall segments of different construction designs have been created. Close collaboration with researchers from the University of Delft and nature experts from Natuurplein de Baronie and RAVON has been essential to find the best combinations of wall construction and plant selection. The researchers have found that there is no one brick or mortar that's the "best", but rather that an optimal combination of all elements - animate and inanimate - is ideal.
The first small-scale test site was established in May 2020. Since then, mosses and herbs have started to grow at different speeds and with different success rates. Ideas for new combinations of living and non-living material have continued to be tested throughout the trial.
Another iconic feature of the green quay walls will be trees not on top but actually in the quay walls. At the Van den Berk nursery, trees are nurtured in bended tubes before being planted in containers, which are then embedded into the quay walls. Thus, the trees and wall become one!
To continuously monitor the growth and the environmental conditions at the small-scale test-site wall segments, sensors have been embedded into their structure. The first data gathered from the test site was used to support the design of the real-life pilot test site and, as the small-scale test site has been established only recently, learning is ongoing.
To a certain degree, the design of the pilot is, therefore, kept flexible to accommodate new ideas emerging from the data, like the appropriateness of different plant species. The innovative solutions of the NIQ are complemented with further green growth above, and with installations in the river, such as platforms or gabions, that promote the growth of aquatic flora and fauna.
Could NIQs be a model for other cities?
The GreenQuays project will not only boost Breda’s inner city attractiveness but the increase of resilient, nature-inclusive blue-green infrastructure will make it more resilient to future climate change impacts, such as heat waves. Channelled rivers and quay walls with limited space are typical in many cities; hence, solutions like NIQs have a high potential to be upscaled elsewhere in Europe and beyond. As a tangible case study, Breda’s NIQs can inspire many other cities to do the same!