Expert article
Edit 13 August 2020
by Birgit Georgi

Enabling nature to take over – green quay walls in Breda

Future green quays in Breda
Future green quays in Breda
Breda is a lovely city. The dense middle-age centre has many small streets and places to stroll around. This density does, however, leave only little space for urban green. In the 50’s and 60’s Breda even filled parts of its channels and built broad four-line roads and a parking house into the old channel to promote smooth travel by car. The river Mark was no longer flowing through the city but around.  With upcoming climate change impacts, such as prolonged heat waves and more severe and frequent flooding risks, more green and blue infrastructure would however be urgently needed and would be nice for many other benefits as well. Fortunately, in the 90’s the mindset has changed again and nature in the city was valued. Step by step, the city will restore its harbour and old channels. Still, these are artificial waterways with vertical walls. How could they be made green?
Shallow channel that was reopened when closing two of the four lanes of the road
Shallow channel that was reopened when closing two of the four lanes of the road. It will now be dug to full depth, connected to existing channels and greened.

 

During this UIA project, different innovative nature-based solutions will be tested , a new section of the river will be dug, and a 175 m long real-life pilot established. See the first pilot approaches and solutions here:

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Planning around the broader development of the Nieuwe Mark (rebuilding the river Mark) went on for many years. Experts and citizens participated in early stages of planning and many ideas came up. The application for the UIA project GreenQuays, which is part of this broader development, has spurred the discussion by thinking even more innovative. What if ...? 


One of these questions was:  What if we would stop cleaning quay walls? Would some vegetation develop spontaneously? Which plants could cope with the conditions and what about animal life? Hence, the team around Roel Klei, projectleader Ruimtelijk Economisch Domein (Spatial Economy) in Breda convinced the maintenance department to stop cleaning a section of an existing quay wall to explore what would happen. Not completely unexpected, maintenance staff was first not in favour of this approach. It would go against usual practice and they raised concerns about the long-term stability of the quays. Nevertheless, stopping maintenance in a small section was agreed. Indeed, nature took over quickly by itself. Smaller and bigger plants and mosses have started to invade the walls, which are nice to look at and provide also breeding space for animals above and below water. In the end, also the maintenance staff went along with the trial as there were no issues with the stability detected so far and less work to do. This test, starting prior to the GreenQuays project, provides the design team with further inspiration on bringing in not just green solutions but truly nature. The real-life experience is also extremely helpful as a tangible show case for sceptic stakeholders. Additional inspiration for the design has been taken from studying quays in other cities, e.g. in Rotterdam. 
 

Nature invades the quay walls once maintenance was stopped.
Nature invades the quay walls once maintenance was stopped.
Small wooden installations support the invasion of plants and animals at the quay walls
Small wooden installations support the invasion of plants and animals

 

The question for the design was now, how nature could be mimicked. Could the new walls be built in a way that the invasion of nature could be boosted and accelerated? At that point, Breda came into contact with its now project partner University of Delft. There, Koen Mulders has a long experience with experimenting with different wall constructions. He and his colleagues have analysed the stability and other qualities of bricks, mortar material, joints, bonds, and wall pattern. Which provide stability and enable nature to invade? Lab experiments suggest that the optimal solution is not about the best brick, best mortar, or best pattern but where the three components fit perfectly to each other.  
 

Different bricks and joints
Different bricks and joints

In May 2020, a small-scale test - wall segments with different combinations of material and pattern – has been set up. In small wall niches of different design, plants have been set. After just a month, differences in the development of the plants can be seen as well as between the wall segments facing the north and the ones facing the south side. With sensors, variables such as temperature, wetness, capillary movement of water and other parameters are observed, to figure out which design forms and plants work best. The results will be used for the design of the real-life pilot. Practice has also shown that the design of the joints and mortar used seem to have a big influence on vegetation. As it currently looks, the mortar mixed with straw and clay in the outer part of the joints seems to provide a better ground for plant development. Despite all greening attempt, special attention is still on the stability of the walls. 
 

Small-scale test with different wall segments in the quay
Small-scale test with different wall segments
The first plants start to grow in niches and joints
The first plants start to grow in niches and joints offer favourable conditions for spontaneous vegetation

 

Have you ever seen a small tree growing out of a wall? Here and there one can observe it at old buildings and ruins. Nature can be amazing. The design team of GreenQuays was wondering if they could find a way to plant such trees in the quay walls. With Jan van Kempen and Jeroen den Brok from Treenursery Van de Berk, they found competent partners. In preparation of the planting, they grew six tree species in bended tubes on their site to give them the right form. The first trees have been planted at the small-scale test site in relatively small but deep containers that are part of the quay wall.  These trees and parameters are also monitored frequently to learn, which species thrive well, what micro-conditions they need, how the substrate works, etc. Both solutions, the walls greened with herbs and flowers and the bended trees, are brilliant and noticeable in public space. Citizens frequently stop at the test site and have been curiously reading the explanatory boards to understand what is going on here. And also, for the partners behind the solutions, the project is super interesting as they can finally test their research results in real life. 
 

Bended trees coming out of wholes in the wall segments at the small-scale test site
Bended trees in wall segments at the small-scale test site

Next year, the experience of the small-scale test will be used to build the real-life pilot of the river. While necessary information is gained from the small-scale test, there won’t be enough time to completely prove its results. For the real-life pilot, the team will therefore make the best guess and keep the specific design flexible to a certain extent. For instance, it will enable to change to other plant species if needed. Furthermore, the team intends to maintain the small-scale test site and continue the monitoring and evaluation. At the end, the intentions are much bigger than a 175 m river section. Further river sections and additional public space will be built using the lessons learned from GreenQuays. 

information board on the project
Information board at the side of the test site

Green will also spill over the quay walls. Together with citizens the project team will design the sides of the quay with further nature-based solutions – conventional and innovative ones - to green the full space from building front to building front. All that innovative greening will increase Breda’s resilience to climate change impacts and further boost the city’s attractiveness, provide space for social contacts, recreation, nature and nature observation. New opportunities for local businesses, like extended cruising on the channels and attractive space for restaurants and cafés will open up, and the innovative solutions provide an excellent showcase for the involved partners, which can be upscaled and exported elsewhere. 
 

Blue dots on the street show where water will flow in the future
Blue dots on the street show where water will flow in the future

 

See also: 

https://www.greenquays.nl/

 

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