Expert article
Modifier 05 October 2022
by Birgit Georgi UIA Expert

Ideas from the GreenQuays project start stretching beyond the initial plans

Plant grow on the drystackwall
Plant development at the GreenQuays spin-off in Delft. Image: Koen Mulder
While most of the innovative tasks of planning the quays and testing different technical solutions have finished, GreenQuays is still running with the focus on the physical work of constructing this stretch daylighting the covered river Mark again. Partners from eight different organisations put their heads together, raised questions, learned from each other, and have developed a completely new technical solution: Nature-Inclusive Quays (NIQ). Here, plants will grow directly in the joints and niches on the wall, as they often do spontaneously in/on old, weathered walls and that is what the GreenQuays are geared towards now. Does this mean that the innovative part of the work is on hold, and everybody is waiting for the results of the established quays that will be built in summer next year?

During my frequent talks with project partners over the last months, I got aware of interesting side-developments going beyond the GreenQuays project with two partners, who had worked hard on the foundation of the NIQ: Koen Mulder from the University of Delft, who has been responsible for testing different wall materials and designs at the project’s small-scale test site from 2020-2022 and Erwin van Herwijnen from Tree Ground Solutions, who found the solutions to grow small trees out of the quay walls (see articles: The brickwork story behind GreenQuays and Making trees and wall plants thrive at steep quay walls).

While it appears reasonable to assume that these solutions will be applied and eventually further improved during the implementation of GreenQuays and other sections of the New River Mark development in Breda, the question is what else has been learned for other projects. Have there been spin-offs already? Something beyond GreenQuays that takes its legacy further?

Both have confirmed having learned a lot. Developing the NIQ for GreenQuays has been very experimental compared to other implementation work for Erwin and very practical for the rare occasion of seeing research results coming to life in a real project for Koen. Thus, the project offered both a testbed for new innovative solutions, which then can be used at other places and to inspire further NIQ ideas. 


For Erwin, GreenQuays meant in particular collecting valuable experience on appropriate substrates for roots to grow in. The right substrate plays a particular role for trees where limited space for growth poses a challenge. Due to that, it is difficult for the roots to develop in order to get sufficient water, nutrition and oxygen for the tree to thrive. In the case of GreenQuays, the space has been restricted by the demand to grow trees out of the walls. This requires small containers with an effective substrate providing the tree all it needs. The substrate needs to make the water from the river rise through its capillary system to the roots and at the same time, ensure enough oxygen in the substrate by its structure as the roots need both water and oxygen. In other urban settings, underground space is often limited too, e.g., by building foundations, sealed surfaces of roads, underground infrastructure such as pipes and wires, or underground parking levels. Equally, space is limited on green roof tops. 

Planting the trees in Hanze University
Erwin explaining how the trees are planted. Image : Tree Ground Solutions

Tree sand is now being tested at the Hanze University of Applied Sciences in Groningen (BuildinG0) in combination with the Permavoid Capillary Irrigation System, and here too, sensors have been installed to learn more. Erwin was even surprised to see how well the solution worked here, especially how quickly the growing area recovers from excessive rainwater. It is indeed the use of an effective substrate in combination with the Permavoid Capillary Irrigation System and an underground construction that can handle both too much and too little water while maintaining the balance with oxygen and water. The research impressively demonstrates the dynamics of water in the soil.

building the Permavoid Capillary Irrigation System
Establishing the Permavoid Capillary Irrigation System and planting the trees. Image : Tree Ground Solutions.

Results of the small-scale test site of GreenQuays and the trees at the Hanze University on the appropriateness of substrates and its use in a Permavoid Capillary Irrigation System at Hanze University were subsequently used in designing and upscaling these solutions in a much larger system - the Grote Markt square in Groningen, which is currently under construction. The complex underground structure with storage capacity, overflows, a capillary system, and different layers of substrate, tree sand and a forest layer allow the trees to cope with the different amounts of water throughout the year. The site becomes a stable growth area for the trees. 

The lessons from the GreenQuays, together with the many tests already carried out, provide the current developments of an integral growing place that will make Europe's cities climate proof and heat resistant. Extreme situations with too much or too little water will increase due to climate change. Therefore, a high demand for solutions like this is expected, where cities remain dense, but trees can still thrive and provide their shade for cooling and other ecosystem services. 

In the middle of the COVID-19 lock down, Koen and colleagues experimented with different wall designs and materials, which then have been transferred to the small-scale test site in spring 2020, which delivered results to choose appropriate solutions for the GreenQuays’ walls. In parallel, the design process of the quays has been going on and the solution assessed to work best in regard to the planned construction was picked. GreenQuays was designed as a 3-year project and timely decisions had to be made to finish the construction on time.  This situation did not stop Koen as a researcher in thinking and testing further ideas that just emerged during the construction of the small-scale test site. While such ideas that surfaced during this experimenting phase did not make it into the test site or the GreenQuays design, it led to new developments that can be applied at other wall constructions. 

This has been the case with the idea of a dry-stacked system that are walls built without mortar, which makes it easy to assemble and reassemble them. The idea simply surfaced too late, seemed to be not the type of what the design team of GreenQuays was aiming for, and nobody would know at that time, if this solution would work. Nevertheless, it was a child of GreenQuays, which Koen did not give up. Benefitting from the research done in GreenQuays, the system came finally to life as the Quay Wall Garden in Delft in April 2022. 

building the drystack walls
Koen and his team building the dry stack system of the Quay Wall Garden in Delft. Images Delft University.

The development of the Quay Wall Garden was enabled by KIEM – a small grant program from the Dutch government geared towards supporting the development of innovative ideas between researchers and companies. The small project was started with two companies; other partners joined later, such as one that recycles ceramics and produces the bricks for the wall. 

However, the grant has been very small even for a prototype and the prototype itself would be too small for making a research project out of it. In this situation, it was very fortunate, that the city of Delft got interested. Having been conventional and financially very limited in earlier years, the city aims now for being open minded and innovative on urban development. Koen and colleagues contacted the innovation manager of the city and the ball got rolling. The city has embraced the idea that has originally been surfaced but not applied during the GreenQuays’ design process, has provided a wonderful site to build the Quay Wall Garden prototype and even has supported the prototype financially. The current focus in the Netherlands on nature in cities and the “competition” of Dutch cities such as Amsterdam or Breda may have also spurred Delft to invest in this innovative idea. And even if not having taken the dry-stacked system further in the GreenQuays project, the municipality of Breda is still highly interested to follow the performance of its prototype in Delft too. Maybe that system will be relevant one day for other parts of the new river Mark or to green other places in the city.

Read more on the drystack wall system

GreenQuays did not just provide the idea to test dry-stacked walls, also the contacts made in the project, collaboration and mutual learning has been beneficial. Koen had already known one of the companies now partnering in the Delft Quay Wall Garden project from the wider circle of stakeholders around the GreenQuays project. During the testing of different wall designs and materials in GreenQuays, plant invasion and growth as well as animal life on the test site’s wall segments has been monitored by Edwin Dijkhuis, colleagues and volunteers from FLORON (Plant Conservation Netherlands). Hence, Koen asked him to participate as an advisor in the monitoring of Quay Wall Garden.

While these two examples worked out, it also shows the challenges in developing innovative solutions – in particular, money and time. GreenQuays and the UIA program offer a unique opportunity to develop them, but the duration of the project is very limited to sufficiently develop and test a larger number of possible solutions, which would be feasible with a longer project duration or by having a continuous process. 

The interests of the involved stakeholders also differ. For example, Koen is a researcher that develops the ideas, but does not see the University in the role of implementing them and making a business out of them. Broadcasting such solutions requires different types of stakeholders, such as local authorities and businesses that apply them in practice and further sell these solutions. Getting from research and a prototype to a broad production of stackable plantsoil containing layers is still not solved in the dry-stacked system. This experience can serve as a valuable lesson for GreenQuays while it is still running: How to ensure upscaling the NIQ technology and make it a replicable solution and a business beyond the project? Who needs to be involved and in which way?