Long-term performance of Urban Blue-Green Infrastructure

Written by Ruth Webber, on 9 November 2020

Interview with Feikai Yang (Frenk), joint PhD fellow IHE Delft and South East University, China.

Blue-Green Infrastructure (BGI) are landscape components such as water bodies and green and open spaces, which provide multiple benefits such as water storage, flood control and water purification. Widespread uptake of these green technologies is still hampered due to a lack of insight into their long-term performance, and detailed monitoring and evaluation frameworks are still under development.


IHE Delft participates in a research programme entitled "Blue-Green Solutions: challenges and opportunities" spearheaded by Professor Floris Boogaard of the Hanzehogeschool Groningen, University of Applied Sciences. One of the objectives of this programme is to gain insight into the long-term behavior of BGI. My PhD research at IHE Delft is partly supported by this programme and partly through a scholarship received from China Scholarship Council. Professor Dafang Fu of the Southeast University and Professor Chris Zevenbergen of IHE Delft are my supervisors.

What is the title of your PhD thesis?
The title is ‘Long-term performance and model simulation of bio-swale (Wadi) in the Netherlands’ and for my research, I am collecting and analyzing data from the first projects of blue-green infrastructure projects in The Netherlands. These projects encompass bioswales or wadis. The oldest wadi in Ruwenbos, Enschede, was implemented more than 20 years ago, with another built in Castellumknoop, Utrecht, around 15 years ago.

For the non-scientist, why were these wadis built?
The expansion of the urban impervious hardened underlying surface has changed the hydrological mechanism under natural conditions. When the rain comes, the flood peak flow is fierce, the flood peak time is advanced, and the impact of flooding expands. Pollutants carried by urban roads would be discharged into rivers or directly infiltrated with rainfall runoff, which is the main source of groundwater supply, not only polluting rivers and lakes, but also affecting the quality of groundwater. Bioswale (wadi) can reduce the urban stormwater runoff and improve the water quality.

In China, your home country, do wadis or similar infrastructure exist there?
As part of the Sponge Cities project, which was launched nationwide in 2014 other green infrastructure has been built, including raingardens, constructed wetlands, bio-retention. They serve the same purpose as wadis in reducing the volume and peak flow of stormwater runoff, thereby avoiding flooding, and also purify the water before they flow to surface and groundwater. Since this initiative is only six years old, there is only a small amount of hydraulic and water quality data from before 2014, whereas there is plenty from the wadis, which date back 15 and 20 years. Therefor the outcomes will likely be relevant for the design and further upscaling of BGI under the Sponge Cities programme.

What is the next step in your research and when do you hope to finish your PhD?
After analyzing the data on the wadis’ ground water levels and infiltration, I will compare them with previous data to find how the infiltration rate changing with time. I will set up a model and then use long-term data to validate it. Next year we will do the heavy metals test in both soil and groundwater and again compare with data from earlier years. The results will give important information about the long-term behaviour of the wadis.

I am conducting most of my research in the Netherlands, but I may do a case study in China and see if model is also valid there. I am hoping to finish my PhD at the end 2021 and at the moment, I am on track.

How do you intend to use and apply the knowledge you have acquired by doing your PhD research here?
When I return home, I hope to join a company to do some further research in China and also some projects as part of the Sponge City construction. Monitoring work and method, data collecting and a standard database, more accurate models to assist design and decision-making are the main areas I want to focus on after my PhD.


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