Climate change is changing precipitation patterns across Europe and, indeed, throughout the globe. Each year, rainstorms and flooding events are increasing in both frequency and severity. In recent years, the end of May to early June marks the beginning of flood season. Europeans begin to brace for the inevitable: heavy rainstorms, flooding, and urban havoc (street closures, vehicle damage, power outages and more). In other words, it’s the “new normal.” The question that urban planners are asking is: how do we mitigate these challenges and what role does stormwater management play in the design and build of a climate-resilient city? In a sit-down interview with Delft University associate professor and urban water management expert Dr. Ir. Frans van de Ven, Wavin asks these questions and more. This is the first of a two-part blog series based on this very topical interview.
WAVIN: You are the associate professor of Urban Water Management at the Faculty of Civil Engineering and Geosciences at the Delft University of Technology, can you tell us a bit more about your work at the University?
DR. VAN DE VEN: My primary role is of course to do some research and teach in the field of urban water management and sustainable water management, focusing in particular on SUDS (Sustainable Urban Drainage Systems) and what is nowadays called the circular economy: closed cities. So, how to close cycles in the urban water system. I focus on the whole urban water system and not specifically on the drinking water and sewerage system – instead, I focus on the urban surface water, groundwater, sewerage, stormwater drainage and water supply and how these hydrological systems coexists.
WAVIN: You are also an expert advisor in the Urban Land and Water Management team at Deltares. We see you were involved with many projects. As our focus lies within Europe, what was the most interesting European water management project you were recently involved in?
DR. VAN DE VEN: My role here at Deltares is, first of all, that of team leader urban land and water management – which means that I'm coordinating work here in the Institute, applied research in the field of urban water management but also water management in relation to spatial planning and urban development and redevelopment. An interesting recent project is the Smart Sustainable District project, part of the European Climate - KIC programme:
The Smart Sustainable Districts project focuses on a number of districts in Europe, where we focus on water, land use and urban redevelopment opportunities, creating climate resilience in the first place of course, but also paying due attention to liveability, social resilience and other aspects that could be relevant.
Urban water management is part of a bigger process
WAVIN: Are you also closely involved with urban architects and especially urban planners?
DR. VAN DE VEN: We are indeed very closely cooperating with the urban planner in particular, and the landscape architects. We are doing green infrastructure planning, making conceptual and detailed designs. While they make the detailed designs on how these facilities could look like, we – for example – promote the multifunctional use of these facilities and evaluate the expected performance of this plan from a water management perspective.
WAVIN: These functional requirements start probably with water management and then there are the aesthetic requirements – the requirements which come from the architects. How do these two come together?
DR. VAN DE VEN: It is really a cooperative process to come up with a decent design, taking care that all the hydrological requirements regarding water quantity, water quality and in ecology are met, meanwhile, designing something beautiful, something attractive or something that could be used in other ways in the urban environment. Whether it's a green roof , an artificial wetland, a water square or whatever other blue-green element.
(left) Geertjo van Dijk, Wavin European product manager Storm Water Management interviews (right) Dr. Ir. Frans van de Ven, associate professor of Urban Water Management at the Faculty of Civil Engineering and Geosciences of the Delft University of Technology and team leader Urban Land and Water Management at Deltares
Validity of design standard in relation to climate change
WAVIN: Floods on the streets… we know it's coming every year, but how come it's still happening?
DR. VAN DE VEN: We designed our stormwater drainage/sewerage systems to fail about once every two years – that's standard design. So things like flooding will happen frequently. The question is whether the design standard is still applicable nowadays. We're going to see flooding more frequently in the future simply because of climate change, since we expect more frequent and heavier storms.
WAVIN: Aren't municipalities or other stakeholders taking the problem seriously – that the storms actually can occur every year?
DR. VAN DE VEN: I think they are taking the problem seriously, flooding is a wide concern nowadays. The problem is not so much that there is flooding on the street, the problem is the damage it does. So the question is, how much are you going to invest in resolving the problem of flooding and how much are you willing to invest in resolving the problem of the damage? You can either invest in increased drainage and storage capacity to reduce frequency and degree of flooding, or in reducing the damage sensitivity of your urban environment – two ways to go that are both widely applicable. Can we design an urban system that minimizes the damage when it fails due to hydraulic overloading? That is an important challenge.
The importance of storage everywhere and protection of vital infrastructure
WAVIN: What are the three quick wins for a municipality to practically do something to resolve pluvial flooding?
DR. VAN DE VEN: I think the quick wins are in storage and not in discharge capacity – Increasing discharge capacity on flat lands like we have (here in the Netherlands) is always difficult. It's very hard to make water flow if there's no gradient. Another quick win could be avoiding that essentials components of the urban system fail, even though the street is flooded. Investigate the damage sensitivity of your project area, see where vulnerable vital objects are located and protect that vital infrastructure in a better way.
WAVIN: You mentioned storage is a first quick win especially in a flat country like the Netherlands. This can also be the case for European countries where there is a lot more level difference.
DR. VAN DE VEN: Many of our cities are located in low lands and in flat areas, but even in sloping terrain storage is extremely important. If you can retain or detain water higher on the hill, you will avoid that it rushes downhill and causes flash floods downstream.
Urban storage solutions are extremely important and will become even more important in the future.
Opportunities of water with climate change
DR. VAN DE VEN: Climate change will bring more pluvial flooding but also cause more droughts and more heat stress. And first of all, during a drought you need water so you have to retain water to have it available for, for example irrigating your garden during dry periods. But more important is the fact that you need water for urban heat stress reduction and for energy reduction in the urban environment. And to that end we can use that very harvested water that is retained in our retention facilities.
Heat stress explained
DR. VAN DE VEN: We have to realize that the urban heat island is largely caused by the fact that urban areas cannot sweat. The fact that they are so dry and there is insufficient evaporation causes temperatures to run up. It is like your body temperature. If you are unable to sweat, your body temperature will run up. The same holds for urban areas. And reducing the ambient air temperature would also reduce the need for cooling and the energy demand for cooling. So, if we can make more water available for evaporation during these hot periods, then that would reduce urban heat stress.
The future of rainwater harvesting
DR. VAN DE VEN: At the moment we see an enormous increase in attention for rainwater harvesting. I consider that an extremely important development for the future of our urban drainage systems.
WAVIN: On the back side of that, the argument often comes up that our drinking water is so cheap, so why retain water? But actually, you're saying that it's much more than drinking water supply. It is more the drought and heat stress that creates new water demands. It is the heat island effect that we can combat with harvesting and storage solutions.
DR. VAN DE VEN: That’s a good point. When it comes to toilet flushing, the question is why would we just not use drinking water for that when we have plenty. However, the moment you want to use water to irrigate your lawn during extreme drought… our drinking water supply system wasn’t designed for that. And suppose you would like to use more water for evaporation (evaporative cooling); this demand was never considered when your supply system was designed. So, I see another water demand coming up at the moment, that could be covered better by harvested rainwater – rather than by our public waterworks system.
Stay tuned for the next blog in this two part interview series: Wavin talks climate resilience with urban water management expert Dr. Frans van de Ven - PART TWO.
For the full video interview, go here.
Download the Urban Stormwater Management Toolkit at www.wavin.com/toolkit.