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Heavy rainfall drenched American cities from coast to coast this year. As climate change intensifies storms, many municipalities are updating their stormwater management approaches and thinking about how to design more resilient cities.
On Wednesday, December 13, 2023, SciLine interviewed: Dr. Lauren McPhillips, an assistant professor of civil and environmental engineering at Penn State. She discussed topics including: how changes in the frequency and intensity of storms affect a locality’s infrastructure needs; how urbanization and other land uses affects the movement of water; pollution risks associated with stormwater runoff; integrating stormwater solutions with natural watersheds; green stormwater infrastructure, nature-based solutions, and their ability to provide many benefits.
LAUREN MCPHILLIPS: Hi, I’m Lauren McPhillips. I’m an assistant professor at Penn State University, copointed in our departments of Civil and Environmental Engineering and our Department of Agricultural and Biological Engineering. And generally, I work on water and soils. In the past, I have been more interested in kind of understanding different aspects of how humans have often negatively impacted or changed these resources. But increasingly, I’m really focused on solutions. I consider myself an ecological engineer. And so this is leveraging the power of nature and ecology as we think about solutions to deal with the fact that humans have to live somewhere, we need to grow food, but we need to figure out how to do it in a sustainable way and minimize our impact on the environment.
Interview with SciLine
How does a city determine its stormwater infrastructure needs, and what factors are changing those calculations now?
LAUREN MCPHILLIPS: When we design infrastructure, we are generally designing it to have a certain capacity and that capacity is based on a mix of things, it has to deal with the risk that we’re willing to accept. So, how often are we willing to be okay with our storm sewer system being overwhelmed, and they’re being flooding? Obviously, we don’t want that to happen that often. But it also would cost a lot of money if we were to build our infrastructure to withstand any size event. And so, we have to balance those factors. So, in general, our infrastructure is designed for some event. And for storm sewers, that could be something like the rainstorm that comes every two or so years and so a rainstorm bigger than that would exceed the capacity. So, with climate change, if we’re seeing same amount of rain coming more often than that means we’re going to be exceeding that capacity more often. The other intersecting issue is that our cities are changing, we’re developing the landscape and so when we built out that infrastructure, we also were thinking about what the city looks like at that time, and how much hard surface there was and that has changed too. So, we have this intersection of urbanization and climate change coming together to cause bigger challenges together.
How does the size of a city affect its stormwater infrastructure needs and its capactiy to adapt to changing needs?
LAUREN MCPHILLIPS: One thing that’s common across any size city is that you have hard surfaces added and that’s always going to have the same impact of preventing water from soaking into the ground and being taken up by plants and causing more of it to run off. Obviously, big cities—the scale of the problem is even bigger. But one of the other main differences is that bigger cities tend to have more access to financial resources, they have more people, a bigger tax base, which means they have more capacity, sometimes for solutions to be implemented. This isn’t always the case—in some cities with declining populations, like, say, Baltimore, they may be struggling more with having the amount of people to support the financial resources needed. Another issue to mention is the access to knowledge. So, larger cities have more staff, a lot of design firms there and so there may be more access to innovative ideas and and dealing with new designs related to stormwater management. Whereas smaller towns may just have more trouble having access to those resources and knowing what might be the best new stormwater management strategies are to use. There are a lot of folks trying to change that and to make different resources more accessible, but the challenge still exists.
What are green stormwater infrastructure and nature-based solutions?
LAUREN MCPHILLIPS: We’ll start with nature-based solutions first. So, this is kind of the umbrella category. The name is somewhat straightforward and what it’s implying—we’re talking about something that is helping us solve some problem. Here, we’ll talk about the stormwater context. But I can say that we’re also thinking about nature-based solutions when it comes to climate change related things. So, how can we sequester carbon using nature-based solutions? The nature side of things is the idea that we’re leveraging the power of nature, so vegetation, and soils in these types of features that we’re talking about. So, this can mean preserving or restoring existing features in the landscape. So, for example, if we’re considering some new urban development, there is intact forest there, which has all of this mature vegetation and healthy soils. We would want to try to do our best to actually preserve that and to develop around that rather than just developing over that and then entirely engineering from scratch new stormwater infrastructure. So, we can think about all these ways to preserve existing features. But then we might also, in many cases, have the need to be engineering some sort of hybrid nature-based engineered solution. And so this is where green stormwater infrastructure comes in. So, here, we’re thinking of a whole suite of solutions, but one that we hear about more often is something called a rain garden. So, these are features that are typically designed to capture stormwater off of some hard surface, be it a roof, or a road, or parking lot. They are a depression or basin in the landscape that’s capturing water. And then there is soil there that is well draining, so the water can soak through it. And then there’s vegetation there—that’s the green part of this—and so the vegetation is able to also take up water, keep the soils healthy. And so these features are able to slow down the water, help improve its quality and treat it and potentially provide other benefits as well.
What are the benefits of green stormwater infrastructure and nature-based solutions?
LAUREN MCPHILLIPS: If our target goal is stormwater management, then a lot of times we’re designing these features to be able to capture a certain size storm event. And so, we are holding that water back and slowing it down from reaching the storm sewers or some receiving water body. If we are able to infiltrate water or soak it into the ground, then we can remove some of that water that is eventually even going downstream. So, we can slow it down and maybe even remove it altogether from going into the sewer system. We’re also getting a host of water quality benefits. So as the water moves through soils or is taken up by plants—we can remove all these different types of urban pollutants that we have. But then what really the value is of nature-based solutions and green stormwater infrastructure is all the potential for these other benefits that can come. So, they’re not just singular function, dual function. The fact that we have plants that may include a diverse range of species with different flowers means we may be providing pollinator habitat. Now, we have the ability to sequester carbon in our soils and in the vegetation. If we have trees there could even be providing some cooling. And in even some larger types of green stormwater infrastructure, they can be designed for recreation. So, you could have a soccer field that doubles as a stormwater retention basin. Depending on the goals you’re trying to meet, there’s a lot of potential to match a certain design to provide a whole suite of different kinds of benefits.
How might large green stormwater infrastructure projects affect city planning?
LAUREN MCPHILLIPS: A lot of times—when we design these—we’re designing them for relatively small storm events. What happens if we’re thinking about these really large-scale events that come less frequently? The challenge is that we can’t design stormwater infrastructure that can hold all of that water—it costs a lot of money. And so we need to think a little bit differently about these large events that we’re going to be getting more often. And this is where we really need a systems approach, we have to think about how can we actually plan for areas of our city to be okay with flooding. So, this could mean designing our recreation infrastructure to also serve a dual purpose as stormwater retention infrastructure in a large event. If you can’t play soccer, you know, once a year because the field is flooded. That’s a lot better than having that water ending up into areas where it can have worse impacts and so some cities are really starting to think about this into their sort of whole scale planning. And I think it’s really an important area as we consider how to adapt to climate change.
What advice do you have for reporters covering water infrastructure?
[Posted December 13, 2023 | Download video]
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