Cities Are Turning Flood Water Into Freshwater

IRA FLATOW: This is Science Friday. I’m Ira Flatow. 

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In case you just joined us, we’re kicking off our ongoing series Degrees of Change and examining how we, as a planet and a people, are meeting the challenge of a changing climate. And water, water is where we are seeing dramatic effects of climate change. This year, record downpours in the Midwest washed out levees causing catastrophic floods, while in California, a seven-year drought ended with an atmospheric river of water, literally, falling from the sky. 

Cities are starting to rethink their water futures and how they can make their communities more resilient. And it’s a completely different mindset from what we’ve been doing for centuries. Like instead of trying to hold back the floods, they are welcoming the water, finding ways to turn it into a fresh valuable resource. Engineers are looking toward nature for inspiration, replacing dams and pipes with green roofs, learning how the natural landscape wisely handles the water. 

And my next guest is here to walk us through all of this. Erica Gies is an independent journalist based out of Victoria, British Columbia. Welcome to Science Friday. 

ERICA GIES: Thank you. 

IRA FLATOW: Now, when it comes to water management, the idea has been to contain water, as I say, usually by building up dams and levees. But you say that cities are now seeing water as a resource rather than a nuisance 

ERICA GIES: Yeah, that’s right. There are a lot of problems with the gray infrastructure that we’ve used for the last couple hundred years, this effort to control water. And the biggest one is that it breaks the natural water cycle, so it cuts rivers off from their floodplains. And it tends to increase water use. 

So a dam actually increases demand. So a lot of our, quote unquote, “solutions” have counterintuitive problems associated with them. And urban sprawl is a big cause of both flooding and water shortages, because it prevents the water from absorbing into the ground and going down into the aquifer like it would have done naturally. 

IRA FLATOW: Hmm. Yeah. There’s parking lots, and sidewalks, and things like that. What do you see as the way out? What is the green infrastructure that could help us get out of that problem? 

ERICA GIES: Right. Well, we’re starting to see this in cities around the world, like you mentioned, green roofs. There are things like bioswales, which are kind of lower elevation little gullies that are typically planted with water-loving plants, pavement that’s permeable that the water can pass through. But a lot of it is also looking at– trying to see beneath our cities. 

Because we have creeks that have been put into sewers. And we have wetlands that have been filled with dirt and paved over. And the thing is, the water still wants to go to these places. So the extent to which we can recover, or reclaim, or uncover these natural waterways can help a lot, because we’re allowing water to do what it wants to do. 

IRA FLATOW: Let’s talk about some of the success stories and projects that are going on. There’s something called the Sponge City Program. It’s a national plan in China. What are they trying to do? How are they doing it? And what are their goals? 

ERICA GIES: Mm-hmm. Well, China has a bunch of water problems. It has massive urban flooding. Between 2011 and 2014, 62% of its cities flooded. And China’s had this massive urbanization over the last few decades. And they’ve sort of built their cities the way Western development did with all the same kinds of river channelization and pavement. And they’re seeing the problems with that. 

And China, despite it getting a monsoon, is actually a pretty dry country. So water scarcity is a problem in more than half of its cities. And more than 400 cities rely almost exclusively on groundwater, pumping groundwater, which also causes the land to sink. So the urbanization has caused both a lot of flooding and water shortages. 

And of course, China also, notoriously, has a lot of pollution problems with water. And the president, Xi Jinping, has made the environment one of his three pillars of government. And so when he learned about sponge cities, he made it a national priority. And in 2014, he created, well, initially, 16 and then 30 pilot cities. And their goal was to take a 10-acre area and make that capture 70% of the storm water that hits it. 

IRA FLATOW: Let me bring in a guest who knows a lot about that, who was based in Europe. As you say, one of the places that is leading this type of thinking about water is in China where there’s a river of humanity flowing to the cities. For example, Shenzhen in the south has gone from a city of 50,000 people to over 13 million. And that’s just in three decades. 

The countryside has been paved over. Mix that with bigger storms due to climate change, and that predicts future water disasters. And as you say, China is trying something new called sponge cities, and trying to find a way to soak up and reuse 70% of the rainwater in these cities. 

Chris Zevenbergen is a professor of Urban Flood Risk Management at the Delft Institute for Water Education in Delft in the Netherlands. Welcome to Science Friday. 

CHRIS ZEVENBERGEN: Good afternoon. Good afternoon. 

IRA FLATOW: We heard how, Erica was explaining how sponge cities idea is working. Give us a little bit more of the details. How is it different than, say, the green infrastructure ideas that we hear about in the US? 

CHRIS ZEVENBERGEN: Well, I think what Erica just said was correct. It’s a very, I would say, comprehensive plan of President Xi to transform the cities into sponge cities. And it goes a bit beyond the, say, the insulation of low-impact development, which we have in the US, rainwater systems which control big runoff and store [INAUDIBLE] our rainwater. 

It’s also about upgrading the traditional drainage systems to the standard level. It’s also, yeah, install or reintroduce the, say, canals, and water bodies, and multi-functional storage facilities. So it’s more a concept than a technology. 

IRA FLATOW: Earlier this week, we talked to Kongjian Yu. He’s a landscape architect based out of Beijing and founder of Turenscape, a company that is building many of these projects. And this is what he said about why the sponge cities concept is important in China. 

KONGJIAN YU: We are facing some serious survival issues, such as flood, drought, pollution, to something about our survival, because we are suffering from the previous urban development models. 

IRA FLATOW: These are really interesting. We have some pictures linked up on our website at ScienceFriday.com. Erica, this is a very different type of project than we’re used to hearing about. Please, paint us a little radio picture of what they look like. 

ERICA GIES: Yeah. Well, Kongjian Yu has a vision that is creating a path for water, or like recreating the natural path for water, not just at the scale of a little project, but at the scale of a city, or a watershed, or even the entire country of China. So he’s really looking at trying to recreate the natural water cycle. And so some of his projects are ambitious. 

And one that I visited while I was there was in a Beijing excerpt called Dongxing, and it’s called [? Yongning ?] River Park. And basically, the river there had already been put into a concrete channel. And the government recognized that, as that area developed, that flooding was going to become a bigger problem. 

And so they hired Turenscape to do this project. And basically, they removed the concrete so that the sides of the river were dirt once again. And they widened it so that it could hold more water. And then they planted a lot of little sedges to hold the earth in place. And then the dirt that they excavated they made into a berm, sort of dividing the widened river into two channels. 

One of them will have the river flowing. And the other one will be, during the dry season, filled with partially cleaned effluent from a sewage treatment plant. And wetland plants in that pool will clean the water further and then allow it to filter down into the aquifers. And then during the monsoon, that extra channel will be reserved for the extra flood waters. And the sewage will just be treated industrially. 

IRA FLATOW: Chris Zevenbergen, one of the criticisms of people who get flooded out is that they continue to rebuild in a floodplain. Isn’t that a bigger solution, if you want the water to naturally go where it wants to go, isn’t a solution not to build in the floodplain? 

CHRIS ZEVENBERGEN: Oh, yeah. That’s, of course, the right thing to do. But also, in countries like the Netherlands where we have low-laying floodplains, we have a lack of space. And so there is enormous pressure on those areas to get built and developed. So it is inevitable that also the low laying areas in China will get urbanized. 

But we see that there are also concepts which allow, say, that flood water will enter into the urban areas without having real damage. An example is, for instance, in Hamburg, where we have, on a floodplain, an urban area which can deal with 7 meter of fluctuating water level. So I think we can also adapt our cities to floods much more than we were used to. 

So I think there is a lot of opportunity there. And what we see in China, for instance, urban agriculture, which is now being promoted in [INAUDIBLE] And I’ve seen their green areas where the citizens can use those green areas for crops and for urban agriculture purposes. 

And so there are a lot of combinations possible where you see that floodplains can be used to allow flood waters to come in, but also, to urbanize it. We have a concept of floating houses. We have amphibious housing. We have floating greenhouses. So there’s a lot possible. And China is really exploring, also, those opportunities. 

IRA FLATOW: And one of the advantages of allowing the water to come in, you want to reuse, as you say, 70% of the rainwater, that will clean it. As it percolates back down into the soil, it will be cleansed by the environment, will it not? 

ERICA GIES: Yeah, that’s right. And one of the things that is kind of crazy is a lot of places are importing water or desalinating water. At the same time, they’re rushing this storm water out of the city as fast as possible. So it’s a underused resource that we’re basically throwing away at this point. 

IRA FLATOW: I have another clip from landscape architect Kongjian Yu. He talks about if the mindset about how to build is really moving towards this direction in China. 

KONGJIAN YU: It’s changing, at least from the leadership. Gradually, we are changing the code system also. But that take a long time because of the interest conflict between different groups of academia, of engineering, and of business. But at the same time, many of the concrete wall are being removed by some cities because the mayors understand and say, now adapt to this idea. So I think we are very promising. 

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios, talking about our new series on climate change. But China is unique in the sense that because there’s no opposition to the leader in China, if he wants to do something, he can just say let’s spend the money on it. Isn’t that true, Chris? 

CHRIS ZEVENBERGEN: Yeah, that’s true. And that is also an advantage. If we see, for instance, in Western countries to really get the plans flying and to get inclusive process for– it takes states quite some time. But in China, we have no time. It’s the demands for housing is huge. And so everything is going in a haste. 

And of course, the counter side of that is that there is no time to reflect on mistakes, and to piloting new technologies, and to really learn from that, and to upscale it. Everything is going in a huge pace. And that is one advantage, of course, is that the change, the transformation goes fast. But the counter side is that we make mistakes in those designs. Imperfections will be there, undoubtedly. And they cannot be corrected slowly because everything is going so fast. 

IRA FLATOW: But Erica, what– 

CHRIS ZEVENBERGEN: So that is a bit what I want to say about the issue. 

IRA FLATOW: Yeah. No. And I’m saying that, in a sense, it’s their loss. But it’s, Erica, it’s the rest of the world’s gain because they watch this experiment going on in China. 

ERICA GIES: Yeah. 

CHRIS ZEVENBERGEN: Exactly. 

ERICA GIES: I think that’s true. And Kongjian Yu is part of a government advisement group that is trying to teach practitioners in China to be mindful that these water problems are common across the world, but every area has unique geology, climate, soil. And so, as Yu says, each one is a unique patient. And so that’s something that I think China will need to be mindful of as it goes forward. 

IRA FLATOW: And Erica, how would other countries adapt to this? And can they adopt what the Chinese are doing? 

ERICA GIES: I think they can. I think, so far, the projects in most other countries have been significantly smaller scale. But it’s not just smarter water management and less expensive. It can also be a climate mitigation solution. 

Wetlands store 40 times more CO2 than forests. And both conservation of wetlands and forests are a key part of this nature-based water management. And a recent report found that these natural climate solutions can actually help us meet 37% of the climate target for Paris of keeping the world warming to 2 degrees. 

IRA FLATOW: So you can leverage all of this? 

ERICA GIES: And yet, they’re only getting 2.5% of public climate financing. 

IRA FLATOW: Wow. That’s very interesting. I want to thank you, Dr. Zevenbergen, for being with us. Chris Zevenbergen is a professor of Urban Flood Risk Management at the Delft Institute for Water Education in Delft, the Netherlands. Thank you for staying up late to be with us today. 

CHRIS ZEVENBERGEN: Thank you. Thank you. 

IRA FLATOW: We’re going to take a break. Journalist Erica Gies is going to stay with us after the break and talk about how these new ideas about managing water are happening in the United States. We’re going to talk about what you can do right in your own backyard. We’ll start off by talking about Houston. Houston is on a forefront of water management. We’ll talk about it. And stay with us. We’ll be right back after this break. 

This is Science Friday. I’m Ira Flatow. 

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Kicking off our Degrees of Change series about how communities around the world are adapting to climate change. And we want to know what’s happening in your community. Are there plans to boost your city’s resilience against floods, fires, heatwaves, and storms? Or are things moving a little more slowly? 

We want to hear about it either way. Go to ScienceFriday.com/degreesofchange. ScienceFriday.com/degreesofchange to share our story. This hour, if you want to discuss our Degrees of Change series, you can give us a call 844-724-8255. 844-724-8255. You can also tweet us @scifri. 

And we’re going to become a little more local now from moving a little around the world from China. And we’re going to talk about, in our first episode, about how cities are going green. We’re talking about putting back grasslands, and wetlands, and green roofs to be more flood and storm proof. 

And one example, a good example, is deep in the heart of Texas in Houston, where so-called pocket prairies dot the city. What’s a pocket prairie? Well, here to tell us is Laura Huffman, Texas Regional Director for the Nature Conservancy in Austin. Welcome to Science Friday. 

LAURA HUFFMAN: Thanks for having me. 

IRA FLATOW: Still with us is Erica Gies, a journalist based out of Victoria, British Columbia. Laura, OK, what is a pocket prairie? 

LAURA HUFFMAN: So picture a pocket prairie as a very small-scale sponge. You were just talking about sponge cities in China. This can be your front yard, your backyard. It can be a vacant lot in a neighborhood or a parking lot. And imagine that you take all that concrete out and replace it with healthy soils and native plants. And in this case, you then have a pocket prairie. 

IRA FLATOW: And how effective is a pocket prairie in dealing with the water, let’s say? 

LAURA HUFFMAN: You know, they can be pretty amazing neighborhood-level solutions to solving floodwaters. And one of the reasons we really like this movement in Houston is, first of all, it gives people something that they can do. Second of all, these pocket prairies, we absolutely know that they will hold more water than the average lawn. 

The average lawn will retain about a half inch of water. And pocket prairies can hold as much as 9 inches of rainfall. So they are better at absorbing and holding rainwater. They are local solutions. And they can scale-up to a citywide solution. 

IRA FLATOW: 9 inches? 9 inches of rain water. That’s amazing. That could take care of a hurricane if it comes ashore, right? Give me an idea of what you have to plant to make it a pocket prairie. If I’m listening, I may be in Texas or some other places, how do I do that? 

LAURA HUFFMAN: How do you do that? Well, in this particular area in Houston, you’d be planting things like blue bonnets, wild indigo, sunflowers, native milkweed which, by the way, butterflies love. So not only will these pocket prairies help you with managing rainfall, they’re also wonderful for increasing urban biodiversity. 

And of course, one of the reasons we like it is because it allows people to connect to nature in their own neighborhoods. And the way that these work is the root systems are so much deeper and more effective that they really create– picture channels underground and holes that absorb water. And it literally would turn your front or backyard into a sponge. 

IRA FLATOW: So how many pocket prairies are there in Houston? 

LAURA HUFFMAN: There are about 50 right now. And if you can imagine a situation, Houston’s one of the largest cities in America, there are over 6 million people, and if everyone that owned a lawn, or every business that had a lawn in front of it, would convert that lawn to a pocket prairie, you could have a pretty effective system of rainwater catchment. 

IRA FLATOW: So you basically have to find out, in your neighborhood, what’s good to plant there, because– 

LAURA HUFFMAN: Yeah, you do. 

IRA FLATOW: –you’ll be different than Houston. 

LAURA HUFFMAN: You do. But there are lots of nurseries all over the state and all over the country that can help you understand what the native species are, so you could turn your front and your backyard into whatever ecosystem happens to be appropriate for where you live. 

IRA FLATOW: It’s a lot more useful, a lot easier, and a lot more environmentally sound than just mowing your lawn every week, right? 

LAURA HUFFMAN: Well, absolutely. For those of you that don’t like mowing your lawn, this is a money solution. And if you do want to keep your lawn, we recommend that you mow it less frequently and leave the clippings on the ground. 

IRA FLATOW: That’s an idea. Erica Gies, in the bayou down around Louisiana and Texas, there is this idea of beautiful ditches. What is that? 

ERICA GIES: Well, Houston has had a lot of development. And it’s sprawled over a massive area because it has a very pro-development attitude. And in fact, these pocket prairies, or pothole prairies, are what Houston used to be before all this development. And so with every new apartment building that’s built, there’s a storm water requirement where the apartment needs to– the developer needs to build, basically, a big storm water runoff tank. 

But increasingly, they’re using bioswales, which are what I was talking about earlier, which are lower lying land that is then planted with water-loving plants. And so that can be a way to capture the water. And the developers like it because home buyers like it, because it’s more beautiful than a storm water tank underground that they don’t see. 

IRA FLATOW: Interesting. One of the cities really leading the way in the US is Philadelphia. They’re creating something called Greened Acres to deal with storm water runoff, right? 

ERICA GIES: That’s right. So in Houston, the main problem is flooding. In Philadelphia and other cities in the Midwest and Northeast, they have a problem called combined sewer overflows. And that’s because traditionally, they would capture the storm water and then run it through the sewer, which sounds like a good idea because then you’re cleaning it a little bit before you’re discharging it to the river. 

But the problem is that sometimes the storms are too big and these systems overflow. And then you have untreated sewage going into the river. So in the last decade or so, the EPA has been cracking down on this and requiring cities to do something to address it. And of course, they can build more gray infrastructure to treat it. And some cities have done that. 

But Philadelphia realized that it would save money if it really expanded green storm water infrastructure, which is these kinds of projects that we’re talking about. So when I was there a couple of months ago, like at the zoo, they have this big parking lot. But they’ve created bioswales all along between the street and the parking lot. So typically, the street is kind of bent and then the water goes into the storm drain. But this funnels the water into the bioswale and holds it, and it creates this little habitat. 

And then they had another bigger project, I saw, called Indian Creek, which had long ago been buried in a sewer pipe. And the problem with that is the sewer pipe has a set capacity. So when you reach that capacity, it can’t handle anymore. So instead, they’ve moved the creek back up to the surface and put it in this public park where people and wildlife can enjoy it and where it has room to spread out if the waters rise. 

IRA FLATOW: And Laura, of course, pocket prairies will cleanse the water that runs through it, too, won’t it? 

LAURA HUFFMAN: It sure will, because those healthy, natural soils and those native plants can help remove some of the pollutants, which can be a really big problem when you’re experiencing a flood and you’ve got all of the oil and pollutants that are associated with urban development. So they can be very effective little treatment plants. 

IRA FLATOW: Now, I understand that the Texas legislature is thinking about a state flood recovery fund, which would include more funding for green infrastructure. 

LAURA HUFFMAN: Yeah, it sure would. The legislature is still in session, so we’ve got a little ways to go, but the bill is doing quite well. And really, what this is recognizing is that we’re going to experience more frequent and more intense storms because of climate change. And so how we rethink recovering from these disasters is essential. 

And the thinking at the legislature is we’ve got to rebuild with resilience so that the next time this happens we’re in better shape. And it’s everything from pocket prairies to great big regional open spaces. And of course, there is a role for traditional infrastructure. But I agree, even that can be smarter traditional infrastructure. 

IRA FLATOW: A tweet coming in, “I’ve already started the process of converting a chunk of my front lawn into bee friendly, a mix of local flowering plants. I didn’t even think about the positive benefit of mowing less, except for just having to mow less.” Let’s go to the phones to, is it Tina, on Long Island. Hi, Tina. 

AUDIENCE: Hey. Thanks for taking my question. I love this concept. And in many communities, I mean here in Long Island, we don’t have very sizable lawns a lot of the time. And we have to deal with neighbors which is a big point. 

But in these semi-urban environments, a lot of us are also dealing with, when you let your land go, more wild like that, you have a lot of issues regarding mice, and rats, and bugs, mosquitoes. And so I wonder if there’s a way to get your neighbors on board and a way to avoid the troublesome side of the vermin issues? 

IRA FLATOW: Laura, any answer to that? 

LAURA HUFFMAN: Yeah. that can be an issue. I think one thing is making sure that you are, in fact, dealing with some native plant materials. I think that can help with that issue. It also just takes a little while for these ideas to normalize in a neighborhood. 

You now have people that are going around looking at the front yards that have native prairies in them in Houston and places like that. And because you may not have access to that many front yards, think about school yards. These make excellent places to have native landscapes. Think about parking lots, the land that sits under utility lines, which is often just mowed and not biodiverse. You can work this concept in a lot of different ways in your community. 

IRA FLATOW: Erica, the cities are already paved over and built up. So how do you find space for water in a big urban city? 

ERICA GIES: Well, you can use things like green roofs and permeable pavement. But there’s also a fair bit– we tend to think of our cities as static. But, in fact, a lot of change happens. Buildings tend to turnover in about 50 years or, in a place like China, 15 years. So that’s one solution. 

And a lot of places are setting regulations, like California, regarding new developments. So if you have a new building going in, then you have certain storm water or landscaping requirements. And then there’s also disasters, when people flood options to buy them out of the floodplain and recover that area for water. 

IRA FLATOW: So you change building codes about how you’ll build any new structures, what has to be included with them? 

ERICA GIES: That’s right. And I just wanted to say one more thing about this idea of attitudes changing. I mean, you see that in the West with xeriscape, which is the use of low-water plants or native desert plants in place of lawns. And at first, that was an idea that people thought was weird. But now, it’s something that people really embrace as a sign of their local area. 

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios. It’s our Degrees of Change series. We’re talking about water usage, what to do with all that rain water, how to make new uses of it. And also, I imagine, and it’s not just people, and their lawns, and their homes, that there are different changes in farming and agricultural uses, correct? 

ERICA GIES: Yeah, that’s right. California has really been a leader in this. It has to be because it has such a giant agricultural industry and has always suffered from droughts and flood. But this last big drought in the earlier part of this decade really caused some rethink. 

And climate change is a big factor in that because, historically, about a third of California’s water was in the Sierra Nevada snowpack. And it would sort of melt slowly into the spring and summer. And as temperatures warm, that is no longer going to be a resource that we can count on. 

And also, the winter storms are getting a lot bigger. You mentioned the atmospheric rivers. One of those can contain as much flow as the Mississippi River. So these are really vast, vast dumps of water. So the challenge is to try to capture that water and save it. 

But unfortunately, California has dammed most rivers, so reservoirs, additional reservoirs, are not an opportunity. And so people are looking to store that water underground. And there’s a lot of space underground because during the drought, farmers pumped a lot of water out of the aquifers. 

But then the challenge is, where do you put it? And there’s a couple of different ways to do that that scientists are looking at. One is soil considerations. Is it clay soil? Is it sandy soil? What is the land being used for? Is it conservation land? Is it farmland? 

How can we do that to make sure it doesn’t interfere with crops? And then one thing that’s really exciting are these things called paleo-channels, which are ice age channels underneath the surface of the Central Valley that are quite porous because they filled up with gravel. And so if we can find where those are and put water on top, we can get the water underground very quickly. 

IRA FLATOW: Wow. That is interesting. Before we go, we said, as part of our series, one of the things we’re going to talk about is doing some of the little things, something our listeners might think about doing to get involved. And we already mentioned something that I just want to go over again, and that is changing the way your lawn grows and making possibly a pocket prairie there. Or don’t mow it every week, and let it grow a little longer, and leave the clippings there. Anything else that comes to mind that our listeners might do on their own? 

LAURA HUFFMAN: Well, I’d add to that list, definitely ditch the fertilizers and the pesticides. So if you’re going to keep your lawn in place, mow it less frequently. Water it less frequently. Leave the grass clippings after you mow. And get rid of the fertilizers and pesticides. 

And then just start growing your prairie or whatever ecosystem is appropriate where you live. Once you’ve done that, you’ve become a demonstration project. So take that show on the road and start talking to your schools, and your churches, and your local businesses to start growing prairies in front of, or in back of, their buildings. 

These also make wonderful opportunities for children to connect to nature and to really understand the many values that nature brings to a community, its biodiversity. You can have butterfly gardens. And then they can also see that nature is an amazing way of helping in times of crisis, like when there’s a storm. 

IRA FLATOW: Well, this is a great kickoff to our Degrees of Change series. I want to thank both of you for taking time to be with us today. Laura Huffman, Texas Regional Director for the Nature Conservancy. She’s in Austin. Erica Gies, a journalist based out of Victoria, British Columbia, who’s working on a book proposal about ecological water management. Let us know when you’re kind of published there. 

ERICA GIES: Thanks. I will. 

IRA FLATOW: Thank you both for taking time to be with us today. 

ERICA GIES: Thank you for having me. 

IRA FLATOW: You’re welcome. 

LAURA HUFFMAN: Thank you. 

IRA FLATOW: Just to let everybody know, we’re going to be running radio specials every month on how your community and others around the world are adapting to climate change, sending you news about policy and legislation too. Join us. Share your story. Let us know what you think by going to ScienceFriday.com/degreesofchange. ScienceFriday.com/degreesofchange. You can sign up for our Degrees of Change newsletter there too.

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