PubTalk 3/2019 - Land Subsidence

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Detailed Description

Title: Land Subsidence: The Lowdown on the Draw-down

The link between groundwater use and sinking landscapes

  • What is land subsidence, where does it happen, and why does it matter?
  • How do weather and land use affect land subsidence in California?
  • Why are we optimistic about the future of land subsidence in California?

Details

Image Dimensions: 1272 x 720

Date Taken:

Length: 01:20:23

Location Taken: Menlo Park, CA, US

Transcript

This video is a one-hour presentation of the USGS Public Lecture Series titled, Land Subsidence – The Lowdown on the Drawdown. The presentation is being hosted in the USGS Menlo Park facility. The host welcomes the audience and introduces the speaker, Michelle Sneed, who is a USGS hydrologist. As Michelle is giving her presentation, she is continually pointing to and referring to slides presented on the screen. The slides are a mixture of charts, graphs, and photos. At the end of the presentation, there is a question-and-answer session with members of the audience.

- I always have to figure out the logistics of my script and the microphone. Well, good evening, and welcome to the United States Geological Survey’s public lecture for March 2019. I’m Diane Garcia, and I’m with our Science Information Services group. And I just – I’m really, truly happy to see you all here after our brief hiatus, so thank you for making the effort to get here in person. Before we get started, we always like to plug the next lecture, and we are having it in April, on April 18th. It is the Story of California’s Changing Ecosystems as Observed from Space. There are fliers in the back. I hope you grab one and you save the date and you come back for that. It’s being given by Kristin Byrd from our Pacific Region. So that promises to be an interesting and wonderful talk too. But what you’re here for is tonight’s lecture – Land Subsidence – The Lowdown on the Drawdown – the Link Between Groundwater Use and Sinking Landscapes. And it’s being presented tonight by Michelle Sneed. She’s a hydrologist with our California Water Science Center since 1994. She received her bachelor and master’s degrees in geology from California State University-Sacramento, where she periodically teaches geology classes. She has published many studies of land subsidence related to fluid pressure changes in areas throughout California and other areas in the western United States. Recent studies in the San Joaquin and Coachella Valleys explore the impact of subsidence on water conveyance infrastructure. She is a member of the United Nations Educational Scientific and Cultural Organization – UNESCO, Land Subsidence International Initiative, the recognized leader in promoting global land subsidence studies. The USGS monthly public lecture is just tickled pink to bring you a program about land subsidence. And I’m going to ask that you please hold your questions until the end. And now I’m going to ask that you give Michelle a really nice, warm welcome.

[Applause] Thank you, Michelle.

[Applause]

- Thanks, Diane. Thanks, everybody, for coming tonight. I know that we have had a couple of months off here, so I’m really happy to see you all. So I’ve been working in land subsidence for quite a while, and being part of this UNESCO group the last four or five years or so has really broadened my knowledge on subsidence that’s happening all over the world. My focus certainly is California, but I’m going to start with kind of a world perspective. I don’t want you to feel like California is sort of alone in this issue. It is widespread. So if you’ve seen any image of land subsidence ever – you’ve ever seen a talk, you’ve probably seen this image of Joe Poland. He’s a USGS guy. And he was really smart to use a power pole as a way to illustrate land subsidence. Land subsidence is not an easy thing to photograph. And I get plenty of journalists, photographers, say, show me where I can take a picture of land subsidence. And then I have to kind of talk them off the ledge a little bit. [laughter] So he’s showing here, using a telephone pole, where the land surface was in 1925, which is 30 feet above where he’s standing in 1977. Though we haven’t come up with a better idea of how to illustrate land subsidence, so we just copied Joe. And so here’s a more recent photo, using the same kind of idea, to show where the land surface was in 1965, which is above my head – or, above my feet about 8-1/2 feet or so. So I’m going to show a couple more of these images as we go along. So first, to just get us on the same page of what land subsidence really is, in the broadest sense, it is a gradual or a sudden sinking of the Earth’s surface owing to processes that are happening either on the surface or below the surface. And I’ll expand on that idea. Almost all of the land subsidence in our nation, more than 47,000 square miles, which is about the size of Pennsylvania or so, is a result of our exploitation of groundwater. Almost all of that subsidence is caused by the compaction of susceptible alluvial aquifer systems that accompanies overdraft. Overdraft just means we’re pumping more out than is replenished, year to year to year to year. Overdraft. Kind of like a bank account. You can’t, right, keep taking money out of the bank without putting as much back in, at least at some point. So I want to start with a world perspective of where subsidence is happening in the world. So this map shows a lot of locations in the United States and China. You don’t see any dots in Africa. You don’t see any in South America. One in Australia. The reason that it’s prevalent in the United States and China is because we have a lot of people. We’re rich countries. Rich countries use more resources than poor countries do. And so we have a lot of subsidence in richer countries. Now, that doesn’t mean that it hasn’t happened in Africa or South America. We just don’t know if it has or not. We don’t have any data to support that. So this is sort of an unknown. Some of the places in the world that are fastest rates recently – Tehran, Iran, is subsiding very, very quickly. But just a few years ago, when we were really in the sort of third, fourth, fifth year of our drought, the fastest subsidence rates were happening in the San Joaquin Valley – worldwide. Luckily, we’ve had a couple of reasonably good precipitation years, and so the situation has changed a little bit for us. We’re not leading the race anymore, which is good. This is a race you don’t want to win. So scoping down to the United States, you’ll see that we have a lot of identified subsidence areas in the West. You’ll also see some in the Gulf Coast area – Texas and Louisiana – as well as some on the East Coast. Now, in the West – all right, we’re talking about groundwater withdrawal, right, and the West doesn’t have a lot of surface water. So we use more groundwater than most eastern states do and some Midwestern states. And so that’s why we see a lot of subsidence issues in the West. On the Gulf Coast, they withdraw groundwater for use, but they also pump oil and gas. And oil and gas is just another fluid, and aquifer systems respond – alluvial aquifer systems respond in a very similar way to pumping oil and gas as they do water. The benefit that much of California has, where our severe areas of subsidence are, are not necessarily on the coast. We do have them on the coast in the Gulf and in the east. In the Chesapeake Bay, you see some areas over here that have identified land subsidence. It is a big problem on the coast. Even really small amounts of subsidence are a big problem on the coast because sea level is rising. So you have the land sinking and the sea level rising, making the relative land subsidence much worse. Not only that, but in the Chesapeake Bay on the East Coast in particular, we have lots of infrastructure and assets that are right on the coast. Biggest naval shipyard – things like that. So really small amounts of subsidence can cause a big problem. And that’s something I have learned over the last, oh, probably 15 years or so, that it really started to take hold that, you know, it doesn’t necessarily matter just how much subsidence you have, but where that subsidence is occurring. And that’ll be a sort of a reoccurring theme of this talk. Scoping down to California – so I have a map here on the left side of the screen that shows the areas that have been identified as having land subsidence issues at one time or another. And, again, California – you know, we use a lot of water. We have surface water in the north. We do have these huge conveyance systems that move that water to the south, but there just sort of isn’t enough to go around much of the time, and so groundwater pumping makes up that deficit. So we have a lot of groundwater pumping. I have a few images up here. So this image is of the California Aqueduct and the Delta-Mendota Canal. So they’re very close to each other near the pumps in Tracy. And, as we’ll learn going through this talk, these canals are being severely impacted by subsidence. They’re very, very sensitive infrastructure to subsidence. And I’ll explain more about that. To the right of that is just a photo of a benchmark. These are monuments that we use to survey over and over and over again to get an idea of what kind of vertical land surface change is happening between the surveys. This image down here is a protruding well. Now, if you’ve ever poured concrete, you probably haven’t done it in air. [laughter] All right, so what’s happened is that, when the concrete was poured, the land surface was higher. And that concrete is bonded to the well casing. And so, as the land has subsided, the well casing is holding all of this up. If it hasn’t happened already, this well casing likely will collapse on itself. It won’t be able to sort of take those stresses of the – that causes – the stresses of the subsidence. So that will probably collapse someday. This is a telltale sign of subsidence. This is a image here on the lower right of the Delta-Mendota Canal. And, you know, you see a rupture in the concrete lining of the canal. And we don’t know for sure that subsidence caused this rupture, but it’s in a suspicious location because this area has been affected by what we call differential subsidence for quite some time. And when I say differential subsidence, I’m talking about subsidence that happens in different places at different rates. It’s not all happening at the same rate everywhere. And so you can imagine, if you have one area that’s subsiding, and one that’s not, any infrastructure that crosses this area that isn’t really flexible is going to break, right? So this is an example of what can happen. Like I said, we don’t know for sure that it’s caused by subsidence, but it’s pretty suspicious. So I’m going to talk about the San Joaquin Valley today – the area in red there. But before I do, I just wanted to make you aware that there are lots of land subsidence studies that are going on now or that have recently been happening. And this is going to – there’s going to be more and more land subsidence studies in California as we move forward because of a new law that’s been passed. And I’ll get to that near the end. But today, I’m just going to talk about the Central Valley or the San Joaquin Valley in particular. So a lot of times in these talks, one of the first questions that I get at the end is, you know, well, what about subsidence in the delta? Is that the same process, or is that a different process? So I preemptively strike here to tell you about it. And it is not the same. The subsidence in the delta is very surficial process, while subsidence in places like the San Joaquin Valley, the Coachella Valley, the Santa Clara Valley, which is a little closer to home, are quite different. It’s a deep process. So with delta compaction, it all lies in the peat. So when there’s a waterlogged system, right, and it’s tidal – the delta is very, very wet – and when vegetation decomposes, it decomposes very, very slowly in the water. And it makes this wonderful soil for farming – very, very rich. So we like to use that soil for farming. But you can’t farm in waterlogged soil, so we pump it out, right? We drain the soil. As it turns out, when this peat – this peat layer – this really rich organic sediment is exposed to the air, it vaporizes. It oxidizes. It disappears. Turns to gas. So this process is kind of like somebody going along with a shovel and removing the top bits of the land surface. Very surficial process. It’s very different when we’re talking about aquifer system compaction. This is a very deep process. Now, aquifer systems are composed of sands and gravels and clays and silts – different types of sediments. Well, if you’ve ever been to the beach, and you’ve picked up a handful of sand, and you look at it, if you look at it carefully, you notice that the sand grains are fairly rounded. Well, clay is not. Clay is platy. And clay is kind of our villain in the compaction story. Aquifer system compaction is concentrated in the clay layers. So clay layers have this structure, where it’s very platy. And when it’s deposited, it’s deposited in, more or less, random orientations. Now, this is a bit exaggerated for illustrative purposes. But you get the point. In between these grains is water. Okay, that’s where water is stored. And that’s called a pore space. And, as we withdraw water, this pore space here, the pressure drops as water levels drop, and the grains get a little bit closer together. When water levels come back up, that pressure increases and it pushes those grains apart a little bit. That’s a very elastic response – like a rubber band. You know, you just pull it in, pull it out, right? It goes back to the same shape. But when you start to withdraw water in a way that continuously lowers groundwater levels, we get to a point that’s called – it’s a critical threshold of water level. Call it the critical head. Might hear it called the pre-consolidation head or the pre-consolidation stress. And when we pass that threshold, which is sometimes estimated as the previous lowest groundwater level, those grains rearrange themselves. So they’re not just bowing out anymore and, you know, deforming elastically. They rearrange themselves into more of a stack. And so a couple of things happen. One is that it’s going to take up a lot less space, right? So your clay unit is going to get thinner. And you can see that the pore spaces have collapsed, right? They’re much smaller. And this is a – this is not recoverable. Those grains – even if you really put a lot of water back in the aquifer system and really pressurized it, yeah, it might push these grains apart a little bit, but they’re never going to go back into this random orientation. Okay, so this represents a permanent loss of storage capacity of the aquifer system. Now, through history, this has been estimated in various basins In the desert, sometimes we hear somewhere between 5 and 15% of the aquifer system capacity has been lost due to compaction. In the San Joaquin Valley, there was a study done in the ’60s by Joe Poland, and they estimated that about 30% of the water that was being produced was caused by the compaction of clay. And in the San Joaquin Valley, we have a lot of clay. Something like 60% of the aquifer system is clay. So the potential for compaction is really, really large. Again, this is not fixable. And as – you know, we’ll start – we’ll talk a little bit at the end about why this really matters. And it’s because, in California, we’ve built reservoirs in all the best places already. Not that we couldn’t build a couple more, but aquifer systems are going to be used as managed reservoirs. That’s already happening in some places. And so, moving forward, we’re impacting the ability for these aquifers to store water. Very similar to – maybe you’ve heard about dams through time, and reservoirs, they silt up, right? As the sediments are coming in with the water into a reservoir, the sediments settle out, and your reservoir is smaller now. Because now there’s sediments taking the place where water could be stored. So it’s analogous to that. So why does subsidence matter? Most people care about subsidence because it damages infrastructure, and to fix it is very expensive. Some of the most sensitive infrastructure are canals. And the reason is because canals are built on very small gradients because we like to use gravity to move the water. It’s cheap, and it’s relentless, right? Gravity is always there. And if the whole canal subsided the same, that gradient would be maintained, and you’d probably be listening to somebody else tonight. [laughter] But that’s not how it goes. It’s differential, right? And so, for a canal to work under gravity, every elevation upstream has to be higher than every elevation downstream. When you have differential subsidence, you have a little sort of hole, right – a sag in the canal. And so, you can see here, well, that’s probably okay. You know, water’s still going to flow downhill. But it’s going to get backed up here. And the result is that that canal cannot move as much water as it was designed to. So the capacity of the canal is impacted. Freeboard is the term that’s used for – to describe the distance between the top of the water surface and infrastructure that crosses it – so a bridge. So when you go to a bridge, and you look over the bridge, you expect to see water going under the bridge, right? In this case, you see water going – if I can find my mouse – into the bridge, right? So this creates kind of a chokepoint, right? So you have this slug of water moving through, and now it has to fit in this space underneath the bridge. And so it’s running into the bridge. And this also can impact the integrity of that bridge as erosion. You know, water is pretty magical at finding its way around places. If you’ve ever done plumbing work, you know that. [laughs] And so you could damage the bridge as well. In fact, there are several bridges that are slated to be replaced over canals in the San Joaquin Valley. You used to be able to kayak underneath that, by the way. That’s how they used to inspect the bottom of the bridges. So while canals are the most sensitive to differential subsidence in particular, really any infrastructure that crosses these areas can be impacted – roads, railways, bridges, pipelines, wells that I’ve already explained. Here’s another picture of a well in the upper right-hand corner. And this is in an active vineyard. And it’s a very deep well. It was drilled for oil and gas exploration. And when they drilled it in 2010, they painted the top of it orange so that farm equipment wouldn’t hit it, right? It’s in an active vineyard. Well, within two years, you can see that two more feet of that pipe are exposed. So I think I’ve already shown you pictures of a ruptured canal, and I’ve showed you this as well. So the other sort of side of impacts from subsidence are natural resources. And I’ve already explained the aquifer system storage capacity being reduced. But as you can imagine, right, when you’re in a landscape, you find wetlands and rivers in the lowest places of the landscape. As those lower – as the topography is changing, right, you might have spaces now that are lower than where the river is. So the rivers may change course, right? They may migrate. As well as wetlands. Maybe some wetlands disappear and new ones emerge in new places. So we measure subsidence using a variety of methods. We use benchmarks a lot – showed you a picture of this already – where we survey over and over again. Back in the day – and even sometimes now – we use some leveling surveys on these benchmarks to track their change over time. More recently, we tend to use GPS. And this is a case where this is a continuous GPS station. It’s set up all the time and measures the land surface elevation every 15 seconds or so. On the upper right is InSAR. Interferometric Synthetic Aperture Radar. And this is a remote sensing technique. We tend to use data more from satellites, but this can also be collected from airplanes. And, in this way, we orbit the Earth, and we take pictures – radar images of the land surface over and over again. We can process those together and make a change map. And then the lower-right photo is of an extensometer. And an extensometer is different from these other methods. Because GPS, spirit leveling, InSAR – they all measure the change of the land surface. What is the land subsidence? Extensometers actually measure the thinning or the slight thickening of aquifer systems. So there’s a specific depth that these are anchored to. In this particular photo, that one’s anchored at about – almost 1,200 feet. And so it’s measuring the aquifer system thickness and how that changes in that interval. That’s a very helpful measurement for water managers. Because, okay, you know you have land subsidence, but where is the compaction happening? How are you supposed to manage the land subsidence if you don’t know if the compaction is happening at 100 feet below land surface or 1,000 feet below land surface, right? So it’s a really valuable measurement. And it’s the only way that we know to date how to measure that compaction – that thickness change. So I have two lists up here. And they’re the same content, but their order is slight different. Because I’m going to show you a lot of maps, and I’m going to show you some time series of what’s happened at particular locations. And so, as we make maps, right, we want higher spatial resolution, right? If we want to make maps, we get more measurements per space as we move down in this list. On the right-hand side, we get more measurements in time as we move down the list. And we use these data sets together. We use – we get maps of subsidence, and then we really need to understand what’s happening through time, at least at some locations. So I’m going to show you data from almost all of these methods. The two I’m going to leave out are Lidar and radar altimetry. And the reason that I’m going to leave out Lidar is because it’s really not being used for subsidence measurements yet. The technology is there, but it’s very expensive. So it’s just not being used. I think it will be as we move forward. And radar altimetry is kind of in its infancy. There’s a few papers out there that have been written using radar altimetry for subsidence, but I’m not going to talk about that today. All right. So the history of subsidence in the San Joaquin Valley shows that – and this is a map on the left-hand side of 1926 to 1970. And I know it’s kind of light, but the take-home point here is that most of the subsidence was happening on the west side of the valley. Okay? So this is a map, right? And so we used spirit leveling techniques on benchmarks to make this map back in the day. Well, now I’m going to show you a time series of a particular location on that map. And so, in the upper graph here, you see water levels declining, right? There’s a seasonal thing going on here, right? We pump more in the summer than we do in the winter. And water levels were declining up until about here – early 1970s. And they started to recover rapidly. Here you see the same thing with compaction. So there’s an extensometer at this location. And you can see, yeah, compaction was happening, but, wow, it really kind of minimized in the early ’70s. So what happened in the early ’70s? California Aqueduct started to deliver water. And so farmers over here didn’t have to pump nearly as much groundwater as they did. Some probably didn’t pump at all. And so water levels came back up, except during droughts, right? So we have a huge water level decline here. You see that subsidence re-initiated. It was a short but severe drought – 1976 to ’77. And then you see water levels resume recovery and compaction, right, that stopped happening. If you notice, there’s a couple little bars right in the bottom here. That’s expansion. So that’s – there’s an elastic component that was occurring, like the rubber band, okay? Which that happens in the coarse grain materials all the time. And so, again, another drought. Water levels decline. But then, after the drought, recovery again. So this looked very promising. It looked like the California Aqueduct kind of fixed the problem, right? And so when you fix a problem, you don’t keep throwing money at it, right? And so, what happened was that subsidence studies, subsidence measurements, sharply reduced at this time. Because, you know, you fixed the problem. You have other fish to fry, and you’re going to put your resources there. Well, what we found when we started to look at subsidence again, really because of the 2007 to 2009 drought – so the drought before the one that we just had – you know, we thought we’d find maybe something similar. You know, that, okay, we’ll probably find subsidence during drought, but then, when there’s enough water coming down the canals, it’s probably going to be relieved again. Well, what we found was that subsidence was occurring. But it wasn’t really happening in the locations that it was before. And it’s not that no subsidence happened over here, but not very much compared to up here and down here. It was kind of embarrassing because we stopped looking for a while. So the next two graphs I’m going to show you – the first one is this location here. And the second one is this location. So this is kind of what we expected to find, right? So, in all my graphs, by the way, brown is subsidence and blue is water level. Okay, so what we see here – this is a continuous GPS station, and we see – okay, yeah, okay, during droughts, there’s subsidence. You might expect that. But between droughts, it pretty much flattens out, right? And then here’s another drought. Lots of subsidence. But then it kind of flattened out. It even got a fair amount of rebound here during that really wet year a couple years ago. So this is what we thought we’d find, and we did. Until we started looking at other locations. In those locations, we found that it wasn’t necessarily a drought-related phenomenon anymore. In this location, you see that subsidence happened even between the droughts and even during that wet period. It kind of slowed down a little bit, but still, subsidence happening. So this is no longer a drought-related phenomenon. Not everybody gets surface water, and certainly not everybody gets enough surface water to meet their demand. So here’s a map of more recent subsidence. So this is just a two-year period from 2008 to 2010. So largely a drought period. And you can see that a large part of the valley is impacted by at least an inch of subsidence. So if it’s pink, it’s at least an inch and as much as 21 inches or so. So almost a foot a year was happening. And to give you some perspective on the historical subsidence compared to this more recent subsidence, here you go, right? So it’s kind of on the west side, and now it’s sort of moved to the east a little bit. There’s that recent subsidence again. So I’m going to show you 84 years of data from this particular site. And it’s on the Delta-Mendota Canal. And the Delta-Mendota Canal was completed before the aqueduct. And the things that were learned at this site by Joe Poland were actually applied to the California Aqueduct. They said, you know, where the Delta-Mendota Canal is coming out into the valley, we see more problems. So make that California Aqueduct closer to the Coast Ranges, and we think there will be less problems. So here’s what that site looks like. And this is a combination of early leveling surveys – as early as 1935. And here’s where the extensometer came into operation in 1957. And this one actually has quite a bit more data than almost all of the other sites. The folks that run the Delta-Mendota Canal – the Delta-Mendota Water Authority – kept this site going. And there’s only a 10-year gap or so, which is really small. Most of the extensometers have a 40-year gap. They were kind of put to sleep in the Early ’80s or late ’70s, and some of them we’ve brought back into operation. So this really kind of shows how this is related to the groundwater levels. So, again, you have this sort of rebound starting in the early ’70s when the California Aqueduct started to deliver water. And then you see, you know, big declines of the groundwater level during drought. And by the way, these declines are really, really fast. They’re very large-magnitude declines for really short droughts, in some cases. And this is partially a result of that reduced aquifer system storage capacity. It can’t store as much water as it could anymore, so water levels decline and recover much faster than they did before. So you can really pick out the droughts here. This is sort of hidden behind here – the brown, but you see a little step down during that drought. And here you see a step down during the drought. And this one’s real obvious too. So when I was talking about the process of aquifer system compaction, I talked about two main things. One is declining groundwater levels, and the other is the presence of clay, right? So in the San Joaquin Valley, we have both of these things. We have water level declines, and we have lots and lots of clay. And I will show you here in just a moment what the Corcoran is. So I know that’s probably a term maybe you haven’t heard. So water level declines. Yep, we got ’em. So here, this is wells in the town of Mendota. And I’m showing a shallow well in the light blue and a deep well in the dark blue. And when I say shallow and deep, the shallow is above the Corcoran clay. I’m going to show you what that looks like in a minute. And the deep well is below the Corcoran clay. You can see they kind of mirror each other, but certainly, the water levels in the deep system have a lot more variability. Maybe not seasonally. You see large seasonal swings here. But these respond with much greater declines during droughts and recover more between the droughts. And I circled historically lowest groundwater levels because remember I mentioned that that critical head, that threshold at which the clay starts to respond differently, is a result of the history of the aquifer system and historical stresses that that aquifer system has experienced. And, in this case, it looks like, if we use the previous lowest groundwater level as a kind of proxy for that, then these groundwater levels are certainly below that depth. And I’ll talk more about that in a little bit. So this is what the aquifer system structure looks like. I said, it’s a bunch of sands and gravels and lots of clay. And there’s kind of two systems. There is some connection between the two, particularly since humans got involved because we drill wells through them both, right, and provide a conduit – a pipe, basically – that connects the two. So here you see this Corcoran clay. It’s a regionally extensive confining layer. It’s a clay. And a lot of folks, even to this day, think that – and you might think this right off the bat – oh, that must be the offender. That must be the clay that’s causing all this subsidence. Well, as it turns out, it’s not our biggest enemy. It is draining. It is compacting. But it’s these clay lenses – and they’re all over the place – if I drilled a well where I am standing, and I drilled a well in the first row, and I tried to correlate units across that, I would not be able to do it. It is an assemblage. It’s mixed up. It’s complicated. But there is a lot of these clay lenses. And so we find that these are our biggest offenders. And especially in the confined aquifer system. But that’s because we’ve pumped more from the confined aquifer system than the shallow system. The reason is the water quality is better down there. And so that is what has primarily been pumped. And so there are some thoughts out there that think, well, if we just pump the unconfined aquifer, figure out a way to use that water that’s reduced water quality – ways to use it beneficially, they we won’t cause compaction and subsidence. Well, there’s a lot of clay in that area as well. It’s all the way down from the top. The more you drill you down, the more – it’s just clay, clay, clay, clay – lots of clay. So this is another way to look at that. And I know this is a little bit strange to look at. But here’s Redding up here, and here’s Bakersfield down here. And these are well logs kind of hung in space. And so Claudia Faunt has put together – my colleague has put together the Central Valley Hydrologic Model. And this simulates flow throughout the system. Well, to do that, you really need to understand the geology to get that right. And so we digitized a bunch of well logs, and then we kind of hung them in space, and it looks like this. And the take-home here is that there’s a lot of blue, right, which is clay. So we’re going to take a look at this area briefly. We’ll come back to it. But I just wanted to show how much water conveyance is in this one area. We can see the California Aqueduct on the edge. The Delta-Mendota Canal. The San Joaquin River. All of those deliver water, right? The Eastside Bypass was built for flood control. So it doesn’t deliver water. It moves water away. San Joaquin Valley has a rich history of flooding. And the San Joaquin River would just get overwhelmed. And so the Eastside Bypass was built to help ease flooding on the San Joaquin River and move water out faster. But before we go on, I want to show you something that was kind of surprising to me during this study is that the box you see, most of that is out of the sort of contour area, meaning that there’s less than an inch of subsidence that’s happening wherever it’s not pink. So here’s a close-up of that area. And when we were studying subsidence along the Delta-Mendota Canal, we looked at their infrastructure locations along the canal and figured out what amount of subsidence was happening at each of those locations. And so, in the northern part here, you see, okay, yeah, there’s some – a little bit of subsidence, but really not very much. You see a lot down here and a lot down here, right? So you think, wow, that’s the big problem. That’s where maximum subsidence is. Well, when we were in the drought and we got some spring rains. And so the Delta-Mendota Water Authority was given five days to move as much water as they could from the delta to Felipe San Luis Reservoir. San Luis Reservoir was critically low levels. Five days – not an amount of water, but an amount of time. And what they found out was that just this little bit of subsidence impacted their ability to do that, right? So they had what they would call chokepoints at Check 7, and then another one at Check 9, where the water – you know, you can see that the gradient’s kind of messed up, right? It’s uphill. And so they weren’t able to fill San Luis as much as they could if it weren’t for subsidence. Now, granted, this is only a three-year period. Probably more happened before then and more has happened since then. But that was really an eye-opener for me. Again, it doesn’t necessarily matter how much you have, but where it’s occurring. This is another way to look at that same information. So this blue line is the original design elevation of the canal. And the red was created by using the Central Valley Hydrologic Model simulating subsidence based on the data that we had. And here, maybe, is a little bit clearer how these chokepoints affect the ability to move water. All right, so let’s look at some time series now. We’ve been looking at some maps. Let’s look at some time series. And so here are four locations where continuous GPS data is collected. And I’ve circled this axis here because it’s different than the rest. Everywhere else is zero to 20 inches. But Chowchilla, this particular site, needed a bigger Y axis. So I just wanted to call your attention to that. And so we see a couple of different things happening here. At this location, we see subsidence only during droughts. And this is the same drought that you saw earlier. It’s at this location. So this tells me that this location around here, when surface water is available, they have access to it, they use it, and they’re not – they’re not pumping enough to cause subsidence. Right, but these other locations – and this – by the way, this is the other one that you saw already as well – you see that there is still subsidence even between the drought periods. So this tells us that they may have access to surface water. They may not. But if they do, it’s certainly not enough to meet demand, even between drought periods. This is a cross-section of this Eastside Bypass. This is this flood control structure I mentioned. So water flows northwest, right? It’s going to go out the Golden Gate, eventually. And so water is flowing here. Right, you see it has to fill up this hole before it can continue. And now it has to fill up this hole before it can continue. And it hasn’t happened yet, but it’s possible that it would spill over the sides of the levees before it could – before it would continue going downhill. That didn’t happen, even a couple years ago when we had all of that rain – that really heavy year. I was pretty impressed. Water managers actually did a really fantastic job of controlling flows and stopping flooding. And it was kind of impressive. So a couple of images. This is – this is sort of my good news slides. And so we’ve been doing a series of these images, and this one’s to 2016. And you can see there’s 8.6 feet of subsidence at this location. We did it again in 2018, and we got no additional subsidence, right? It’s been a good couple of years. So this location really benefited from that additional availability of surface water. Here’s another location. Just about the same story. What’s interesting here is that this really gives you some idea of how rates have changed. So, in 16 years, 2.3 feet. In the next four years, 0.6 feet. That’s about the same rate, right? If you multiplied this times 4 and that times 4, to be equal to 16 years, that’s about the same rate. But then the next eight years, right, 3.3 feet. A hugely ramped-up subsidence rate. We were in a drought during much of the time between 2008 and 2016. And 2018, just a little bit more, right? And so here you can see that, right, that rate has actually decreased the last five years compared to the previous five years. All right, so let’s take a look at Pixley – the same kind – the southern part of the valley, I call it the Pixley area. There’s a little town called Pixley. And so this is the same kind of situation. Again, Corcoran – notice 70 inches of subsidence is the – is the Y axis here. The rest are 30. Again, this is subsidence only during drought, so look at that. The Friant-Kern Canal – apparently that area gets surface water when it’s available. By the way, the Friant-Kern Canal has been in the news a lot lately. And it’s because it’s been severely impacted by subsidence. It could only move about 60% of the water that it was designed to move. Been severely impacted by subsidence. Here you can see, wow, you know, really rapid subsidence during the drought at this location. During that very wet year, it flattened out, but it sort of continued on after that. Well, I’m going to show you a few graphs of extensometers. I won’t spend a lot of time on these, but I spend time with these extensometers, so I have to show you the data because it’s hard to collect, you know? [laughter] And so, again, brown is compaction. Blue is water levels. And the arrows are really just showing what happened that year, right? So probably not a huge surprise. During the drought, right, we had subsidence, but that really wet year, we got a little back, right? In this case a little less than an inch and a half. About a half-inch here. And these, by the way, are the depths of these extensometers. Remember we’re measuring very specific depth intervals with these sites. Here’s the southern few sites. And this site in Porterville, right on the Friant-Kern Canal, is brand-new. So we don’t have very much data from it. We just started to collect data from it last June. I was pretty shocked when we first put in the instrument to see this guy tick down so fast. But we’ve gotten some back. So some of that is an elastic response, at least. And last time I was there, water levels were still going up, so I expect that we’ll get a little bit more rebound out of the site. And that’s really – that’s really good news for that – for that canal and those folks that have to manage it. All right, so depths of compaction. As I – as I mentioned, extensometers is the only way to really figure out at what depth intervals this might be happening. And so what I’m showing here is just a schematic of this particular extensometer, which is anchored in the top of the Corcoran clay – just above the Corcoran clay. So this is just shallow system that this extensometer is measuring. And then the GPS theoretically goes right to the center of the Earth. So this is the whole deal. This is all of the subsidence. But graph these together, and you see that there’s much less compaction at the extensometer than at the GPS site. So we conclude, then, that most of the compaction is happening below the top of the Corcoran clay, right? Because that’s where this is anchored, in the top of the Corcoran clay. We’ve done quite a bit of work to figure out if the Corcoran clay is a big offender. And, as I mentioned, it’s really not. It’s a very thick clay, hydrologically very, very tight. You know, you could think about maybe Silly Putty. If you spread Silly Putty out, and you poured water on the top, and you’d wait for it to come out the other side, you’ve got a long wait. It’s going to evaporate, right? You’re going to fall asleep long before it’s going to go through to the other side. Well, the Corcoran clay is very, very tight like that. It doesn’t move water very fast. And so, through some sort of modeling studies, and geological studies of the actually material that’s in the Corcoran clay, we find that it is – it is draining. It is – those pore spaces are getting smaller, but it’s really, really slow. In maybe a couple thousand years, we’ll shake our fist at it and say we should have tried to do something about it. But it’s just – it’s not in the right time horizons for water managers to really think or worry about it. Okay, so then sort of the next question people want to know, is the compaction permanent? Was it inelastic? Or was it elastic? Right, recoverable or permanent? And so we start to look at the critical head – right, the previous lowest groundwater level. And how the system responds to that. And so here we see that the critical head in this upper graph – so this is above the Corcoran clay, and this is below the Corcoran clay – it was set in July 1991 for this particular well, right? We don’t have a record going back hundreds of years or anything. But it’s a pretty old well, and the lowest was set in 1991. By the way, that was the end of a drought, right? And so that’s not surprising that water levels got to low levels. Well, in this case, we see that water levels did go beyond that level in 2016, but for a really, really short period, and just barely. It takes time for these clays to drain and compact. And so the conclusion is, is that, in the upper system, that any compaction that occurred during 2016 was probably elastic – probably recoverable. If we look at the lower graph, see the critical head is set in August 1992. Same drought as this guy, but set a little bit later. That was the lowest groundwater level. And you can see here, in 2009, we did surpass it for a little bit. Right? But not for very long. And you kind of – okay, reset the critical head. That’s the new previous lowest groundwater level. But then we move forward, right, and we see, we’re just lowering, lowering, lowering. So the critical head is going down. And so our conclusion then would be that, yeah, most of the compaction that happened in the deep system is probably permanent. Probably not going to get that back. So what can be done about it? Well, from a scientific point of view, it’s super easy. Just stop lowering groundwater levels. No problem. [laughter] You ask a manager that, and they’re going to put out their hair and – you know, and so it’s a really hard problem to address. But that really is the secret. If you stop lowering groundwater levels, then your subsidence will stop. And so it’s going to be some combination, right, of reducing groundwater withdrawal or increasing recharge, right? So maybe you decrease groundwater demand. Maybe you limit or redistribute the groundwater used. Or bring in some surface water supplies if there are some available. Or recharge the aquifer system. Of course, there’s natural recharge of the aquifer system. But remember, the aquifer system that’s in trouble is the deep one, right? It has that Corcoran clay on top of it. It’s really hard to recharge that deep system using artificial means. Sometimes we build big ponds and we put water in it and let it infiltrate. There’s a lot of experiments going on now in the San Joaquin Valley where they’re using what’s called on-farm recharge. So some brave farmers have allowed floodwaters to be redirected onto their land during the winter to let that infiltrate. Again, depending on where you are, that means you’re recharging the upper system. But there are some places that are recharging the deeper system, and that tends to be closer to the Sierra Nevada range. Kern County is really, really good at it. They have a lot of coarse grain material. Not as much clay in that area. And so they allow the water to infiltrate, and it recharges the aquifer system. Where we’re really going now is trying to figure out how to use or store the water when it’s available. Because it’s available in the winter and the spring, and the farmers really need it in the summer. So the good news is, is that California finally implemented a law to manage groundwater resources. There has not been laws to manage groundwater resources in California. We’ve had laws in place since 1914 to manage surface water. But they left groundwater off of that. And to not let a good crisis go to waste, right, during the drought, they implemented this law. And it’s really a pretty cool law because they give the locals the responsibility to do it. And they’re not going to – the state’s not going to say, oh, well, you have to, you know, reduce your withdrawal, or you have to do this, or you have to do that. They said to the locals, you figure it out. But you’re not allowed to cause undesirable results. [laughter] The undesirable results include land subsidence. Okay, they include a bunch of other things too – surface water depletion, reduction of storage, you can’t degrade the water quality, seawater intrusion. All right, so surface water depletion – you can’t just put a well right next to a stream and pump the hell out of it and – that’s not permitted, right? So it really gives the locals a ton of flexibility. Also an enormous responsibility to figure that out. And they’re working on that now. They’re writing plans. The plans are due next year. And they submit those to the Department of Water Resources. The Department of Water Resources will look over the plans and say, okay, this looks like a reasonable approach. Go for it. Or they may say, well, wait a minute. You think a foot a year of subsidence is reasonable? That’s not reasonable, right? So there’s going to be some sort of iterations in some cases. They have 40 years to come into sustainability – I’m sorry – 20 years to come into sustainability. And that may seem like a really long time, but there are check-ins. We didn’t get into this problem overnight. And this a – you know, without groundwater laws previously, there’s not a lot of data that’s been collected in some areas. They’re really scrambling to try to learn about their aquifer systems and figure out a plan of how to bring them into sustainability. And so it’ll be – you know, it’s a really, really interesting time to be sort of in the groundwater world to see how this is all going to play out. There’s new groundwater agencies that have been created to do this. And, like I said, they’re sort of scrambling now to figure out how are we going to bring it into sustainability? How are we going to avoid these undesirable results? And so I’m optimistic. You know, we’ve never had groundwater laws before. Usually California is kind of first on a lot of things, and we’re last in this case. Right, and so we know lowering groundwater levels and land subsidence are linked. So really, if they take care of the lowering of groundwater levels, we take care of the subsidence. This is just a summary of the things I’ve talked about today. I’m not going to read it. But I have enjoyed this, and I hope you have too. I hope you’ve learned something. I really appreciate you coming, and I would be happy to take any questions that you might have. [Applause]

- Thank you, Michelle [Applause] If you have a question, you’re going to need to get up and go to the microphone to ask it so that our viewers online can hear your question.

- My daughter lives in the Coachella Valley just south of Palm Springs. And there’s a huge number of golf courses there that water from brown water all the time. Now, I imagine most of that water that hit the ground seeps back down into the ground. Is it – is it just true that they just lose it mostly through the evaporation?

- So Coachella Valley is actually a really cool story. I’ve been working down there since the mid-’90s. And fortuitously for them, they actually paid attention to the – they sort of contacted us in the mid-’90s to say, you know, we’re worried about subsidence because we know we have lowering groundwater levels. So we’ve been measuring subsidence since the mid – since the mid-1990s. And just around 2010, they’ve been really implementing a lot of programs to reduce groundwater withdrawal, including agreements where they get more out of the Colorado River Basin, tiered rate structures, and managed groundwater recharge. And since 2010, we’ve seen a remarkable change in the Coachella Valley. And almost everywhere that had been subsiding before that stopped. And the few small areas that continued were at about half the rate. So that’s – it’s actually a success story. And they got – they didn’t know this law was coming in 2014 when they were doing all this. They’ve been working at this since the early ’70s – all these projects to try to reduce groundwater reliance. And so they’re sort of a good example of how other water agencies can look to see what they did to reduce their groundwater withdrawal. I mean, they’re in the desert. So it seems to me, like, if they figured it out, then there is a way for most basins to figure it out.

- What made it stop? They still have the evaporation from the golf courses.

- They do. They do have evaporation, but they’ve put most – not most, but many of the golf courses on surface water. So they’ve essentially reduced their demand for groundwater. That’s how they have dealt with it.

- I see.

- So there’s still water in the golf courses. [laughter]

- Hi. Thanks for your talk. Can you give me some idea of how fast groundwater moves? Like, you know, you recharge from a basin or something – I mean, I’m sure it varies with the composition of the [inaudible] and everything, but …

- It does.

- … can you just give me a range? I have no idea.

- Yeah. It does. It’s not – it’s not weeks. Maybe months. It depends on high the groundwater table is. It also – as you first start recharging, and it’s working its way down through dry sediments, it’s really not even getting to the water table. It’s really just wetting the sediments. And then water that is applied after that goes through much, much faster. But it’s not weeks. It’s months to years.

- So what kind of effects do you think you’ll possibly see draining the world’s largest natural gas field, like the Marcellus Shale? And maybe keeping in mind that it’s not, you know, the same permeability, porosity, kind of regime that you would see in, like, a sand aquifer?

- Repeat the question, please?

- What kind of effects, if any, do you think you’ll see draining the world’s largest natural gas field, like the Marcellus Shale?

- Yeah. So I haven’t studied that area, but there is also oil and gas withdrawal in the San Joaquin Valley. Especially around Bakersfield, little bit as you go south. And what we see from oil and gas fields is that it tends to be much more localized. It’s pretty severe subsidence. But it’s fairly localized around their wells. And they have regular collapsing of their wells, and that’s sort of a cost of doing business to them. They realize that that’s going to happen. And we do see severe subsidence. And, in fact, some of the InSAR data that we use sort of covers part of, like, the Kettleman Hills area that there’s a lot of, you know, withdrawal. And it sort of swamps some of the other areas. It really sticks out as an area that subsides very quickly. But it tends to be very local. So not knowing about the shale that you’re talking about, I’m not – I’m not really sure. But, you know, like, in the Netherlands, the Groningen gas field has had a lot of subsidence there. But the Dutch are pretty – they’re pretty smart about water. [laughter] They are. They’re really – I mean, they have to live with it. You know, where they actually talk about, yeah, we’re going to have to, you know, migrate our people away from the coast as more subsidence happens. But they actually make that stuff happen. We just kind of talk about it, mostly. [laughter]

- Thank you. On one of your charts, you had the – a lot – you know, a lot of subsidence underneath that one bypass.

- Yeah.

- Is that a coincidence?

- Well, it’s not because of the bypass. It’s because that is an area that doesn’t have access to surface water. And we’ve been changing land use out there. So in areas that used to be either range land or maybe row crops or truck crops have now turned to permanent crops. So trees and vines, primarily. And that kind of creates a – what we called demand hardening. You know, with crops like tomatoes and peppers, you can fallow that land when the water isn’t available. But with permanent crops, you have to water them no matter what, or you lose that entire asset. So it’s not that the – that the bypass is there, but it’s that land use has changed significantly in that area.

- Yeah. So that would indicate that maybe these farmers, when they figure it out, will change their crops.

- I think that’s definitely going to be part of the solution.

- Options, yeah.

- Yeah.

- But it just reminded me of – like, I lived in Davis. And they had the Yolo Causeway. And so every winter, that thing would flood, and that seems like a wonderful way to, you know, recharge the aquifers is just let it flood.

- Yeah. Right. Right. And taking – you know, taking the floodwater off of those channels and putting them into farms and putting them into places that will actually, you know, take more advantage of that water when we have it. And, you know, moving forward, as the climate warms, you know, more precipitation is going to be falling as rain as opposed to snow. And the snowpack is our biggest bank of water, right? Stays nice and frozen, comes down slow. We can take advantage of that in the winter. And now that’s – you know, that is going to become less and less as the climate warms. So the idea of being able to capture that water – because in winter now, right, it’s going to be coming down more as water and flowing out fast. So if there’s a way to capture that and recharge our aquifer system, then we’re really using it as a – as a managed reservoir just like we would a surface reservoir.

- Yeah. Correct. And use some of that injection to get it into the deeper areas.

- Yeah. Yeah. We’ve done direct well injection in a couple experiments here and there. There’s a – you know, on large-scale issues, it’s hard. Because it’s just a well. You can only put so much water in a well. And not only that, there’s some – there’s some chemistry issues that happen, especially with treated water that you put in a well, that it reacts with the native sediments and can cause some water quality problems. So it’s a – it’s a way to go, but it’s probably not the answer.

- Okay. Thank you. Sir?

- Hi. Toward the end of your presentation, you had the – kind of an eye-opening photo. The guy is standing with a pole – 1965 to 2016.

- Yeah.

- 1965 – that was where the land was? Now, how much – the question I have – how much of that, in those 51 years, the drought we just had – four- or five-year drought – I would imagine the drought contributed to a good chunk of that drop.

- So I showed you a couple of photos, but yeah, what we’re finding is there’s definitely more subsidence during droughts.

- Yeah.

- But subsidence is also occurring when we’re not in drought. So it’s really not a drought-related phenomenon everywhere. It’s – what’s happened is the land use change has ramped up the water demand, and we’re not – you know, we don’t really have sort of more water for it. So it’s really a land use change that’s affecting it – that has increased our demand, our needs, for water.

- Yeah. We had – a follow-up question, we had these rains – we’ve had a pretty decent winter for a change.

- Mm-hmm.

- How much does that help with the groundwater? You know, it’s probably – in 51 years, it’s probably a drop in the bucket, I guess – the rain we had now, but how much – we have – winters like we’re just coming out of now, does that help as much as I think it would?

- Yeah. When I showed those photos comparing 1965 to 2016 and then 1965 to 2018, really, between 2016 and ’18, subsidence stopped in a lot of places because that – you know, 2017 was really, really quite wet.

- Yeah.

- And water levels recovered – in all the sites that I monitor, water levels recovered all summer long. And I haven’t ever seen that in my career. And I talked to farmers, and they said that – some of them never even turned a well on that summer. Because enough surface water was being delivered at the right time for them to be able to utilize. So they didn’t even have to turn their pumps on. So it does help a lot.

- Pretty amazing. Yeah.

- Yeah. But we don’t have years that like that often enough, at least, you know, in the past 15 years. It’s been mostly dry.

- Yeah. That’s why – that guy showing the pole, 1965 through ’16, that was a very eye-opening photo. Look at that thing there.

- Yeah. Well, that’s why it’s used in, I would say, 97% of all the subsidence talks I’ve seen around the world. [laughter] It was brilliant. It was really – it was a brilliant way to illustrate subsidence. Because it really does – it really does open your eyes.

- Thank you.

- You’re welcome.

- Thank you. How much does it cost to collect all this data?

- What’s a GPS station cost?

- So [chuckles] – it depends who installs it. There’s – so we don’t actually install those. There’s other agencies that do that. And I think the last time I asked about a cost was something like about 50,000 to put one in. And then they maintain the data. So it’s all telemetered, and they process the data every day. And I think the sort of operation and maintenance costs were pretty low. As long as the sites aren’t vandalized or anything like that, those equipment can last a long time.

- Thanks.

- Mm-hmm.

- Where is all this leading? What’s the – what’s the future? Subsidence is – I know. I know. It’s a difficult [laughter] – difficult question, but you’ve painted a rather gloom-and-doom story. Subsidence – we don’t recover from subsidence.

- Oh, I ended on a happy note. We have laws. [laughter]

- You haven’t – really haven’t factored in climate change very much. And I’m wondering – well, you did talk about sea level rise. But I’m wondering how climate change and other factors might, you know, tell – inform us about the next 50 or 100 years. Any ideas?

- Yeah. Well, so climate change – the way it’s kind of looking – the climate scientists think that it’s not necessarily that we’re going to become drier. We’re just not going to have as much snowpack. And so that impacts when the water is available, right? And we really like a deep, good snowpack because our reservoirs that hold the water, right, those get drained – start get draining in March, April, right, as we plant the crops. And those start – and then they’re getting sort of backfilled with this slow drip of snow melt. And, as less snow is going to fall because it’s getting warmer, well, that water is going to come down too soon. And so – right, it’s going to come down as water. It’s not going to stay as snow, right? It’s water, so it comes down much, much faster. And so, to figure out a way to capture that water when it’s coming down, by these on-farm recharge projects or these settling ponds that I’m talking about, seems to be a really good approach. And there is a ton of work going on in that area. So the other part of sort of the good news story is this new groundwater law. Because it doesn’t tell them how to use the water. It just says you can’t cause these bad things to happen. Right, and so they can start to figure out what works in their particular basin. And that’s going to be vastly different for basins in, you know, northern Sacramento Valley as opposed to basins in the deserts. And their solutions are going to be vastly different. And it’s going to be a combination of a lot of things. With sort of the goal to being – you know, not reducing, you know, those groundwater levels – to have them level off. Seasonal changes are normal. If we just seasonal change, right, elastic response, no problem. These are very small. These don’t damage infrastructure on the surface. It’s when we do this over and over and over again.

- Hi. I'm Esther with Save Palo Alto’s Groundwater. And I’m going to bring the groundwater to the Bay Area. We got involved with groundwater because here in the Bay Area, the groundwater level is high. And to build basements, people were pumping out the water. And some of the neighbors – not me [laughs] – thankfully, had damage to their houses. And we kept saying, it’s subsidence. And the cities kept saying, it can’t be. This is just anecdotal. Nothing happens. No problems. They’re starting to accept that we’re having subsidence with pumping out so much groundwater. One basement pumped out 30 million gallons of water just to build one basement. So the neighbors were impacted. And we have a talk coming up on April 24th. And this will be about the impact of sea level rise on the groundwater in the Bay. Thank you.

- Great.

- What area? What area?

- The Bay – the Bay Area. Yes. The Bay Area.

- Well, that looks like – one more question? Oh, please come on.

- Burning question.

- Burning question. Yeah, right. I work in the maps office ...

- You need to get to the microphone.

- They’re going to – yeah, make you go to the mic. [laughter]

- As I said, I work in the maps department at one of the companies around here. I’m just curious about the remote sensing part that you talked about.

- Yeah.

- These days, there’s a lot of satellites being launched. Just curious if some of these are going to be deployed for, you know, the groundwater that we’re talking about here in the – in the area. Places where, you know, some of these GPS units are too expensive or vandalized a lot or whatever – those kinds of things, how do you see this working? Not only in California, but around the world, the other places that really don’t have the resources that we have here in the United States? Yeah. So interestingly enough, the United States does not currently have the capability to collect that kind of data. But we’re working on it. There is a satellite that is scheduled to be launched in 2021.

- One satellite?

- One satellite. It will have a eight-day repeat, meaning it’s going to image the same area every eight days. The data we primarily rely on these days is a European Space Agency satellite constellation called Sentinel. And it is collecting data every six days. And so – and there is a – there is some rumbling in industry and have – and private contractors launching satellite constellations that will collect this type of data. So right now, it’s worldwide every six days in many places from the European Space Agency.

- Okay. I’m not seeing anybody else at the microphone. Going, going, gone. [laughter] Let’s …

[Applause]

Yeah. Give a warm round of applause for Michelle. Thank you very much.

[Applause]

And I’m going to remind you if you can please come back on April 18 for that talk on ecological forecasting for California. Look forward to seeing you then.

- Thanks, everyone.

- Goodnight.