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The Anatomy of Floods: The Causes and Development of 2011's Epic Flood Events

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Bob Holmes: This was a difficult topic to address for me because trying to cut it down I have so much material, that we want to make sure that we get out of here in a reasonable time because there are a lot of things that went on in 2011. So I am going to try to break this down into talking a little bit about anatomy of flooding and also getting into what we experienced in 2011, both in the midwest and here on these East coast.

First of all, just to define what we are talking about: There is a long technical definition that the USGS uses, and but I really like the bottom, "Too much water and too little time in one location." And so basically, we have this all over the country. And so why is it important over the past 30 years in the U.S. flooding, as Bill has as mentioned: Ninety lives lost in excess of seven billion dollars annually. It occurs in all 50 states all months of the year we have the floods and we have more fatalities than any other severe weather related phenomenon with the exception of heat.

Heat and drought itís a little harder to quantify when somebody dies of it. It is easy to know they died of flooding but heat does take a lot of lives as well.

In the United States, alone there are 3800 towns and cities over 2500 inhabitants that are in the flood plain. That is why we have a problem. We are at the intersection of human population and a natural hazard. It only becomes a disaster when people or property are impacted.

When we want to characterize and understand floods, these are some of the things we try to think about and talk about Ė understand: magnitude, cause of floods, what is the geographic context, why does it flood in one spot and not in other, probability of frequency from looking at risk analysis we have to know something about that, how does it vary with time, and then, then the process of understanding -- when you have rainfall on the ground, what's the physical process that governs it? What do we want to model there? What's the so what? Are we just a bunch of scientists wanting to know this, and engineers? The so what is we're trying to mitigate floods, we're trying to provide risk awareness to people as well as we look at environmental damages that happen. How does that flooding affect the biota, and the natural ecosystem.

What is the USGS' role in this? I want to accept the context of this, because I get asked this a lot. What is USGS? Aren't you just about geology? We have a role in most of the earth sciences in the natural sciences, and the biological sciences. We characterize in hazard areas, in four areas  observations, fundamental understanding, assessment products and services, and effective situational awareness. What I mean by assessment products. That would be things like flood maps that we're assessing the floods, flood probability.

The risk awareness or the effective situational awareness  we do things like we put out on the web the real time flood data and things like. How high is the river, what is it doing right now? When is the river cresting, things like that. If we look at all these in our fundamental understanding and our observations and situation awareness, they're all kind of interrelated. This is the sort of context that we use to formulate our science and our data collection around.

So if I start with our observations, that's really the backbone of any scientific understanding and really for societal action. If you want to decide if you're a home owner out there, "Hey do I move out, or do I not? Is this flood going to affect me?" You need to have some information, right? You have to have some observations. So we're going to start with that. What do we observe during floods?

Preceip, stream flow, watershed characteristics are very important and not necessarily just during a flood. We need to know something about the watershed, and what is in response to floods, the earth, the environmental, and biological response.

You know, during the 1993 floods, we had a tremendous biological response in the fish population. It was detrimental to the humans, but the fish really thrived after the '93 flood, just because of the dynamics of the flood and the interaction there.

And so, not only were we interested in the risk awareness things, but what's going on after the flooding happens to the natural systems?

What I'm going to talk about tonight and going to concentrate on when we talk about observations, we're going to be talking about volumetric stream flow. That's one of our basic data program things that we do within the USGS, that's absolutely critical to flood science and understanding of floods.

This is a picture of the United States, or a graphic of the United States, showing the distribution of our streamgages around the country. We have over 7800 streamgages that are there and operational 24x7. And they're reporting out on the web, and a number of other agencies, not only USGS but other agencies depend on this, especially during floods.

This is just some pictures of some streamgages. I'm not going to get into detail about streamgages, probably those of you who are veterans of these lectures have probably heard other discussions about those, and that's not my point here. But this graphic is just to show that we have it from the Rockies to the West Coast all the way across the Midwest and the Eastern part of the United States.

When we talk about a streamgage, really quickly, a 30 second primer on streamgaging. We have a sensor out there that looks sort of like this on the left. That's an old type of still-in-well we have much more compact type streamgages now. But the bottom line is, we sense the water elevation 24x7  sometimes every five minutes, sometimes every minute, sometimes every hour.

But water elevation is not what we need. It's important, but we need volumetric stream flow. So, what we do is, we get out and collect a lot of observations of the volumetric stream flow, cubic feet per second. You can think of it in gallons per minute, is another expression for the volumetric stream flow.

And we will relate the elevation of the water surface to that volumetric stream flow in the form of what's called a rating curve, down here on the left. And so, we're collecting stage as a surrogate and we're getting out of that stream flow. OK?

And so those little red dots you see on the graphic down there in the lower left are discreet observations where we had one of our staff out there collecting data. At that point in time, they knew what the stage was, they collected the volumetric stream flow, and they could plot that, and we come up with a rating curve.

And on the right is what you see the final product, is we have what's called a hydrograph where we have both the stage and the discharge plotted there. Actually, I think that's only discharge. But in the blue is the stage, or the discharge hydrograph. The red dots are where we actually collected discrete data and that's the information we collect.

So we're collecting 24 hours a day, seven days a week, we're collecting the stage. But we're putting out the product as stream flow, biometric stream flow.

This is just a graphic during the 2011 floods on the Mississippi River. This is immediately downstream of Cairo, Illinois, where the Ohio and Mississippi Rivers meet. This on the upper left is a boat, that we have Acoustic Doppler Current Profiler, which is an instrument that we use. In the right you see a little cartoon, it's using sound waves to bounce off the particles in the water and it's receiving that. And it's able, through the Doppler principle, to get a three dimensional velocity and the depth of the river.

And so they're going back and forth across the stream as you see on the left there and they are determining the depth, and they're determining the velocity and that product gives us volumetric stream flow.

And in the lower part is a cross section of what that channel looks like. You can see there the maximum depth is about 118 feet over on the left side and that's near the Kentucky Shore, and they're going all the way across and more then a mile over to the levee on the Missouri Shore. So, you can just get a kind of an idea of what the depth is.

These instruments are revolutionary. In 1993, before we really used these in a wide spread manner, unless we had a bridge, we were pretty much at a loss of making a discharge measure. We could do it out of a boat, but it was a lot of work.

I made discharge measurements out on the Mississippi River at Thebes, we hung under a rail road bridge in an old car that was built in 1948 and every time the train would come by, it would just rock you like crazy. And we're lowering a 300pound weight and a spinning cup current reader and it would take us five to six hours to make a measurement.

In 2011, we can make these measurements in about in about 45 minutes and the only reason it took 45 minutes is because you're going almost two miles across the river. And so, we're able to collect a lot better data, a lot quicker and a lot safer.

This is a hydrograph and I'm just going to throw this up and again this part of talk I'm just kind a introducing you to the observation side of things, where we can kind of set a context of what we're talking about.

This is a hydrograph which is a time plotted on the Xaxis and on the Yaxis, we've got volumetric discharge and this is our gaging station on the Mississippi River at Vicksburg, Mississippi. That's twomillion cubic feet per second. So to get an idea, if you multiply roughly, seven and a half times that value, that gives you gallons per second. There's roughly seven and a half gallons in a cubic foot.

We're basically talking there somewhere in the neighborhood of 16million gallons per second  greater than that actually.

At Vicksburg, during the peak of the flood, so that's a whole lot of water. And as we look and put in context, this is our annual peak discharge for every year that we collected data at Vicksburg, and you can see that in the 2011 flood, there on the very end, and that is the peak of record. That is the all time record.

If anybody has read John Barry's book called "Rising Tide," it's about the 1927 flood and the geopolitical dynamics going on there after that flood and all that. The '27 flood is there, the other one thatís almost as big as this one. So the 2011 flood was the granddaddy at this point in terms of volumetric flow at this point in the river.

Now, at other points on the Mississippi River, it's a very dynamic system. It didn't set the record, it was near it, but it wasn't quite the record. But here at Vicksburg, we have a record flood during 2011.

So, a product I'm going to highlight here in a second is WaterWatch. One of the things that we really stress is the situational awareness. This is a product you can get on WaterWatch. On the left, it shows every streamgage that weíve got, reporting in real time in the country. This is May 1, 2011. You can look up August 1, 2012 right now. You can get on the web its

It puts in context, hydrologically. Every gage, we have more than 25 or 30 years of record. It would put in context how it compares with all the other May firsts in the record.

So if it's in the cooler colors, it means we've got higher flows compared to all the other May firsts. If it's the warmer colors, especially if it's red, that's the lowest value of flow we've had for that particular day in the year.

And in the lower right, is another product within WaterWatch that gives us all the flood data. The black triangles there are the sites that we've got that are above flood stage. If it's not quite above flood stage, but it's in the higher end of the spectrum for the flows, it plots the 95 to 98 percent, and the greater than 99th percentile. That means 99 percent of the flows were less than that value for the period of record.

So, this is a situation awareness product. And now that we're in a drought, you could actually use this product to look around the country and see, where are the rivers low and where are they high? OK? That's kind of something that, gives you kind of a good thing to put the flow today, if you're interested in a particular gaging station, in context.

All right? So, a major product that we have is our streamgage data and we feed that to the National Weather Service. And what you're seeing there is a forecast. So, the forecast, we need to know on major rivers around the country and some of the smaller rivers, what is the river going to crest at? Because emergency managers need to make decisions, people need to make decisions about their lives. And so, we can look four or five days out at what the flood is going to do and how high it's going to get.

And a big component of that is the streamgage data that the USGS provides the Weather Service. It allows them to calibrate their models and validate their models to give an idea of what, if the model, what the model

The observations that we use are crucial, because if the model's wrong, and if they're off by a foot or two, that makes a huge difference of whether they build the levee up or whether they decide to evacuate a town or whatever. So, it's very crucial.

The last point I want to make about our data is, we're moving now towards, from the point of just forecasting the flood at a point, to now we're looking at inundation maps. And one product that the USGS is working on in concert with a number of other agencies, including the Weather Service, is to put out these real-time flood inundation maps.

Where you, as a citizen, could look on one of these maps and say, OK, the forecast is for 28 feet tomorrow or the next day. But that may not mean much to you. But if you can look in context with a map and see spatially whether something's going to get wet, i.e., your house, that means a lot more than just 28 feet on a stage hydrograph. It puts it in context.

So, this is still the early development phases. We're developing these maps around the country. It's not widespread yet, but that's coming. That's kind of the future of where we're going to be at with looking at flood forecasting.

So, if we look at observations and research together. So, we've been talking about observations, and then we took and look at fundamental understanding in our research. We get that, we do our research. We get to the point of fundamental understanding.

That's the next part I want to talk a little bit about is, we have floods based on the type. We've got rainfall floods, we have snowmelt floods. We have rain on snow floods, storm tide floods. We have man made dam break floods. You're not that far from Johnstown, Pennsylvania, more than 2,000 people killed. That was 1889.

There's also the geologic process control floods. Not too many happen these days, but the days of when we had glaciers covering North America, this was a more common phenomena. And some of the biggest floods that we've looked at in the paleo studies show that those glacial outburst floods, we looked two million CFS on the Mississippi River at Vicksburg. That would be a very small glacial outburst flood. I mean, we're looking at five to ten times that, maybe an order of magnitude bigger than that in some of these.

And so, and then lastly, our ice-jam floods, where you have ice building up on some of the mountains, especially the mountainous areas. And then, all of a sudden, catastrophically fail, releasing a wall of water. Those are catastrophic.

Now, the ones at the top are meteorological based. All right? Atmospheric waterfalls on the ground and we have the flooding. All right? The others are nonmeteorological. Storm tide floods are from hurricanes or tropical storms. These other floods that we're talking about down here, I'm not going to discuss those tonight. I'm going to stick to either meteorological floods caused by rainfall or snowmelt or whatever, or the storm tide kind of situations.

I do want to make a quick categorization is the flash floods. That's a category based on onset of the flooding. Some of the floods, like on the Mississippi River are very slow. They come up gradually, maybe a foot every couple days, and they stay forever. They're like a bad houseguest. OK. Whereas flash floods, you can have two or three feet of water come up in five minutes. OK. And these are more in the hillier terrains, smaller basins that are usually suspect, having flooding based on convective thunderstorms.

We also have dam breaks. That would be a flash flood. You lose your dam or your ice- jam or whatever, that would be a quick onset. As I've said, we're going to concentrate on that area of the spectrum, in terms of our flood types.

And so if I look at the hydrology of meteorological flooding, most of you have seen this. This is the water cycle. You get the moisture circulation. Basically all floods are, is just the water cycle gone bad. You've just got too much water and too little time in one location, more than normal.

And so if I look at that, I have to look at the rainfall runoff response. And this is just a little cartoon kind of showing you the elements that we have to consider when we try to understand the physics and we have to model the situation.

And so we have precipitation falling. You have interception if you've got plant cover out there, or tree cover. It's going to intercept some of it. Some of it's going to fall to the ground. Some of it, once it gets to the ground, it's going to infiltrate. Some of it will directly run off after infiltration through surface runoff. Some will percolate into the deep groundwater. Some will have through flow or interflow, where it will actually go through the shallow zone of the ground and go out into the river.

So we understand a lot of these processes physically. But it's very difficult to actually model these in concept, because the ground is so nonuniform, in terms of its characteristics. The plant cover is nonuniform. That becomes a real challenge whenever we try to understand what the process is of moving water from a rainfall or an atmospheric process into actually a stream flow.

So what are some of the factors that govern meteorological flooding? Geology and soil plays a big role. The land use. The type and amount of precipitation, where it came from, the storm track. What was the orientation of the basin of that storm track? How long is it? Was it an elliptical, long watershed, or was it really short and squat?

If it was really long, it takes a little longer for the water to get from the upper end of the basin down to the bottom end. So you have all those characteristics. And here is a cartoon of looking at two different types of floods from the same rainfall. You can see these in practice, where you actually have different types of responses with the same rainfall, just because the basin characteristics are a little different.

Let's look at land use. I can't look at all those characters. I just want to show you a couple of examples. These are from Washington State. And this is rural versus urban. You pave over things. You hydraulically connect people's roofs to the street.

And it goes right into the gutters, which goes right in the stream. That's a very rapid response to the rainfall. And so that's a much more rapid response than what you'd have in a rural setting, where it falls into agricultural land that's not hydraulically connected, directly, to a gutter or a street system. And so you get two different types of responses there.

If you look at the annual peak flow data, and remember I showed you the Mississippi River Vicksburg rule. We had the annual peak. So we take the largest stream flow in any given year, we call it our peak flow for that year. And then we take all those peak flows of every year, and we plot that. That's what we've done here.

You can see the impact of urbanization on these particular streams through the years, starting in 1960 on the left, proceeding to present day. And you can see that an urban situation, with this particular gage here, you've got very little trim to the data. It's, in fact, the trim line is pretty flat. Whereas in the urbanization, you look at the scatter plot of that, there's a definite trend upward and that's purely due to the urbanization of the system.

Precip has a huge role in basically, the proximity to your moisture source is the big driver there. If you look here in the United States, our big moisture source for the eastern part is the Gulf of Mexico. You do have some Atlantic Ocean influence at different times of year, but for the predominant moisture producer, is the Gulf of Mexico, you can see that, and this is the annual mean precipitation. The farther away from the source you get, the less precip you get.

On the west coast, obviously the Pacific, and you get away from the Pacific and you start to lose it. This is a very arid, dry location. But you do have pockets of high precipitation totals for the year. And a lot of that is due to what we call orographic lifting, where you have masses of air move in and as they rise up over the topography, they dump out a lot of rain. And so, on the windward side of these topographic features, you have a lot of the rain.

By the time it gets to the leeside, in most cases, the eastern side of the United States, it's dropped out, its rain and you get more arid. So, you can see the arid, the rain shadows in these arid areas in the Rockies. You get along the Rockies, you get a lot of rain. But, once it gets out into eastern Colorado and Kansas, you quickly drop off. And so, the topography enhances the precipitation. And you see that in a lot of places.

We see that down here in the Ozarks and Arkansas and Missouri, where the gulf moisture comes up, hits the Ozarks, rises up and drops out a lot of rain. We have a lot of tremendous rain storms coming out of that area, just as well. Texas is another one with the Escarpment of Balcones. Escarpment is another location for that.

So, what are some generalities? I can't go into all the details, but let's just talk about some generalities that control flooding in the United States, or basically anywhere for that matter. Floods can happen at any time. But by the most part, most areas have a rainy season that's going to dominate the flooding picture.

Northern U.S. and mountain basins, snow melt plays a huge role. The closer you are to the source of moisture, the more likelihood for extreme flooding. Small basins, the dominant feature, meteorologically, that's going to drive flooding, are short duration, high intensity convected thunderstorms.

Large basins are going to be those longer duration, more frontal or extratropical cyclonic or even tropical cyclonic, which we're talking about with Irene and Lee today. We're going to talk a little bit about that tonight.

Those are going to be forces that are going to be wide spread. They're going to dump a lot of rain over a long period of time. And they're going to get those basins up and really flooding. And then topographic relief plays a large role in how severe the flooding can be. And we'll talk a little bit about that, as well.

Here's the snow melt potential here. This is basically just the average snow fall. And you can see that along the Rockies, in the northern tier states, that's where we're getting our snow. Also, along the Cascade Range and the Sierras, we also have a lot of snow.

So, where you get a lot of snow, you can sort that moisture potential, in the form of snow, and once you melt it, that's just like it rained. Only it may come much quicker than if you have ten inches of snowwater equivalent in the snow. And it melts in a couple of days. That's like having a ten inch rain storm in 48 hours. Pretty, pretty intense rain.

This is a graphic out of a USGS water supply paper. This is, basically, the typical seasons for the largest annual flooding. And I didn't believe this at first. So, I did a lot of plotting and data. I started looking around and what I did was I played with a lot of the gages that I know about all around the country. I just picked out various gages and this is the Mississippi River at St. Louis. I took the annual peak flow file with all the floods and I said, when does the Mississippi River at St. Louis typically flood?

So, there's 115 years of record there. And I said, how many floods do we have in March? How many of the annual floods were in March? How many of the annual floods were in April? And, so on. So, that's what this graphic is. And you can see that, predominantly, we're talking April to June, OK, in there for the peak flow.

I did that for a number of the gages around here and surprisingly, I shouldn't have doubted, it was USGS publication. It should have been right, right? So, we see on the west coast in California, predominantly driven winter storms. OK, winter floods.

Colorado, this is Clear Creek at Golden, Colorado. This is June. I mean, this is dramatically driven by snow melt. OK, you have thunderstorms in Golden, Colorado, as well. But the primary driver for flooding in Golden, Colorado is snow melt.

You see this down in Arizona where you get the monsoonal system of flows in the late summer. This is, again, this is a small watershed. So, sometimes it's a little more driven by thunder storms.

But, here is the Mississippi River. This is the Potomac River at Point of Rocks, Maryland, and you can see it's driven by some of the similar kinds of things. It's a large watershed, not quite as big as the Mississippi, but it's driven by the same kind of distribution with floods.

With the exception, it has a tail out here, it has a second peak of flooding. And that's due to usually the hurricanes. OK, as you get those moisture sources occasionally you get up through the east coast. And we'll talk about Irene and Lee as one of those types of systems that drive a lot of moisture.

This is Sarasota Springs, I'm sorry, Suwannee River, near Suwannee Springs, Florida. And you can see that's also a bimodal distribution. You get the spring flooding, but then you get this flooding that happens in September. And what is the peak season for hurricanes in the United States? It's September. OK, as you look at it. The hurricane season runs from June 1st into November. And we've had relatively minor hurricane activity. But, folks, we're still not quite at the peak of hurricane season yet. So, there's a lot of the season left.

I also wanted to put this up here. This is the difference in talking to you about what's the major driver for flooding. This is a large watershed in the midwest. Wabash River, Terre Haute, Indiana, this in the order of 10,00015,000 square miles. And you can see the distribution is mainly late winter into the spring.

Then we have Boneyard Creek at Urbana, Illinois, which is about ten square miles. This is on the University of Illinois campus. I know this stream really well. And, so, you can see here, that it's got a wider distribution. This is a small watershed and it's more susceptible to thunder storms. So, you have much more of a distribution of rain, or floods, out and later into the summer thunderstorm season that will be the peak driver of flooding there.

One of our research team, Jim O'Connor, who's out of the west coast. And John Constant who is my predecessor in this job did a lot of research looking at the largest floods in the United States. So what they did was they took all the streamgages that we've ever operated and they took the largest flood on that streamgage and they plotted it. Drainage area and square miles versus the peak flow rate here.

This black cloud here is all those, there's probably 10,00015,000 points there. Because even though we just operate 7800 streamgages right now, we've got others that have been discontinued. So, this is a bigger data set than that.

And so, they took, and said, OK, of those, what are the bigger peaks? Let's look at the 13 percent, is basically what this line is. These are the larger of the floods, because you can see that this is Willamette River at Salem, Oregon. It's only 7280 square miles. It has a peak flow rate, up here, around 300,000 cubic feet per second.

And over in Nebraska, we've got a gage on the Platte River that's much bigger in order of magnitude, in terms of drainage size. But, it has a much smaller flow. And so, they were looking at the aspect, what drives large floods? I mean every stream floods. But, some flood a whole lot more and a whole lot more catastrophically than others.

So, what are the controlling features of that? And so that's what their research was about. They took those 13 percent of floods and these are all the gages that plotted in that upper 13 percent of all those floods. OK. This is the original graphic here, of all the gages around the country, in the lower right hand corner. And then, these are the gages that made that upper cut. So, they looked at, OK, what are the drivers here that are causing this particular kind of flooding? And basically without going into a tremendous amount of detail, proximity to the moisture source.

Because you see here, coming out of the Gulf, you can have, we have a large distribution of the points are right here. And the midsouth and the central midwest, you have a lot around the western edge of the United States. And then, again, up here in the Appalachians. OK, around the corner. And so, it's not just proximity to the moisture source.

That's an important factor, but why don't we have more in Florida? They have a lot of stuff going on down there. But, it's flatter than a pancake. So, you'd have to have something to do with topography, as well. Because the steeper that a gradient on the watershed, the quicker it can funnel water together and then you get these catastrophic types of floods. And, so, the topographic relief plays a major role.

I wanted to set the context for the anatomy. Now, I'm actually going to get into the flooding. 2011, everybody calls it an epic. I mean, I'm always skeptical with words. You get everything in an email and somebody says this or that. We've really, weíre loose with our terminology these days. Because we'll call something fantastic, well, it may not be so fantastic. Or, it's awesome, or whatever. So we've been calling 2011 an epic year. And so epic is extending beyond the usual or ordinary, especially in size or scope. And was it really epic? I've looked at floods for a number of years now, and I have to say, 2011 was an epic year of flooding.

Not only did we have the central United States, March through July. And we had floods from the Canadian border to the Gulf of Mexico  from the Rocky Mountains to the foothills of the Appalachians on the west side. We had a lot of deaths. Again, 36 deaths is not a lot compared to the extent of the flooding, but a lot of that is because the flooding is a lot slower out there in the midwest. OK, people can get out of the way, but we sure had a whole lot of damages.

Hurricane Irene arrived in August and we had 45 deaths. We had storm tide flooding and we had riverine flooding. We had $7.3 billion in damage. This is squishy because I don't have any data that separates out wind from the flooding. So, there's wind damage in here, as well. So, this may look like it's more than the central United States for flooding damages, but I don't really know if it's bigger in terms of flooding damages because wind is included in it, as well.

And then we have, two weeks later, after Irene, we had tropical storm Lee on its tail. And we had 21 deaths. And it was minor in comparison, only $1 billion in damage. But, this is pretty much flood damage, because we didn't have a lot of wind with Lee. I mean, there was wind, but not compared to what we saw with Irene, especially down in the lower part of the basin, or the Atlantic Coast.

When we go out, we have a flood. Our folks are out there. These are a couple pictures from the central United States. And these red dots on our realtime pages are when those guys and gals are actually out there making flood measurements. This is a flooded highway they're measuring the overflow, theyíre in a personal floatation device, here. We have to have these pictures sanitized for our safety, people. So if safety folks out there, we're doing our job. We're keeping them in the PFDs. And they're making a flood measurement in the middle of the highway, there. The flow actually coming over the road.

And so, as we're doing this, we're checking out our rating curve. I've already talked to you about rating curves. We're doing it because those rating curves change. OK, itís a natural system and we can get changes with that natural system. As I look around here, and this, we're going to have to update this slide, because I couldn't get it updated for the talk. This is one we put together for a congressional briefing within The Office of Surface Water.

And basically these are the major flood peaks and the red ones are the peaks of record. So, all the years we've got data, the red dots are we have peaks of record. Northeastern part of the United States, that's just reflective of the May flooding. I don't have Lee and Irene. We had over almost 150 peaks of record in northeastern United States from Irene and Lee so weíre going to update this graphic. I just want to give you that the idea we talk about epic flooding, we had flooding all over the country, not just in the central United States and the northeast.

So when we talk about that central US flooding, you know snow melt rain or snow, rainfall we had over a 100 peaks of record, 450 USGS streamgages. I had floods that were 10% probability or less. We had a lot of snow melt there.

This is snow water equivalent 2011, we had in excess in some parts of 14 to 15 inches of moisture in the form of snow pack in parts of, especially in Montana. So the system was loaded and we didn't, and without any rainfall, we knew we were going to have a pretty good flood and then the rains hit.

And so March through April, we had snow melt with additional rainfall, we had flooding in the Red River of the north and basically the upper Mississippi and down in the lower Missouri then April, May hit we had another round of major rainfall and we got the flooding in the lower Ohio and lower Mississippi, and the Corps of Engineers, it was all over the media they ended up blowing the levee at the Burns Point New Madrid flood way and have to use that in order to protect other towns.

That was during the April, May and then we got the late snow melt in Montana and then on top of that we got a yearsí worth of rain in Montana over Memorial Day weekend.

And so it just overwhelmed the reservoirs in the Missouri River and caused catastrophic flooding there. And then June, July we had excessive rainfall, that basically pushed the Souris River in Minot, North Dakota over the levee. I mean tremendous amounts of rain and snow melt combined with it. It was above flood stage in Minot for over 131 days during 2011. That's a long time to have a flood.

If we look at the observed precip, you can just see that we were as much as 200 to 400 percent above normal in a large part of the country. Rainfall totals, we're looking at anywhere from 20 inches down here in the Ohio River Basin. OK, these white are 20 inches of rainfall. Departure from the normal, greater than eight inches or more. This is April and May. And when we look at the Mississippi River this plot here is looking from Bemidji, Minnesota down to Baton Rouge, Louisiana. And the red is the 2011 flood.

At St. Paul we got all the floods for the entire period of record on here. The red shows you where it compares. So you get down below Cairo, Illinois, that's where the flood was major on the Mississippi River. Upstream of that, it wasn't such a big deal.

Same thing on the Missouri River and the big story on the Missouri was not the peak of the flood, because we had floods that were bigger on almost every location along the Missouri River. It was more the volume. This is a gage on the North Platte River in Wyoming and basically this is through the water here, and this is what normally in this green area here what we would expect in terms to accumulate in terms of volume of the flow.

And you can see by the end we weren't even totally into the year yet...we had eclipsed, and this is not...I didn't just pick this gage out  this was common on most of the gages that we saw out in that Rocky Mountain area in Montana and Wyoming.

All right, so the burst point New Madrid Floodway, that was here at Cairo, Illinois, Ohio, coming into the Mississippi. This is where we're at geographically. And so, the Corps had to make a big decision. They ended up having to blow the levee.

They had, Cairo, Illinois up here was about to flood. And so, after the 1927 flood, the Corps designed this floodway to basically relieve water. If they blew it up here, and blew it down here, they added conveyance and were able to get rid of a funnel and they would, to widen the floodplain, basically, is what they do. And you can convey more water at a lower elevation.

So, that's what they ended up doing. At 10:00 on May 2nd, we were on the levee, not where they were blowing it, about a mile back. They blew the levee up here and this is what you saw. Basically, a lot of water everywhere.

We instrumented the entire floodway, we being USGS, went out and instrumented the entire floodway, because this is a unique scientific opportunity to look at a dam break, or a levee break and to see how the water moves through the system.

And so, every day we would come in after they blew it. This is, I'm standing on the levee here, this is one of our boat crews. We're actually measuring the value of the water. We had as much as 400,000 cubic feet per second going across that floodway.

And basically, it dropped the level of the Mississippi River up at Cairo by about three feet overnight. And so, they were able to preserve and not overtop the levee there along with some of their other levees that they were concerned about.

This is USGS Landsat imagery. This is prior to, and then this is after they breached the floodway so you could see what it looks like.

The Coast Guard was real concerned about navigation traffic. They got all these barges. What happens here when we blow this levee? Are we going to suck towboats into the Missouri shore into these trees?

So, we went out prior to and after the breaching of the levee, we actually mapped the velocities with one of our field crews. And we were able to provide them this data. And about 20 minutes after being done with it, we have software that we can produce this.

And the Coast Guard made the decision, after seeing our data, to reopen the river to navigation traffic. And they felt it was safe because the velocity vectors weren't any different prior to, and after, the breaching of the levee.

All right, so, moving on to Irene and Lee. There's the dates. This is a picture of what Irene looked like on the 27th of August.

And storms, hurricane storm tide is the thing that kills most of the people. It's not the wind. And so, the USGS has been involved, since Katrina, has been involved in a program where we try to measure storm tide.

Why is that important? Because NOAA runs models to try to predict storm tide as they have a hurricane coming on shore. And so, you have to, just like we do for riverine flooding, we have to have data to calibrate those models. We need the same kind of thing for calibrating models at storm tide.

So this is a sensor. It's selfcontained. We go out and install it in the onset just before the hurricane makes land shore. We have our field staff out there strapping these instruments to anything we think will still be there once the hurricane leaves, OK? We'll go out and recover the sensor, and then we can survey in the sensor elevation. We have basically a look at how much the storm tide rose.

This is after Rita. You can see that we had, that's about six, seven, eight feet of storm tide there, and we were able to look at that time series of data. And we have them all over the place. And during Irene, well, this is just a look at some of the data here. You can see during Irene, this is down in North Carolina; we didn't quite get the storm surge that we wanted. Most places were four to five feet down there.

But we really were looking at category three and above storms. We're really trying to measure those storm tides. You know what? Iím having trouble getting my. I have a slide that's embedded here somehow, and it's disappeared on me. We had the largest deployment of storm tide sensors that USGS has ever put out for Irene. We deployed all the way from Georgia almost to Maine, OK? It's on my slide. I think we had 278 sensors that we deployed out during Irene in anticipation of that storm tide.

This is the track of Irene. Lee came in from the south, and you can see the amount of rainfall that it dumped with it. We had an excess of 10 inches in some parts for Irene and the same kind of thing for Lee. It was a little shifted to the west, and you had a lot more rain down in here in the southern Gulf Coast states.

In this area, this is the total precip for Irene and Lee. We had somewhere in the neighborhood of 15 to 24 inches in the areas of northern Virginia and southern Maryland. You see that's a whole lot of rain in a short amount of time. This is a graphic of two sites, Schoharie Creek and Susquehanna. The two major rivers that were impacted by Irene and Lee were the Susquehanna and the Schoharie Creek.

Those were some of the major massive floods we saw. There were a lot of other rivers that were involved and had peak of records, but these are two of the more dramatic examples. And you can see here, this is a hydrograph.

This is Schoharie Creek here peaking. There's a really huge flood peak here with Irene and not so big with Lee. It's still quite a bit, though. It's a fairly rare flood even for Lee, but Irene looks like it dwarfs it. So if you were to put up just the Lee data in comparison with everything else, it would like a huge flood. But Irene was so much bigger in terms of that particular site.

If we look at Susquehanna, it was the opposite, where we had the huge flood during Lee. You see that here in the lag time. So you had a double whammy with Irene and Lee separated by a couple weeks. These are the peaks of record, and you can see geographically where they're distributed here. We've got the track of Lee here. Of course, we lose a track here because it turns into more of an extra tropical cyclone at that point, and they don't track it anymore.

Then this is Irene, and you can see where we've had Irene peaks. Just to the west of that is where we had most of the Lee peaks. Near here, this is Fourmile Run into Alexandria. Basically, I pulled this up to look and see what the comparisons were. And just to show you, this is the peak for Lee but, just prior to that earlier in August; this is just a peak from a normal thunderstorm.

So this just drives home the point. Four Mile Creek is a small watershed, that you don't have to have these massive storms to drive the flood peaks up there. They're not necessarily a controlling feature. You can have just a convective, isolated thunderstorm causing a major flood. OK, Lee and Irene were big floods, obviously.

But the driving factor for them are more the larger watersheds, the 1,000 to 10,000squaremile watersheds, where these smaller watersheds like Fourmile Run are more controlled by convective thunderstorms.

All right. This is the flood peaks here. You can see that the 2006 peak is the big one. The one we had here in 2011 wasn't anything special. We have a whole lot of floods that were higher than that, just for this area. Now we did have some streamgages or some streams in the Reston area that were hugely impacted. Thereís very isolated, huge rainstorms. I mean I know in Reston here, the estimate was greater than 500 year rainfall amounts. In some parts there was a lot of destruction. But you move over several miles, and you don't get quite that rainfall.

So it's highly spatially variable, all right? When we look at the flooding from Lee we had over in Irene, we had over 140 peaks of record. This is a picture taken. This is a house hitting the bridge. I think this is on the Susquehanna. Bob Hainly, do you for sure? I got this picture I think from one of your guys at the water science center. Susquehanna, Schoharie and then the Deerfield over in Massachusetts. Those were three of the bigger rivers that we had issues with.

This is the Patapsco River and I'm slaying this pronunciation. But I throw this up because Agnes was huge flood in 1972, and you can see where it was at. Then you can see a comparison with Irene and Lee just to kind of put things into context. OK. This is over west of the Baltimore area. This is the Potomac River at Point of Rocks, and you can see here this is 2011, that we've got a whole lot of floods that were much bigger for the Potomac.

The Susquehanna, this is in the lower part of the Susquehanna. The Susquehanna was a big flood in the upper part, but not so big in terms of other floods. There were a couple of other floods that were bigger, OK. It was not a peak record. But as you look at your Schoharie Creek at Prattsville, New York you can see that this dwarfs everything else. This is the 2011 flood and then everything else is down in here.

So again, it was a huge flood in certain areas but not so big in others in terms of what we see in context.

Now where does everything fit in terms of what we had historically? This is that line that I showed you from Jim O'Connor's research and John Costa. And so you can see, I've got the 2011 Central US floods, the Irene and Lee floods are plotted here.

We had some of those that would now fit above that 13 percent line. We had some massive flooding, some catastrophic flooding. Real quickly in the closing minutes here I want to talk to you, real briefly, about flood frequency and probability. The 100 year flood. Everybody says what the heck? We had two of those in the last 20 years. What is this hundred year flood business?

Basically all it is, is a probability concept. The 100 year flood has a one percent chance of happening in any given year. Just like the 10 year flood has a 10 percent chance or the 500 year has a 0.2 percent chance. It's a statistical concept. It does not mean itís an exact thing you're going to have 100 years between 100 year floods.

And so, as you look at this on long term average, weíre going to statistically have a flood of that magnitude every 100 years. And you can think of it in looking at the 10 year flood. This is some data I put together to demonstrate this concept on, thatís not embarrass thatís the Embarrass River by the locals over in Illinois. And so this is basically from 1910 to I put this all together in about 2009.

What you would expect to see if I am looking at the 10 year flood, thatís right long here, I would expect to see a flood every 10 years, if I am thinking along that concept that we are stuck in that mindset. But you can see sometimes I go 17 years between 10 year floods. Sometimes I go as small as four years between 10 year floods. Here I got a span of 28 years between 10 year floods.

But if I average those spans, it comes out to  guess what  10 years, right. That's all we are talking about here. We could have two 100year floods, one year right after the other. Itís possible

In fact, in the 30year life cycle of a mortgage, I don't have it committed to memory, I think it is something like 26 percent chance of having a 100year flood in 30year period. That's one thing I wanted to mention. I'm running out of time here, we have to have long term data. Our 100 year floods  any kind of a flood probability  is based on data that we collect. So, the longer our data's time span, the better we do.

So if I only had 20 years of record here, this is the 100 year flood  this is Cedar River at Cedar Rapids, Iowa  I collect 100 years of data, you can see that that value changes. Not only do we have to understand it's very difficult for the common person to understand what we mean by the 100year flood because we can have two within successive years. Through time as we are collecting more data, the targets moving because we are getting better at predicting or estimating what that flood is actually about.

So anyway, I am going to flip through these really quickly. I want to show you really quick, when we talk about the 100year flood, this is on a gaging station in Missouri  44,300 cfs, cubic feet per second, is the 100year flood but the air bars around that are quite large, 56,400, this is our 95 percent confidence interval. We are 95 percent sure that it's somewhere between those bands.

So you can see that's pretty good error. If you are trying to determine whether your house is in a flood plain based on a 100 year flood, there is two feet of difference here in the estimate. The caution I always offer people is  it's not a set absolute number. We are talking uncertainty here that we have to deal with.

I am going to, in the interest of time, Iím going to flip through the rest of these. I was going to talk to you a little bit about Paleohydrology where we are trying to extend our records and collect ancient floods as much as two to three thousand years old based on paleo data where we go in and look at slack water deposits, and carbon dating and other mechanisms to look at it.

We can extend the flood record and you can imagine if can extend that flood record we get a better idea of what the floods are actually about. So I tell you what, at this point, I'm going to turn it over to questions because I want to be respectful of everybody's time here. I did want to say that maybe we should've been talking a drought in this talk. This is 2011 and you can see how wet it was and this is June 2012. So maybe we should have had Harry Lins up here up here and talking about drought.

This is the Palmer Drought Index, how much rain is needed to get us out of drought. You can see in some cases in the Midwest, we need over 15 inches of rain to bring that Palmer Drought Index back to normal standards.



Title: The Anatomy of Floods: The Causes and Development of 2011's Epic Flood Events


Flooding costs the United States more than $7 billion per year and claims more than 90 lives annually. During the Spring and Summer of 2011, the central U.S. experienced epic flooding, while Hurricane Irene followed by Tropical Storm Lee caused severe flooding in the east and northeastern U.S, setting numerous flood records at USGS streamgages. Dr. Robert Holmes discusses cause and effect of flooding, including a look at aspects of the 2011 epic flooding, and how USGS science assists in the overall flood mitigation efforts of the United States.

Location: Reston, VA, USA

Date Taken: 8/1/2012

Length: 49:01

Video Producer: Hannah Hamilton , U.S. Geological Survey

Note: This video has been released into the public domain by the U.S. Geological Survey for use in its entirety. Some videos may contain pieces of copyrighted material. If you wish to use a portion of the video for any purpose, other than for resharing/reposting the video in its entirety, please contact the Video Producer/Videographer listed with this video. Please refer to the USGS Copyright section for how to credit this video.


For more information go to: USGS Public Lecture Series

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