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


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 mid
west 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 it’s 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 — 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 inter related. 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 24×7. 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 24×7 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 300 pound 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 X axis and on the Y axis, we’ve got volumetric discharge and this is our gaging
station on the Mississippi River at Vicksburg, Mississippi. That’s two million 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 16 million 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 geo political dynamics going on there after that flood and all that. The ’27 flood
is there, the other one that’s 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
we’ve 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 www.WaterWatch.usgs.gov.
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 non meteorological. 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 non uniform, in terms of its characteristics.
The plant cover is non uniform. 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 lee side, 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 extra tropical 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 snow water 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 mid west. Wabash River, Terre
Haute, Indiana, this in the order of 10,000 15,000 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 10,000 15,000 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 mid
south and the central mid west, 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, we’re 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 mid west. 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 real time pages are when those guys and gals are actually out there making
flood measurements. This is a flooded highway they’re measuring the overflow, they’re
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, it’s 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 we’re 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 years’ 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 self contained. 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? I’m 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 10,000 square
mile 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.
There’s 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 it’s 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,
we’re 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, that’s not embarrass that’s 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, that’s 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 100 year floods, one year right after the
other. It’s possible In fact, in the 30 year 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 100 year flood in 30 year 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 100 year 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 100 year flood,
this is on a gaging station in Missouri 44,300 cfs, cubic feet per second, is the 100 year
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, I’m 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.
p.

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