Defining the 100 year flood

Designing infrastructure is a tricky endeavor.  The day-to-day workings are easy to deal with, but you always have to consider the extreme events.  During and after an extreme event is when you’re going to need that infrastructure the most.  Early on you have to face up to the fact that you can’t entirely flood proof your bridge, earthquake proof your water treatment plant, or airline proof your skyscraper.  You can spend all the money in the national treasury at a structure but there’s always some remote chance that mother nature will throw down an even bigger disaster.  Then you have a very expensive pile of rubble and no more money to rebuild it.  We won’t even get into all the other stuff you couldn’t build because you spent all your money on the aforementioned pile of rubble…

This is where the concept of acceptable risk comes into play.  It’s always delicate using saying ‘acceptable risk’ in a situation where lives might be lost.  Most people tend to think in terms of ‘cost doesn’t matter if we can save one life’.  Maybe in a perfect world that would be true, but in the real world cost matters.  Resources are finite and if you spend an extra million to save one life here then you run the risk of these other four places where tragedy could have been prevented if you had only spent $250,000 at each.  Quantifying flood risk is a way of prioritising your efforts to make sure you get the most use out of your scarce resources.  

The concept of the 100 year flood was invented to try and quantify acceptable risk.  I’m using ‘100 year flood’ as a typical example because it’s fairly commonly used in the media and is threshold used for flood insurance requirements.  Engineers regularly work with 2 year floods, 500 year floods, and so on…  And it’s a concept that’s applied to other types of natural disasters as well.  There are designs for 100 year earthquakes and I’ve even seen it applied to tsunamis.

Before we go further, let’s take a closer look at that phrase, ‘100 year flood’.  What does that mean?   It means ‘the flood that has a 1 in 100 chance of happening or being exceeded in a given year’.  Essentially, you have a 1% chance of getting a 100 year flood (or worse) in any particular year.  A 2 year flood means a 1in 2 chance (50%), and a 500 year flood is a 1 in 500 (0.2%) risk.  The number of years being used is called the recurrence interval.  Larger recurrence intervals mean more severe floods, but they are also less likely to occur.

There is one huge misconception that needs to be addressed.  These various flood levels are based on statistics and not science.  Surviving a 100 year flood doesn’t mean you’re safe for the next 99 years.    The 1% chance is the same every year.  The idiosyncrasies of statistics indicate that it’s very unlikely to have 100 year floods in back to back years, but it can happen easily enough.  And that’s leaving aside the perils involved in deciding what actually constitutes a 100 year flood.  (Which I will be addressing in another post.)

Flood recurrence intervals are often reported in the press, but their primary use is as a design tool.  One of the biggest decisions in any infrastructure project is determining what recurrence interval a project should be designed to survive.  Now that we’re quantifying the risk of a particular storm, it greatly simplifies the decision.  The design storm is based primarily on the size and importance of the project, and the potential damage if something goes wrong.

Let’s take bridges as an example.  The average interstate bridge in Metro Nashville has thousands of cars crossing it daily, while a rural county road may have a few dozen cross it.  (I’ve worked on a few that had an average daily traffic count in the single digits.)  A flood in Nashville may destroy entire subdivisions, strip malls, or industrial plants while a similar size flood in rural Cheatham county might destroy a few acres of corn and drown a few cattle.  Since the potential for damage is so much greater the interstate bridge would be designed to stand up to a 100 year storm while a rural county road will be expected to endure a 10 year storm.  Most TVA dams are designed to handle events even beyond the 500 year recurrence interval due to the huge potential for damage if something goes wrong.

This is a somewhat simplified discussion, but it gets you started in understanding the design process.  In a future post I’ll be discussing how the size of floods of various recurrence intervals are determined.

Building the Star Wars universe

One of the things that’s made me a fan of science fiction and fantasy is the world building. Even mediocre to poor writing can be forgiven if you manage to get me interested in the overall mythology of your world. I think that’s primarily why I’m such a fan of Star Wars. Even now the movies are good enough to get me to watch, but the enduring appeal is the expanded Star Wars universe. I’ve always been a fan of larger, sometimes even ongoing, stories and the Star Wars universe certainly appeals to that.

The expanded universe (the EU as it’s referred to by fans) refers to the entire collection of books, comics, and games about Star Wars. George Lucas has kept tight rein on the mythology of the EU which has resulted in a cohesive body of work where what happens in one author’s work is often referred to in another’s. The EU started slowly, I suspect because Lucas didn’t want to have anything impinging on his mythology before he got his original trilogy all the way out there, but even before Return of the Jedi was released there were a few novels and a weekly series in the Sunday comics filling in the action between A New Hope and The Empire Strikes Back.

The really fun thing here… the EU builds off the movies, but in a lot of cases some contributor has created something that was added back into the movies in one of Lucas’ many tinkerings.  It’s every fanfic writer’s dream.  The original versions of A New Hope and The Empire Strikes Back had signs and labels with modern English, but a set designer on Return of the Jedi included a sign a language that didn’t have our standard Latin alphabet.  This was expanded into a full alphabet during the development of a Star Wars roleplaying game which was in turn used to replace the English in the original films.

In the early 1990’s author Timothy Zahn published the Thrawn trilogy which created some of the most endearing Star Wars lore. He was the first to mention the city planet Coruscant which is the capital of both the empire and the republic which came before it. Scenes from Coruscant were added to the celebrations shown at the end of Return of the Jedi. Zahn also created some fan favorite characters that some (or at least me) find at least as interesting as the ones in the films.  I’m not entirely clear whether Zahn came up with this first, or Lucas cut it out of his early drafts for technical reasons but Zahn was the first to include details about Coruscant.

The EU answered one question that I’m constantly wondering about in any movie I see. “What happens next.” At this point the timeline extends more than fourty years past the end of Return of the Jedi and includes several major galactic upheaveals along with the adult children of a lot of the original SW characters.  It’s also been filling in the blanks between movies and sparked an entirely new franchise into the early history which took place thousands of years before the movies.  (I do have a bit of trouble with this because culture and technology are remarkable similar over the thousands of years.)

All this discussion is a long winded way of saying……. I’ve been doing a lot of reading in the Star Wars expanded universe and it’s probably going to be showing up on the blog over the next few weeks/months. A lot of it is mediocre writing that becomes interesting to me BECAUSE it’s Star Wars so I won’t be too insulted if you skip over those posts.

Hydrology for Engineers

The hydrologic cycle (source)

You may not be able to tell so far this year, but we’ve had ample evidence over the last couple of years that May is the high season for flooding in Tennessee.  Today is the two year anniversary of the huge flood that swept Nashville clean two years ago, and various parts of west Tennessee (and the rest of the Ohio River and lower Mississippi) spent most of May a year ago under water.  In light of that recent history it seems like a good time to introduce the idea of hydrology.

Hydrology is the study of the most plentiful resource on the planet.  Water.  Nearly everyone is aware of the hydrologic cycle to some extent.  It’s a never ending cycle of water falling from the sky, being used, and evaporating back into the sky.  It’s a subject as deep as the ocean but I’m only going to cover it here as it is usually implemented by a civil engineer.  The US Geological Survey has a pretty good discussion of what a dedicated hydrologist does.  (The difference between the USGS description and mine goes back to the difference between the scientist and the engineer.)

For a civil engineer, hydrology is important because it answers one staggeringly important quest, “How much water am I going to have to drain off my project?”.  There are countless different mathematical models available to figure this out.  They vary from extremely simple to eye numbingly complex.

The general purpose of hydrologic modeling is to get from rainfall to runoff.  You start with the amount of rainfall and determine all the losses due to various physical and chemical processes and you end up with runoff.  The aptly named runoff is the amount of water which is actually draining from the surface of your land.  Some of the losses hydrologic modeling attempts to account for are:

• Infiltration into the ground
• Interception by vegetation
• Depression storage in low spots (ponds, sinkholes)
• Soaking of the plan

Detailed, accurate runoff modeling is staggeringly complex due to the enormous number of variables involved.  Doing it well requires a lot of experience on the part of the modeler because factors as simple as how wet the ground is before the storm or how the storm crosses the drainage basin can markedly change the results.

We’re coming to the border of ‘too long: didn’t read’ so I’m going to continue the discussion in a few upcoming posts.  I’ve got some future posts in the works to discuss different methods as well as some background on the elusive elusive ’100 Year Flood’.

Exploiting the Southern stereotype?

Photo from the Swamp People Facebook page.

As much as I’ve enjoyed watching Swamp People, one thing has bothered me about it. It felt exploitive. The Louisiana bayou is about as rural and southern as it gets in the US, and all the hunters on the show are unabashedly country. They’re the kind of people a lot of us like to refer to as hicks or rednecks.

When it comes to the ‘ignorant Southerner’ stereotype I’ve always had a chip on my shoulder. I spent my childhood in a fairly rural area in east Tennessee and I wasn’t really a hunter or farmer but I bristle at the stereotype. After I became a ‘city boy’ I had regular clashes with one of my more smug friends (Swedish daughter of a Vanderbilt professor) who thought Southern accent = ignorant hick. So the choice to use subtitles for most of the Cajun hunters was pretty offensive to me at first.

After a few episodes I realized it was my own preconceptions and defensiveness that were the real problem. The gator hunters on Swamp People don’t sit in board rooms and they have thick accents but most of them are pretty sophisticated businessmen, and I’ve gained a new respect for the small business owner since my wife started up her own business. The profit margin on gator hunting isn’t so great and you have to plan ahead and run a tight organization to make a decent profit from the 30 day gator hunting season. Several of them own successful businesses like gator farms, and convenience markets that carry them through the rest of the year, and one guy even designs boats on the fly with nothing but a Sharpie and a big sheet of metal. He cuts and welds them right there on his property and apparently does a good business at it.

It bothers me a little that I’ve internalized the ignorant Southerner stereotype, but I’m glad to see a few Cajuns doing their part to get rid of it. I suspect that a lot of viewers still won’t see beyond the initial impressions, but maybe that’s just my imagination too.

My guilty pleasure, Swamp People (TV Review)

Every episode of Swamp People (History Channel) starts with a warning. Before you see the title or the ‘tonight on…’ teaser footage you see a black screen as ominous music plays and the following warning fades in:

The way of life depicted in this program dates back 300 years.

Hunting, especially alligator hunting, lies at its core.

Some images may be disturbing.

Viewer discretion is adviced.

It sounds overly dire, but it’s probably not a bad idea to give a little warning about what the viewer should expect.

Swamp People is all about gator hunting in the bayous of Louisianna. You aren’t going to see a lot of blood and guts, but you will see lots of dead gators getting dragged around and lots of action shots of the hunters standing on piles of previous catches while they try to shoot a live one.

It’s definitely an action oriented, testosterone heavy show. The show follows several groups of gator hunters throughout the gator hunting season. The producers do a good job of editing out the tedium of driving around the swamp putting out the bait and waiting for the gators to take it. Most on-camera time is spent showing the hunters reeling in a hooked gator and there are some really beautiful helicopter shots of the swamp.

In most episodes they follow one of the hunter teams home for a end of the day look at family life. It’s a blatant effort to remind the viewers that the hunters are actual people rather than actors playing a part, and it’s mostly unnecessary. Most of the hunter teams are father son duos or very close friends because gator hunting requires a partner you can trust with your life or at least your health.

One of my wife’s favorite parts of the show is the interplay between the father and son teams. Most of them refer to gator hunting as a family tradition and both halves of the team seem to enjoy the process of passing along the gator hunting skills. The fathers are visibly proud of their sons after a particularly hard fought catch and the sons can be seen enjoying their dad’s pride.

The producers keep it moving and they do a fair job of editing the episodes into a storyline with a tenuous unifying theme. The most recent episodes have been about a tropical storm blowing boats around and making the gators dive deep below the hooks or holing up in the lairs for an early hibernation. Past episodes have shaken up the status quo with things like potential poachers or nearly getting the boat stuck due to water level changes while exploring a remote fishing hole. (That episode included some really amazing shots of one of the hunters jumping his boat over a levee. You could literally see the guy’s adrenaline rush afterward.)

Despite the producers best efforts though, the repetitive nature of the show is a definite drawback. Even shots of angry gators fighting the line and gorgeous overhead shots of the bayou get monotonous after too many viewings. I recommend you watch it in small increments rather than a marathon viewing of every episode on the DVR.

While it’s not appointment television, I think Swamp People is a darn good show. It’s a pretty testosterone soaked soaked show but it does seem to have its appeal to the ladies. My wife actually is the one who turned me onto the show. At first it felt a bit exploitive, especially due to the extensive use of subtitles translating the Cajun accents, but I’ve gotten past that aspect.  Even if you’re not up to a season’s worth of episodes it’s worth watching a few just to see how they actually go about hunting the gators.

All photos are from the Swamp People Facebook page.

TV Review: Hunting the Elements on Nova

Back when I was an impressionable youngster chemistry seemed like a lot of fun. Acids, open flame, liquids cool to the touch that bubble over when you mix them… As an adult I still have some interest in your basic household chemistry, but any thoughts of a career in chemistry got stomped out of me when I went from lab to lecture. Balancing chemical equations and counting electrons got old real fast.

Hunting the Elements is a recent episode of Nova that almost made me regret my choices. The episode is a two hour documentary on the table of elements and presents it in a real and exciting way. It pulls you in with ‘real world chemistry’ but it manages to lay down some actual basic chemistry education in an interesting way. (Probably because it had a higher production budget than most text books.)

The organization of the segments throughout the episode is a bit haphazard from a scientific point of view but it does the work of a showman in pulling you in and keeping you interested. It starts out with a trip to a gold mine and takes you through the process as they pull huge dumptruck loads of soil out of the mine and refine each load down to a tiny nugget (approximately one gram of gold per heaping truck full of soil) and end up with a refined gold ingot worth $1.5 million.

Gold may not be the best place to start a discussion of the periodic table, but it’s certainly the most eye catching sequence and does the job of catching your attention. Other highlights include a sequence on combustion (lots of stuff blowing up and some cool high speed photography of it), a physical representation of the periodic table (with samples of each element), and visiting a lab where they’re manufacturing new elements.

The unifying theme of the episode is the periodic table itself. It’s digitally superimposed on random surfaces throughout the nearly two hour episode. It’s a bit distracting at times, but it does serve to recenter viewer attention after each sequence. Most of the major elemental groups are covered through the course of the episode and the host provides a succinct explanation of the periodic tables structure that brought back the fundamentals I learned back in Chemistry 101 and would probably be a good overview for people who haven’t seen the periodic table since high school (or for high school students seeing it for the first time).

I think the biggest problem with the episode is the humor. There are several extended scenes meant to be comedic and the host gets off some real groaners, much to the fake chagrin of the actual scientists. It may be my imagination, but I think the eye roll inducing humor is intentional. As annoying as it is, the humor grounds the episode and reminds the viewers that science isn’t some mystical subject akin to magic. I just wish they hadn’t let some of the comedic moments go on for so long.

Overall I really enjoyed it. It was educational but it moved quickly enough to keep from being overly boring. It was structured in a way that grabbed your attention and moved from the more exciting visual subjects (gold mining) to the less concepts that are less visually impressive but more exciting in their potential (making new elements). I recommend it for any novice in the chemistry field, and I think it would make great viewing for a high school chemistry class. I’d make my own kids watch it if they didn’t have the attention span of four year olds (though the explosions do appeal to a four year old boy).

You can watch the episode over at PBS.org, but I don’t guarantee how long that will last. They also have an iPad app and some teaching games on their website. There’s also a fun interactive periodic table here.

Civil Engineering 101 – Water Resources

Civil Engineering is a term that covers a lot of space.  It’s a field that allows for a lot of specialization, but today I want to talk about my own little corner of that giant space.  Hydraulic Engineering, these days better known as Water Resources Engineering.

Since the beginning of my career I’ve been in hydraulic engineering.  In this case ‘hydraulic’ means ‘related to water.  The industry and most practicioners have been moving toward ‘water resources’ in the intersts of avoiding confusion related to the other uses of the word ‘hydraulics’.  Also, when you get into the nitty gritty (which I’m avoiding for the moment) of it, water resources covers a wider range of topics than hydraulics.  In the 1960′s and 70′s water was only an impediment to get away from your building as quickly as possible or a tool to make electricity, these days it’s so much more complex.

So what does a water resources engineer do?  The title encompasses anything related to water, and water is 70% of the earth’s surface and vital to every form of life we’re aware of, so it’s a pretty broad spectrum of resonsibilities.  So here’s a bullet list:

• Designing water and waste water treatement plants.
• Flood modeling to determine those pesky 100 year floodplains that journalists like to talk about when it rains a lot.
• Road drainage so we don’t have to stay in the garage on rainy days.
• Bridge design to make sure the Walmart upstream doesn’t get flooded.
• Restoring damaged and polluted streams.
• Designing levees to make land more useful.
• Land development that turns forest or pasture into your local Target.
• Water distribution systems so something wet comes out when your turn the faucet.  (including those awesome water towers)
• Erosion control on construction sites to keep dirt out of streams.

That’s just a list off the top of my head.  Nearly every civil engineering has a water component of some sort and most civil engineers have a working knowledge of the basic principles no matter what area they practice in.

Me personally?  I’m a specialist.  I work for an organization that builds a lot of roads so my primary job is to keep the roads above flood waters and making sure the good taxpayers of this state don’t get blamed for roads that flood people who live nearby.  When something goes wrong and water gets in someone’s house my colleagues and I are the ones that get the call to figure out what went wrong.  (It’s important to note though, water resources engineering is one of the few specialties where catastrophe can happen even if no one screws up.)  It’s a rewarding job, but it does involve a lot of routine design work to keep things from going wrong.  Unfortunately though, when my workday is at its most interesting it probably means someone else had a really bad day.  I sometimes feel guilty about deriving the most enjoyment out of the parts of my job based on someone else’s bad fortune, but I do take a lot of satisfaction in fixing what’s broken so it won’t happen again.

I’m planning some future posts with details about some of the projects I’ve been involved with (mostly from that bullet list above), but for today I just wanted to give an overview for anyone who might be interested.