Monday, July 28, 2008

Here's mud in your eye

A recent headline on Yahoo! News decried the loss of soils in the recently flooded states to the north of us. This is particularly significant to us on the southern end of the Mississippi River.

A lot of people have said that we could solve Louisiana's coastal erosion problem by just letting nature do the work for us. We need "The river wild" they say.

But here's a part of the story nobody likes to talk about: sediment load.

That is, how much mud does the muddy Mississippi River contain?

The answer: Not nearly as much as she used to.

Going back as far as 1935 and the birth of the Soil Conservation Service, government at all levels has teamed with private citizens to halt the flow of topsoil washing into the nations' rivers. In recent years EPA has been tightening what is called Total Maximum Daily Load (TMDL) regulations--standards that seek to keep turbidity down.

These and a hundred other well-meaning and beneficial initiatives mean that water flowing past New Orleans today contains just a fraction of mud one would have found in that same water even just a few decades ago.

And what that means is if historically the river was able to build a few hundred square miles of marsh per century, it would take centuries longer to do the same job today.

Would it help to let the river run wild? Yes, but don't count on any help from our neighbors north of the 30th parallel. They need that mud just as much as we do.

Wednesday, July 23, 2008

Wetlands for hurricane protection might make cents

A study published in the June 2008 journal of the Royal Swedish Academy of Sciences attempts to calculate the economic value of wetlands as hurricane and storm surge defense features. I first heard of the study online and was fortunate to find the full text of the journal article here.

It is first important to note what this paper is NOT. It is not an engineering analysis; it is an exercise in econometrics. It does not propose any new design methods, nor does it test any of the natural mechanisms by which wetlands can provide storm protection for human populated areas. Early on the authors acknowledge this fact and note that the best empirical studies they find place the storm surge reduction benefit of wetlands at about 3 inches per mile. Regular readers of this blog will likely recognize that factoid.

What the researchers have done is gathered a ream of existing hurricane data, applied some simplifying assumptions to fill data gaps, and crunched the numbers through a series of statistical tests. The result, the authors can claim with some credibility, is that the value of wetlands as hurricane storm barriers can be expressed in dollars.

This is not a new problem. Economists have struggled to quantify the monetary value of natural features for decades. The vexing part of the problem is how to properly and fully equate wild lands and habitats in economic units of dollars used to store and trade wealth in human commerce.

Take any forest, for example. What is it worth? Is it simply the market value of its trees cut down and shipped to the mill plus the going rate for its developed acreage? We know this is not the right answer because forests have ecological value as carbon storage centers and aesthetic value as places humans enjoy seeing in person and in pictures.

Government agencies have for this reason studiously avoided placing economic value on wild lands. If forced to complete in the market of capitalist values, naturally occurring features will almost always lose out to commercial development. Environmental scientists instead have been using other more nature-based measures such as the Wetland Value Assessment and assigning "Habitat Units" in lieu of pure dollars to compare alternative land uses.

The authors of the Royal Swedish study set out to define the relationship between raw acreage of natural features as storm defense systems and the avoided damage from those same storms. First, they obtained a data set of hurricanes that struck the US Atlantic and Gulf coasts since 1980. This data included storm path, intensity and estimates of damage. They found a wealth of scientific and economic data in the Emergency Events Database ( created and maintained by the World Health Organization, the Centre for Research on the Epidemiology of Disasters, and the Belgian Government.

Next, they needed to calculate the total possible damage of strike locations. By comparing the experienced damage with the theoretical maximum possible damage, the researchers aimed to quantify the value of avoided damage. And this is where the econometric gymnastics kicks in. The authors took statistical data on US and individual state gross domestic product (GDP) and assigned a GDP value to a map of coastal America on a grid resolution of 1 kilometer square. Because GDP data is not readily available in this resolution, they interpolated and assigned GDP value by looking at satellite photographs taken at night. Areas brightly lit were given higher GDP values than dim or dark areas of the country.

Armed with this data, the authors ran the numbers and found some statistically significant relationships. Their primary discovery was that damage in areas near wetlands was reduced proportionally with the quantity of wetlands. Everyone has long acknowledged this fact, but here was proof--expressed in dollars.

The researches went further and attempted to calculate the average annual benefit of wetlands as storm protection. Their conclusion: wetlands save America from billions in storm damage year in and year out.

But let's not get too far ahead here. I have some serious misgivings about the methods employed and with the way the results were tabulated and presented. I will elaborate on some of them here.

1. It is interesting to note that the methods employed here failed to provide satisfactory results in several key instances. For instance, researchers had to limit their analysis to only the US Atlantic and Gulf coasts because of the scarcity of data. They admit to wishing they could apply their skills to the thousands of known disastrous tsunamis, monsoons and other coastal storm events, but found insufficient data to do so. The resulting data set includes just 34 hurricanes out of the nearly 270 major storms to strike the US during the selected period.

2. The researchers initially set out quantify the storm barrier benefits of forested wetlands, too, but found the statistical correlation not significant enough to support their hypothesis. Several widely published papers have touted the benefits of mangrove and cypress swamps in knocking down storm effects. The authors of this study could not validate that claim, and it makes me wonder why they proceeded with their work in spite of that glaring problem.

3. The use of GDP as a measure of potential storm damage leaves much to be desired. GDP is an expression of economic productivity; it says nothing about the present value of homes, businesses and other infrastructure that fall victim to nature's fury. Likewise, the Emergency Events Database records the total estimated damage wrought by storms. This would include wind and rain damages, but it is primarily the storm surge damage that is thought to be muted by wetlands.

4. To convert their calculation of avoided damage into an annually recurring value, the authors developed hurricane return frequencies using a data set with a period of just 25 years. This is hardly a large enough sample to extrapolate reliable return frequencies.

5. The authors conclude their paper with an editorial on the virtues of wetlands far beyond the apparent correlation to protection of human economic activity. They opine how coastal wetlands are "maintained by nature" and that such features are "far more cost-effective than constructed levees." But there is absolutely nothing in this article to support these conclusions. Indeed, the authors themselves note that Hurricane Katrina alone destroyed some 50,000 acres of wetlands.

These are just a few of the shortcomings of the study.

It is also important to note that the study tells us nothing about how and where to build wetlands as part of a storm defense system. The study considers gross acreage in the path of hurricanes assumed to be 100-km wide; nowhere does the study enlighten us as to how we would go about designing a wetlands plan.

I was disappointed that the researchers included the rather colloquial analogy that wetlands function as "horizontal levees." In fact, all physical features exist in three dimensions: earthen levees and wetlands both have length, width and height. The difference is the primary storm defense benefit of levees lies in their height, while the frictional resistance of wetlands is manifest in their area--length and width. But to equate the two, as if to suggest one could substitute some acreage of wetlands for some or all of a levee is ludicrous--if not dangerous.

It is noted that as I was preparing this blog entry, The Times-Picayune ran a story on the study that seized upon the expression "horizontal levees" as if it were a valid scientific result of this study. It is not.

I think the study represents a remarkable effort to quantify the hurricane defense benefits of wetlands in dollars--not an easy task--even if the results seem exaggerated to my eye. As an engineer, I find little in the study to help me understand and design these vital systems. But perhaps the study gives our society the justification and incentive to take wetland preservation and construction seriously as a bonafide contributor in our overall strategy to protect coastal developments. In the end, much research remains to be done before this general appreciation of wetlands can become a plan of action with predictable results.

Friday, July 11, 2008

A space oddity?

It was 29 years ago today that America's first space station, Skylab, came falling down to Earth. Some people at the office were talking about it and I recalled that it was quite a newsworthy event.

Pat O'Brien's even created a potent cocktail to commemorate the event. They called it the "Skylab Fallout."

But I was surprised to find I was the only person in the group who had ever heard of it.

Surely other people recall getting knocked dizzy in the French Quarter by a Skylab Fallout!

Wednesday, July 09, 2008

Exposed weaknesses

At the Rising Tide 2 conference, writer and panelist Joshua Clark commented that Hurricane Katrina exposed many weaknesses in our lives. I wrote it down back when I first heard it last August, and I've been thinking about it here and there since.

The idea stuck with me.

As an engineer, I recognize how minor flaws can become major problems under certain conditions. A hairline crack in concrete can let in moisture. That moisture can cause rust in reinforcing steel, which in turn exerts pressures that will further crack the encasing concrete.

Weaknesses can go undetected for weeks, months, years, and then... a bridge falls, or a tower crane buckles, or a floodwall bends and bows to failure.

Engineers also understand that loads transfer from one part of a structure to another. If one connection of a truss fails, it might not result in an immediate collapse. The load will be transferred to another connection, much the same way a current of electricity will seek the shortest path to ground, or water the swiftest path to the ocean. This load transfer is automatic and instantaneous.

If the new connection can't hold the load, it too will fail and send the load to the next connection. Sometimes this transfer/failure/transfer cycle happens quickly--resulting in a successive collapse. Sometimes, it goes undetected for a while.

I've been thinking about the load of Hurricane Katrina on us, our lives, our community, and our support system. When something fails to hold up, do the others race in to help? And if the load and stress of this disaster and the rebuilding process pile on, will we stay strong, or will we suffer sudden or rapid successive collapse in our lives?

You could say we've already seen this happen at the District Attorney's office. Inefficiencies, blunders and scandals accumulated and brought down Eddie Jordan's office and career. It started out small, but grew over many months until the ability of the public to stomach the news had been completely diminished. It was a textbook illustration of the expression, "The straw that broke the camel's back."

I also think we see this happening with housing. With so many displaced from their homes, demand for rentals and rental rates are up dramatically. Amazingly the federal government and the city decided this was the time to tear down most public housing projects. The stress of housing has transferred from one market to the next, so that we can truly say there is a housing crisis in New Orleans.

Families feel the strain, too. The recent death of NOLA blogger Ashley Morris shows us how the burdens of life are distributed. The stress and strain was quickly transferred--shared--throughout the Morris family's circle of friends. Several NOLA blogger stepped in mightily to help them bear the load.

And the Morris family survives.

So I think I'd like to add a thought to Joshua Clark's observation. Katrina exposed weaknesses, yes, but she also revealed our strengths.

And not just as a matter of contrast. Just because one floodwall fell over and the one next to it did not is no reason to think that remaining floodwall is somehow representative of an ideal design; it just means it was at least a tiny bit better than the one that fell.

No, I'm thinking that New Orleans is a city of many strengths--strengths that were there all along, but we overlooked them or forgot them in the day-to-day journey of life.

Sense of community, love of neighborhood and civic pride are some examples. Would we say that these have sprung full-grown from our wounded city? Or isn't it more likely we had these things all along? I think it took several feet of flood water to push these powerful sentiments to the surface. And to this day if anybody says a cross word to us about being "stupid to live below sea level" you can bet they'll get both barrels of love right back.

Like travelers on a yellow brick road, we've been through hell and high water just to find out that what we were searching for we had all along.

I know we'll never forget that awful August three years ago, when unforgiving nature exposed and exploited all our weaknesses.

But I also hope we'll remember our discovered strengths, and that it's because of those strengths that we're still here.

Tuesday, July 01, 2008

"Those tiles will be replaced"

That's what Entergy V.P. Rusty Burroughs said. His letter of apologies and promises was printed in the newspaper.

And so two months later, NOLA Blogger Oyster goes back to check and finds...