Thursday, March 30, 2006

Less than 8 inches of water

That much water would just cover your ankles. That much water would barely be enough to float a flatboat.

And that's how much water the MRGO contributes to hurricane storm surge.

I know it's incredibly popular to say that St. Bernard and the Lower Ninth Ward flooded because of the evil Mississippi River Gulf Outlet. I know that the press, politicians and people from all over blame the MRGO for the catastrophic flooding that occurred there, but the science of the situation says otherwise.

Everything I write now is detailed in a paper titled, "Note on the Influence of the Mississippi River Gulf Outlet on Hurricane Induced Storm Surge in New Orleans and Vicinity." You can read if for yourself here.

Both before and after Katrina, engineers and scientists investigated the impacts of the MRGO on hurricane protection. Using the latest computer modeling and laser surveying techniques, they ran a variety of hurricanes through a digital rendering of southeast Louisiana. They ran the existing conditions, and then they ran the model with the MRGO completely filled to marsh elevation. They also ran it with a gate closure at the southern end of the MRGO. They ran hurricane models that mimicked Betsy, Katrina and other historical and synthetic storms.

And here is the result: the difference in storm surge with the MRGO was, at most, less than 8 inches. In most places, the difference was less than 4 inches.

Hardly a smoking gun, is it?

The primary author of the paper I refer to is Dr. Joannes Westerink of Notre Dame, a worldwide authority in hydraulic modeling. It is part of the government's official IPET investigation of what went wrong in hurricanes Katrina and Rita.

I expect critics of the Corps and the IPET investigation will want to dismiss this report as a whitewash of the effects of the MRGO. But they should know that the Louisiana Department of Natural Resources, often at odds with the Corps of Engineers, conducted their own model runs and came up with almost identical results.

How can this be? How can The Times-Picayune and public perception be so far off from the reality?

Well, part of the problem is simply a lack of understanding of hurricanes and hydraulics among the public. And it certainly doesn't help when newspapers and politicians jump on the bandwagon to ride public opinion for profit and populism. We all need to learn more before we form opinions on important matters.

Part of the blame falls on the Corps of Engineers, too. The Corps has not done a good job of educating their customers, the American public, about what they do and why they do it. The paper I cite is an example of this lack of communication and engagement with the public. Why haven't these findings been more prominently announced?

I think the average person can grasp why the MRGO contributes less than 8 inches to large storm surges. The simple explanation is that for events like Katrina, the storm surge is so high that water is flowing outside of the channel. When there's 18 feet of water moving toward St. Bernard and New Orleans, it just doesn't matter that there's a shipping channel down at elevation 1 or 2. The water is spread out miles wide in front of an advancing hurricane, so even the 1,000 feet wide MRGO gets lost in the massive storm surge.

Now, I'm not defending the MRGO or saying it should remain. There may well be other problems related to this channel that should be addressed.

What I am saying is that the magnitude of flooding, death and destruction was brought by Hurricane Katrina without the help of or need of assistance from the MRGO.

I think we should be talking about what to do with the MRGO. But let's stick to the facts and listen to the science.

12 comments:

Editor B said...

Thanks for pointing this out, Tim.

bayoustjohndavid said...

I think the B.R. Advocate's slightly more balanced, while googling for a post a couple of weeks ago I found a story featuring the state study, the day after an anti-MRGO editorial in the same paper. Felt obligated to mention the story, cause I'm not the Dead Pelican or Jeff Sadow or any of the area repubs. Question, have there been any conflicting studies, or is the popular conception all based on theoretical models?

Also, you can't do any fishing in St. Bernard w/out seeing how much it's accelerated erosion. I know you don't think that has much effect on storm surge.

bayoustjohndavid said...

I didn't express myself well in that last comment. My point was that even though the local paper didn't choose to publish the state report (or the other one either), I have to wonder how many people have been chosing to ignore. If the people making the state's case don't have an answer to those studies, they'll end up looking stupid or dishonest. I assume the people working for Tom Tancredo or Haley Barbour can do a google search.

Marco said...

If we let the river go and seek it's natural meander to the Gulf what would happen?

Tim said...

editor b: You're welcome!

BStJD: I don't know of any models that conflict with this study. It's a popular belief that the MRGO is the cause of massive flooding without any models. Period.

Marco: If we step aside and let the Mississippi River do what it wants to do, it would change course and go down by Morgan City. Baton Rouge and New Orleans would not be on its route any more.

da po' boy said...

I am not an engineer, so I must place my faith in the engineering gods.

I have one group who built the levees which failed in the outfall canals telling me that the MRGO did not contribute to the flooding in St. Bernard parish and the Lower 9th. I have another group that has been looking out for my ass for the past few years telling me that the MRGO did contribute. A report commissioned by the Army Corps of Engineers vs. the hurricane experts at LSU.

From WWL-TV:
----Using a computer model to measure a Katrina-like surge with and without the MRGO, the new report said the channel only adds a few inches to the height of the water.
“If you envision a 15-20 foot storm surge that just overwhelms the wetland, I guess it’s easier for me to envision that that little channel becomes less and less important,” said Bruce Ebersole, who helped write the new report.
Dr. Hassan Mashriqui, an LSU storm surge expert, said the corp’s report ignores a key factor in levee destruction. Mashriqui said his models show the ship channel increases the velocity of the water as it pounds and scrapes against the levees.
"The MRGO’s like a fireman's hose. It not only poured water there, it poured water with a speed, with a faster rate. Anything in its path got washed away, period,” he said.----

The speed portion of the argument carries a lot of weight with me. Fast moving water does more damage than slow moving water.
So, going on my assumptions, the next question would be: Did the levees breach because of overtopping by catastrophic storm surge? Or, did they breach because of the faster moving water? Would they have held with the storm surge not influenced by the funnel?

It seems the engineering gods quibble about that, too:
----LSU researchers said levees on the MRGO and the intracoastal waterway may have started to fail before they were overtopped by Katrina’s storm surge. They said that when that surge reached the Paris Road Bridge, the water was racing at a rate of eight to12 feet per second, and it may have been that rapid movement of water that was scouring and breaching the levees.
Mashriqui said he believes the levee breach at the Bayou Bienvenue gate may have occurred before the water topped the levee.
“This side of the fate was totally failed because this gate was inside the soft levee. Six feet per second or 3 feet per second could scour this area easily,” he said.
The corps disagreed and said the levees did not fail until they were overtopped by the storm surge.----

The levees protecting the MRGO were 17 feet – big, but not bigger than the surge. But there were secondary levees protecting St. Bernard that could have stopped what managed to get over the levees *if the levees had held.*
So, if the levees breached because MRGO caused the surge to go faster, it contributed. If they breached because of overtopping, then dammit, the ACE should have armored them better.
As I said, I am not an engineer. I can only go by the information I receive from the media. And, I can only interpret that with my untrained eye and (I hope) well-exercised sense of logic.
Go easy on me.

Tim said...

Well, at least you're headed in the right direction. Mashriqui is an engineer. The other famous talkng head from LSU is Van Heerden, who is a geologist. He, in my opinion, has no clue! It drives me crazy when they quote him as an expert in the press.

I have not seen Mashriqui's model, because the folks at the LSU Hurricane Center do not post their research on the web for all to see, so all I can do is respond to what the news people have been reporting about Mashriqui's analysis.

The first problem with any forensic analysis of these washed out levess is that most of the evidence is washed away. As you know, there are two levees protecting St. Bernard; a federal levee next to the MRGO and a parish levee at the edge of the developed lands. It is possible that fast moving water contributed to destruction of the levee next to the MRGO. Water moving at 12 feet per second will do a lot of damage, no dispute about that.

Unfortunately I can't find any velocity guages for that area--not the Corps, USGS, DNR, NOAA--none seem to have any data on that. So I don't know if that's a real number.

I spoke to one engineer at LSU back in December who said he was working on a mass balancing model to determine at what point the water got past the levees. The idea is this: the storm surge rises and falls over a short period, 1 to 2 days. If we know the location and size of levee breaches, we can calculate how much water will pour into St. Bernard, and at what elevation the water will peak. The sooner the levees are compromised, the higher the water levels inside the parish get; later breaching will result in lower water levels because the storm surge goes down before the parish can fill with water.

Okay, that said, I have not heard the results of that engineer's analysis. He's been very quiet since then. I suspect that he could not prove his thesis that the levees failed sooner than later.

My frank opinion is simply this: I think the whole MRGO issue is irrelevant. We need better hurricane protection PERIOD. Any plan to raise levees to Cat 5 levels will require a gate or closure of the MRGO.

I fear that angry citizens will get Congress and the President to put gates on the MRGO and the three outfall canals in New Orleans, and then Congress will say, "Okay, job done."

They are already complaining that we keep coming back for more. Rather than attack this piecemeal, I would rather see us lobby for an overall level of protection: 1,000 years, 5,000 years, or perhaps 10,000 year-recurrence like they have in the Netherlands. Once we commit to that, the rest will follow out of necessity.

As long as we keep fooling around with 100 year levees, we'll never really be safe. I'm going to rebuild in New Orleans, but I'm going up 8 feet--minimum.

bayoustjohndavid said...

Well, I was basically agreeing with you, when I looked for information to back the assertion that MRGO helped destroy St. Bernard, the state study stared me right in the face. For people making the state's case to ignore it is dishonest and irresponsible, worse they're setting themselves up to be called on a needless bluff.

However, MRGO has definately contributed to erosion of St. Bernard's wetlands, in effect bringing the open gulf closer. I know that you think it's largely irrelevant, but if I lived there I'd want the marsh and the levees between me and the gulf.

As to the innocent question about whether modeling contributed to the popular conception, the same search that led to the state study, also led to Mashriqui's hyronamic modeling. Period.

Zeebart said...

Slim, hang in there... I saw the video...cute family...

signed,

Your boy Z, in Lafayette..

Mark said...

One thing this ignores: from St. Bernard's perspective, the danger is much more from the exposure of the levees in the eastern end of Chalmette/Violet/etc to wave action from Lake Borgne. These levees didn't fact the open lake when they were built. They essentially do now (pre-K) due to the impact of fresh water intrusion and erosion.

Anonymous said...

See if you can follow this, Tim...

a) Deep canal=Salt water intrusion
b) Salt Water Intrusion=Destroyed Wetlands
c) Destroyed Wetlands=Storm Surge Flooding

Capiche?

Tim said...

Anon,

See if you can follow this:

a) New Orleans East and St. Bernard are right next to Lake Borgne.
b) Although wetlands have been lost, there is no scientific evidence that wetlands ever protected them from hurricanes.
c) Current research shows it would take impractical amounts of wetlands to have any significant benefit, i.e., you would have to fill Lake Borgne.
d) Show me science or go away.

Read my research about wetlands as a means of hurricane protection here:
http://timsnamelessblog.blogspot.com/2006/01/quite-distance.html

Peace,

Tim