Monday, January 30, 2006

Quite a distance

Okay, someone has to say it. Someone has to loudly point out that the king has no clothes. Or, perhaps the better metaphor in this case is that someone has to be the turd in the punchbowl.

I guess that’s me.

I’m talking about all this talk about coastal restoration. I’m talking about how a bunch of politicians and environmentalists are linking coastal restoration to hurricane protection.

I’m telling you, it just ain’t true.

The story they’re spinning sure sounds nice. That we in South Louisiana are feeling the pain of nature’s wrath because we have not been good stewards of the land. That South Louisiana didn’t suffer as much a hundred years ago when hurricanes came to visit because there were miles of marsh and wetlands to protect them from high water. That all of this is our own doing, and we better hurry up and fix it before the next hurricane turns toward New Orleans.

It sounds plausible, but like those get-rich-quick-in-real-estate schemes hawked in endless infomercials, the claims just don’t hold up under scrutiny.

Now don’t misunderstand me, I’m not saying that we should not be concerned about coastal erosion. I’m not saying that loss of wetlands is not a problem. I’m not saying we don’t have to be better caretakers of the environment all around us, an environment that supports and sustains us, an environment to which we are inextricably connected.

I am saying that building wetlands and performing coastal restoration has very little to do with hurricane protection.

There’s no dispute that hurricanes “lose steam” when they cross over land. Quite literally, it is the warm water of the Gulf of Mexico that feeds tropical cyclones and can turn a tropical depression into a “Category 5” hurricane in a matter of hours.

Once over land, hurricanes no longer have warm water to power them, and additionally have to contend with dramatically increased friction at the surface. Think of the difference between spinning wind over open water as opposed to a landscape dotted with trees and buildings.

And it should be obvious that rising land will lessen the effects of a hurricane’s storm surge, that slug of highly elevated water that gets pushed ahead of a hurricane. Many cities don’t have to worry about the storm surge because they are elevated higher than any storm surge could reach.

Wetlands, by definition are low-lying areas that spend an appreciable amount of time each year under water and wet. Along the coast of Louisiana, these areas are typically about 1.5 feet above sea level.

The popular notion is that having a lot of wetlands between cities like New Orleans and hurricanes will protect us from the worst of the storm surge. There is some agreement that for small storms, tropical depressions and Category 1 hurricanes, coastal wetlands are an effective barrier.

And why not? Water being pushed inland at a height of 5 feet over land with an elevation of 1.5 feet will feel that land dragging on it. Waves trying to form and break will have little depth to work with and will subsequently not form very high at all. So wetlands are helpful when small storms come calling.

But what about the big ones? What happens when a Category 5 Hurricane, or a monster surge of 24 feet like the one produced by Katrina comes crashing at those wetlands? Well it turns out that wetlands can’t do much. They get covered, buried under that huge storm surge, so that the benefit of friction has only temporary and nominal effect. And the waves get the full height of water in which to form, too, so the waves come crashing as they do in the open sea.

The net result is that wetlands hardly contribute anything to protecting us from major storms.

But don’t take my word for it. The Corps of Engineers has been working on the wetlands problem for many years. They and the Louisiana Department of Natural Resources have teamed up on a number of projects. Many years of study have resulted in reports like the Coast 2050 and the Louisiana Coastal Area Ecosystem Restoration Project.

While these reports have done a yeoman’s job of documenting the ecological and economic importance of wetland protection and restoration, the connection to storm surge protection is tenuous at best. Here is what the Coast 2050 report has to say about it:

It is commonly acknowledged that barrier islands and coastal wetlands reduce the magnitude of hurricane storm surges and related flooding; however, there are scant data as to the degree of reduction...

Hurricane Andrew gave direct evidence that the physiography of marshes where a storm makes landfall affects the degree to which the storm surge is dampened. The surge amplitude in the Terrebonne marsh system decreased from 9.3 ft above sea level in Cocodrie to 3.3 ft (Swenson 1994) in the Houma Navigation Canal approximately 23 miles due north. This equates to a reduction in surge amplitude of approximately 3.1 inches per linear mile of marsh and open water between Houma and Cocodrie. Similarly, the magnitude of the storm’s surge was reduced from 4.9 ft at Oyster Bayou to 0.5 ft at Kent Bayou located 19 miles due north. This equates to a reduction in surge amplitude of approximately 2.8 inches per linear mile of fairly solid marsh between these sites.

Source: Coast 2050 Executive Summary

Now notice the data was collected during Hurricane Andrew, a Category 5 storm when it made landfall, a bona fide "big one."

The data is scarce, but to perfectly Pollyannaish about it, let’s say it's totally true we can get 3.1 inches of storm surge reduction per linear mile of marsh between where we live and where the hurricane comes ashore.

And let’s also say we want to knock down a storm surge from a monster of 20 feet in height to a tame 10 feet in height. That’s 10 feet of reduction at 3.1 inches per mile. The simple math tells us that we would need 39 miles of wetlands out there to make this happen.

That’s quite a distance.

To protect New Orleans East and St. Bernard from the next “big one,” we would not only have to fill the much-despised MRGO--we would have to fill Lake Borgne! And that's IF it really works, which we don't even know if it will.

I’m sorry to have to be the bearer of bad news. I know it really sounds nice that we can be environmentally-minded and save our cities at the same time, but it’s just not true.

Coastal restoration is an admirable, worthy goal. It just has little to do with hurricane protection.

Do you understand now why I keep writing about how much we need those levees? They're our only hope.


Jennifer said...

Thanks for another informative post.... a gentleman I met in St. Bernard had me pretty convinced the wetlands were a major way to go in hurrican protection... I now understand a bit more!

da po' boy said...

I don’t think anybody would suggest a “coastal restoration only” plan for hurricane protection.
However, it is connected to hurricane protection.
Healthy wetlands are indicators of a healthy ecosystem, one that can bounce back after a major hurricane or two and continue to be a healthy ecosystem. We don’t have that now. The Gulf Coast could be irreparably changed by the combination of Katrina and human factors.
Or not, given those same human factors can restore it.
Of course, we need a short term levee plan to get people to move back. But, we must also have a long term plan for restoring the wetlands in combination with more levees so we are not dooming those people.
Without the coast, what do you build the levees on? Do you let the surge arrive full force at the city gates before it reaches a levee? Or do you have a series of levees built from the edge of the coast inward? And with more coast, couldn’t you build more levees?
We need land between us and the Gulf, be it wet land or dry land. Otherwise, you get Tim Kusky’s reverse fishbowl scenario – although, I use that comparison lightly because his scenario is extremely exaggerated.
Southern Louisiana evolved to take a hurricane or two. Or three. And it is still here. And it evolved a healthy coastal ecosystem, even with it being battered by hurricanes. If we want to stay *here* for a while, that healthy ecosystem has to stay *there*.
There is no silver bullet for hurricane protection. Part of my equation:
Mississippi River type levees everywhere + more coast = hurricane protection

Mark said...

As dpb pointed out, it's not one or the other. What annoys me about your sources is the idea is that we've been bad stewards of the land. To some extent that's true, but what was done for coastal oil and gas exploitation was done in the greater national interest. That's why there is a federal obligation to undo that damage. Failing that, the state should imposed an Environmental Impact Fee on every barrel and mcf that comes from or accross the marsh, enough to raise a few billion.

The absence of the old marshlands behind St. Bernard clearly contributed to the failure of the St. Bernard levees, as did the MRGO. These are issues outside the levee system that have to be addressed.

oyster said...

I appreciate this analysis, however distasteful it is to my assumptions about wetlands and hurricane protection.

I think reducing storm surge from 20 feet to, say, 15 feet is worthwhile enough.

I'll definitely bookmark this post and compare my future readings with your information and analysis.

Tim said...

po' boy, I agree, the ecosystem needs help. We should work to fix it. My point is simply that the effectiveness of wetlands as hurricane protection is limited. It's limited to protecting us from weaker storms. And I'm not talking about Cindy, I'm talking Katrina. We do need both, I agree.

Tim said...

Markus, I'm sorry but the storm surge that hit St. Bernard was about 24 feet. The parish levees never had a chance since they were built to a maximum height of 17-1/2. To cut the storm surge down by 6-1/2 feet, using the rough guess of 3.1 inches per mile, you would need about 25 miles of wetlands in front of the St.Bernard levees. And that's ignoring wave action! At no time since as far back as colonial days was there that much marsh out there. Again, we will either need higher levees, or we will have to fill Lake Borgne.

Tim said...

oyster, Please tell me if you find anything more optimistic than what I've found. It either hasn't been thoroughly studied, properly measured, or it just doesn't exist.

oyster said...

Perhaps the study by the National Academy of Sciences referenced in this T-P article will have some more optimistic info. I haven't read the study, but the following quote from the news article seemed pertinent to the discussion:

"For instance, the report concludes that larger population centers along the state's coastline, including the New Orleans region, can only be protected from hurricanes with a combination of levees and a "sustainable coastal landscape," the web of wetlands and coastal forests that act as buffers against storm surge.
The report also warns that the continuous series of barriers used to protect the coast of the Netherlands from flooding may not be applicable to Louisiana's fragile and broken coastline on which much of the Gulf of Mexico's commercial fisheries depend.

Instead, it recommends identifying larger population areas that could be surrounded with stronger, inner defenses. Wetlands would be strategically rebuilt outside those defenses to be self-sustaining, and would be designed to reduce storm surge and dampen waves. Artificial channels would be plugged or gated to reduce storm surge. And barrier islands would be maintained along selected parts of the coast, also to dampen surge and waves.

Some of those barriers might be built between levees and outer parts of the coast to act as a secondary speed bump between surge and the levees.

The report's authors say that while wetlands already lost to the east of New Orleans may have reduced Katrina's storm surge, it's unlikely it would have stopped the surge from topping levees in eastern New Orleans or St. Bernard Parish.

But the importance of wetland and barrier island restoration becomes clear, the report says, when a storm surge model is run that assumes the remaining marshes east of the Mississippi River-Gulf Outlet, Gulf Intracoastal Waterway and Lake Borgne have eroded away and become open water that's 10 to 12 feet below sea level, matching the rest of the lake.

The result would be an increase of 3 feet to 6 feet in the height of storm surge along St. Bernard Parish and eastern New Orleans, the report said. "

Anonymous said...

Well, Mr., I'm glad to see that you are a trained scientist and clearly have enough evidence to refute the hundreds of scientific, academic, and civil groups out there who have been telling us for years that coastal restoration is important for hurricane protection....oh wait. You don't. That little map in there completely neglects to show how much of that land ISN'T THERE ANY MORE. For those of you actually listening to this guy, you should take your time and look into the subject from reputable sources before making a decision on the matter.

Chris said...

Right now, the sediment from the Mississippi River is not flowing naturally into the wetlands, (because of the levees). It is being redirected and dumped off the shelf of the Gulf, (a distance greater than the Grand Canyon), by the Corps. We need to allow some of that sediment to return to the marshes, so minimally we prevent further loss. "Coastal Restoration" is not a simple all or nothing answer. The marshlands is a key variable in calculating the impact of the storm surge, at least that is what they taught me in Coastal and Marine Engineering at UNO.