It’s time to consider forested levees
We need an objective comparison of the long term costs and benefits between (1) relatively inexpensive, low tech, self maintaining, environmentally friendly Chenieres faux; and (2) massive, ugly, hugely expensive, environmentally destructive bare earthen levees - design that falsely implies absolute flood protection.
Editor’s Note: The biggest budget item in Louisiana’s evolving coastal protection and restoration program is spelled L-E-V-E-E-S. This single item drove the original package cost from $15 billion to an unsellable $100+ billion. I believe that the cost of this coastal package could be pared to a realistic figure by considering a radical redesign of storm levees to a more sustainable and environmentally friendly configuration. To date, corps and state officials don’t seem interested.
Waveland Mississippi was ground zero for an awesome three story surge of ocean water generated by Hurricane Katrina. A couple months after the storm I saw mature live oak trees (Quercus virginiana) still standing along the beach – surrounded by the almost total devastation of man-made structures. This experience triggered an idea in my mind that, like those stalwart oak trees, refuses to go away.
Trees represent a natural bulwark against storm destruction in south Louisiana, a bulwark that for too long has been ignored by everyone but a few scientists and environmental advocates. Landowners have logged, developed and even mined sand from cheniers and other natural beach ridges. State and federal agencies have ignored or condoned these shortsighted practices.
And then there is the corps of engineers. This is the agency most responsible for advocating, designing and constructing artificial levees to protect people and property, first from annual river flooding and now from far less frequent – but far more dangerous ocean storms.
The concept of incorporating trees into a radical new hybrid design for storm levees deserves serious consideration. This basic concept has been vetted in previous posts, at two technical symposia* and in conversations with coastal forest experts. To date, no deal breaker or serious objection has been raised that would rule out a serious investigation.
The advantages of this concept include: (1) the potential effectiveness of dense stands of tree trunks to increase friction and absorb surge energy; (2) the soil stabilizing function of intertwining roots of healthy native trees; (3) huge cost savings that could be realized by reducing the design elevation and sediment requirements of orthodox earthen levees to lower level, forested, “porous” storm levees modeled after chenier ridges; and (4) habitat improvement – especially the expansion of the limited forested ridge systems on which migrating birds depend.
Meanwhile, the corps maintains an absolute and unwavering prohibition on the growth of woody vegetation (trees) on levees. Geotechnical engineers who design levees for the corps are not trained in forest ecology and they appear to be either blind to or unwilling to recognize the attributes of stands of trees.
NOLA residents know that levee failure happens (see photo below) but I have not heard of a single documented case of such failure resulting from trees blown down, uprooting soils and triggering failure. On the other hand, mudslides all over the world are typically preceded by deforesting hillsides.
Two massive and extremely costly levee proposals are heading toward ultimate authorization, if not appropriation: Morganza-to-the-Gulf, and Donaldsonville-to-the-Gulf. I predict that in our budget-strapped state rumors that these projects could carry a combined price tag approaching twenty billion dollars or more for clay purchase, construction and mitigation will soon begin to reach the desks of Angele Davis and John Kennedy.*
Katrina-induced failure of orthodox levee; note the complete absence of woody plants.
Chenieres faux would not replace orthodox levees in urban settings. They would instead be intended to replace controversial portions of the long, costly and environmentally damaging levee alignments such as those being designed for the Barataria and Terrebonne basins.
Rather than promising 365 days every year of dry protected landscape, the alternative levee design concept would include overtopping during high to extreme storm events. This would be recognized by coastal residents, who would need to elevate homes and plan evacuation during extreme storms but the power of storm surges would be dramatically reduced, limiting infrastructure damage within a protected “shadow.”
After a recent meeting of the technical panel recruited to comment on the Donaldsonville-to-the-Gulf Project, I met Phil Williams, an engineering consultant from SanFrancisco and member of the panel. After hearing the concept of Chenieres faux, he expressed interest, which was encouraging, in that Dr. Williams has coastal engineering credentials that I lack.
The disastrous 2005 Katrina-induced levee failures in New Orleans sparked concern on the part of the corps about levee integrity all around the country. The agency discovered that many existing levees had become colonized by trees and orders went out to clear the offending vegetation. These orders were challenged by environmental interests in the Sacramento Valley.
In response to these concerns in 2007 the Sacramento District of the corps hosted a technical symposium on the effects of vegetation on levee integrity and and commissioned an independent followup review paper published in December 2008.*** In my humble opinion this symposium and study on levees and trees should have been sponsored by the New Orleans District.
I have reviewed the December 2008 review paper and my comments will follow in another post. Meanwhile it is instructive to note that neither the Sacramento symposium or the report document have ever been mentioned in a coastal meeting in Louisiana. To be continued…
Len Bahr (len.bahr@gmail.com)
*With Buck Abbey, LSU professor of landscape architecture.
**Commissioner of Administration and State Treasurer, respectively.
***One of the three co-authors on this report was Dana Nunez Brown, a practicing landscape architect in Baton Rouge.
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perhaps the problem lies in the unconditional protection that people have somehow come to expect from levees. Of course all of us know that levees will always fail or be overtopped, but somehow we keep expecting them to thwart everything that comes along, and then sue when they don’t. Which is why the coastal levees the Corps propose are 100+ billion.
How would these be constructed along the Outfall Canals; with limited space available??
I believe the Independent Levee Investigation Team has some thoughts on this subject also:
http://www.ce.berkeley.edu/projects/neworleans/
Forested ridges (Chenieres faux) is not an appropriate concept for lining outfall canals but it would seem worth considering for the south shore of Lake Pontchartrain, where space is not limiting and where dense plantings of live oaks would make a beautiful and functional addition to what is now a long unshaded grassy knoll.
Len,
Great post. Likely that the COE believes trees are a threat to levels rather than a help. Looking forward to info on the Sacramento Report.
Len,
Good post. One problem though is salt tolerance and rate of growth. Our native live oaks are somewhat salt tolerant but slow growing above ground, and I don’t know how deep and how fast their root systems develop.
Len:
Try the Mac compatible files from the cerp.lsu.edu
Len,
Another great post. Your forested levees are another term for replication of natural ridges along our coast as recommended in the Multiple Lines of Defense Strategy. Levees alone are a temporary fix a best. Without reestablishing some semblance of a self sustaining coast (and its natural features that reduce storm surge), metro New Orleans, Houma, and many of our coastal communities will become more and more at risk.
Keep doing good.
Carlton
Please see some movies about this method and a MRGO closure plan at
http://cerp.lsu.edu/
Anonymous-
I appreciate the connection to the two videos. Unfortunately the format isn’t compatible with the Quicktime software on my laptop so I can’t open them.
I too have observed post-Rita effects of wooded cheniers . The Louisiana Wildlife Federation has supported wooded cheniers and objected to the sand mining of them in resolutions as recently as the anuual meeting in March.
In addition to providing the storm protection the value as habitat to species including neotropical migrants is another benefit.
These should be looked into wherever possible.