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Why not turn the Morganza-to-the-Gulf project into a worthwhile enterprise?

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by Len Bahr, Ph.D.

This concept could save $ billions in cost, maintenance, ecological damage and public safety. How much of the 72 miles of hurricane levees in the $4 billion Morganza to the Gulf project could consist of Chenieres Faux?

Converting the MTTG seawall into forested ridges could save $ billions in cost, maintenance, ecological damage and public safety. How much of the 98 miles of hurricane levees in the $11 billion Morganza to the Gulf project could consist of Chenieres Faux?

Morganza to the Gulf project – a popular mistake

As a long term outspoken critic of the Morganza to the Gulf (MTTG) Project I never dreamed that I would write this, but here goes. I hereby propose what may be a feasible way to convert what, at $13 billion, is clearly an unaffordable, environmentally destructive, high maintenance sow’s ear into a beneficial, low maintenance silk purse. First, some background is in order.

In 1991, when I first joined my colleagues Dave Chambers and Karen Gautreaux in the newly-created Governor’s Office of Coastal Activities, I noticed a framed illustration hanging on a wall in our office on floor 5.5 of the State Capitol. This diagram  depicted the central part of the Louisiana coast with a solid jagged line extending more or less parallel to the shoreline from the Atchafalalaya River to Bayou Lafourche. The line represented the proposed alignment of a giant earthen seawall proposed to protect the city of Houma and surrounding communities in Terrebonne Parish from an almost inevitable catastrophic hurricane surge within the next 100 years (1 % chance per annum).

Modified from a graphic in The Advocate

Modified from a graphic in The Advocate

I had immediate reservations about the wisdom of impounding a huge swath of coastal wetlands with such a barrier but I soon discovered that even back then the MTTG project had become sacrosanct to the powers that be, both in Houma and Baton Rouge. Sacred or not, the fact that twenty-five years after I first saw the diagram only pieces of the project have been constructed attests to the challenge of its cost and justification.

Massive cost of the MTTG

In September 2013 the U.S. Army Corps of Engineers (USACE) described the MTTG project and its costs and benefits in the following quote from an article by Xerxes Wilson in the Houma Courier:

Morganza would cost an average $716 million a year to build and maintain while preventing an estimated $1 billion in annual flood-related damage. That includes construction and maintenance costs averaged over 50 years. The cost-benefit ratio is $1.40 in benefits for every $1 spent. The benefits are slightly higher than the $1.31 estimated in January. About 53,000 structures will be protected.

The latest plan adds 26 additional miles of levees to Morganza, up from 72 miles. It would extend from U.S. 90 in Gibson to La. 1 in Lockport. Morganza would include 98 miles of levees, a lock on the Houma Navigation Canal, 19 floodgates and 23 water-control structures.

Levees will be built up to 26.5 feet high, and flood-protection and water-control structures would be built more than 30 feet high. Levee widths will range from 282 feet to 725 feet, roughly one to two football fields.

The levee project is designed to protect against storms that have a 1 percent chance of striking in any given year, sometimes referred to as a 100-year storm.

State and local officials must come up with 35 percent of the construction cost. Their combined share is estimated between $3.6 billion and $4.5 billion. Upon completion, the state and local partners will be responsible for operation and maintenance, estimated at $7.4 million per year. The federal government will be responsible for operation and maintenance of the Houma Navigation Canal Lock at $1.7 million per year.

In January, 2015 I posted a warning that the MTTG, even if never completed, was turning into a coastal development magnet, a moral hazard likely to attract unwary investors into harm’s way.

Forested ridges rather than sea walls

In October 2008, December 2009, and March 2010 I published three successive posts proposing a novel coastal restoration concept that I referred to as Chenieres Faux, or arboreal armoring. This concept involves the creation of ‘leaky levee’ systems comprising forested earthen ridges that would function under any level of storm surge, rather than continuous high maintenance 28 foot seawalls with modest protection only against 100 year storm events. Upon maturity the visible portion of the trees would provide over 60 feet of vertical defense against hydraulic energy and dramatically augment wildlife habitat. The invisible root system would provide dramatic erosion resistance and vertical enhancement to the earthen base.

In July, 2016 NPR’s Radiolab ran a fascinating 34 minute podcast on the hidden world of forest root networks that allow widely separated trees to share information, nutrients, and sugars. The unseen forest root horizon consists of a dense platform of stout tangled roots colonized by microscopic fungus tubules that interconnect as many as 50 adjacent trees, forming an extensive, living, soil binding network.

Converting the MTTG seawall into a series of Chenieres faux

By 2014 the state of Louisiana and Terrebonne Parish residents had reportedly spent $250 million to create the foundation of the MTTG project along the alignment shown above, with the assumption that with such a foot in the door the corps would eventually agree to complete the massive structure as currently designed. This assumption seems politically shaky, however, given the $13 billion MTTG price tag, for which the state would be billed for 35%. ~$4 billion. This scale far exceeds any other project in the 2012 master plan and would bankrupt coastal protection and restoration at both state and federal levels.

Thus I propose transforming the orthodox MTTG project design by incorporating the Cheniere faux concept, using the existing levee alignment and foundation as the platform on which to undertake a massive tree planting exercise.

Corps prohibition of trees on levees

Unfortunately, my proposal conflicts with a universal prohibition by the USACE on the existence of woody vegetation on levees. On September 13, 2012 I posted an article on this prohibition, including arguments for allowing a dispensation from this blanket rule under some conditions, at least on an experimental basis.* On April 30, 2014 the corps released an official policy document titled Guidelines for landscape planting and vegetation management at levees, flood walls, embankment dams and appurtenant structures.

Not to be discouraged, on November 29, 2014 I returned to this subject of forested ridges in a post Thanksgiving Day post.

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Precedents for forested levees

It’s high time that the USACE began to consider the value of trees and other woody vegetation as a valid tool for flood risk reduction under certain circumstances. The value of living shorelines was described in a July 2016 article by Erika Bolsted in Scientific American that was reprinted from ClimateWire.org.

The forested ridge concept was foreseen 22 years ago for midwest flood levees, as shown in a 1994 article on Arborial levee armoring of midwest levees by Douglas Wallace, Clifford Baumer, John Dwyer and Frank Hershey, Association of State Wetland Managers.

I’ve been in touch with the program manager of a California levee vegetation program that has been in discussion with the USACE San Diego District on the compatibility of trees and levees under some circumstance. Any dispensation from that district in terms of the blanket prohibition of trees on levees would represent a foot in the door against a close minded policy, with implications for Louisiana.

Artist rendering of Plaquemines Parish forested ridge concept

Artist rendering of Plaquemines Parish forested ridge concept

The officials in Plaquemines Parish decided to attempt a forested ridge project a few years ago, as shown at this link. Unfortunately, this project, which could have been precedent-setting, was not included in the 2012 Master Plan, now under revision. I’ve been told that Lieutenant Governor Billy Nungesser pulled the plug on it while he was Plaquemines Parish prez.

Recommendation

I would urge the supporters of the MTTG project to objectively consider supporting the modification of the current plan into a hybrid, self maintaining system. This would involve mounting a serious scientific design and modeling exercise to transform the current design of a continuous 98 mile massive earthen seawall with multiple control structures into a far simpler, self draining forested ridge project intended to be overtopped. Unlike the current design, this project would be doable. The key challenge would be to convince the USACE to relax the levee-tree prohibition and to fully participate in the design exercise.

That’s a political, not a technical challenge.

*I have long advocated using the Bonnet Carre floodway as an ideal site within which to construct forested ridges in various configurations and elevations that would be exposed to acid test conditions of massive water fluxes during floodway openings every eight or nine years or so. This federally owned, corps managed landscape would make a risk-free sandbox in which to objectively test the compatibility of trees and levees.

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  1. Coastal Whiz Kid says:

    Len,

    There are several problems with your Cheniere Faux proposal. First, these built up chenieres will subside the same as any constructed levee; little potato ridges eventually subside below the water level. The second problem is that most trees will tolerate a high water table and the few that do (for example cypress) will not tolerate salinity. but the most difficult problem is the long time needed for trees to grow to be really strong and by that time the first two problems may have doomed them. Problem four is that once planted with trees, the height of the cheniere faux can not be increased with additional placed material.

    • CWK-
      Appreciate your skepticism but my responses to the issues you raised are based on personal experience during the past 25 years, from having created a microswamp in my backyard in Baton Rouge with flood tolerant species, including seedlings of a tupelo gum, a swamp maple, 8 bald cypress, 1 pond cypress and 1 black willow in the pond. The willow died within 5 years but most of the trees are quite large now, probably 60 ft in height with very stout trunks.
      In addition, I planted a river birch and 6 live oaks on and adjacent to my property at ground level, which have all become mature adult trees with a max dbh of around 3 ft. So much for the time factor. They would have been effective within ten years. Second, the live oaks, envisioned to be planted along the ridge crowns, each elevated footprints comprising root matter. Don’t forget that this project has grown old since it was first conceived around 1990. What’s time to a pig? as the old Aggie joke goes.
      In terms of salt tolerance, I envision the use of black mangroves along the ridge bases where the MTTG trajectory is already in open water. The ridge crowns may require some irrigation but live oaks are quite tolerant of droughts and salt spray, growing on sand dunes in Georgia.
      I’m not convinced that additional lifts would be required for ridges with mature trees, anymore than natural cheepers.
      At any rate, all of these concerns could be tested cheaply.

  2. Until the idea is tested, who is to say it will not be successful?

  3. The obvious driver for levees is flood insurance. Due to uncertainty in estimates of 100-yr surge, levees must be “engineered” to withstand conditions significantly greater than the basic 100-yr estimate. This includes extra height, sufficient side slopes and toe berms to support levee (and thus width), clay quality and compaction criteria, and erosion resiliency (grass and sometimes armoring)on both sides. The NFIP places extra challenges on certifying “sub-levee” embankments to reduce interior surge–including road/railroad embankments. Forested ridge “designs” would have to meet these NFIP requirements. All levees and embankments have to be RE-certified for the NFIP every 10 years–so maintenance is a big issue.

    BUT importantly, the NFIP will be dismantled by Congress in 2017. So the real question will be not what is good enough for the NFIP, but what level of investment in flood risk reduction is cost-effective in a future with no subsidized flood insurance. And furthermore, private flood maps may end up being much more “conservative!”

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