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Bird’s Foot Delta, part two

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Figure 1. Bird's foot delta (a) before (left) and (b) after (right) hypothetical release of all river flow upstream from Head of Passes, effectively abandoning the Bird's Foot Delta

Editor’s note: This concludes a two-part post on the Bird’s Foot Delta at the mouth of the Mississippi River (Figure 1a and 1b), written by one of its biggest fans, Dr. Andy Nyman (click here for Part one). Nyman’s post was written just prior to April 7, when the Associated Press reported that a crude oil spill by Exxon-Mobil operations had fouled about 20% of the Delta National Wildlife Refuge that occupies much of the area (Figure 2).

Delta National Wildlife Refuge (photo from USFWS)

Figure 2. Delta National Wildlife Refuge (photo from USFWS)

I asked Andy to write a paragraph on his thoughts on the likely effects of the spill on the Bird’s Foot (see Addendum below).

by Andy Nyman, PhD

Five years ago I couldn’t imagine saying this, but here it is: I’d be willing to sacrifice all of the publically-owned land in the entire Bird’s Foot Delta if that sacrifice were required to gain two new active deltas upstream, such as is projected in Figure 1b above, from the Louisiana Coastal Master Plan. Don’t expect the numerous private landowners there to agree with me, however.

Those ambitious plans for new delta lobes may never be acted upon but we’ve hastened the loss of existing wetlands in the Bird’s Foot Delta (some of which are privately owned) and foregone opportunities to let the river build new wetlands there.

Since at least the 1970s, a 45 foot deep navigation channel has been dredged across the bar in SW Pass, the main channel of the Mississippi River, and this sediment has been dumped at the head of Pass a Loutre, a major ‘toe’ of the Bird’s Foot. The Pass a Loutre Wildlife Management Area (Figure 3) described in part one of my post, is named for this river pass.

Pass-a-Loutre WMA (map from Louisiana Sportsman)

Figure 3. Pass a Loutre WMA (map from Louisiana Sportsman)

Dredging experts claim that releasing dredged sediments back into the main channel would reduce current velocity, causing more sediment to fall out – and breaking the navigation dredging budget. Most of my colleagues believe this claim.

Dredging experts have also claimed for decades that placing these sediments in Pass A Loutre does not slow water there, nor cause more sediment to fall out there.  Few of us agree, but this claim is the basis for policy.

The river remains unfazed by these Jekyll-and-Hyde explanations. Pass a Loutre, the source of virtually all freshwater and sediment for its namesake WMA, is clogging up. As this eastward river distributary dies the Pass a Loutre WMA dies as a wetland.

A sand bar began to form in Pass a Loutre in the 1980s, contributing to the death of a crew boat worker while I was there. Vegetated islands appeared in the 2000s.

Pass a Loutre carries so little freshwater and sediment that its north fork is no longer usable for navigation as a route to the Gulf as it was in the 1980s and its south fork no longer exists. The distributary now carries so little water that in 2009 I forded its eastern opening to the Gulf of Mexico, which would have been unimaginable in the 1980s – and didn’t even get my knees wet.

The decision last year by the State of Louisiana to declare sediment dumping in the pass inconsistent with state policy was a step in the right direction but seems incomplete to me because it focused solely on the lost opportunity to pump the dredged sediments a few miles away and use them to create new wetlands. There is still no policy that recognizes previous and future losses of existing wetlands and previous and future reductions in natural wetland building in Pass a Loutre WMA, caused by choking the pass with dredge disposal.

The decision this year to close the West Bay Sediment Diversion project appears to be a step in the wrong direction. West Bay is the only large sediment diversion constructed to date; it also is the only one of any size built on the main channel of the Mississippi River. Diversions such as Caernarvon and Davis Pond are river water diversions intended to slow the loss of existing wetlands, rather than sediment diversions intended to build new landscape.

I’m certainly not an expert on delta building but references I’ve read* show that the area of wetland created is proportional to the size of the diversion project. Large projects require considerable time to work, however.

We’re talking decades. The largest artificial sediment diversion project to date is the Wax Lake Outlet that was dredged across a natural ridge in 1942 to expand the flood outlet capacity of the lower Atchafalaya River near Morgan City. The project was not intended to build land but after three decades new emergent landscape appeared in 1973 and the ‘artificial’ Wax Lake delta continues to expand. Much smaller sediment diversions on small channels throughout the Bird’s Foot Delta generally take at least 8 years to produce new wetlands.

Despite its recent construction in 2003, bathymetric surveys in 2009 showed that sediment accretion from the West Bay Sediment Diversion project had exceeded subsidence in parts of the project receiving area for the first time in almost a century. Nevertheless, the public was told that a lack of significant wetland accretion contributed to a decision to shut down this ‘youthful’ sediment diversion project.

The real reason this sediment diversion is being shut down is a stubborn, decades-old denial of the costs of deep-water navigation to Louisiana’s coastal wetlands. This denial has recently been accompanied by widespread misinformation on the impact of this sediment diversion in particular.

A study by the USCOE confirmed that shoaling in the anchorage area downstream of the West Bay Sediment Diversion predated construction of the diversion project. It was also estimated that the project contributed only 20 – 40 percent of the shoaling. Despite the minor contribution of the project to reduced draft in the anchorage area, limited restoration funds will be tapped to pay  the entire cost to dredge the anchorage.  The project will be closed before there has been sufficient time to adequately assess its performance.

The precedent set by this decision appears to doom large sediment diversions anywhere on the main stem of the Mississippi River. If navigation interests can trump sediment diversions in my favorite location, the Bird’s Foot Delta, I presume that such projects will be prohibited everywhere.

The decision to forego wetland building in the Bird’s Foot Delta and hasten the loss of existing wetlands would nevertheless be acceptable to me in exchange for large sediment wetland-building diversions constructed upstream.

Unfortunately, I believe that these decisions were made to save money in the short term. This is like foregoing automobile oil changes to save money; the short-term savings are a tiny fraction of the long-term costs. I would hope that these policies could be changed to protect the wetland building and sustaining capacity of the Bird’s Foot Delta until we are certain that new, large, sediment building diversions can be constructed further upstream.

Once again, a delta in the hand is worth two in a plan.

*Large scale, see: Coleman, J.M.  1988. Dynamic changes and the processes in the Mississippi river delta. Geological Society of America Bulletin 100:999-1015. Medium scale, see: J.T. Wells and J.M. Coleman. 1987. Wetland loss and the subdelta cycle. Estuarine Coastal and Shelf Science: 25:111-125. Small scale, see Boyer, M.E., J.O. Harris, and R.E. Turner. 1997. Constructed crevasses and land gain in the Mississippi River delta.  Restoration Ecology. 5:85-92.

Addendum

An estimated volume of 430 barrels of heavy crude oil was spilled on April 7 from a broken pipeline at Delta National Wildlife Refuge, which contains almost half of the marshes in the entire Bird’s Foot Delta (Pass a Loutre WMA occupies almost the other half). I was more worried during July of 2008 about fuel oil spilled at New Orleans reaching the Bird’s Foot Delta because refined products are so much more toxic than crude oil.

Most of the fouled vegetation will survive if clean-up personnel do not cut it, or cut it so that the remaning stems are tall enough to exceed water level during the next few months. Unfortunately, some areas will be so heavily fouled that vegetation must be removed, generally resulting in permanent wetland loss.

Even in areas where fouled vegetation can survive while oil naturally biodegrades, wildlife will become fouled for weeks to months. This is important because even crude oil is more toxic to animals than to plants.  Thus, minimizing permanent wetland loss by relying on natural biodegradation also temporarily reduces populations of some wildlife.

Simply by walking or using marsh buggies, responders will push oil below the marsh surface where there is no oxygen and natural biodegradation is much, much slower. Thus it is possible to cause more harm than good by traveling through a large, moderately fouled area to reach a small heavily fouled area.

I encourage readers who see fouled vegetation during the months to come to appreciate the difficult decisions facing spill responders today.

Edited by Len Bahr, PhD (leonardbahr@gmail.com)

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  15. Kelly Haggar says:

    All -

    As long as the coastal restoration program is a geology-free zone there’s no point is spending much time on it. I read the T-P story Edtilla linked in the scuttlebutt thread. Once you make the basic error of making engineering the lead discipline you’re pretty much assured of failure. Don’t put anyone else on the team but life science folks and you’ve eliminated the little remaining doubt.

    Jay Huner -

    Don’t want to put any words in Woody’s mouth but I will inform you that he was presenting a poster this past Tues morning at the American Association of Petroleum Geologists (AAPG) national convention in New Orleans. (The AAPG was founded in Tulsa OK in 1917 but it became international years ago, not just “American.” Had nice chats with Brits, Romanians, Canadians, and Poles at the convention.) My better half was a co-author of Woody’s poster, served as 1 of 2 Co-Chairs of the overall Enviro Poster Session, and presented her own poster the next station over from Woody. (Nice MMS poster on the other side of Woody.)

    Wander over to the CEI web site and download the July 03 faulting report Woody, Karen, Burt, and Kathy did for the New Orleans Corps. After that sinks in, ask yourself two questions:

    1. What possible justification can there be for attempting to “save” the Bird’s Foot?

    2. How ANYTHING that happens in the Bird’s Foot can possibly have a favorable effect upstream of it? If La ever did the triage exercise the NAS suggested in 2006 (page 163) the Bird’s Foot ought to be the very first thing we jettison . . . .

    Late and on a “show and tell” subsidence field trip all day tomorrow.

    • These commentators attempt to switch focus from the issues identified in the essay. I encourage readers to focus on the issues raised: Should our tax money that is dedicated to maintaining deep draft navigation also be used to choke off Pass A Loutre, which accelerates the loss of existing wetlands in the Birds Foot Delta? Should our tax money that is dedicated to wetland restoration funds instead be used (1) dredge an anchorage for ocean going vessels, and (2) close a channel that all data suggest will create emergent wetlands within a few decades (West Bay)?

      • Kelly Haggar says:

        Andy, with all due respect, the Birds Foot Delta is doomed. Stop trying to make it into another Chandeleurs. Triage time.

        Should dedicated wetland restoration funds be used for navigation? Of course not; all dedicated monies must be spent for the allocated purpose.

        I’d say the more appropriate question is along the lines of “If there is a conflict between navigation and restoration, which should prevail?” My bet is that navigation will win that contest even if the only voters were all inside La. Factor in the rest of the USA and it’s not a close call.

        Or, for those who place wetlands restoration at the top of their goal stack in all cases, the question becomes “Why would the Bird’s Foot be #1?” Of all the possible wetland places we could create or restore or improve between the Sabine and the Pearl, what sort of scoring/grading maze could result in the Bird’s Foot coming in at #1?

  16. HeidiHoe says:

    Mudder Nature, through the ‘laws of Physics,’ likely dictates what the ‘velocities’ should be…….

    We may think we do, but that might be wishful thinking…..

    Len’s picture’s caption sez it best: HYPOTHETICAL situations…….

    With a LARGE emphasis on the HYPOTHETICAL part……..

  17. Finally!!! Thank you for this post. I have been wanting to read some information othe West Bay Diversion Project for years and there has been virtually nothing written about it… its progress etc.

    It is good news that despite Hurricane Katrina and Rita that the diversion was indeed starting to have a positive impact on the area.

    I have harped for years that the Army Corps of Eng. does not have a right to demand anyone pay for dredging coast when anything is done that increases it. (talking about diversions mainly) Putting diversion in mimics what the river was like years ago. Who gave them right to demand that the cost of dredging be put on anything or anyone that puts things back closer to NORMAL!

    We should be charging their butts for the decades of dredging cost they didn’t incur because of the levees all along the river where it doesn’t even protect a single home!

    Why do they get to dictatte what the river velocity should be? Yes it was artifically faster the last few decades due to practices that destroy our wetlands. Time they start paying their own way!!!

  18. CoastGhost says:

    Policy is oft not based upon the truth or what is correct, only what is believed.

    West Bay was based on faulty premises and never really had a chance. And, I feel we are past a point were we can wait 30 years, like at Wax Lake, for a delta lobe to appear.

  19. Jay Huner says:

    I found the presentation especially interesting. I have only visited the area during the past 6 years so did not even know that it was a willow-based system. Sort of explains where Eads got the willows for his structures!

    Politicians seem oblivious to facts. It seems that the “flim flam man” is the one who secures the funding for projects by playing to the politicians bases and the politicians themselves. Heaven forbid that one has spent a lifetime studying a system directly. Such a person simply cannot be objective – ask Eads!

    Once the collective “they” have made a decision, no contrarians need apply. “Rising Tide” and “Designing the Bayous” both show clearly that there is a process and that process, once it begins, cannot easily be countered when it comes to environmental manipulation. I suspect that Woody Gagliano could write a wonderful book on the topic.

  20. Anonymous says:

    To what degree are our restoration program efforts wasted and constrained in order to accomodate private owners of our state’s (surface) wetlands? Are private (surface) land owners a boon or a bane?

    • Aaron Caldwell says:

      Private owners are both… those that care about the marsh resources on their property are a boon, they just need to be educated. Private owners with a pure resource extraction motive are a bane. Those who think the status quo is optimum will soon find out that they can’t capture this moment in time in a bottle and keep it. As the marsh degrades around them, the status quo will change to something less desirable… only then it will be too late (it might already be).

  21. Oliver Houck says:

    This and other posts reinforce another precept of coastal (or anything else) restoration largely forgotten in the process: first do no harm. We continue to permit more coastal loss than we restore. (The official data overrate mitigation success, and overlook the considerably larger indirect impacts altogether.) Will no one take this problem on?

  22. Paul Kemp says:

    Thanks to Andy for his comments and observations on the Birds Foot and on the effects of the leaking pipeline there. At some point, I would like to post something describing the new data on where sediment is going as the River continues to seek to shorten itself and abandon the birds foot. Best, Paul Kemp

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