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Saving the delta is a pipe dream sans sediment diversion projects.


by Len Bahr, PhD* 

Fig.1. Annual atmospheric Co2 increase from May 2012 to May 2013.

Climate change and delta deterioration

Last week the concentration of atmospheric CO2 reached 400 ppm, more than at any time in human history. This is the legacy of a century of accelerating combustion of fossil carbon, which has triggered dramatic changes in a climate pattern that had been extraordinarily stable for eleven millennia. The world ocean is warming, expanding and becoming more acidic, with very serious coastal consequences. Unfortunately, high levels of atmospheric CO2 will persist for decades, even were global emissions to drop precipitously.

While atmospheric CO2 has been rising annually (see Fig. 1) and anthropogenic climate change (ACC) has become apparent the world’s great deltas have been declining, exacerbated by sea level rise and growing competition for the river water that formerly sustained these dynamic landforms. America’s Delta is currently experiencing an annual sediment deficit of about 1 billion tons, caused by flood levees, river dams and channel dredging. This is equivalent to the loss of about 200 Superdome Equivalents (SDEs) every year and as a result our delta is disintegrating from within.

If you wanna get dirt, you gotta divert!

Fig. 2. Critical delta management study omits Atchafalaya R.!

Most geophysicists, sedimentary geologists and river scientists familiar with the largest delta in North America agree that the ONLY feasible way to significantly reduce this sediment deficit and to restore the delta would be to divert massive pulses of river water and suspended sediments into the heart of the delta during exceptionally high river flood stages, when the water resembles cappuccino. River reintroduction projects will take decades to be effective, however, partly because the lower river carries only half of its historical sediment load.

As pointed out by Bob Marshall last week in, however, projections of the current delta building capacity of the river are based on conjecture and obsolete data from the 60s. Supposedly, the seminal study of the feasibility of restoring the delta with mud and sand from the Mississippi River is a work in progress. Marshall’s article describes this $25 million research effort, called the ‘Mississippi River Hydrodynamic and Delta Management Study,’ as a state of the art effort, with participation by the world’s experts on the river’s current hydrodynamics and sediment budget. On the other hand, IMHO the study, a cooperative effort with the state, the Corps of Engineers and the U.S. Geological Survey, is seriously flawed by its inexplicable omission of the Atchafalaya River (see Fig. 2).

Nitrogen pollution

Reconnecting the river to its delta on a massive scale will be problematic for many reasons, including widespread habitat conversion throughout the Mississippi drainage basin during the past century that has been accompanied by declines in water quality. Most of the huge watershed that formerly included extensive bottomland hardwood floodplain has been drained and converted to row crops (especially corn) to which lots of fertilizer (especially nitrogen) is applied, much of which runs off into the tributaries and heads for the gulf.

Flood levees south of Cairo confine the lower river to its channel and funnel the nitrogen-rich water and suspended sediments offshore, bypassing the drying and dying deltaic wetlands. This results in nearshore algal blooms, high primary production and excess biological oxygen demand, culminating in a large hypoxic zone each summer.

Among their other attributes, coastal wetlands are effective at assimilating and removing excess nitrogen in estuarine waters using three mechanisms: (1) bacterial denitrification; (2) incorporation into plant tissue via photosynthesis; and (3) nitrogen sequestration and burial in coastal sediments. The latter process is especially important in a deltaic setting where the surface sediments sink continuously.

Thus it has been argued that diverting river water into the Mississippi’s deltaic wetlands would capture excess nitrogen before the water flows offshore, which would shrink the hypoxic zone. Unfortunately, however, the nitrogen load carried by the river may exceed the assimilation capacity of the deteriorating wetlands, causing inshore as well as nearshore eutrophication.

Several researchers, including LSU Boyd Professor Gene Turner, USGS scientist Chris Swarzenski and Massachusetts scientists John Teal and Linda Deegan have warned that injecting river water into the Mississippi delta could do more harm than good. They argue that adding nitrogen-rich river water to deltaic marshes with organic soils can stimulate aboveground marsh production, while reducing root production and the soil binding capacity for which coastal wetlands are known.

To address this concern the National Oceanographic and Atmospheric Administration (NOAA) sponsored a workshop in 2011 titled: “Response of Louisiana Marsh Soils and Vegetation to Diversions.” This exercise culminated in a position paper that is summarized here, with the take home message that sediment-poor freshwater diversion projects will not build significant landscape but that pulsed sediment-rich diversions can be effective for that purpose. The inshore nitrogen pollution issue was not resolved and it remains unsettled.

Diversion critics point to the controversial Caernarvon freshwater diversion project built in 1992 as an example of how not to design and operate a river diversion project. In contrast, pro-diversion scientists point to the Wax Lake and Atchafalaya subdeltas that have been growing steadily since the 1970s, under uncontrolled annual flooding by river water and sediments.

Vocal diversion critics

In an April 10 post in Bob Marshall described the organization of a vocal non-technical group of opponents of river diversion projects. This group includes disgruntled oyster growers and commercial and recreational fishers, primarily from St. Bernard and Plaquemines Parishes, who don’t want to give up their oyster leases or be forced to travel further south to catch fish.

On April 17 Mark Schleifstein reported in that Garret Graves, the governor’s coastal advisor, enlisted the help of three coastal scientists to refute the anti-diversion arguments. These authorities included Robert Twilley, an expert on eco-engineering, wetland soils and biophysiology; James Cowan, a coastal fisheries expert and Denise Reed, a specialist on coastal sediment dynamics and marsh hydrology.

Diversion opponents seem to have been energized by the imminent collection of fines against BP that may provide near term funding to move forward with the diversion projects in the Louisiana Comprehensive Master Plan for a Sustainable Coast, approved in 2012. The rise of organized opposition has stiffened the backbone of the state to move forward on sediment diversions.

On April 30 Todd Masson reported in that about 300 diversion opponents met to articulate their opposition to river diversions. According to the article, these diversion opponents have enlisted the formidable political support of St. Bernard and Plaquemines Parish Presidents Dave Peralta and Billy Nungesser, respectively.

On May 5 published a response to these critics, an op ed editorial by David Muth, Louisiana director of the National Wildlife Federation (NWF), as passionate a proponent of reconnecting the river to its delta as anyone I know. Clearly the proponents and opponents of river diversions are talking past each other.**

Mother Nature or diesel fuel?

When opponents of river diversions are asked about alternatives to sediment diversions to address the catastrophic coastal land loss that threatens southeast and central Louisiana, they respond that we should dredge and pump coastal sediments to re-create barrier beaches and marshes on a scale equivalent to the loss rate. One of the prominent advocates of this so-called ‘solution’ is Kerry St Pe’, executive director of the Barataria/Terrebonne National Estuarine Program (BTNEP) and a long time critic of large river diversion projects.

Pipeline conveyance of dredged sediments is an effective way to build landscape on a modest scale, measured in hundreds of acres and tens of millions in dollars…but not in hundreds of square miles and tens of billions of dollars. The Master Plan calls for $3.8 billion in sediment diversion projects and $20 billion in landscape re-creation, using dredged sediments conveyed by pipeline. The former is projected to eventually add over 300 sq mi., while the latter is projected to net 200 sq mi., at a much higher price tag and with no assurance that the recreated landscape would be sustainable in the long run. The high cost of dredging and pumping sediments is primarily the high cost of diesel fuel, which is likely to increase dramatically over the decades.

In January, 2011 Popular Mechanics carried an article  on saving the delta using sediment diversions. The proof of concept rests in the Myrtle Grove medium scale sediment diversion project, yet to be constructed.

Fig 3. Inset photo looking upstream toward New Orleans.

The only sediment diversion project currently in operation is known as West Bay, an uncontrolled opening in the river levee on the west bank above Head of Passes (see Fig. 3) that allows sediment-rich water to flow west out of the channel whenever the river exceeds a certain stage. This corps-designed project has been problematic since it was completed in 2002.

West Bay is building a subdelta but it has caused shoaling along the river channel that has required periodic dredging. Benjamin Alexander-Bloch reported on the West Bay project in on March 13, 2013.

Why not use nitrogen pollution as a political tool?

The river diversion controversy suggests an opportunity for the state to kill two birds with one stone, moving forward on the design of large and medium scale sediment diversion projects, while mounting a campaign upriver to lower excess nitrogen in Ol’ Man River, so as to eliminate the dead zone and resolve the concern of inshore eutrophication.

We should partner with the feds on the Mississippi River/Gulf of Mexico Watershed Nutrient Reduction Task Force to persuade the corn growing upriver states to get serious about nitrogen runoff. This could be accomplished with a financial incentive package for corn farmers, funded at least partly by BP. Their nitrogen pollution is stymieing our fundamental need to reconnect the lower river to its delta.

Mark Davis, who directs the Institute on Water Resources Law and Policy at Tulane University, recently addressed the clumsy attempt by the state to dismiss the nitrogen issue and a missed opportunity to make a stand against nutrient pollution in the river:

Two studies, one in New England on fertilizer pollution and one in Louisiana on freshwater diversions, are questioning the basic premise at the heart of the Coastal Master Plan – putting the river back into the marsh. These studies show that the nutrient pollution in river water could actually weaken salt marshes, an important but not historically dominant feature of Louisiana’s coastal ecosystem. The concern is that the abundant nutrients in Mississippi River water will spark unsustainable above-ground growth of marsh grasses, the root system will not be able to keep up, and the imbalance will lead to failure of the marsh vegetation. The diversion (we prefer the term “river reintroduction” ) study was commissioned by the Coastal Protection and Restoration Authority, but then dismissed by CPRA head Garret Graves as being unresponsive to the state’s needs. Without refereeing what the study does or doesn’t say or whether it was what the state ordered or not, we do note that the aim of the ongoing federal/state Hypoxia Task force is to actually reduce the nutrient levels in rivers feeding the coast so they are fit to use. At the least the studies seem to reinforce the importance of that work. 

Final thoughts: where have the geologists been? 

As important as wetlands are, their function is limited by the sediment platform on which they grow, a platform that formed over 6,000 years of net deposition of Holocene mineral sediments from the Mississippi River. Since its very inception in 1989 Louisiana’s coastal restoration program (later renamed protection and restoration) has been dominated by coastal wetland ecologists like me, folks who deal in relatively short term surface processes, not the long term geophysical and riverine processes that underlie the delta. In other words, the planning expertise has been dominated by those who deal primarily with surface processes on the visible veneer of the delta, not the riverine hydrodynamics and sedimentary processes that created the delta and the underlying tectonic processes and shallow and deep subsidence to which the delta ultimately responds.

It’s a pity that the folks who described in great detail the ontogeny of the largest delta in North America and who performed the forensic work on delta dysfunction were only recently invited to the planning table…after key restoration plans had already been drawn up. Better late than never, I suppose.

*Founding editor

**On April 22 Richard Burgess reported in The Advocate that the corps has agreed to divert more river water into the Atchafalaya Basin this month. This is ironic in that the extra water was requested by crawfishers and other commercial and recreational fishers, philosophical cousins of the river diversion opponents in southeast Louisiana.


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  23. VIDEO The wetlands around Buras, LA .

    This area was recently built by natural freshwater diversions near the end of the Mississippi River.

  24. Chris McLindon says:

    I was just made aware of the blog. Excellent and balanced post. Mandatory reading for this subject should be John McPhee’s 1987 New Yorker piece:

    The Atchafalaya is not the diversion. The lower Mississippi is the diversion. Nature wants to build new land at the mouth of the Atchafalaya. We should find a way to let it.

  25. Not sure if anyone has made the point, but water temperatures in New England are much colder and don’t give soil microbes the opportunity to break down larger chemicals… Doubt the study there can be compared to salt marsh here… One this is for sure, the sea levels are going to rise faster and Louisiana is going to lose its wetlands and salt marshes if massive Sediments and river water are not Diverted… personally I believe we have a great model to use to move forward from the Chesapeake bay area: We should partner with them, see here: “Morton responded by saying that they could not expect government to fix all the Bay’s problems. “There is a great need,” he said, “for a private-sector organization that can represent the best interests of the Chesapeake Bay. It should build public concern, then encourage government and private citizens to deal with these problems together.”

    The answer was not what the group had expected, but the words struck home to several of them. By 1967, the group, led by the late Arthur Sherwood, had formed and chartered the Chesapeake Bay Foundation to be that private sector voice working on behalf of the Bay. They recruited a Board of Trustees that represented a variety of interests from throughout the Chesapeake watershed. Perhaps most important, they adopted SAVE THE BAY™ as CBF’s motto and printed the first run of the distinctive blue-and-white bumper stickers that are now so common throughout the watershed.”

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  32. Kenneth Ragas says:

    As you know Len I have been involved in coastal restoration since CWPPRA began. I favor sediment pipelining over diversions because of my experience as a marine vessel captain. I have traveled the Venice Passes (Momma Natures diversions) for many years and witnessed the non deltaic process that has occurred in that area. That area which has flowed billions of gallons of river water has been in a constant state of erosion for decades. Why has that happened. All of the experts have the data collecting ability yet how can they be so naïve as not to do a study on what has actually been happening where these natural diversions have been flowing. I can send you data from satellite photos and maps which clearly illustrate the performance of the inability of the river to build land. How will diversions build land above sea level. David Muth talks about oak tree growing in X amount of years in the proposed diversion sites. This is foolish. Moving Grand Pass from Venice to Myrtle Grove is not only foolish it is idiotic. Unfortunately for the foolish academic dreamers “the truth stands alone”. You have had to have lived it in order to understand it.
    I get no monthly check except from SS so I have no grant $ or state/federal monthly check to influence my decisions.
    On another point, have you seen the latest data on the Wax Lake Outlet deltaic process. Up stream dedicated dredging has contributed 1.8 million cubic yards of material in the last 12 years. This distorted deltaic process is the main point of comparison used by the CPRA for the effective performance of Mississippi River diversions in the lower delta, what a crock.
    Ken, your old friend from Buras, La. God Bless

    • Ken-
      I appreciate the depth of your conviction and, as I acknowledge in the post, I’m an ecologist, not a geologist or a river expert.
      On the other hand, I have the highest respect for the quantitative, objective, peer-reviewed science that folks such as Harry Roberts, Mike Blum, Mead Allison, Ehab Meselhe, Paul Kemp and Tor Tornqvist, among many others, have been carrying out for years. Their painstaking research indicates that, given subsidence and sea level rise, our only hope for saving some of the delta rests on mineral sediments deposited free of charge by the river and gravity, not sediments artificially dredged and pumped at great expense.

      • Kenneth Ragas says:

        I could use Garrett Graves favorite comment when he doesn’t know the answer “they are misinformed”. Do you agree that actual data is available and should be included in the mix. I’m sure the COE can supply the sediment load and velocity in the Venice Passes. That’s all I’m asking for. I lost your personal email so if you would allow me to show you some comparative pictorial data via attachments it just may have a tinie weenie effect on your perspective.

        • Kenneth Ragas says:

          All of the above mentioned experts are ” misinformed”, they only have keyboard calluses not muddy shoes. If the river isn’t building land south of Myrtle Grove, how will it build land in Myrtle Grove? First grade logic. Unless some miracle is planned that I am not aware of.
          THIS IS FUN!!! Could dredging be the miracle.

  33. Thanks for the info Dr. Bahr. Just for clarification, what are the implications then for sediment diversion projects in the Master Plan? Also, above, you say that BP fines are the only possibility for funding on the horizon. Do you mean that these fines the only “confirmed” source of revenue for implementing Master Plan projects? Thanks again!

    • Jess-
      I’m not sure I understand your question about the implications for sediment diversions in the Master Plan but I think that they’re the most critical projects of the plan.
      In terms of funding, BP and Transocean have already ponied up some money that will be used for sediment diversions and barrier shoreline projects and a lot more should be coming within the next year or so. I don’t see much else except for the GOMESA revenue sharing money in 2017.

      • CMP2012 says:

        Thank you for the response. Let me further clarify my sediment diversion query. Do you think that this ‘new’ information on the problems associated with “river reintroductions” will have any bearing on how the CPRA goes about implementing future projects? Also, any idea where I can find the nitrogen study commissioned by the CPRA and the subsequent Garret Graves comments? Thanks again. Much appreciated.

  34. ed bodker says:

    Len, This is a nice post. You stress the importance of climate change issues and give a representative view of the diversion and nutrient discourse. Thanks for focusing on the technical aspects.

    There are many important details which could add to this discussion but the one I would like to mention here is that much more consideration needs to be given to the need to reduce nitrogen before it enters the natural environment. Diversions practical or not are dependent on sediment and we need sediment…no argument here. But the popular notion that wetlands assimilate nitrogen without negative consequences has ignored the fact that excessive nitrogen accelerates the rate of greenhouse gas production and emissions. There is a legitimate argument as to how much excess nitrogen shifts wetlands from sequestering to becoming a source of greenhouse gases. But in freshwater wetlands, there is no question that excessive nitrogen favors floating and annual species over emergent perennials. When these floating plants die on the water surface they typically decompose so fast there is little chance for methane and CO2 to become sequestered. Additionally, since they have little or no root structure embedded in a stable organic mat and then die during winter, the export of decomposing organic matter becomes an additional problem. As sea level rises, floating plants will become more predominant in the presence of high nitrogen. It seems to me that this is a negative cyclical dynamic that will grow as the globe discharges more and more human waste and agricultural fertilizers, which in turn will lead to more and faster releases of methane and CO2, which then will add to the greenhouse effect and accelerate sea level rise. In my opinion, nitrogen pollution is a major world wide problem that has not been sufficiently recognized by the environmental community. I think this topic should be at the forefront of our environmental concerns yet, I find people avoiding me when I raise the issue. Perhaps I’m not a good spokes person, but personality aside, the issue is important and its not given much, if any attention in the Master Plan.

    • Interesting thoughts, Ed. I understand that 1/2 of everything that our 7 billion global neighbors eat now was grown on synthetic nitrogen!

  35. Walt Sikora says:

    The Diversion critics, acting as Monday-morning quarterbacks can now easily point to “…the controversial Caernarvon freshwater diversion project built in 1992 as an example of how not to design and operate a river diversion project”. Where were they when geographer Woody Gagliano held the bully pulpit?

    The Caenarvon freshwater diversion project was never meant to divert sediment but rather as a remedy for Woody Gagliano’s fallacious, straw man crusade against “saltwater intrusion”, as if this was separate from subsidence and sediment starvation of the coastal marshes.

    • Walt-
      I agree that saltwater intrusion has always been a trumped up boogieman to justify marsh management projects!

  36. Len,
    I guess I concluded that over past centuries the river sediments that formed the rich adjacent farm lands and the natural levees that were part of the process,then aided,later, by building additional heights through mechanical processes thus formed compacted barriers for flood prevention, at the same time depriving the river sediments to build up the adjacent lands, resulted in the natural river sediments being trapped inside the river boundaries, thus forming the shoaling process that eventually resulted in mechanical dredging to prevent the buildup in the river channels necessary for shipping and docking.
    My conclusion was the use of mechanical(dredging) to pump over the levees into the wetlands, rather then let the accumulated sediments deposit into the gulf at the mouth of the river, which is costly any way you look at it.
    Just my opinion.
    Paul J. H, Jr.

  37. 5/13/13
    Pumped in River sediments is the next best approach to what occurred, naturally, for years on end to supply the rich fertile lands adjacent to the river creating natural levees and high elevations – ridges on both banks which results still today in rich citrus and sugarcane crops reaping the benefits of this farmland for generations.
    So, why not continue with the process through mechanical means to restore and replace what has been lost?

    • Paul-
      Two reasons: (1) enormous and prohibitive cost, given the scale of the problem; and (2) human designed subdelta lobes are highly unlikely to function and survive as well as those formed by Momma Nature.
      Remember that to date BP fines are the only funding source on the horizon.

      • Len,

        I’m a diversion advocate – but I think the best chance of using the river more agressively will hinge on a more detailed accounting of ALL costs and benefits over time.

        Perhaps I’ve missed something, but the only economic arguments I’m hearing appear to be end-of-stage, per unit cost comparisons. You get a somewhat different result when you consider the two land-building methods in the context of a time-discounted comparison of ecosystem service flows over time…at least that’s what I’ve found.

        I guess my point here is that the economics of land-building are not quite as simple as they are being potrayed. Time, location, and scale all matter and can shift the efficiency balance one way or another if appropriately accounted for.

        Sorry to hear about your ongoing health battles and I hope your on the rebound. I enjoy reading your comments on this very active blog.

        Take care,

  38. Where did you get Mark Davis’ quote on the nitrogen issue above?


  1. Latest Mississippi River Delta News: May 14, 2013 - [...] Saving the delta is a pipe dream sans sediment diversion projects. By Len Bahr, LaCoast Post. May 13, 2013.…

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