Losing Ground: Southeast Louisiana Disappearing Quickly

Land Loss in Southeast Louisiana

A Response to The Lens/ProPublica Publication Losing Ground: Southeast Louisiana Disappearing Quickly

By Chris McLindon [email protected]

The Lens and ProPublica have collaborated to produce an online publication that does an outstanding job of marrying dramatic visualization utilizing technology with a very personal level of story-telling. This type of approach makes the publication very accessible to the public and is to be commended for encouraging conversation about what is happening on the coast and what can be done about it. The dynamics of this approach would be even further enhanced by the incorporation of a broader objective scientific evaluation. So much of the public discourse on the coast consists of a rehashing and regurgitation of the same story lines that have been in the press for decades. The coastal restoration movement has been built up on those story lines, and there is an obvious reluctance to upset the apple cart by introducing new data or new perspectives. At the same time there are significant amounts of scientific research on the subject that have yet to be fully integrated into the public conversation. This compilation is offered as a basis to begin to incorporate a broader and more comprehensive scientific examination of the processes that have controlled the formation of the coast and ultimately will determine its future. I have attempted to reference every scientific work from which interpretation was derived, and I would encourage anyone reading this to seek out those sources and pursue their own research. I strongly encourage the exchange of ideas that a publication like this can bring about, and I would very much like to exchange ideas with anyone that is interested. Chris McLindon [email protected]

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Venice and West Bay

Any story that wants to create the impression that Southeastern Louisiana is rushing toward and early grave will focus attention on the birdfoot delta of the Mississippi River. It is the site of the most dramatic rates of land loss that have been experienced since measurement began in 1932. Rarely do these stories examine actual scientific causes of land loss and the logical explanations for the rate of loss. An accurate scientific examination would start with the observation that this delta is in fact the most recently abandoned delta of the set of historic deltas that built the coast. As Dr. Paul Kemp said in his 2013 study the river is contracting hydraulically. Since the lowermost Mississippi River has been constrained to stay within a channel that it would have abandoned in favor of the Atchafalaya under natural conditions, a back-stepping from the shelf-edge position of the Balize toward the former Plaquemines delta outlet of 1 ky ago is in progress 2

GAGLIANO 2003

The rate of submergence of historical deltas has been documented by a study of the St. Bernard Delta by Rogers, et.al. in 2009 at U.N.O. During the time of the Roman Empire this delta built out onto the shallow marine clays of Breton Sound. This delta was completely submerged within a period of 300 years after the peak of its formation, and its remnant deposits are now found more than 30 feet below sea level. The rate of subsidence that can be inferred for this delta is very consistent with the rates of subsidence seen today on the most recently abandoned delta. The birdfoot delta reached the peak of its growth almost 80 years ago, and it is on track to entirely submerge below the surface in a slightly faster timeframe than the St. Bernard Delta did. (reasons to be discussed) The reason for the rapid submergence of these more elongate deltas that they protrude out into shallow water and the superposition of the dense deposits of sand at distributary mouth bars onto the ductile marine clays introduces a mechanism of subsidence that is additional to the broader effects of crustal downwarp and fault movement that affect the rest of the coast. The clays flow laterally out from under the weight of the sand creating mudlumps that poke up around the edges of the delta.

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9%

8%

83%

The birdfoot delta is the most rigorously evaluated area of significant land loss in coastal Louisiana. A research group at U.N.O. that included Shea Penland evaluated the causes of land loss in this area and attributed the overwhelming majority of loss to submergence, which is the combination of subsidence and sea level rise. This is one of the more intensively drilled areas of the coast, and the direct removal of the marsh by the dredging of oil and gas canals accounts for 9% of the total loss. Stories of about land loss in coastal Louisiana rarely emphasize that the loss is almost entirely natural and due to submergence. The small amount of erosion that does take place around the fringes of the delta is probably over estimated because some portion of the loss (perhaps 50%) in the areas attributed to erosion is also due to subsidence in those areas.

Area 1

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Fearnely, S. et.al., 2001, Mapping the Geomorphology and Processes of Coastal Land Loss in the Pontchartrain Basin: 1932 to 1990 and 1990 to 2001, Journal of Coastal Research, No. 10054, p. 48-58

The principal reality of land loss in coastal Louisiana that is never discussed in any story about the wetlands may be characterized as the most significant anthropogenic effect of the last two centuries. Tweel and Turner examined the combined effects of agricultural land use across the Mississippi River basin and the construction of locks and dams on the upper Mississippi and Ohio Rivers. The advent of agriculture in the early nineteenth century, and the inefficient practices that led to massive soil erosion throughout the sod-busting era dramatically increased the sediment load of the Mississippi River. As might be expected this rise in sediment load was manifested as a dramatic increase in sediment reaching the marshes at the terminus of the river system. Tweel and Turner showed the rate of land creation in the birdfoot delta increased with this artificial increase of sediment load, and by logical extension it may be assumed that all coastal wetlands that had access to the floodwaters of the Mississippi during this time would have experienced a similar anthropogenetically-induced rate of growth. The improvement of farming practices and the construction of locks and dams in the upper reaches of the river system have caused a dramatic decrease in the sediment load of the river since the peak of land-building (which is ironically coincident with the advent of aerial photography in 1932 our baseline of normality is in fact a period of artificial inflation of the marsh)

Tweel, A.W. and Turner, R.E., 2012, Watershed land use and river engineering drive wetland formation and loss in the Mississippi River birdfoot delta, Limnology and Oceanography, v. 57, p. 1828

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In addition to undergoing hydraulic contraction in the early stages of abandonment, as described by Kemp, the dramatic reduction of sediment load being delivered to the lower reaches of the river has rendered it effectively incapable of building new land. In is 2012 study Allison determined that As much as 44% of the annual total suspended sediment load and 80% of the sand load of the Mississippi + Red Rivers was sequestered between the Old River Control Structures and the MississippiAtchafalaya exits to the Gulf of Mexico in flood years 2008 through 2010. meaning that it did not reach the delta. Allison concluded that The results of the present sediment budget suggest that only a relatively small proportion of the upstream sediment load is available for coastal restoration approaching the Gulf. Kolker conducted a detailed study of the West Bay Sediment Diversion in particular and concluded that In order for land to build in West Bay, sediment deposition must first infill the bay, where depths range from 0 to 3 m. Assuming a linear balance between water depth, RSLR, and sediment deposition rates, it would appear unlikely that large areas of new land would develop in West Bay over a time scale of less than a few decades. The lower Mississippi River has been effectively abandoned. Nature wants to build new land at the mouth of the Atchafalaya River. A recent study by the Corps of Engineers found that as much as 70% of the bed load sediments of the river (with which it builds new land) are already flowing down the Atchafalaya. It is hopeless that diversions of the lower Mississippi will be capable of building new land.

Allison, M.A., et.al., 2012, A water and sediment budget for the lower MississippiAtchafalaya River in flood years 20082010: Implications for sediment discharge to the oceans and coastal restoration in Louisana, Journal of Hydrology, v.432433, p. 8497

Kolker, A.S., et.al., 2012, Depositional dynamics in a river diversion receiving basin: The case of the West Bay Mississippi River Diversion, Estuarine, Coastal and Shelf Science, v. 106, p. 112

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Buras

It is a common theme in reporting about the coast to appeal to heart-rendering stories about names being taken off of maps as various geomorphic features subside below the surface. The real sadness in these stories is the underlying disconnect that we have with the natural processes of the coast that would lead us to expect that any one of them would have any permanence. It is very likely that the native people that inhabited the St. Bernard Delta gave names to its many bays and bayous. Chances are they also lived in a balance with nature that would have prevented them finding sadness in the natural processes that submerged the land of their heritage. We have moved backwards in maintaining balance with nature since then. The beauty of the Buras area is that if provides a textbook example of mechanics by which the subsidence of most coastal marshes takes place the vertical movement of faults.

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The Empire and Bastian Bay Faults are well established as fundamental geologic features of the Louisiana coastal plain. Gagliano documented the effects of the vertical movement of these faults on the marsh at the surface. Faults have been the primary mechanisms of subsidence across south Louisiana for millions of years. The downward vertical movement along the fault is expressed as a subtle rotation of the marsh surface such that maximum subsidence occurs along the trace of the fault and the marsh surface slopes inward toward the subsided area. It is the induced slope of the marsh surface that is the primary means of saltwater intrusion into the interior marshes. The upthrown side of the fault trace is relatively unsubsided and has experienced only minor land loss since 1932. While this is the classic example of subsidence due to faulting, nearly all wetlands loss on the coast occurs in this way.

Gagliano, S.M., et.al., 2003, Neotectonic framework of southeast Louisiana and applications to coastal Restoration, Trans. G.C.A.G.S., v. 53, p. 262272

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Gagliano documented the characteristics of subsidence due to faulting in this textbook example. Vertical movement on the fault creates a visible scarp at the surface which defines the sharp northern boundary of the open body of water he called a fault bay and which is formed by the subsidence of the marsh. The deepest portion of the bay is immediately adjacent to the fault, and the marsh surface slopes up and away from the fault to a area of relatively unsubsided marsh to the south. A comparison of aerial photographs shows that the northern area of marsh on the upthrown side of the fault is also relatively unaffected by subsidence and has not changed much over the past several decades. Gagliano undertook an exercise to calculate the volume of sediment that might be required to fill in the subsided area, but that calculation does not take into account the fact that the area is continually subsiding, and any emplacement of sediment into the fault bay would be immediately affected by subsidence, and would very likely subside below the surface within a matter of decades. This is the fallacy of the concept of marsh creation in these high subsidence areas.

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Texaco Canals

The area referred to as Texaco Canals is so because of the canals dredged for the drilling at the Lafitte oilfield. The common perception that once the oil companies come in and started dredging all the canals, everything just started falling apart can best be understood by examining the relationship between the dredging of the canals and land loss. The most commonly held conception is that the canals allowed for saltwater intrusion into the marsh, which caused erosion of the marsh and subsequent land loss. A simple examination and comparison of this area and an adjacent area to the north and west makes it difficult to substantiate this model. The more scientifically plausible explanation is the correlation of the canals and land loss by the causal links that both have with faults that cross the area.

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Morton, R.A., et.al., 2010, Quantifying large-scale historical formation of accommodation in the Mississippi Delta, Earth Surface Processes and Landforms., v. 35, p. 1625-41

Just like the Empire and Bastian Bay Faults, the Lafitte and Magnolia Faults are fundamental components of the structure of the coastal plain. These faults control the location of the Lafitte and Magnolia oilfields respectively at depth, but they also have a marked expression at the surface. The same mechanisms of fault movement causing subsidence are responsible for land loss here as they were in the Buras area. Mortons 2010 study of the role of subsidence in creating accommodation space for the accumulation of delta deposits as a part of the delta cycle showed the subsidence that created the open bay developing in Bayou Perot. A cross section of shallow cores reveals a layer of marsh deposit that has remained intact as it subsided to create the bay. Had this land loss been caused by erosion, it would have cut into the marsh layer.

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Core section


Barataria Comparison Area

Many of the conclusions drawn in reporting about the coast are made on the basis of relatively narrow areas of examination usually focused on those areas that have experienced the most dramatic land loss. A broader, more scientifically accurate examination of the coast reveals that there are significant portions of the marsh that have not experienced much land loss, and in which the marsh is a relatively healthy ecosystem, and largely unchanged over several decades. One such area is just north and west of the Texaco Canals area, and has been designated the Barataria for this examination

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The effect of the subsidence caused by the Lafitte Fault is even more apparent when compared to the area to the north, where there is little active surface faulting, and consequently relatively minor amounts of subsidence and land loss have occurred over the past several decades. What is also apparent is that the amount of dredging of oilfield canals is roughly equivalent in the area to the north of the fault. Canals for the Barataria, Delta Farms and Bayou de Fleur Fields have been responsible for direct removal of the marsh, but there is little collateral land loss that should be apparent if the saltwater intrusion/erosion models or the weight of the dredge spoils causing subsidence model were accurate. The truth is that the land loss that has occurred in the Texaco Canals area is a result subsidence caused by vertical movement on the same fault that controls the location of the Lafitte Field. The fields to the north do not have major controlling faults that cut to the surface, and therefore do not have significant land loss that should be associated with dredging in the fields if either of commonly accepted explanations for land loss caused by oilfield canals were accurate

Lafitte Field

Delta Farms Field

Barataria Field Bayou de Fleur Field

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What the examination and comparison of this set of fields and their relative relationships to faulting and land loss dramatically underscores is the correlative relationships between faulting, oil fields and land loss. There is a strong causal relationship between faults and the location of oil and gas fields. Nearly all major faults have oil and gas fields associated with them. It is the vertical movement of faults that provided the accommodation space within which the sand layers that make up the reservoirs were deposited. The faults also commonly act as a trapping mechanism for accumulations of oil and gas, and are likely to be the conduits by which hydrocarbons migrated into the reservoirs from greater depths. Although only two examples have been shown so far, faults are also primarily responsible for subsidence and loss of wetlands at the surface. Every major hot spot of land loss can be directly tied to a major fault system that cuts to the surface. Because the faults control the location of the fields and faults control where wetlands loss is occurring, there is an apparent, but non-causal, correlation between where canals were dredged to drill the fields and where land loss is occurring. This observation does not mean that direct removal did not result in some measure of land loss, it obviously did. What it does say is that the intentional attempt to blame a broader scope of land loss on dredging serves no purpose. In order to deal with the issue of land loss the model to explain how it is caused must be scientifically accurate. If there is an insistence on a model that invokes dredging as a primary cause of land loss for some reason other than scientific accuracy, then that insistence will result in a diminished ability to properly understand and deal with the issue of land loss.

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Leeville

While there is invariably a reference to the oil and gas field canals in the area it is hard to escape the reality of subsidence when reporting on the area of lower Lafourche Parish around Leeville, and most stories usually do a fair job of capturing that reality. The area around Leeville is perfect for integrating one of critical methods by which subsidence is measured into the conversation historical tidal gauges. Tidal gauge data provides a direct measurement of the rate of subsidence across the lower coastal plain, and some simple math reveals what the cumulative effect of those rates has been over time, and what it will be projecting into the future.

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1932

470 mm = 18.5 total relative sea

level rise since 1932

sea level rise

subsidence

One of the most reliable ways to observe the effects of subsidence over a period of decades, and to begin to assign it a numerical value is the historical record of tidal gauges. The daily recordings of tidal gauges are elevations of the high and low ranges. It is well established that the global rise in sea level can be seen in historical tidal gauge records all over the world. Graphing the of tidal range over a long enough period of time reveals a sloped line that is the relative rise in sea level. The slopes of these lines can be different for different areas, and it has been determined that the more steeply sloping lines on tidal gauge graphs are due to subsidence. The slope of the Grand Isle gauge is greater than the slope of the Pensacola gauge over the same period of time. It turns out the Pensacola is on a very stable ridge crossing the Florida Panhandle, and it is not effected by subsidence. The slope of the Pensacola graph is very close to the accepted value for global sea level rise. The Grand Isle gauge on the other hand slopes more steeply, and the difference in slope between these two gauges is due to subsidence at Grand Isle. In this way the tidal gauge records can be used to get a measurement of subsidence. In the case of Grand Isle it has experienced 470 mm or 18.5 inches of relative sea level rise since 1932, most of that being due to subsidence.

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Blum, M.D. and Roberts, H.H., 2012, The Mississippi Delta Region: Past, Present, and Future, Annual Review of Earth and Planetary Sciences, v. 40, p. 655683

Penland, S., et.al., Relative Sea Level Rise and Delta-Plain Development in the Terrebonne Parish Region, Louisiana Geological Survey, Coastal Geology Technical Report No. 4, 121 p.

A research group led by Shea Penland of U.N.O. examined the tidal gauge records for the stations in this area. The black dots show the locations and names of the gauges. The numbers are the estimated rates of subsidence for each gauge in millimeters per year. The colored lines are the contours of subsidence showing a pattern of high subsidence across the interior marshes, which diminishes toward the coastline. There have been significant advances in the technology of measuring subsidence in recent years including measuring changes in elevation, and therefore subsidence velocities, using GPS. It may turn out that the estimates of subsidence rates derived from tidal gauges will be corrected to some extent by advancing technology, but the relative pattern of change will not change. This map clearly shows a belt of relatively high subsidence across central Terrebonne and Lafourche Parishes.

6.3

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8 per decade

Overlaying and slightly adjusting the colored contours from Penlands map onto the fault trace map shows a very clear relationship that documents the subsidence of the coastal marshes due to the downward movement of active faults. It makes perfect sense that areas downthrown to the active faults would be experiencing the highest rates of subsidence, and that the effects of that subsidence would be evident in the land loss that has occurred in the area. On this map the rates of subsidence estimated from the tidal gauges has been converted to inches per decade. The cumulative effect of these values over several decades is obvious, and it is consistent with the depth of the open bodies of water in the highest subsidence areas. Some areas may have subsided by as much as 4 feet since 1932.

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The colored patches, that have been called hot spots of land loss across the coastal wetlands, have an obvious causal relationship with the traces of the active faults. Once the supply of freshwater and sediment flowing into the network of bayous from the Mississippi River through Bayou Lafourche was cut off in 1904, the downward movement of the faults was no longer matched by the addition of new sediment at the marsh surface. Subsidence of the marsh surface due to faulting began to have an effect in the beginning of the twentieth century, but that effect could not be reliably measured until the advent of aerial photography in 1932, which is why land loss figures are quoted from that year. There are several ways that subsidence can be observed, but it turns out that getting very accurate measurements of subsidence values has been technologically challenging. The subsidence experienced at Leeville is a combination of the movement of faults and downwarping of the basin the have formed called the Terrebonne Trough

8 per decade

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Proposed Sediment Pipeline

Marsh Creation Areas

Proposed Morganza-to-the-Gulf Levee

This is the extent of the proposed Morganza-to-the-Gulf Levee and the proposed sediment pipeline and marsh creation projects. The Advocate reported on June 17, 2014 that a report released by the U.S. Army Corps of Engineers revised the cost estimate for the levee project upward to $12.9 billion, a dramatic increase from the $887 million estimate when the project was authorized by Congress in 2007. The initial estimated cost for the sediment pipeline is $1 billion. As is true for nearly all coastal restoration projects, the rates of subsidence due to faulting in the area, which can be seen by comparing this with the previous pages, make it virtually impossible to build and sustain either the levee, as it is currently proposed, or the marsh creation areas. Coastal restoration and protection projects of this kind are not only staggeringly expense, they have no realistic hope in their attempt to push back against the forces of nature. They would be subsumed by the subsidence almost as soon as construction was finished. 20


Bayou Penchant Comparison Area

Another area that should be considered for comparison with the high land loss areas is north and west of the area just evaluated, outlined in yellow and named the Bayou Penchant area here. A map presented on page 26 shows that the trend of major faults cutting the surface of the marsh stretches in a WSW-ENE orientation across the coastal plain. The demarcation of that trend is obvious here even with out the overlay of the fault traces. Marshes to the north of the line are not subsided and have not experienced significant land loss. This was true for the Barataria area and it is true for the Bayou Penchant area.

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Bayou Penchant Field

Bayou Penchant Field

The oil and gas fields in this area are outlined in red on the maps. Bayou Penchant Field is of particular interest because it is one of the larger fields in the area, and all of the wells in the field were drilled from dredged slips. It is also of interest because the field produced from very large reservoirs that are characterized as classic pressure depletion reservoirs, meaning that the reservoir pressure depleted over time as the gas and condensate were removed. In the largest such reservoir the operator of the field installed large compressors that were used to draw down reservoir pressure even further to recover hydrocarbons. At the end of its life the produced reservoir had a pressure of 500 psi, virtually a vacuum for a large reservoir at depth. If there were ever a case where the production of hydrocarbons should be expressed at the surface by subsidence, this should have been it. There has in fact been no measurable subsidence at the surface because the faults that control the location of the field do not cut to the surface. The large fault systems in the area that do cut to the surface are north and south of the field area, and they show the land loss due to subsidence that would be expected from the vertical movement of faulting. Bayou Penchant is also another example of a field in which the direct removal of marsh by dredging did on lead to additional land loss, as the erosion model would require.

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Delacroix

The reference to oil and gas drilling in reporting on land loss in the Delacroix completely misses the point. There have been relatively few wells drilled in the area, but the Delacroix stands alone as an example of the accelerated rate of land loss that has occurred over the past decade. A cursory examination of the U.S.G.S. Land Loss Map reveals an obvious concentration of land loss exclusively in the Delacroix area whose purple color indicates it has occurred within the last decade. The staggering irony of this is land loss is the inescapable conclusion that it has been caused by the Caenarvon Diversion. For all the discussion of oil and gas drilling the single biggest cause of land loss over the past 30 years has been a coastal restoration project.

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Caenarvon Diversion

The Caenarvon was never intended to be a land-building diversion. The original intent was to try to reverse the effects of saltwater intrusion be reconnecting the river with the marsh. The fallacy of this thinking was two-fold. The progression of change from freshwater marsh to saltwater marsh is part of the natural evolution that has been occurring due to subsidence in the coastal plain for millennia. The St. Bernard Delta that once extended past the Chandeleur Islands went through the progression from freshwater to saltwater marsh to open bay, and is now 30 below sea level. It was foolish to interfere with this natural process. Secondly, the river water is loaded with excess nutrients from upstream agriculture. This nutrient-loaded freshwater is effectively toxic to the salt marsh.

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Several very prominent scientists, including Eugene Turner at L.S.U. have been very clear in their interpretation of the detrimental effects of diversions on the marsh. In short the nutrients weaken the root bases of the marsh grasses and they are ripped up during hurricanes. The map from a different study by Turner shows the area of dramatic land loss in red represented by the top photograph, and the area of reference or control marsh outlined in yellow, and represented by the lower photograph. A conservative estimate puts the land loss caused by the Caenarvon Diversion at 40 square miles. The photographs were published by John Burras. Turner and his group summarized their evaluation of diversions in their 2011 study as follows: Ultimately, the scientific basis for river diversions needs to be more convincing before embarking on a strategy that may result in marshes even less able to survive hurricanes. The evidence indicates that diversions not only fail to conserve mature brackish and tidal freshwater marshes, but disrupt plant physiology in ways that endanger individual plant vigor and overall marsh survival. In this regard, there is no better illustration than the Hypoxia Zone of what high nitrogen levels can do to delicate nutrient balances evolved over millennia in nitrogenlean ecosystems, and the daunting challenges for reversing that damage. Kearney, M.S., et.al., 2011, Freshwater river diversions for marsh restoration in

Louisiana: Twentysix years of changing vegetative cover and marsh area,

Geophysical Research Letters, v.38, p L16405

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The superposition of the known surface fault traces onto satellite imagery clearly shows the delineation of the areas of high subsidence that are being converted to open water. The land loss associated with this conversion is shown on the next page. The New Orleans East Land Bridge is associated with another set of faults that arguably have deeper and more tectonically significant roots. This fault system is part of a large system that extends up to Baton Rouge. Effects of faults in this system have been studied in Lake Pontchartrain by John Lopez, and are examined in a study of Goose Point on the north shore of the lake by Kathy Haggar. Haggars study will be published in the October 2014 transactions of the G.C.A.G.S. It is significant because like much of the New Orleans East Land Bridge, there is no other viable explanation for land loss at Goose Point other than subsidence due to faulting

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Fearnely, S. et.al., 2001, Mapping the Geomorphology and Processes of Coastal Land Loss in the Pontchartrain Basin: 1932 to 1990 and 1990 to 2001, Journal of Coastal Research, No. 10054, p. 48-58

27%

9%

64%

Although reporting in the popular press commonly holds up land loss in the New Orleans East Land Bridge, and adjacent Central Wetlands Unit as an example of coastal erosion, the Penland group attributed the majority of the loss to submergence. The more significant value attributed to direct removal is almost entirely due to the dredging of the M.R.G.O. and the Intercoastal Waterway. Contrary to popular belief, the U.N.O. team did not attribute any additional land loss to saltwater intrusion caused by the M.R.G.O. An examination of this area reveals that the land loss which is attributed to submergence has been caused primarily by subsidence due to the vertical movement of faults.

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Dixon, T.H., et.al., 2006, Subsidence and flooding in New Orleans, Nature, v. 441, p. 587-588

This area is of particular interest because recent developments in technology that have allowed for the direct measurement of subsidence velocities using GPS have been applied here. The rates of subsidence range up to the values of over 20 mm/yr that were measured using tidal gauge data on the downthrown side of the Golden Meadow fault north of Leeville. The use of this technology requires measurement from dry land surfaces, so the points in the marsh are somewhat scattered, but it is clear that the highest rates of subsidence are across the Landbridge and in the Central Wetland Unit.

Subsidence in mm/yr

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Dokka, R.K., 2011, The role of deep processes in late 20th century subsidence of New Orleans and coastal areas of southern Louisiana and Mississippi, Journal of Geophysical Research, v. 16, B06403, 25 p.

Roy Dokka of L.S.U. did the foundational work in this area on the relationship between subsidence and faulting. In his 2011 study he published a map of two principal faults that are a part of the larger fault system shown earlier. Dokka was able to document variations in the subsidence velocities measured by Dixon across the area due to faulting, meaning that the faults are clearly active and causing the subsidence that is resulting in land loss in the area.

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By color-filling Dixons subsidence map to emphasize the areas of maximum subsidence revealed by the scattered readings, and overlaying the traces of the faults mapped by Dokka, the relationship between the patterns of subsidence and the faults is more obvious. All of the significant land loss that has occurred in this area is within the outline of maximum subsidence. That subsidence is due to faulting.

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Fort Proctor stands as a measurable documentation of the effects of subsidence. The fort was constructed at Proctor Landing in 1865, but never used. Historical documents show the fort was positioned 150 from the shoreline, and based on comparison with other forts around the Gulf, it was almost certainly at least five above sea level at the time of construction. The fort is now in Lake Borne, and the foundation is about four feet below sea level. The implied rate of subsidence is very similar to the values measured in 2006 by Dixon. A logical extension of the area of maximum subsidence that has been measured by GPS is shown in red dashed outline. The green outline is the marsh creation project being undertaken by Ecosystem Investment Partners. This project will be subject to nearly the same rates of subsidence that have been experienced across the area resulting in the burial of the barrier islands, the submergence of the cypress swamps in Breton Sound, and the sinking of Fort Proctor, and the mud flats created by the project will very likely be submerged below sea level in less than 20 years.

Dixon Area of Maximum

Subsidence ~ 8 inches per decade

Ecosystem Investment Partners

Marsh Creation Project Outline

Fort Proctor

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The visually stunning online publication by The Lens and ProPublica provides an excellent jumping off point for a conversation on coastal land loss in Louisiana. To fully make sense of what is apparent in the imagery there must be a more thorough and comprehensive integration of the science that explains the changes that are occurring. It is important to appreciate that the technological advancements that made these visualizations possible have also provided an opportunity for people the experience the changes taking place in a natural system for the first time in a way that is within the range of our perception. Consider two other natural settings: I recently took a vacation on the beaches of Pensacola. The day we arrived there was a configuration of the sand bars that made it perfect for our family. Instead of the bar being 100 yards offshore, as is often the case, it was about 10 yards off the beach and was exposed most of the time. We could put our chairs on the bar and be near the surf without being in the traffic of people walking along the beach. My granddaughter could play in the shallow lagoon formed behind the bar without being in the surf. I loved this configuration, but I intuitively knew that it would not last. It was going to change, and very possibly it could change with one storm while I was there. On another vacation I went to the Smoky Mountains. To me they looked exactly the same as they had they year before, and as they had twenty years before that. Within the range of my perception the mountains were permanent and unchanging. The thing is that the Smoky Mountains used to look like the Himalayas, and one day they will be a flat plain. The mountains are changing every bit as much as the sand bars, the only difference was my ability to perceive the change. The same is true of the coastal plain of Louisiana. We all intuitively tend to think of the marshes and bayous and bays to be permanent features of the earths surface, just like the mountains. The truth is they are much, much more like the sand bars on the beach. What the visualization of this publication has done is to allow us to experience the changes occurring to the coast in a timeframe that we can perceive. In the same way the we expect the sand bars to change their configuration with every passing weather system, we should learn to expect that the coast of Louisiana is going to change with the natural progression of the delta cycle. The changes that are occurring across the coast are almost entirely natural. The fundamental geologic forces that control the mechanics of subsidence and the delta cycle are much greater than any engineering system that humans could contrive to try to affect them. The people that insist on telling a story about the magnitude of human impacts on the coast are doing so with an agenda in mind. If I can be made plausible that humans caused the changes to the coast, then it is believable that humans can reverse the effects of those changes. That will require money, and it is the money that ultimately pushes the agenda.

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Commetary

Documents

Losing Ground: Southeast Louisiana Disappearing Quickly