LOUISIANA: They’re trying to wash you away

News Analysis by Kip Hansen

 

Jean_Lafitte_map_420Jean Lafitte, Louisiana, is situated at two feet above sea level and about ten miles south of New Orleans.   It has the misfortune to sit just outside of the protective system dykes and levees that keep New Orleans from flooding.

John Schwartz, at the New York Times, writes about “the ecological crisis facing Louisiana’s vanishing coast” in “Left to Louisiana’s Tides, a Village Fights for Time”, a long narrative magazine piece relating the struggles of this small town to save itself from what appears to be the ultimate fate of much of the Mississippi Delta:

“Saltwater intrusion, the result of subsidence, sea-level rise and erosion, has killed off the live oaks and bald cypress. Stands of roseau cane and native grasses have been reduced to brown pulp by feral hogs, orange-fanged nutria and a voracious aphid-like invader from Asia. A relentless succession of hurricanes and tropical storms — three last season alone — has accelerated the decay. In all, more than 2,000 square miles, an expanse larger than the state of Delaware, have disappeared since 1932.”

“….Just two miles north is the jagged tip of a fortress-like levee, a primary line of defense for greater New Orleans, whose skyline looms in the distance. Everything south of that 14-foot wall of demarcation, including the gritty little town of Jean Lafitte, has effectively been left to the tides.”

The Times’ piece lays out the emotionally rending story of this small bayou fishing village’s political attempts to somehow, anyhow, get itself included inside that 14-foot tall fortress-like system of levees that protect New Orleans from the  rise and fall of the tides, storm surges and seasonal  floods that relentlessly eat away at the coasts along the Gulf of Mexico.

levees_800

FULL SIZE image

Schwartz asks:

“Jean Lafitte may be just a pinprick on the map, but it is also a harbinger of an uncertain future. As climate change contributes to rising sea levels, threatening to submerge land from Miami to Bangladesh, the question for Lafitte, as for many coastal areas across the globe, is less whether it will succumb than when — and to what degree scarce public resources should be invested in artificially extending its life.”

Isn’t it a shame, what the river has done to this poor crackers’ land?

What has happened here?   Where has all that land gone, and why?  According to the US Geological Survey:

“The swamps and marshes of coastal Louisiana are among the Nation’s most fragile and valuable wetlands, vital not only to recreational and agricultural interests but also the State’s more than $1 billion per year seafood industry. The staggering annual losses of wetlands in Louisiana are caused by human activity as well as natural processes. U.S. Geological Survey scientists are conducting important studies that are helping planners to understand the life cycle of wetlands by detailing the geologic processes that shape them and the coast, and by providing geologic input to models for mitigation strategies.”  – S. Jeffress Williams, U.S. Geological Survey

What are these forces that are causing the demise of the Mississippi Delta?

USGS and other studies indicate that major shifts in the course of the Mississippi River have contributed significantly to the demise of the wetlands.

“The 300 kilometer-wide Mississippi River delta plain and its associated wetlands and barrier shorelines are the product of the continuous accumulation of sediments deposited by the river and its distributaries during the past 7,000 years. Regular shifts in the river’s course have resulted in four ancestral and two active delta lobes, which accumulated as overlapping, stacked sequences of unconsolidated sands and muds. As each delta lobe was abandoned by the river, its main source of sediment, the deltas experienced erosion and degradation due to compaction of loose sediment, rise in relative sea level, and catastrophic storms. Marine coastal processes eroded and reworked the seaward margins of the deltas forming sandy headlands and barrier beaches. As erosion and degradation continued, segmented low-relief barrier islands formed and eventually were separated from the mainland by shallow bays and lagoons.”  —  Louisiana Coastal Wetlands: A Resource At Risk

There is a nicely done, if simplistic, animation that illustrates some of the problems with the Delta at interactive-earth.com:  How Have We Changed the Delta? (requires Flash).  Here’s a few stills from the animation so we can see the situation today:

How_We_Changed

In words, from the American Museum of Natural History in NY City,

Disappearing Delta:   Humans have upset the delicate balance of land gain and loss in the Mississippi River Delta. Dams, levees and channels along the Mississippi have prevented land-forming sediments from reaching the delta, and most of those that do are discharged deep into the Gulf of Mexico. Meanwhile, old land continues to compact and erode, a process aggravated by human activity. As a result, over the past 75 years, almost 5,200 square kilometers (2,000 square miles) of wetlands, which once sheltered coastal cities from storms, have been lost to the ocean.”

Here’s the long-term historical perspective on the Mississippi Delta:

Through-the-ages

Today’s delta comprises the darkest black portions of the image. The graphic is organized from the smallest area to the largest, dark to light.   The Delta has grown and shrunk over the last 6,000 years — and appears to have been at its historical largest limit about 3,000 years ago.  Change in the Delta seems to be the constant, the rule, and not the exception.

The Times’ article draws parallels between the Mississippi Delta and both Miami and Bangladesh.  Long-time readers here know the story with Miami, it is a disaster-in-waiting, and  Bangladesh  is the delta of a major Asian river system, diked and bermed and no longer being renewed, continually sinking below the level of the sea and rivers.

The Times’ Schwartz  comes on strong about Sea Level Rise:

“…the master plan’s authors adopted far more pessimistic forecasts of the impact of climate change. They effectively doubled their previous 50-year projections for likely sea level rise to more than two feet, the highest rate in the country, according to the National Oceanic and Atmospheric Administration.”

The link goes to NOAAs Sea Level Trends map, which shows two nearby tide gauges that show a trend of around 9 mm/yr (3  ft/century) of ….. relative sea level rise.  Yes, that it perfectly correct, USGS also blames many of the Delta’s problems on changes in relative sea level rise.

Reminder:  “The mean sea level (MSL) trends measured by tide gauges that are presented on this web site are local relative MSL trends as opposed to the global sea level trend.  Tide gauge measurements are made with respect to a local fixed reference level on land; therefore, if there is some long-term vertical land motion occurring at that location, the relative MSL trend measured there is a combination of the global sea level rate and the local vertical land motion.”

Relative sea level is the only sea level of concern to local residents and planning officials — it is where the sea meets the land at that spot.  Local relative sea level rise (or fall) is the surface of the sea getting higher (or lower) in relation to the land.

Yet the Times’ Schwartz keeps referring to sea level rise caused by climate change.  It fascinates me that Schwartz is allowed (or forced) by his editors to keep going on about climate-change-caused sea level rise yet somehow he actually never makes the distinction between changes in local sea level caused by subsidence and compaction of the land — the land sinking — and the type of sea level that can be caused by climate change — Absolute Sea Level and its rise or fall.  Schwartz does not quantify Absolute Sea Level rise at all.

So what’s the real deal here in the Mississippi Delta?  The USGS and NOAA both tell us the land is sinking — this is subsidence caused by the pumping of petroleum (and water) out from under the Delta and compaction of the sediments that make up the land.

In order to understand how much the surface of the Gulf of Mexico is rising, we have to have two things: a reliable measurement of the relative change between some point of land and the surface of the Gulf, which we can get from a good Tide Gauge, and a reliable measure of how much the land at that same point is moving up or down.   The nearest Continuously Operating GPS Reference Station at a Tide Gauge (CORS) is at nearby Dauphin Island:

Lousiana_Delta_800

C. Letetrel et al. (2015) — “Estimation of vertical land movement rates along the coasts of the Gulf of Mexico over the past decades” gives us the two figures from “13 years of data from January 1995 to December 2010.”  At Dauphin Island, the relative sea level is rising about 3 mm/yr.  The land, however, is sinking at a rate of 4.2 mm/yr.  The result for rate of Absolute Sea Level Rise is minus 1.26 mm/yr — at Dauphin Island, the surface of the Gulf of Mexico is not rising at all, it is falling.  Now, if you’ve been following my series here, Sea Level: Rise and Fall,  or Dr. Curry’s series at Climate Etc., you are well aware of the fact the sea level doesn’t rise evenly everywhere — so we can’t assume that the surface of the Gulf is falling at all points along the Gulf Coast.  The same paper supplies a usable answer:

“We corrected the tide gauge records from the vertical land rates and estimated the absolute sea level rise [averaged along the US Gulf Coast]  to be of about 2.07 (± 0.4) mm/yr. This value is comparable to the global absolute sea level rise estimates over the last 50 years (Church and White,2011): 1.970.4 mm/yr over the period 1961–2009.”

That makes about 100 mm over the 50 year period, or about 4 inches (or about 8 inches per century).  There is nothing unusual about Absolute Sea Level Rise in the Gulf of Mexico — and at the Delta, the surface of the Gulf may even be falling — not rising at all.

So there may be a small contribution of the rising sea to the problems of the Delta but this is comparatively tiny when weighed against the effects of subsidence, compaction and erosion all compounded by the total lack of soil replenishment.

What has happened down here?

watershedMan is losing yet another battle against Nature.  The Mississippi River carries water from 1,245,000 square miles (3,220,000 km²) of its watershed which extends all the way up into parts of Canada  in the northwest and southern NY State in the northeast.

This river system has experienced tremendous flooding — the Great Flood of 1927 being the most recent mega-flood.   It was that flood that prompted a massive engineering project:

“Following the Great Flood of 1927, the US Army Corps of Engineers was charged with taming the Mississippi River. Under the Flood Control Act of 1928, the world’s longest system of levees was built. Floodways that diverted excessive flow from the Mississippi River were constructed.  While the levees prevented some flooding, scientists have found that they changed the flow of the Mississippi River, with the unintended consequence of increasing flooding in succeeding decades. Channeling of waters has reduced the absorption of seasonal rains by the floodplains, increasing the speed of the current and preventing the deposit of new soils along the way.” – Wiki

That project, initiated 90 years ago, is the cause of the little village of Jean Lafitte’s problems today.  The Great Mississippi is literally washing Jean Lafitte away — the river’s replenishing soil loads are being washed far out into the Gulf instead of being captured by the vegetation of the Delta.  The barrier islands that in the past have been replenished each flood season have diminished and been washed away by Gulf storms — a reiterative process of erosion, death of the swamp and  marsh, and more erosion as storms keep coming.   After Hurricane Katrina, the Delta got a ten year streak of good luck and a chance to recuperate, but the 2017 hurricane season was harsh and extremely damaging.

The Mississippi Delta has further been damaged the dredging of canals to facilitate oil drilling and oil pipelines that crisscross the delta.  Traffic on the canals causes boat wakes that eat away at the banks of the canals, widening them year after year.  Almost everything that moves in the Delta moves on boats. The wider canals are subject to more wind chop which further erodes the banks, especially when storms come.  We want the oil but it comes at a terrible cost for the Delta.

Is there a solution?  Can Jean Lafitte and the Delta be ultimately saved?  Should it be saved? If so, at what cost?  These are questions that cross the lines between science, engineering and public values — and I have no suggestions to offer.

But one thing is certain — climate change, by any name, is not responsible for the fact that the Mississippi Delta is washing way.

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Author’s Comment Policy:

 It takes a lot of time to dig up all the [alternative] facts to correct the skewed impressions that poor science writing in the media can create.  Often, the task is to supply the rest of the story, or the details in which the devil lies.

The NY Times piece is part of a long series of stories on the human interest side of ecological and environmental disasters that insist placing the blame on “climate change” and specifically “climate-change-caused-sea-level-rise”.   It appears so very easy to shift the blame for relative sea level rise to climate — which can only be responsible for absolute SLR. It is always possible that the journalists themselves actually don’t understand the point, I guess — but it stretches my imagination to think that someone could be hired as a science journalist without even basic science knowledge.

Randy Newman, one of America’s musical geniuses,  wrote the song “Louisiana: 1927” — he performs it here.  The incomparable Aaron Neville recorded the definitive version.

Address your comments to “Kip …” if you are talking to me, I’ll see it and try to answer best I can.

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via Watts Up With That?

http://ift.tt/2GRrcuS

February 27, 2018 at 05:31PM

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