The Debate Over Subsidence in Coastal Louisiana and Texas

The Debate Over Subsidence in Coastal Louisiana and Texas
Arthur E. Berman
 
On August 29, 2005, Hurricane Katrina devastated coastal areas of Louisiana and Mississippi. New Orleans may be lost.  In that city, levees were breached and pumps failed. Eighty percent of the city is flooded with up to 20 feet of water this morning. 
 
Bad policies by politicians and planners contributed to the city’s vulnerability.  Geologists and coastal scientists have been arguing for decades, unable to agree on the causes or rates of subsidence.   Officials and the public understandably felt justified in making no decisions or temporary decisions because experts could not reach agreement. The scientific community must now accept some responsibility for choosing debate and inaction over collaboration and consensus for the public good in Louisiana. 
 
An editorial in the New York Times stated, “At the same time, there must also be an honest recognition of the fact that no amount of engineering - levees, sea walls, pumping systems, satellite tracking systems - can fully bring nature to heel” (New York Times, 2005).
 
Katrina will be called a natural disaster but subsidence is the root cause of the problem. An event like this was anticipated for decades by geologists and coastal experts because of ongoing subsidence in the northern coastal region of the Gulf of Mexico.  If it had not been Katrina, it would have been some other hurricane; if it had not been this year, it would have been another, probably in our generation. 
 
The latest chapter of the continuing debate over subsidence in coastal Louisiana and Texas was triggered by publication of NOAA TECHNICAL REPORT NOS/NGS 50 (Technical Report 50) a year ago.  The report warned that subsidence rates in southern Louisiana were far greater than many workers believed and that swift height modernization was imperative.   
 
Scientists are clearly divided into camps that support different views of the cause for subsidence.  Some believe that ground water withdrawal is the principal cause for subsidence. Others blame oil and gas extraction and many blame the reclamation and restoration efforts of the Army Corps of Engineers.  Technical Report 50 suggests that none of these causes fully account for subsidence rates in southern Louisiana and that natural, geological processes must be considered.
 
The great American geologist Thomas Crowder Chamberlin gave an address to the Society of Western Naturalists in 1889 about the unfortunate tendency of scientists to promote their ideas and theories often to the exclusion of an integrated and balanced perspective of all possibilities.  There is, I believe, a tragic lesson in the debate over subsidence in the Gulf Coast of Louisiana and Texas that Chamberlin described precisely.
 
 “Our desire,” he said, “to reach an interpretation or explanation commonly leads us to a tentative interpretation that is based on relatively hasty examination of a single example or case. Our tentative explanation, as such, is not a threat to objectivity, but if we then begin to trust it without further testing, we can be blinded to other possibilities that we ignored at first glance. Our premature explanation can become a tentative theory and then a ruling theory, and our research becomes focused on proving that ruling theory. The result is a blindness to evidence that disproves the ruling theory or supports an alternate explanation” (Chamberlin, 1890).
 
The silent disaster that Technical Report 50 co-author Roy Dokka has been describing found its voice this week in Hurricane Katrina.
 
 
Reaction To NOAA Technical Report NOS/NGS 50
 
In July 2004, NOAA TECHNICAL REPORT NOS/NGS 50 (Technical Report 50) was published by the National Oceanographic and Atmospheric Administration (NOAA)’s National Ocean Service (NOS) and National Geodetic Survey (NGS).  The subtitle of the report aptly abstracts its content:  rates of vertical displacement at benchmarks in the Lower Mississippi Valley and the Northern Gulf Coast.  Technical Report 50 concludes that rates of subsidence in southern Louisiana are significantly higher than previously thought.  The report’s authors, Kurt Shinkle, National Geodetic Survey, and Roy Dokka, Louisiana State University, estimate that southern Louisiana rates of subsidence are between 200 and 5000% greater than previous estimates.  The mean subsidence rate for southern Louisiana, they say, is 11mm (0.43 inches) per year (Berman, 2005). 
 
The report has ignited a debate of surprising intensity considering its conventional method of analysis and its geologically unremarkable inference that the Gulf of Mexico basin is subsiding at rates greater than can be explained by human efforts to extract fluids from the subsurface.  Dr. Roy Dokka, the report’s second author, has been attacked both for the rates of subsidence cited in Technical Report 50 and for his belief that much of the subsidence is due to natural, geological causes. 
 
“Subsidence is much more widespread and much faster than previously thought,” Dokka says. While the rates (in Technical Report 50) are specific to the past 100 years and may not reflect the current rate of subsidence, Dokka says,  “you can’t extrapolate these rates without looking at the future,” and he “absolutely” thinks the rates are natural and will continue (Sever, 2005).  Natural causes, according to Dokka, include tectonic and depositional processes such as crustal down-warping, sediment loading, compaction, salt movement and gravity slumping, as well as eustatic sea-level rise.
 
Bob Morton, a geologist at the USGS Center for Coastal and Watershed Studies (CCWS), is Dokka’s most vocal critic.  Morton believes that most, if not all, of the subsidence and accompanying land loss in southern Louisiana is due to oil and gas production.  In a recent interview with TexasMonthly, Morton stated that Dokka’s research was “scientifically questionable” and suggested that the LSU scientist may be more interested in grabbing headlines than in scholarly pursuit (Cartwright, 2005).
 
“Terms like sediment loading and gravity sliding made perfect sense millions of years ago but they don’t necessarily apply today,” Morton says. “What Dokka doesn’t tell you is that his data is recalculated from data that is at least ten years old. Maybe it applies today and for the next 100 years and maybe it doesn’t. Withdrawing fluids from the subsurface produces the same results as sediment loading---but it’s induced, not natural” (Cartwright, 2005).
 
Kristy Milliken, a gr