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New Orleans' Levees Sinking after Massive Upgrading

  • 1.  New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-18-2019 03:09 PM

    An article published by the E&E News (April 11, 2019; picked up by the Scientific American Newsletter) caught my attention. It is about the sinking and possible redundancy (in about 4-years time) of the recently upgraded $14 Billion levees of New Orleans.

    The massive upgrading was undertaken by the US Army Corps of Engineers (USACE) after the devastating 2005 Hurricane Katrina. It is rather well-known that the Mississippi River delta is facing higher than average sea level rise (some 9 to 12 mm per year) due to the combined effects of global sea level rise and deltaic subsidence.

    The article has argued that the actual sea level rise (ASLR) in New Orleans area is occurring at a rate faster than anticipated. Although it is not clear whether the sinking is overall, or in some pocket areas of the levee, it raises some questions about the planning vision on part of USACE (being redundant in such a short period is not something anyone or any entity expects). And how much additional sinking the levee itself is causing on the ASLR?   

    Perhaps it teaches us a lesson about the limits of predictability (such as ASLR) and the consequent planning process. I invite all to reflect and react.                        

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    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    Website: https://widecanvas.weebly.com
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  • 2.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-19-2019 04:59 PM
    Dilip, I see you are in Canada and are using the word redundancy in the British sense.​  To a Brit it means "no longer useful"  as in "the employees were made redundant when the factory closed."  To an American, it means more than needed, as in "having two levees would be redundant."

    I would suspect that, in addition to the factors you mentioned, deep subsidence of soft soils would cause some localized settlement of the levees.  Something like an old creek channel, filled with silt, then overlain with additional sediment, and missed by the geotechnical exploration.  After all, you can't do enough soil borings on a project that is miles long to be sure that you didn't miss some features that may be only a few dozen feet wide.

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    William Forbes MASCE, PE, ME, BCEE
    Forensic Analysis & Engineering Corporation
    Virginia Beach, Virginia
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  • 3.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-22-2019 09:40 AM
    This seems to be conflating two separate issues that combine to reduce the effectiveness of the levees.  ASLR will not cause levees to sink, but it will reduce the freeboard.  Consolidation of the underlying soft sediments will cause the levees to settle.  Both factors result in reduced effectiveness of the levee and give the appearance that a levee is sinking.  As professionals, we need to be careful to be clear about the factors in play and not fall into the habit of using popular press terms.  Arguably, the consolidation may be easier to predict than the sea level rise, though conditions surrounding both aspects in New Orleans are complicated.   ​

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    Michael Byle P.E.,D.GE,F.ASCE
    Tetra Tech Inc.,
    Langhorne PA
    (215) 702-4113
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  • 4.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-22-2019 11:32 AM
    ​Indeed there are significant societal issues. I commend to you John McPhee's essay "Atchafalaya" in Control of Nature, 1989.

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    Dudley McFadden, D.WRE, PE, M.ASCE
    Sacramento Municipal Utility District
    Views are my own, not of my employer
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  • 5.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-23-2019 07:36 AM
    I am wondering about the studies which were conducted for this structure with such high cost. I am with Michael Byle that we should not take from the press what is said about all the factors that cause such failure. Sinking is caused by settlement due to weakness of the subsoil but not due to land subsidence and sea level rise that have a long term effect which we can not observe in this short term. The question now is "does the sinking continue?", As such, I advise to make extensive inspection and monitoring program to identify the locations and causes for this sinking.

    Kind Regards,
    Ahmed Sayed Mohamed Ahmed, PhD, D. CE., M. ASCE,
    Senior Coastal Engineering
    Dar Al Handasah (Shair and Partners)
    Egypt


  • 6.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-23-2019 03:05 PM

    The purpose of this post was to raise awareness among the members of civil engineering communities – of a problem as important and massive as the New Orleans flood/storm surge protection levee. Indeed, the problem is more complicated than what one could discuss in this forum – not knowing what the actual conditions are. But a major undertaking – becoming ineffective (or less effective on the premise of designed scenarios) in about 4-years time after completion – is not something anyone can swallow easily. Of course, only a test – perhaps the likeness of Hurricane Katrina – can prove or disprove whether or not the assertion is true – but then it would be too late.

    Thank you, Bill for pointing out my use of redundancy. I meant ineffectiveness, which is more aligned with Oxford English, but the Webster English and engineering define it as an extra layer of safety exceeding what is necessary. Yes, one should be careful in wording – because linguistic, cultural and technical connotations may not always agree.   

    While ASLR results from the additive effects of global sea level rise and local subsidence – the variability and predictability of both are understandably not the same (Michael Byle's point). And one weak area or areas of the levee (weak for whatever reasons – inadequacy of site specific borelog data and assumptions to compensate that, or other flaws) is often sufficient for failure of the entire system in the face of a storm surge/flooding episode like that of Katrina.

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    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    Website: https://widecanvas.weebly.com
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  • 7.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-24-2019 10:05 AM
    Dilip,
       Ahmed Ahmed makes an excellent point about the press.  Your comment that the problem is more complicated than what one could discuss in this forum also means that it is WAY too complicated for the press to report accurately!  Remember, a reporter has to 1) explain the problem as he or she understands it, and 2) in a way that the audience will read it.  The end result is that a LOT gets lost!

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    James Justin Mercier, P.E., CFM
    Life Member ASCE
    Sr. Life Member IEEE
    Austin Texas
    512-442-4016
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  • 8.  RE: New Orleans' Levees Sinking after Massive Upgrading

    Posted 04-26-2019 07:28 AM
    • Earth's crust is being depressed under the weight of the Mississippi Delta;
    • Mississippi Delta itself, which in places is thousands of feet thick, is consolidating/compacting, particularly of course the upper younger layers.
    • Local compaction under the levees undoubtedly occurs, unless they are founded on very deep piles; and of course
    • Sea level is rising. 

    All of these factors have been relatively well understood for some time; whether the USACE cost/benefit analyis took adequate account of them will become obvious with time.  Most of Louisiana SE of Baton Rouge (including New Orleans) was laid down by the Mississippi River within the last 6,000 years (when sea level rose to an elevation that allowed delta building.  It is very "young" land and composed mostly of fine sands, clays and organic silts.  The outlook is challenging at best.

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    Larry Demich Ph.D.,P.E.,M.ASCE
    Obelus Design Group, LLC
    Lake Forest Park WA
    (206)818-5567
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