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  • 1.  Lesson from Palu Indonesia Tsunami

    Posted 10-02-2018 04:29 PM
    Edited by Tirza Austin 10-02-2018 04:28 PM
      |   view attached

    The September 28th 2018 tsunami (3 – 5 m high) triggered by a 7.5 M earthquake on the island of Sulawesi, Indonesia teaches us some lessons, perhaps the two important ones are:

    • It has been triggered by a land-based coastal earthquake.
    • And Indonesian authorities despite their good effort of applying modeling tools and sensors, were confused and failed to predict the possibility of a tsunami at the head of Palu Bay.

    I have attached an impressive image of this event published by the New York Times – prepared by USGS scientists.

    Apart from amplifications resulting from long-wave transformation processes (e.g. shoaling and funneling), many inlets and bays respond in resonant modes to an incident tsunami wave. Subject to further investigation, it is likely that the tsunami episode at the head of Palu Bay might have occurred in some resonant modes (e.g. in sub, peak or super resonant frequencies). Among others, my own research (published by World Scientific in 2006, https://doi.org/10.1142/9789812709554_0135) for the case of 1964 Alaska tsunami, showed a sub-resonant response from the 64-km long Alberni inlet. The small-amplitude incident tsunami at the inlet entrance, amplified to 3 times at the head of the inlet – causing substantial damage to the Port Alberni in British Columbia.

    While we will know more in the coming days and weeks, I invite all to share insights and experiences. Our thoughts and prayers are for the family of the deceased and other affected people of Indonesia. 

    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    Website: https://widecanvas.weebly.com

  • 2.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-03-2018 08:10 AM
    Edited by Tirza Austin 10-03-2018 08:10 AM
    Thanks Dilip for sharing your thoughts about the recent tsunami at Palu Bay.
    We need to learn from this tragedy event using any available documents, the mechanism of forming tsunami due to land-based earthquake and how it is propagated leading to the amplified run up at the head of the bay.
    Based on the problem diagnosis, I think a certain mitigation measure may be constructed to change the natural frequency of this bay.

    Ahmed Ahmed C.Eng, D.CE, M.ASCE
    Senior Coastal Engineer
    Dar Al Handasah (Shair and Partners)

  • 3.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-08-2018 08:11 AM
    Edited by Tirza Austin 10-08-2018 08:10 AM
    Regarding amplification of earthquake generated waves in bays of certain shape & hydrographic conditions, where earthquakes occur, and cities or other developments are located in potentially hazardous locations, maybe in some cases it might prove feasible to make certain modifications to bottoms & sides to reduce the potential effects., and if not, to restrict certain types of developments.

    John Chapman P.E., M.ASCE
    Environmental Engrg
    Eagle River AK

  • 4.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-09-2018 08:08 AM
    Edited by Tirza Austin 10-09-2018 08:07 AM
    One cost effective solution is to avoid high density use buildings near the shoreline. It is a question of land use and zoning.  For example, residential buildings could only be built at the 5 meter contour.  Unfortunately, this is normally not the case as a result human and property losses are high. Having this requirement would also reduce damages from storm surges. 

    Derek Sherman P.E., M.ASCE
    International Infrastructure Consultant
    Mitchellville, MD

  • 5.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-09-2018 10:37 PM
    Edited by Tirza Austin 10-09-2018 10:36 PM

    It is nice reading the interesting discussions contributed by ASM Ahmed, JF Chapman and D Sherman. As some of you are aware, preventative mitigation measures such as configuring, sizing or modification of bays or embayments are indeed done in small scales. For example, harbors for marina and ship berthing are usually sized to avoid resonant amplifications of waves in the infragravity range – and are configured with the help of breakwaters and dampers to diffract waves in such a way that shadowed tranquil areas are maximized, and the exposed illuminated areas and undue reflections are eliminated or minimized.

    However, any such modifications to mitigate the effects of large-scale events like tsunami or storm surge can be very overwhelming and challenging (perhaps and I hope that some cutting-edge research is going on somewhere) – in part because such long-period waves would tend not to see or feel the effects of some known engineering measures – to deter them from causing havoc (or having only marginal deterring effect). We have seen how the stone-wall tsunami barrier failed in Japan during the 2011 tsunami. I invite interested readers to have a look at some pieces in my website – the Science & Technology has a piece on Tsunami and Tsunami Forces. 

    The issues related to Coastal Zone Management (CZM) such as managing the developments in vulnerable coastal areas do need attention – in particular due to the new realities of accelerated sea level rise, probable enhanced storminess in coming years, etc. All coastal countries have CZM bodies to account for such planning issues – one can argue however – whether or not, and to what extent – the plans and policies are bearing the fruit or would do so (in case not done carefully and meticulously), in ensuring the soundness and location of coastal infrastructure, or in benefiting people living in the coastal zone. Some countries are studying the possible effectiveness of extensive buffer zones of mangrove fields or something similar – in absorbing the onslaught energies of tsunami and storm surge.

    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
    Website: https://widecanvas.weebly.com

  • 6.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-10-2018 03:50 PM
    Edited by Tirza Austin 10-10-2018 03:49 PM
    There is also the work of Akira Miyawaki, a botanist and plant ecologist, in Japan on creating tsunami barriers using native trees. For example see: https://www.navdanya.org/attachments/phyto_0571_Miyawaki_wm-1.pdf.

    John Kretzmann P.E., M.ASCE
    Santa Fe NM

  • 7.  RE: Lesson from Palu Indonesia Tsunami

    Posted 10-11-2018 10:55 AM
    Edited by Tirza Austin 10-11-2018 10:54 AM
    Thank you all for sharing your info on Tsunamis and resilience.  As an engineer working on the US East Coast and living in Miami, FL we can all learn from this.  The tsunami land clearing from most of your photos looks more devastating than many hurricanes we have, which are horribly tragic as well.  I hope we all can start planning these strategies into our coastal cities, regardless of the calculated exposure - as you note the Sulawesi event was not expected at all by the scientific modeling.

    On the East coast we should be implementing these type of strategies into our coastal dune systems, and living shorelines.  Praying for all folks affected by the storm events this year.  But more importantly I urge everyone to push all of our coastal cities, engineers, planners, and politicians to plan better during the coastal development processes - and especially during the repair after these storm events.  North Carolina and Florida in particular can take a lesson.

    Thank you all for the useful information!

    Patrick Shearer P.E., M.ASCE
    Water Resources Eng
    E Sciences Inc.
    Miami, FL