• Lessons from disasters

    6
    Giovanni Tapang, Ph.D.

    Giovanni Tapang, Ph.D.

    Last October, during the first general assembly of the People’s Niche or the People’s Network for the Integrity of Coastal Habitats and Ecosystems, I was tasked to present some slides that were prepared by geology expert Prof. Dr. Kelvin Rodolfo who was at the United States at the time. In his slides, and in the accompanying short paper, he discussed three main reasons why reclamation projects in Manila Bay is a bad idea.

    The first reason that he raised: Manila and its surrounding environs are sinking due to high water extraction rates. This land subsidence was borne out by measurements of Dr. Rodolfo and Dr. Fernando Siringan in a paper that came out in the journal Disaster in 2006. Earlier measurements by Jacob in 2004 cites sinking rates of around 6.4 cm per year in Caloocan. Subsequent measurements through radar remote sensing by Dr. Mahar Lagmay supported the claim. Some areas in Caloocan, Malabon and Navotas sank as much as 4 to 5 centimeters in the past decade.

    Land sinks from aquifer depletion
    Land subsidence is due to overextraction of water at rates faster than the recharge rate. Water recharge comes from precipitation and nearby bodies of water. Much like using a phone at full capacity while it is being trickle charged, using an aquifer at these rates will deplete it. The soil and rock layers will compress when the water in-between their interstices disappear. This subsidence can cause building damage and for the long term can put current Manila surface levels lower than the sea. Floodwaters will recede slower and drainage patterns can change. Drainage solutions by reclamation proponents such as fixed channels can rapidly become inadequate or inappropriate.

    Dr. Rodolfo’s second point: the vulnerability of reclaimed areas to storm surges. Storm surge is the increase in water height near the shore as a storm passes by due to pressure changes and wind patterns. During Yolanda, storm surge heights reached up to more than five meters.

    The metro area of the Manila Bay has experienced storm surges as recent as Typhoon Pedring in 2011, which inundated the whole stretch of Roxas Boulevard and affected the operations of the US Embassy. Storm surges have been observed in coastal areas around Manila Bay and have been recorded to reach up to around four meters in height especially in Cavite. These can be aggravated in the future by changes in seawater level due to global warming. Storm surges can also be enhanced by tidal fluctuations and can be difficult to prepare for unless one has an hour-by-hour estimation of the weather situation.

    Even before Pedring, Manila has seen the effects of storm surges in the 1970s. Typhoon Patsy in November 1970 and Ora in June 1972 has caused damages when ships were dragged inland as the typhoons brought the sea water level above normal.

    When I first explained this in that October forum, it was not clear how intense the damages can be from a storm surge. Unfortunately, with the Tacloban tragedy brought by Yolanda, we now are all familiar with storm surges and have even debated what to properly call it. Yet it is now as real as the images of destruction that we see in the television straight from the Visayas as Yolanda passed by.

    Danger posed by liquefaction
    The third point made by Dr. Rodolfo is about liquefaction. Again, in the October forum, liquefaction was an abstract geological term to many despite it happening in Dagupan in the 1990 Luzon earthquake.

    Liquefaction happens when ground shaking from earthquakes helps loose material and rock settle closer to each other and allow water to rise as the material compacts itself. Buildings on top of these areas can crash or lean towards a certain direction when liquefaction happens. Reclaimed areas are prone to this phenomena and makes structures built on them at risk because of liquefaction.

    In the magnitude 7.6 Niigata eartquake in Japan, buildings leaned toward one side due to liquefaction. Bay areas, especially reclaimed areas, are especially prone to liquefaction. A case in point is the Bay Area in California which has high hazard levels to liquefaction in areas that are reclaimed along the bay. A strong earthquake such as the Loma Prieta earthquake shook the ground loose and caused buildings to crumble.

    A few weeks after the October meeting, the Bohol earthquake happened and sink holes appeared in some areas. These sink holes and liquefaction areas were shown in the television and made the danger clear to all.

    Ground subsidence, storm surges and liquefaction: three reasons why reclamation in the Manila bay is a bad idea. Dr. Rodolfo has put it clearly. The disasters of the earthquake in Bohol and Yolanda in the Visayas had made it graphic and real to all. We just need to learn the lesson and not repeat the problems in Manila Bay.

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    6 Comments

    1. I say Yes to the Geo-Hazards. But No to the “we can’t do this” attitude. We should say “Hey lets find a way to mitigate these hazards.” The fact is we are here to stay – every part of the world has some sort of hazard and the only way is to move forward and do “something” about it. A defeatist attitude is not of them. Go Pinoy, We can Do It !!!!

    2. Roger Alama, PE, SE on

      Drs. Rodolfo’s & Tapang’s understanding of reclamation project in Manila Bay as a bad idea is tantamount to the saying,” little knowledge is a dangerous thing”. Many successful projects had been built all over the world and needless to say did not experience any adverse incidents. Appropriate structural engineering, design criteria and construction with respect to good geotechnical understanding of the foundation and structures to be used to support the loads imposed on the soil or rock underneath are the keys to mitigate adverse forces caused by earthquake, wind (typhoon, hurricane, even tornado), wave action (storm surge & tsunami), etc. The newly finished flood control infrastructure in New Orleans is a good example of mitigating storm surges, the Palm Projects in Dubai exhibited a excellent housing reclamation, Japan’s new airport, even our own simple reclamation with the Asia Mall & PICC in it, etc. As long as these kind of projects are being done properly by experienced team of engineers & contractors who are available around the world waiting to be used, reclamation projects with the appropriate financial backing can be achieved without difficulty.

    3. Normally, being a practicing technical person myself, I would agree on the points raised in your column because of sound, and reasonable/logical or technical/scientific merits. Unfortunately, I would have to disagree on the point of outright disapproval of reclamation as a potential engineering solution to highly urbanised and congested metropolis such as Metro Manila. (Note that I’m not in anyway affiliated to the developers of the proposed reclamation in Paranaque).

      First of, with regards to the sinking of certain areas of Metro Manila because of groundwater drawdown on the aquifers, this was brought about by the lack and equitable water distribution system particularly during the era when MWSS was entirely
      in-charge of potable water distribution and they were excellent in poorly doing it. Remember the time when the non-revenue water (i.e. water leak) is as high as 70%? With no water coming in to households, people (regardless whether rich or poor) had no choice but to resort to backyard pumped wells (motorised or otherwise) to sustain their daily water needs. With the proliferation of backyard wells all over Metro Manila, particularly to the areas with poor water service (which is, not surprisingly, still the areas with poor water service even after the two water concessionaires have taken over the water distribution), the ground water level on the aquifer are getting deeper and deeper than ever. You forgot to mention that with the ground water level in the aquifers getting deeper than mean sea level there is a serious issue of seawater ingress in the aquifer which is already being experienced in some parts of Paranaque (but that’s a separate issue to discuss some other time). The groundwater drawdown on aquifers could be mitigated by providing artificial recharging wells which should be part of the infrastructure upgrade of the two water concessionnaires. Thus, reclamation does not in anyway pose as an issue to groundwater drawdown.

      Secondly, on the issue of storm surges. The mitigation measures for storm surge inundations can be provided by a multi-disciplinary coastal engineering in a regional scale that is compatible with maritime traffic which is a vital economic activity in Metro Manila. Unfortunately, coastal engineering is unheard of in the Philippines and I’m
      not even aware of any educational institution providing this program in the country (ironic considering that Philippine coast line when stretched from end to end can circle the globe twice over, and we don’t even have a program for coastal engineering).
      Reclamation, as a mitigation to storm surges (sometimes called coastal defense) have been successfully used by the Dutch through the decades.

      Thirdly, liquefaction, which is a seismic hazard that is quite understood by the civil engineering community particularly the geotechnical engineers and structural engineers, can be addressed by an array of engineering solutions such as soil-densification techniques, piling, etc. Liquefaction phenomena is better understood now by the civil engineering community (unlike 20 years ago pre-1990 Luzon Earthquake) thus reclaimed soils/sites can be engineered to mitigate liquefaction and structures
      on top of it to be seismic resistant.

    4. If it will be good for Manila, do it but building should be pattern with those countries with successful reclamation.

    5. The Manila Bay reclamation area is just one of the places where a disaster is waiting to happen. It is really just a question of when and where. But do we see anyone from the government, doing anything about them? No. Just as there is not enough action on planting more mangroves in many of our coastal areas, building flood control projects, de-silting of polluted rivers, etc.. We have a government without a long-term plan. It is a reactive government. Always waiting for something to happen, before acting on it. But nothing is ever put in place, to keep a disaster from happening, ar at least to lessen the impact of a flood, a tidal surge, a typhoon. Nothing.

    6. expatsteve1012 on

      Article is all negative about reclamation works. With proper engineering, reclaimed land can be made safe from earthquakes. Just look at Kansai airport, built on reclaimed land in the harbor, undamaged by the Kobe earthquake. Granted there is an additional cost for this kind of engineering solution but it is entirely possible and done all the time.