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.