Bay reclamations prone to disasters
(We have inadvertently picked the wrong copy of this column which appeared on March 10. My apologies. – RML)
The government has lined up 102 shore reclamations covering 38,272 hectares nationwide. A third of those are in Manila Bay. Four are about to commence: two in Manila City, one in Pasay, and one in Cavite. The new real estate would bring mega-profits to the proponents. But wait, warns earth and environment scientist Kelvin Rodolfo. Those reclamations also would cause floods, storm surges, and liquefaction. Millions of coastal residents in Metro Manila, Bataan, Pampanga, Bulacan, and Cavite would be left in misery.
The NGO Save Our Shores recently presented the study of Rodolfo, a Filipino-American PhD at the University of Illinois in Chicago and a Balik-Scientist of the Philippine government. Three looming disasters were explained:
• Seawater will flood coastal communities. Due to sea temperature warming, sea levels are rising, especially near the equator. In the Philippines the rate of rise is as much as 14.7 mm a year, or just below an adult's calf in ten years. At the same time, the bay area is fast sinking. Unbridled extraction of groundwater is causing the surface to subside. The rate of subsidence in Greater Manila is about 19.2 mm a year, or mid-leg deep in ten years. (Rodolfo likens that subsidence to the sinking of California's San Joaquin Valley by eight meters, or a three-story house, due to groundwater overuse in the 1920s to 1970s.)
The Manila Bay coastal plains slope up inland very gently. Ten to 20 kilometers of land from the shore are only one meter above sea level. The combination of rising sea levels and land subsidence would make seawaters advance inland. Large swaths of the bay area perpetually would be in knee-deep seawater in ten years.
Reclamations, being soft earth, would be susceptible to the combination of rising sea levels and subsidence. They would even hasten and deepen the flooding in other parts of the bay area as natural outflows of rivers and high tides would be clogged. Rodolfo cites the experience of Dagat-Dagatan in Navotas, Metro Manila. Starting in the 1970s the government poured billions of pesos for landfill and dikes – all for naught. More areas of the city are flooded today than before.
• Storm surges would lash the coastal communities.
Typhoons are becoming stronger than ever due to climate change. Most at risk from storm surges and giant waves are coastal plains that slope up very gradually, like the Manila Bay area. History has shown evidence of typhoon destruction. Ships have become unchained from anchors and crashed against each other or onto Roxas Boulevard due to strong waves. Reclamations artificially would change the coastal contour, making them prone to storm surges and destructive waves.
• Liquefaction would sink the coastal areas into the bay water in case of earthquake.
Liquefaction is when loose, saturated soil and sediments lose cohesion and temporarily behave like liquid. That’s what happened when buildings in downtown Dagupan City, beside the
The new real estate would bring profit to the proponents, and misery to the population.
Lingayen Gulf, sank as deep as one meter from the 1990 Luzon earthquake. Yet the epicenter was one hundred kilometers to the east, near Cabanatuan City. In case the Big One strikes when Greater Manila's West Valley Fault moves, the reclaimed areas could suffer liquefaction. Structures could collapse.
Rodolfo warns against the reclamation of Sangley Point in Cavite, at the southern tip of Manila Bay, for a new airport. Such earth-filling could sink large parts of the heavily populated urbanized province due to hastened seawater rise, land subsidence, storm surges and waves, and earthquake liquefaction. Rodolfo cites Japan's engineering fiasco with the Kansai Airport, built on a reclaimed island off the bay coast of Osaka. More than $20 billion – 40-percent over-budget – was spent to reclaim land from the sea, pave two runways, build the terminals – and trying to outpace the sinking. Still it sunk, by 11.9 meters, or a four-storey building. Ten percent of the cost went to waterproofing alone to save basements. The island continues to sink to this day.
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