Saturday, August 18, 2012

Some parts of Metro Manila sinking, say experts

There’s a bigger culprit behind the recurrence of massive flooding than deficient drainages in Metro Manila. In fact, top geologists in the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and University of the Philippines (UP) agreed that too much construction of buildings in an area sinks the land mass over which Metro Manila lies. PHIVOLCS director Renato Solidum referred to the phenomenon as “ground subsidence” or the downward displacement of surface. “There are two types of ground subsidence. There are natural and man-made causes. It’s man-made when you build structures and buildings. It’s natural when there are earthquakes,” Solidum explained. “As the ground subsides, more flood occurs,” he told Yahoo! Southeast Asia. Solidum said that the building of infrastructure adds further load on a surface, which makes the sediments weak or less intact like those in the areas near Manila Bay. The geologist also noted that the extraction of too much groundwater also worsens the extent of floods in low-lying areas such as Malabon, Navotas, Caloocan, Valenzuela, and other towns in Bulacan. “Ground water actually supports sand sediments. The support eventually weakens especially when you take away ground water faster than it is replenished like in construction of deep wells,” Solidum said. He confirmed the study of UP Professor Fernando Siringan, who called on public works and highway officials to compensate ground subsidence before allowing the construction of new infrastructures. In a public hearing in the Senate on Thursday, Siringan said that in Malabon, some areas have been sinking by 10 centimeters a year while others descends by as much as one meter in four years. He said that the subsidence is easily noticeable, as several places that used to be flood-free now experience flooding. Siringan also told the Senate Committee on Climate Change that the sea level is also rising by almost one centimeter per year because of global warming. The committee, chaired by Senator Loren Legarda, was looking into the Senate Resolution No. 560 filed by Senator Miriam Defensor-Santiago. Defensor-Santiago expressed alarm that the rate of subsidence in Bulacan and some parts of Metro Manila are “becoming somewhat like Venice, Italy where the area is perennially underwater.”