SCIENTIST PREDICTS: More floods,  faults for Metro

A Filipino scientist has expressed alarm at the rate Metro Manila is sinking, saying that the overextraction of groundwater is to blame for land subsidence and other negative effects.

One such effect, according to Dr. Fernando Siringan of the University of the Philippines’ Marine Science Institute, “is the reactivation of old faults, for example in Muntinlupa.”

The consequence of the lowering of land over very large areas is that “floods are getting worse. The major indicator is that large portions of Metro Manila, especially in the Camanava area, are now experiencing floods even just during high tides. No rains, just high tides, and now they are getting flooded,” he said in an interview after a presentation held at the Communication Foundation for Asia (CFA) in Sta. Mesa, Manila.

Siringan said the rate of land subsidence is already alarming and noted that some parts of the country, such as some areas in Bulacan, have become somewhat like Venice, Italy, where the area is perennially underwater.

“It is alarming in the sense that we now have municipalities experiencing floodwaters for several weeks or even months, even without rains. And that enough should alarm us,” he said, adding that these areas were not as flood-prone as they are now.

Siringan said global warming does not cause the increasing rate of land subsidence, “because the global sea level rise” brought about by melting ice caps is “very, very small… two millimeters per year at most.”

Proof that groundwater extraction has caused land subsidence at the rate of “several centimeters per year” is by correlating the “sea level rise and groundwater withdrawal, sea level rise record in Manila Bay, in the South Harbor area, and the rate of groundwater withdrawal,” he said.

Another piece of evidence, according to Siringan, is that flood-prone regions are also those with high groundwater extraction rates. “Where the water table lowered about 100 meters, those are also the regions experiencing high rates of land subsidence, which are also regions now experiencing floods,” he said.

While land subsidence cannot be reversed, Siringan said people can slow it down by reducing groundwater extraction.

He called on water concessionaires to “accelerate their pipe-laying projects” in areas still “unserviced by their companies” so residents would no longer draw water from the ground.

Siringan also advised the public to limit wells to a few operated by municipalities or water utilities; to minimize ecological damage by developing small reservoirs and groundwater-replenishing structures; and study and implement rain harvesting techniques such as trapping and storing rainwater from roofs.

Camanava flood project flawed

Siringan said he and his colleagues have presented the data on land subsidence and flooding to the Department of Public Works and Highways (DPWH) for the Camanava flood control project, which started in 2003.

He said they have gone “all the way up” to President Arroyo, then environment secretary Angelo Reyes, Science and Technology Secretary Estrella Alabastro, and Metro Manila Development Chairman Bayani Fernando in objecting to the project’s design.

Siringa said Fernando told them during a meeting in December 2006 that “it is more expensive to change the design of an ongoing project, and it is probably cheaper to let it finish. And do the modifications after.”

He added there was even a congressional hearing sponsored by then Navotas Rep. Ricky Sandoval, “but nothing came out of it.”

Siringan also lamented that their study was not considered by the government, and stressed that data presented by the government on the Camanava project was not accurate.

He said the engineers and consultants hired for the Camanava project designed the project for a lower rate of subsidence, “because they think the area is practically not subsiding.”

“The elevations used in the Camanava project are not the correct elevations… The elevations are wrong, and we’ve told them that. They blame NAMRIA (National Mapping and Resource Information Authority), which gave the benchmark elevations,” Siringan said.

He called on the government, including those involved in the Camanava flood project, to “open their eyes to what’s happening in the environment. Because they can see it. And if they listen to people who are in the affected areas, then they will get to realize that what we’re saying is basically what the people have told us. Listen to the people.”