Is Metro Manila better prepared for another ‘Ondoy’?

(Second of three parts)

On Sept. 26, 2009, large parts of the sprawling urban jungle of Metro Manila were underwater.

In just six hours, Tropical Storm “Ondoy” (international name: Ketsana) poured a month’s worth of rain onto the metropolis, killing over 700 and causing billions of pesos in damage.

So many things went wrong on that day, says engineer Geramie Quitain of the Department of Public Works and Highways-National Capital Region (DPWH-NCR) flood control office. Manila, already disadvantaged by its topography at zero meters above sea level, was built atop a flood control system of waterways and drains built for a 25-year flood projection.

But Ondoy was a monstrous phenomenon that, experts say, happens only once every 100 years.

In submerging the metropolis, Ondoy exposed its raw vulnerabilities during natural disasters: the absence of a clear road map for disaster risk management, weak infrastructure and lack of preparedness, says engineer Baltazar Melgar of the Metropolitan Manila Development Authority (MMDA) flood control division.

It’s why the NCR’s flood control managers have drastically changed the way they view disaster risk mitigation. Ten years after Ondoy, both the DPWH and the MMDA have significantly firmed up the metro’s flooding infrastructure in accordance with the $350-billion Metro Manila Flood Management Master Plan (MMFMMP) laid out by the National Economic and Development Authority and the World Bank.

But the pace of development is still staggeringly slow even as climate change amplifies the risk of disasters. Both departments concede that if another Ondoy were to pummel the nation again soon, there might be less deaths—but “Manila would still definitely sink,” Melgar says.

“The infrastructure we have in place is really not enough,” Quitain says. “For now, our lack in structural interventions would have to be augmented by nonstructural measures,” such as constant relocation of informal-settler families from waterways, constant dredging and solid waste management, and disaster risk preparedness and response.

For disaster scientist Mahar Lagmay, executive director of Project Noah (Nationwide Operational Assessment of Hazards) now housed in the University of the Philippines Resilience Institute, the problem also lies in the dearth of science-based anticipatory planning needed in disaster mitigation.

“The failure to anticipate is the problem of resilience,” he says. “We are still falling short of what we need to understand disasters.”

Aggravating circumstances

The Philippines, a tropical archipelago with long, meandering coastlines, consistently ranks high among the countries most vulnerable to natural hazards, says Jerry Fano, a project impact evaluator at the DPWH-NCR flood control office. At least 60 percent of its cities and municipalities, including Manila, are coastal and low-lying, making it naturally flood-prone.

Lagmay makes a distinction between nuisance floods brought on by heavy rainfall that may still cripple the day’s economy and “killer” floods like those triggered by Ondoy. Thus, he says, solving the flooding problem first means “knowing exactly what it is we’re trying to solve.”

There were records of floods in Manila as early as the 19th century, according to Fano. Back then, urbanization and gentrification had yet to eat up much of the 273 waterways, creeks and estuaries crisscrossing Manila, all linked to the hydraulically complex Pasig-Marikina River system feeding into Manila Bay.

Even now, the MMDA still doesn’t know how many of these have been buried under construction projects.

Open waterways are crucial to flood control, Melgar points out. When it rains, floodwaters flowing into the roads’ drainage inlets feed into these waterways and are then forcibly pumped into the bay by the 64 pumping stations scattered across the metro.

Informal-settler dwellings now cover these natural waterways, Melgar says. Worse, all sorts of garbage get into the drainage systems and on to the decades-old pumping stations, most of which are now less than 100-percent efficient. “Sometimes,” Melgar says, “we even get mattresses, sofas and pieces of metal from our pumping stations. And once trash coils itself around the pumps, it makes discharging floodwater more difficult.”

This, coupled with the fact that the drainage systems in the metro have only a two-year return period, is also why nuisance floods still hound the capital 10 years after Ondoy.

According to an MMDA study conducted in 2018, over 50 out of 60 national roads in the metro will be inundated by 10-centimeter to 20-cm floods with 40-millimeter to 49-mm rainfall. With 80 mm of rain, all of these would be submerged under 30-cm to 114-cm floods.

For now, the MMDA is resigned to making flood recession faster—between 10 and 20 minutes—as it looks to the DPWH to follow through with the World Bank-funded flood master plan.

Structural interventions

There has been no shortage of flood control master plans for Manila—the earliest recorded was in 1942—but it was only after Ondoy that “the country was able to have a new set of standards,” Quitain says.

In 2012, the government approved the MMFMMP, which consists of structural and nonstructural flood mitigation measures to be implemented between 2018 and 2035, Fano says.

Of the 11 structural projects shortlisted, the highest priority is the Pasig-Marikina River Channel Improvement Project split into five phases of dredging and construction of floodgates and embankments.

Phases 3 to 5 are in various stages of completion, per DPWH records. But the first two phases—the construction of a high dam (P12.9 billion) and a retarding basin (P23 billion) in the Upper Marikina River catchment area—are expected to quadruple the metro’s flood capacity from 25 to 100 years.

During extreme rainfall, the dam and the basin will serve as the first line of defense against floodwaters coming from the Sierra Madre. The basin will hold the waters from flowing into Marikina River, and allow the river to carry the waters conveyed by its creeks, estuaries and tributaries.

Sierra Madre was one of the reasons Marikina went under during Ondoy, Quitain says. The waters rushing from the Cordillera range was too much for the low-lying river, which rose to as high as a three-story building.

Other projects in the MMFMMP include the improvement of drainage projects in the metro; the construction of pumping stations in flood-prone areas (Valenzuela, Manila and Makati); the improvement of Manggahan Floodway; and the construction of a spillway along the Parañaque rivers to reduce flooding in Laguna de Bay.

Without these, the World Bank projects will be inundated by a 100-year flood, affecting 2.3 million people and causing P151 billion in damage.

But the entire master plan will be implemented within 23 years, during which climate change is expected to aggravate the effects of extreme weather and slow-onset disasters.

But Lagmay worries that the master plan is still not enough.

Science-based solutions

For one, he says, the plan is hinged on the flood projection models of Pasig, Marikina and San Juan rivers, and does not take into consideration the hundreds of waterways that feed into these rivers.

If there is one lesson to be learned from Ondoy, he says, it’s that even these waterways will also wreak destructive flooding once these three rivers swell. It’s why even areas beyond these rivers still bore the brunt of Ondoy, he says.

In 2015, Lagmay recalls, Project Noah generated flood hazard maps using probabilistic multiscenario models gleaned at the municipal level. These showed that, compared to DPWH projections, larger swaths of the metro would be flooded.

It was thus imperative to invest in such technologies and to tap local scientists to better understand the risks, Lagmay says.

“There is a pattern that emerges whenever disaster strikes. People always say they were all surprised … We never anticipate disasters [worse] than what came before. Instead of looking at historical records, we need to go beyond the community experience. Science will be able to address that anticipation.

“If we do that, we stand a better chance to survive.”

(To be concluded)