Remember the week-long rains last July 19 to 25 wherein the rainwater dumped was comparable in volume to Typhoons “Ondoy” and “Carina"?

Surigao del Sur 1st district Rep. Romeo Momo Sr. identified this freak weather--with accounted for nearly one-third of Metro Manila’s annual average rainfal in just seven days--as a major factor behind the recent episodes of floods.

Momo made this observation Wednesday, Aug. 13 during the House Committee on Public Accounts' briefing on the Department of Public Works and Highways (DPWH) failed flood control projects. Panel chairman Bicol Saro Party-list Rep. Terry Ridon presided over the hearing.

Citing data from the Effective Flood Control Operation System of the Metropolitan Manila Development Authority (MMDA), Momo said the week-long rains totaled 665.5 millimeters, or 28 percent of Metro Manila’s yearly average.

“Lagi kasi nating sinisisi ang flood control, ‘di rin natin tinitingnan kung gaano ang volume na pumasok sa mga flood control systems ng MMDA at DPWH (We always blame flood control, but we don’t look at how much volume actually entered the flood control systems of the MMDA and DPWH),” Momo said.

Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) Deputy Administrator Engineer Roy Badilla said Ondoy and Carina brought intense, short bursts of rain, while the recent weather disturbance “Crising” delivered the same total over a longer period.

Momo said that week’s rainfall equaled a 100-year return period, as confirmed by DPWH Project Manager Jerry Fano, who noted that Crising’s rainfall matched this threshold based on PAGASA’s intensity-duration-frequency curve.

On further questioning, Fano admitted that Metro Manila’s drainage systems were designed for only a 15-year return period, upgraded from 10 years in 2005 to account for climate change.

“You can just imagine ang buhos ng ulan (the rainfall for a) 100-year return period, but the capacities of our drainage system is only 15-year return period. Saan papunta ang mga tubig na ‘yan kundi mag-overflow talaga (The water has nowhere else to go but overflow from the drainage),” Momo said.

Momo said the mismatch explains why Metro Manila experiences frequent flooding. He batted for the full implementation of the Metro Manila Flood Management Master Plan to upgrade all drainage systems.

In the same hearing, MMDA Chairman Romando “Don” Artes said that the clogging of Metro waterways--no thanks to garbage--was also a big contributor to the worsened flooding at the capital.

Artes backed President Marcos' earlier statement that trash obstructing the flow of water significantly undermined the performance of pumping stations, which were critical to Metro Manila’s flood control system.

“Kahit ano pong ganda ng pumping station natin at mga project, kung nahaharangan po ng basura ay hindi po magiging [epektibo]. Ito pong mga basura ay nakakapagpabagal po ng daloy ng tubig at nagre-render inefficient ng ating mga pumping stations,” he explained.

Artes said that each pumping station is equipped with screens designed to block garbage from entering the pumps. However, some debris, including sticks and other solid waste, still manages to slip through, causing blockages that can stop the pumps from operating.

He cited an instance when a pump automatically shut off because its intake had run dry, even though the area it was meant to service remained flooded. This occurs when rainwater cannot reach the pumping station due to clogged drainage lines and waterways.

“May salaan po ‘yung ating pumping stations para harangin po ‘yung basura. Minsan po may nakakalusot talaga at papasok sa ating mga bomba [kaya] kailangan po naming tumigil. Isa po ang explanation doon: hindi makarating sa aming pumping station ‘yung tubig ulan para mabomba palabas ng major waterway,” Artes said.

(Our pumping stations have strainers to block debris, but sometimes trash still gets through and enters the pumps, forcing us to stop operations. One explanation for this is that rainwater can’t reach the pumping station to be discharged into the major waterway.)