DPWH proposes Marikina Dam, Parañaque Spillway to control flooding

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The Department of Public Works and Highways bares their plan to build a multi-purpose dam in the upstream of the Marikina-Montalban River Basin to control flood water which would come from typhoons that could be as strong as Ulysses and Ondoy.

Metro Manila (CNN Philippines, November 25) — In a bid to protect low-lying communities from massive flooding, the Department of Public Works and Highways pitched infrastructure projects that would contain and channel flood water in Metro Manila.

Facing a joint Senate panel hearing Wednesday, Public Works Undersecretary Emil Sadain presented the DPWH's plans to improve flood control structures along the Pasig-Marikina River Channel and in Parañaque.

The agency bared their plan to build a multi-purpose dam in the upstream of the Marikina-Montalban River Basin to control flood water which would come from typhoons that could be as strong as Ulysses and Ondoy.

Sadain added plans on the proposed dam, which were already forwarded to the National Economic Development Authority for its insights, include allocation for water supply "which can be utilized during dry season."

He explained the Manggahan Control Gate Structure is already under construction, designed to only allow up to 500 cubic meters of flood water to go into Pasig River.

"We have to increase the capacity of Pasig-Marikina River by putting up flood walls," Sadain said, noting that water passing through this system will eventually go to Laguna de Bay.

Water discharge starts at 3,200 cubic meters per second from the headwaters of Marikina without infrastructural interventions, Sadain explained. However, there are 21 other river systems that contribute to the discharge of Laguna de Bay, contributing to potential flooding.

The DPWH also expressed the need to revive the Parañaque Spillway Project to regulate the elevation of floodwater, with shafts designed to "pump out water from the Laguna Lake going to Manila Bay." The project was initially part of the Metro Manila flood control master plan but failed to materialize under the Arroyo administration.

"All in all, these systems can work harmoniously and mitigate flooding in Metro Manila to cut discharge during a storm," Sadain said.

Sadain added these major flood control projects in Metro Manila may cost around ₱138 billion in total. It would take at least three years to finish the Parañaque Spillway project with an estimated cost of ₱67 billion, while the Marikina Dam can be constructed within five years within an estimated cost of ₱38 billion. Meanwhile, putting up flood walls along Pasig River may cost around ₱33 billion.

Also present in the hearing, Architect and urban planner Felino "Jun" Palafox said around 4,600 cms of water flowed through denuded mountains and flooded urban land and low-lying areas of Metro Manila when Typhoon Ondoy hit the country in 2009.

"Climate change is also a double whammy. Because of land subsidence, bumababa iyong urban land dahil sa groundwater, overpumping of deep wells. Tumataas ang sea level," he said. "At the same time, dumami ang subdivisions, development in the highlands, midlands."

[Translation: Because of land subsidence, urban land sinks due to groundwater and overpumping of deep wells. Sea level also starts to rise. At the same time, more subdivisions are being built, allong with the development in the highlands, midlands.]

"[We must] address the hazards before they become disasters because they are 90% cheaper than post-disaster rehabilitation," Palafox added.

On Tuesday, a joint House panel held a separate probe into the impacts of Typhoon Ulysses and looked into the protocols regarding dam water discharges, disaster response and coordination efforts of government agencies during calamities.

Disaster response officials last reported that Typhoon Ulysses killed 73 and injured 82, while 19 people remain missing due to heavy flooding in various provinces. The total number of affected residents reached 4 million.