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Sofa in the Drainage

Out of the 171 countries assessed in the 2016 World Risk Report, the Philippines ranked third most exposed to natural hazards. According to PAGASA, the Philippines is visited by at least 20 tropical cyclones every year. Last August 2018, heavy rains brought about by tropical storm Karding led to the evacuation of at least 50,000 individuals after Marikina River’s water level peaked at 20.6 meters (as compared to 23 meters during Ondoy). During the clean-up operations that followed, I was surprised to see all sorts of garbage, from sofa to refrigerators, inside our drainage canals — sediments that impede the natural flow of water.

In the World Bank’s flood risk assessment study for the entire Metro Manila and Surrounding Basin Area, flooding was mainly attributed to three factors: (1) the huge volume of water discharge coming from the headwaters in the Sierra Madre mountains flowing downstream, (2) drainage capacity constraints in core area of Metro Manila, and (3) a heavily silted Laguna Lake.

The masterplan composed of 11 structural mitigation measures with an estimated cost of around ₱351 billion proposes to reduce the peak discharge of inflow equivalent to 3,600 m/s under a 100-year return period by about 75 percent by building a dam in the upstream portion of Upper Marikina River and constructing flood control structures along the priority critical sections of Pasig-Marikina River.

In May 2018, DPWH completed Phase III of the Pasig-Marikina River Channel Improvement Project (PMRCIP), which spans from the Lower Marikina River Improvement (Napindan Channel to the downstream of Manggahan Floodway) to Delpan Bridge. Revetments, parapet walls, dike embankment, sluice structures, and bridge foundation protection were constructed and installed along priority critical sections of the Pasig-Marikina River.

The civil works for Phase IV are currently ongoing and address the downstream of Manggahan Floodway to Marikina Bridge. This would also include the construction of the Marikina Control Gate Structure and will further decrease flood inundation by 7.5 percent.

Apart from this, DPWH Secretary Mark Villar has adopted the Integrated Water Resources Management Program, which will complete and update the flood control and drainage master plans and feasibility studies of 18 major river basins (drainage area of more than 1,400 square kilometers), 421 principal river basins, and other critical river basins.

Phase 1 of the Metro Manila Flood Management Project, which involves the modernization of drainage areas, reduction of solid waste in waterways, and participatory housing and resettlement, among others, has also started.

The Flood Risk Management Project for Cagayan, Tagoloan, and Imus Rivers, which expects to address the serious bank erosion in Cagayan, construct river dikes and drainage channel along Tagoloan River, and build two off-site retarding basins along Imus and Bacoor Rivers, have been completed.

The Flood Risk Management Project in Cagayan de Oro (CDO) River is now protecting 290 hectares and about 18,000 structures in CDO. Based on a 25-year flood return period, the number of people affected by flooding in the area will also be reduced from about 281,000 to only 31,000.

Since its completion in 2020, the Integrated Disaster Risk Reduction and Climate Change Adaptation Measures in the Low-Lying Areas of Pampanga Bay reduces flood depth from 1.4-2.9 meters to 0.6-1.4 meters and will shorten flood duration from 66 days to 17 days.

Other projects include the Cavite Industrial Area Flood Management Project, which mitigates the flood damage caused by the overflow of the San Juan River and the poor drainage system of the Maalimango Creek; and the Leyte Tide Embankment Project, a 31.28-kilometer flood control project, which will protect 27.30 square kilometers of coastal communities and 30,800 houses/buildings from the destructive effects of storm surges.

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