Effectiveness of CAMANAVA Flood Control Project : A Case Study of Selected Flood Control Structures during Typhoon Gener and Monsoon Rains in August 2012 <Research Note>
JIDC_19-3_131.pdf 21.3 MB
Ven Johnson, Savin
Pascua, Marie Claire L.
Rahaman, Md. Masumur
Tenorio, Arnel L.
Disaster Risk Management
Malabon City, a municipality in north-western Metro Manila near Manila Bay, suffers frequent flooding which has led to its reputation as the "Local Venice" of the Philippines. Eighteen natural and artificial waterways segment Malabon and crest during high tide and heavy precipitation. In 2003, the national government, with funding and partnership from JICA, initiated the CAMANAVA Flood Control Project, aimed at reducing flood prone areas by 75 percent within Malabon and its three neighboring municipalities. Ten years and over 5 billion Philippine pesos (PhP) later, the project remains incomplete, and Malabon continues to experience debilitating floods. This research note presents a report of the effectiveness of selected flood control structures in Malabon through field observations of structures in the city's three most flood prone districts, locally called barangays - Catmon, Tonsuya, and Tanong - during Typhoon Gener and heavy monsoon rains which followed in early August 2012. To evaluate the effectiveness, the research team consulted the initial project design and hydrological and geotechnical studies to ascertain expected flood mitigation results, and evaluated them against site visit observations conducted in early August 2012 before and after torrential rainfall. The findings reveal failures in flood control structures, such as collapsed river walls, resulting in extensive flooding during and immediately after the rainfall.
Interviews with local experts and policymakers reveal that these failures stem from several factors. First, the baseline hydrologic parameters used in the original designs are outdated and no longer accurate. Second, the designs failed to consider other factors such as land subsidence in its conceptual planning. Third, some construction remains incomplete and as built do not meet design specifications. To improve flood control management in Malabon, this research team recommends a complete recalculation of hydrometeorological forecasts and structure design based on recently procured data, maps, and modelling techniques. The new models should recognize increased severity and frequency of hydrometeorological activity resulting from climate change, such as greater maximum high tides, rising sea levels, and increased magnitude and frequency of precipitation. Design recalculation should incorporate land subsidence caused by pressures from population growth, water usage, and urban planning. The second recommendation is to rebuild CAMANAVA flood control structures capable of sustaining longer term extreme hydrometeorological conditions based on the outputs derived from the modelling.