No abstract

Abstract. In September 2009, Tropical Storm Ketsana (local name: TS Ondoy) hit the Manila metropolitan area (Metro Manila) and brought an anomalous volume of rain that exceeded the Philippines' forty-year meteorological record. The storm caused exceptionally high and extensive flooding. Part of this study was a survey conducted along the stretch of the Marikina River, one of the major rivers that flooded. Postevent resident interviews were used to reconstruct the flooding in the absence of stream gauge data. Hydraulic and hydrologic modeling were carried out to understand the mechanism that brought the flood. Peak floods occurred at different hours along the river resulting from the transmission of water from the main watershed to the downstream areas. Modeled peak flood and flood timing coincided well with actual observations except for downstream stations where actual peak floods were observed to have occurred at a later time. Compounding factors such as other flood sources and stream backflow could have caused this discrepancy. Nevertheless, prediction of flood heights and the use of the known time lag between the peak rainfall and the peak runoff could be utilized to issue timely flood forecasts to allow people to prepare for future flooding.

In September 2009, tropical storm Ketsana (local name: TS Ondoy) hit Metro Manila and brought an anomalous volume of rain that exceeded the Philippines' forty-year meteorological record. The storm caused exceptionally high and extensive flooding. Part of this study was a survey conducted along the stretch of the Marikina River, one of the major rivers that flooded. Hydraulic and hydrologic modeling was carried out to understand the mechanism that brought the flood. The study revealed that while there were anthropogenic factors that exacerbated flooding in Marikina, the observed flood heights can be simulated in the models generated. Peak floods occurred at different hours along the river resulting from the transmission of water from the main watershed to the downstream areas and the contribution of smaller tributaries entering the main river. Prediction of flood heights and the use of the known time lag between the peak rainfall and the peak runoff could be utilized to issue timely flood forecasts to allow people to prepare for future flooding

No abstract

The SW sector of Mount Natib, a potentially active volcano in the Bataan volcanic arc in western Luzon, is the site of a mothballed nuclear power plant that members of the national legislature have proposed to activate. Detailed geological fieldwork was conducted to assess the capability of the volcano and to identify any volcanic hazards it might pose to the nuclear plant. The nearest eruptive centre is 5.5 km away from the plant. SW Natib Volcano is underlain by lava flows, lahar deposits and at least six pyroclastic density current (PDC) deposits, three directly underlying the nuclear reactor facility. A fault trending N308E is aligned with the Lubao Fault, a capable fault NE of the volcanic edifice. Radon emissions at the traces of these faults are high and comparable to those at known active faults. An associated thrust fault at the nuclear site cuts through lahars up to the ground surface. The results presented here can be used for general hazard preparedness of local communities, and may assist the government to decide whether or not to recommission the nuclear power plant.