防災科学技術研究所 自然災害情報室 - DIL

Research Report on 2009 Floods and Landslides Disasters Caused by Typhoons 16(Ondoy), 17(Pepeng) and 18(Sante) in the Philippines

3. Conclusions

The Typhoon Ondoy flood in 2009 occurred in the Metro Manila with a growing population of over 10 million in a developing country has characteristics as follows;

1) The flood control plan to protect the population of 10 million people from flooding is to cope with the 30 year flood. The flood control facilities are still under construction and these differences in the state of development were one of factors behind the differences of flooding in the four flood plains of Metro Manila. In the flood plains of the San Juan Rivers and the Marikina River where the discharge capacity of the river channel does not meet the design scale, a severe large-scale external flooding occurred and caused many deaths. On the other hand, in the Laguna Lake Plain and the Coastal Lowlands of central Metro Manila, parts of the external overflow remained behind, with inner flooding becoming the main inundation cause, and the inundation was not as severe as in the flood plains where external flooding prominent. Especially the Manggahan Floodway played an important role in protecting central part of Metro Manila from severe external flooding by reducing the flood discharge of the Pasig Rive.

2) After flooding outbreak of the infectious diseases was caused by standing of floodwater for long periods, and presents a large damage to humans. To reduce the human damage in Metro Manila, it is important to take actions to reduce this sort of damage steadily.

3) In Metro Manila, flood risk is continuing to increase. As the population grows, the river basin is further developed. This brings about changes in the flood run-off characteristics and inundation characteristics, increases the potential for damage, and reduces the functioning of flood control facilities due to illegal settlements and the dumping of refuse in channels. Also, illegal dwellings of poor inhabitants encroach into the river zones through which floodwater flows, thus increasing the number of people affected by flooding. To reduce flood risk, it is needed to make effort to find a solution to these complex issues involving a variety of social, economic and governmental factors, in corporation with social scientists and engineers.

4) In interviews on 2009 Ondoy Flood with governmental bodies and other such organizations, we were told about the importance of working to improve the ability of communities to mitigate disasters and about the activities of disaster relief volunteers. I hope that these movements become more active in introducing diverse and wider range of human resources.

5) To improve flood control structures is essential for reducing the flood risk in Metro Manila, but it is difficult to reduce damage solely by flood control facilities. To reduce the flood risk of this region, it is also necessary to instigate comprehensive measures targeting whole river basins and whole components of flood risk by the cooperation of various concerned bodies. For example, hazard control measures in flood plains by local people, land use management for reducing damage potential in flood plains, and flood run-off in river basins, etc..

Japan has contributed to improve the flood control in Metro Manila. Through Japan's long-standing experiences, we have accumulated a considerable amount of knowledge on characteristics of flooding, land environments, social structures, and so on. When taking the next step forward in mitigating the flood risk of Metro Manila from a new perspective, we expect that Japan's experiences will be useful.

References

• ADB(2009) Information and data collected by interview on the Ondoy Flood at ADB in 2009.
• Hara Y., Haruyama S., Okubo S. and Takeuchi K.（2002）"Flood response to the urbanized bank up areas of Laguna Lacustrine Plain, Metro-Manila", Proceedings of the Noson Keikaku Gakkai, Vol.4,pp19-24.
• Google(2009) Typhoon Ondoy Maximum Flood Height in the Google Website
• JICA(1994) "Afforestation Program of the Marikina River Water Source Forest in the Republic of the Philippines.
• JICA(2004)　"Final Report of the plan for the countermeasures against earthquake disaster in Metro Manila of the Republic of the Philippines",Vol.7.
• JICA(2005)　 "Final Report of the survey on the improvement of function for the urban drainage in the central part of the Metro Manila of the Republic of the Philippines (abridged edition)",pp97．
• JICA(2009)　 Information and data collected by interview on the Ondoy Flood at JICA in 2009.
• MMDA(2009)　 Information and data collected by interview on the Ondoy Flood at MMDA in 2009.
• MGB(2009)　"Flood Hazard Map in Metro Manila".
• Manila Shinbun (2009) Articles from September 2009 to November2009.
• NDCC(2009a)　National Disaster Coordinating Council Situation Report about Typhoon Ondoy, No.1～53.
• NDCC(2009b)　 Information and data collected by interview on the Ondoy Flood at NDCC in 2009.
• PAGASA (2009) Information and data collected by interview on the Ondoy Flood at NNDC in 2009.
• NAMRIA (2009) Flooded Area in eastern Metro Manila ts "Ondoy"26 September, 2009 1:15,000
• NAMRIA Geographical Maps 1:250,000　；　1:25,000　；　1:10,000
• P. B. GATAN, Department of Public Works and Highways (2009) Presentation at at ADB Short Seminar "Water for all:　Learning　from the Ondoy flood: A Dialogue with Experts" held on 14 Oct. 2009, Asian Development Bank.
• PNRC-Rizal (2009)　 Information and data collected by interview on the Ondoy Flood at PNRC-Rezal in 2009.

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