1. UPCOE-ICE-NHRC Public Presentation Typhoon Ondoy (Ketsana) and the Marikina River Flood of September 26, 2009 Venue: Beta Epsilon Multi Media Hall, Melchor Hall, UPD Time: 9:00-10:30 AM, Friday, October 2, 2009 PROGRAM Opening Remarks (9:00-9:10 AM) Dean Rowena Cristina Guevara Presentations* (9:10 – 10:20 AM) Typhoon Ondoy Rainfall Intensity-Duration-Frequency Statistics Marikina River Basin Flood, Hydraulics and Issues Proposed Multi-Hazard Risk Assessment & Capacity Building for Metro Manila Flood Issues, Management and Climate Change Open Forum (10:20 – 11:00 AM) Closing *Speakers include Dr. Leonardo Q. Liongson and Dr. Guillermo Q. Tabios III of the UPCOE Institute of Civil Engineering

2. TS Ketsana-Ondoy Rainfall Intensity-Duration-Frequency & Flood-Frequency Statistics Leonardo Q. Liongson Professor, Institute of Civil Engineering and Research Fellow, National Hydraulic Research Center College of Engineering, UP Diliman 2 October 2009 Beta Epsilon Multi-Media Hall Melchor Hall, UPCOE, UP Diliman

3. METRO-MANILA: Meycauayan (until early 1980s) Kamanava: Kalookan, Malabon, Navotas, Valenzuela Manila Quezon City, Marikina, San Juan, Mandaluyong, Pasig, Makati, Pateros- Pasay, Taguig, Parañaque, Las Piñas, Muntinlupa. Brief Background: the River Basins of Metro Manila.

4. Metro Manila - is composed of 7 small highly urbanized river sub-basins (702 sq. km.) which drain directly to Manila Bay , and through Pasig River , serves as the only outlet of one major tributary basin, the Marikina River Basin (535 sq. km.) in the northeast , and one extensive lake region, the Laguna de Bay Basin with 21 tributary SBs : 2300 sq. km. Lake area : 929 sq. km. Total basin area: 3229 sq.km. in the southeast. Marikina River Pasig River Laguna de Bay Manila Bay

5. Top: Marikina River @Wawa Dam at Montalban gorge as seen in the early 1990’s. Left: The towns of Rodriguez (Montalban), San Mateo, Marikina & Pasig along Marikina River.

6. Metro-Manila Rivers: Name of River Basins Drainage Area (sq.km.) Marikina RB 535 Mangahan Floodway-Taytay RB 63 Taguig-Napindan RB 45 Meycauayan RB 169 Obando-Malabon-Navotas Estuary 35 Novaliches Reservoir-Tullahan RB 72 San Juan RB 94 Pasig RB (north and south) 91 Parañaque-Las-Piñas RBs 73 Zapote-Bacoor-Imus RBs 168 Source: NHRC

7. The detailed river network of Marikina River Basin above Sto. Niño (DA=535 sq.km.): the basis of the NHRC SWATCH physics-based distributed hydrological (rainfall-runoff) model .

8. (NHRC) Marikina River Basin (535 sq.km.) and the 21 sub-basins & lake of the Laguna de Bay Basin (3229 sq.km.)

9. (NHRC) Marikina River Basin (535 sq.km.) and the 21 sub-basins & lake of the Laguna de Bay Basin (3229 sq.km.)

10. (Wikipedia) Marikina RB Pasig RB Mangahan Floodway

11. (Badilla 2008)

12. (JICA)

13. (NHRC)

14. (NHRC)

15. Mean daily streamflow in Marikina River at Sto Ni ñ o in year 1990.

17. The Mangahan Floodway diverts floodwaters of Marikina River to Laguna de Bay. The Napindan Hydraulic Control Structure (NHCS) regulates flow between Pasig River and the lake via the Napindan Channel The navigation lock of the NHCS allows water traffic between Pasig River and Laguna de Bay through the Napindan Channel.

18. Track of TS Ketsana (Ondoy) – from Joint Typhoon Warning Center (JTWC), US Navy

19. (PAGASA)

21. Flooding started fast at the SM North EDSA, Quezon City (Flickr) .

22. Large runoff on pavements and underground floods in the Ayala underpass, Makati (Flickr).

23. Inundation of the Provident Village in Marikina City (Googlemap; Flickr).

24. Coping aboard fiberglass boats in Bay, Laguna (Flickr – IRRI).

25. Collapse of a wall of the Mangahan Floodway near Rosario Bridge, Pasig City. (Googlemap; Flickr).

26. Property damage (Flickr).

27. Suffering and death (Flickr).

28. And a safe passage. (www.op.gov.ph and Flickr)

29. 8 meters high 5 meters high Marikina Riverbank 9/28/2009. Downstream view of Rosario Weir along Marikina River.

30. Preliminary Computations SWATCH-computed Peak Flood Discharge = 5770 cu.m./s of Marikina River at Sto Ni ñ o on 26 September 2009, based on the Point Hourly Rainfall at Science Garden, QC Synoptic Station with applied area reduction factor = 0.6 (NHRC)

36. 4. Probable Annual Max. Discharge of Marikina River at Sto Nino station (by Log Normal Prob. Dist. and Flood Runoff Model) Return Max. Discharge, m 3 /s period Existing Future (years) Land Use Land Use Sto Nino Sto Nino Rosario 2 1350 1470 1480 5 1870 2020 2000 10 2210 2350 2320 20 2550 2740 2720 30 2740 2900 2890 (design flood) 50 2980 3120 3070 100 3310 3430 3440 Comments: The 30-year flood of 2740 m 3 /s has not yet been experienced in the 42-year period of record, 1958-2000. However, the 20-year flood of 2550 m 3 /s was exceeded in 1986. 3. Historical Annual Maximum Discharge of Marikina River at Sto Nino, Marikina Year Max. Discharge, m 3 /s 1986 2650 1970 2464 1959 2072 1977 2051 1966 2036 2000 1895 1998 1680 1995 1676 1999 1642 1967 1609 etc.

38. Thank You.