UPCOE-ICE-NHRC Public Presentation

Typhoon Ondoy (Ketsana) and the Marikina River Floodof September 26, 2009

Venue: Beta Epsilon Multi Media Hall, Melchor Hall, UPDTime: 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

TS Ketsana-Ondoy Rainfall Intensity-Duration-Frequency

& Flood-Frequency Statistics

Leonardo Q. LiongsonProfessor, Institute of Civil Engineering

and Research Fellow, National Hydraulic Research CenterCollege of Engineering, UP Diliman

2 October 2009Beta Epsilon Multi-Media Hall

Melchor Hall, UPCOE, UP Diliman

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.

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

Lagunade Bay

ManilaBay

Top: Marikina River @Wawa Dam at Montalban gorge as seen in the early 1990’s.

Left: The towns of Rodriguez (Montalban), San Mateo, Marikina & Pasigalong Marikina River.

Metro-Manila Rivers:

Name of River Basins Drainage Area (sq.km.)

Marikina RB 535Mangahan Floodway-Taytay RB 63Taguig-Napindan RB 45

Meycauayan RB 169Obando-Malabon-Navotas Estuary 35

Novaliches Reservoir-Tullahan RB 72San Juan RB 94Pasig RB (north and south) 91

Parañaque-Las-Piñas RBs 73Zapote-Bacoor-Imus RBs 168

Source: NHRC

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 .

(NHRC)

MarikinaRiver Basin(535 sq.km.)and the 21 sub-basins & lake of the Laguna deBay Basin(3229 sq.km.)

(NHRC)

MarikinaRiver Basin(535 sq.km.)and the 21 sub-basins & lake of the Laguna deBay Basin(3229 sq.km.)

(Wikipedia)

Marikina RB

Pasig RBMangahanFloodway

(Badilla 2008)

(JICA)

(NHRC)

(NHRC)

Mean daily streamflow in Marikina River at Sto Niño in year 1990.

EFCOS: Effective Flood Control Operations System(located in Metro-Manila & Rizal province)

• Aims to achieve an effective flood control operation for Pasig-Marikina-Laguna Lake Complex through

• real time rainfall and water level data collection at the Rosario Master Control Station via telemetry system;

• the effective use of the warning system along Mangahan Floodway; and

• the multiplex communication system among Rosario MCS, Napindan HCS, DPWH Central Office and PAGASA Data Information Center.

Effective Flood Control Operating System (EFCOS) of Metro Manila – was discontinued by MMDA.

The Mangahan Floodwaydiverts floodwaters ofMarikina River to Lagunade Bay.

The Napindan HydraulicControl Structure (NHCS)regulates flow between Pasig River and the lakevia the Napindan Channel

The navigation lock of the NHCS allows water trafficbetween Pasig River andLaguna de Bay through theNapindan Channel.

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

(PAGASA)

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

Large runoff on pavementsandunderground floods in the Ayala underpass, Makati (Flickr).

Inundation of the Provident Villagein Marikina City(Googlemap; Flickr).

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

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

Property damage(Flickr).

Suffering and death(Flickr).

And a safe passage.

(www.op.gov.phand Flickr)

8 meters high5 meters high

Marikina Riverbank 9/28/2009. Downstream view of Rosario Weir

along Marikina River.

Preliminary Computations

SWATCH-computedPeak FloodDischarge = 5770 cu.m./sof Marikina River at Sto Niño on 26 September 2009,

based on thePoint Hourly Rainfall at Science Garden, QCSynoptic Station withapplied area reduction factor = 0.6

(NHRC)

• Rainfall Depth starting at 8:00 am, 26 September 2009: 6 hours: 347.5 mm 9 hours: 413.012 hours: 448.5

• Sliding Maximum Rainfall Depth: 6 hours: 381.5 mm 9 hours: 418.012 hours: 448.5

For Rainfall depth, P = 347.5 mm in D= 6 hours duration, its Return Period, T = 100 to 150 years.

• Based on the PAGASA web-published chart (below) of Science Garden station: P = function(T, D);• also on the DPWH-JICA (March 2003) regression equation: P = D* A(T)/[C(T) + D]^b(T) based on PAGASA data.

Computation of MAXIMUM RIVER WATER LEVEL

• Using the published DPWH-JICA Discharge Rating Curves (March 2002) in the case of Marikina River at Sto Niño (DA = 535 sq.km.): Q = 17.01 (H – 0.00)^1.85 for H < 5.33 meters Q = 0.20 (H – 0.00)^4.49 for H > 5.33 meters which relates river gage height, H (meters), to flow discharge, Q (cu.m./sec), by regression of historical data -

• then the Peak Flood Flow = 5770 cu.m./sec computed by the SWATCH hydrologic model corresponds to a gage height of H = 9.8 meters,

• which means that starting from an initially low H = 1 to 2 meters, the gage height (river water level) can rise by (8 to 9) meters,

• these computations being consistent or matching with the observed maximum flood water levels on 26 September 2009 relative to the low banks.

Computation of FLOOD FREQUENCY

• Compared to the 30-year Flood = 2740 cu.m./sec (design flood capacity of PMRCIP) 50- year Flood = 2980 cu.m./sec 100-year Flood = 3310 cu.m./sec

• taken from the flood frequency distribution for Marikina River at Sto Niño as derived and adopted in the DPWH Pasig-Marikina River Channel Improvement Project (PMRCIP) and also reviewed by NHRC in 2005,

• it is clear that the computed 2009 Peak Flood Flow = 5770 cu.m./s has exceeded the previous 100-year flood and therefore necessitates a review and possible revision of the flood frequency distribution.

• Nonetheless, it can be concluded that the Ketsana-Ondoy tropical storm of 100-150 year return-period has produced a record maxum flood discharge of 5770 cu.m./sec that has greatly exceeded the previously projected 100-year flood discharge, whereas the PMRCIP design flood capacity of 30 year return period was never exceeded before September 26, 2009.

It is expected that when more rainfall and river flow data become available for the storm period, more refined values will be obtained without resulting in the revision of the main conclusion already made with respect to storm and flood frequencies or return period exceeding 100 years.

NHRC Re-evaluation of the Hydrologic Design Parameters of DPWH-PMRCIP (2005)

1. Rainfall analysis – methodology is accepted after review - utilized the annual maximum rainfall intensities at Port Area station (1907-2000) which has longest data in Metro Manila - applied the Gumbel-Chow probability distribution for annual maximum rainfall - applied the accepted rainfall intensity formulas to express intensity as function of return period and duration of annual maximum rainfall - derived center-concentrated type of hyetographs from rainfall intensity formulas - obtained design storms by multiplying hyetographs with areal adjustment factors 2. Flood Run-off Analysis – methodology is accepted after review - fitted the Log Normal probability distribution to the annual peak discharge data at Marikina River, Sto Niño station to statistically derive design flood discharge. - used the Storage Function Model to generate flood hydrographs from the mountainous Upper Marikina River Basin (DA = 505.9 sq. km.) under both existing land use (1997) and future land use (2020). - used the Quasi-Linear Model to generate flood hydrographs from the urbanized lower part of the Pasig-Marikina River Basin (DA = 115.1 sq.km.) under both existing land use (1997) and future land use (2020). - applied the areal adjustment factor to hyetographs in order for the simulated flood peak discharge by flood runoff model to be equal to the probable discharge from statistical analysis of annual maximum flood at Sto Niño station.

Highlights of the Hydrologic Design Parameters of PMRCIP

1. Rainfall Data - Historically highest 1-day rainfalls at Port Area were as follows: Year Max Rainfall, mm/day (post-war with asterisks) 1970 403.1 * 1976 371.6 * 1919 310.6 1923 309.1 1924 285.0 1918 271.5 1931 265.7 1972 265.1 * 1921 263.6 1985 252.8 * 1997 241.5 * 1958 239.8 * 1961 236.2 * 1914 234.7 1977 234.4 *

2. Probable Rainfall at Port Area by Gumbel-Chow Disribution: Return 60-min 1-day period Rainfall Rainfall (years) (mm) (mm) 2 53.3 147.2 5 68.4 210.6 10 78.4 252.5 20 88.1 292.7 30 93.6 315.9 50 100.5 344.8 100 109.8 383.8 150 115.3 406.6

Comments:The nearly 150-year rainfall wasexperienced in 1970, while the nearly 100-year rainfall wasexperienced in 1976.

4. Probable Annual Max. Discharge of Marikina River at Sto Nino station (by Log Normal Prob. Dist. and Flood Runoff Model)

Return Max. Discharge, m3/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 m3/shas not yet been experienced in the42-year period of record, 1958-2000.However, the 20-year flood of 2550 m3/swas exceeded in 1986.

3. Historical Annual Maximum Discharge of Marikina River

at Sto Nino, Marikina

Year Max. Discharge, m3/s 1986 2650 1970 2464 1959 2072 1977 2051 1966 2036 2000 1895 1998 1680 1995 1676 1999 1642 1967 1609 etc.

5. Sea and Lake Boundary Conditions Manila Bay (Pier 15)Tide Levels Mean Sea Level (MSL) = 10 + 0.599 mMean Higher High Water (MHHW) = 10 + 1.128 mMean Spring Higher High Water (MSHHW) = 10 + 1.391 mDatum Level (DL) = 10 m

Laguna de Bay (north shore)(1949-1999 data)Historical MaximaYear Annual Max. Water Level (m above DL)1972 14.031978 13.581988 13.551986 13.341960 13.171952 13.08etc.Annual mean = 11.50 m.Mean annual max = 12.34 m.

Thank You.