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

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

Laguna

de Bay

Manila

Bay

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.

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

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)

Marikina

River Basin

(535 sq.km.)

and the 21

sub-basins

& lake of the

Laguna de

Bay Basin

(3229 sq.km.)

(NHRC)

Marikina

River Basin

(535 sq.km.)

and the 21

sub-basins

& lake of the

Laguna de

Bay Basin

(3229 sq.km.)

(Wikipedia)

Marikina RB

Pasig RB

Mangahan

Floodway

(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 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.

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 pavements

and

underground floods in

the Ayala underpass, Makati (Flickr).

Inundation of the

Provident Village

in Marikina City

(Googlemap; Flickr).

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

Collapse of a wall

of the Mangahan Floodway

near Rosario Bridge, Pasig City.

(Googlemap; Flickr).

Property damage

(Flickr).

Suffering

and death

(Flickr).

And a safe passage.

(www.op.gov.ph

and Flickr)

8 meters high

5 meters high

Marikina Riverbank

9/28/2009.Downstream view of Rosario Weir

along Marikina River.

Preliminary Computations

SWATCH-computed

Peak Flood

Discharge = 5770 cu.m./s

of Marikina River

at Sto Niño

on 26 September 2009,

based on the

Point Hourly Rainfall

at Science Garden, QC

Synoptic Station with

applied area reduction

factor = 0.6

(NHRC)

• Rainfall Depth starting at 8:00 am, 26 September 2009:

6 hours: 347.5 mm

9 hours: 413.0

12 hours: 448.5

• Sliding Maximum Rainfall Depth:

6 hours: 381.5 mm

9 hours: 418.0

12 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 was

experienced in 1970, while the

nearly 100-year rainfall was

experienced 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/s

has not yet been experienced in the

42-year period of record, 1958-2000.

However, the 20-year flood of 2550 m3/s

was 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 m

Mean Higher High Water (MHHW) = 10 + 1.128 m

Mean Spring Higher High Water (MSHHW) = 10 + 1.391 m

Datum Level (DL) = 10 m

Laguna de Bay (north shore)

(1949-1999 data)

Historical Maxima

Year Annual Max. Water Level (m above DL)

1972 14.03

1978 13.58

1988 13.55

1986 13.34

1960 13.17

1952 13.08

etc.

Annual mean = 11.50 m.

Mean annual max = 12.34 m.