Ondoy Tragedy

Lessons to be learned…

Fernando Siringan ando.msi@gmail.com

Marine Science Institute, University of the Philippines Diliman

Gemma Narisma, Rosa Perez, Celine Vicente, Antonia LoyzagaManila Observatory

Mahar LagmayNational Institute of Geological Sciences, University of the Philippines Diliman

http://earthobservatory.nasa.gov

Observations from TRMM from Sept 21 to 27, 2009

Wind Direction and Wind Speed

Hourly Rainfal, Average Pressure and Winds in Manila Observatory (26 Sep 2009)

0

10

20

30

40

50

60

70

12 AM 3 AM 6 AM 9 AM 12 PM 3 PM 6 PM 9 PM

Time (pht)

Rai

n (

mm

)

985

990

995

1000

1005

Pre

ssu

re (

hP

a)

Rain

Barometric Pressure

• The highest rainfall was measured in Manila Observatory between 9 AM and 1 PM.

• Highest rainfall of 61.4 mm/hr was measured at 10 AM

Weekly Accumulated Rain = 459.8 mm

Accumulated Rainfall in Manila Observatory (21-28 Sep 2009)

0

100

200

300

400

500

9/21 9/22 9/23 9/24 9/25 9/26 9/27 9/28

Da

ily

Ra

in (

mm

)

Accumulated Rain

Daily

Normal Monthly Accumulated Rain for September

Daily Rain 26 Sep 2009 368.6 mm

• “Ondoy” brought a total of 368.8 mm of rain over Manila Observatory on September 26, 2009.

• This daily rain measured in Manila Observatory is higher than the monthly normal (330.3mm) in the Port Area.

330.3 mm

Accumulated rainfall over a week measured by TRMM was over 500 mm in Metro Manila. This value is higher than the monthly normal.

http://www.nscb.gov.ph/headlines/StatsSpeak/2009/030909_rav_climatechange.asp

http://trmm.gsfc.nasa.gov/trmm_rain/Events/manila_rainfall_perspective_21-28sep09.jpg

Rain Accumulated in Southern and Central Luzon (21-28 Sep 2009)

Ondoy is an extreme event. But is Ondoy a manifestation of climate

change?

Daily rainfall at Science Garden (1961-2004)

334.5276.5 267

246.4223

Daily rainfall at Port Area (1961-2004)

403.1

265.4257.4 252.8

371.4

Essential parts of a warning system …

Since rainfall is highly variable even over a small area, it is best to have a good network of weather stations – data can be viewed by anybody through the internet.

A similar network of river gages – also viewable through the internet.

Water level of dams can be included in the network.

River channel capacities are decreased by…

Encroaching houses and fishpondsIncreased siltation due to deforestation

Garbage

What is causing our worsening floods?

Riv

er

Guagua River

Pasa

c

Sta. 7+000

130m

250mMalusac River

Fishpond encroachment (from DPWH)

Whe

re is

the

river

?

channel capacities decreased by…encroachment of structures …filling up of river channels … by sediments and garbage

In Metro Manila worsening floods are typically attributed to insufficient drainage …

disappearance of about 21 km of small rivers (Zoleta-Nantes, 2000) – converted for housing or other uses by government and private entities

drainage structures are outdated relative to degree of urbanization … some are century old

Climate change?

Where is the river?

Missing river?

RiverLongos area

Letre Rd

Decrease in floodplain areaUrban sprawlFlood control dikesFishponds

Global sea level riseLand subsidence. The least understood, but very important.

Other causes of worsening

floods

Lowering of land, even large areas, due to:

Natural compaction ofunderlying soil and sediment

Compaction sped up by rapid withdrawal of groundwater

Land subsidence

Long-lasting floods that now last for months occur in…

coastal CAMANAVA

and the Pateros-Taguig-Muntinlupa area where floods are due to elevated lake levels during the rainy season

But in CAMANAVA, floods can be caused by high tide alone… but this was not so in the past.

At Manila’s South Harbor mean sea level rose at about 2 millimeters per year from 1902 to the early 1960’s. . .

. . . then started rising ten times as fast. WHY?

Groundwater withdrawal!

<20 million liters per day (MLD)

250 MLD

778 MLD

1770 MLD in 2004 (CEST 2004)

989 MLD in 1990 (JICA 1992) Metro

Manila`s groundwa

ter demand is

still increasing

.Consequent

subsidence will

continue and may

even accelerate

!

If too much water is pumped out of the aquifer, the pressure is reduced in the pore spaces between grains of sand and gravel.

Water in the clay layers is sucked into the aquifer.This causes the clay layers to shrink . . .

. . . and the ground surface to sink.

Pipe appears to rise out of the ground

Pumps extract water from “aquifers” –layers of sand and gravel soaked with water.

How groundwater withdrawal causes land to subside

We need to lessen our dependence on groundwater.

Benchmarks used for re-leveling (1978 vs 2000) survey (Jacob 2004)

Tuff

Coastal/Alluvial

Lake

/Allu

vial

0.95

1.40

1.46

0.76

0.790.1

60.77 0.9

6

0.96

0.88

0.57

0.67

0.95

0.73

0.61

0.59

0.51

0.57

0.43

0.46

0.46

0.46 0.4

7

0.64

Maximum magnitude of subsidence – 1.46 m (6.1 cm/y)

Change in height of maximum high tide, from 1991 to 2002 based on social survey ranges from 0.5 - 1.0 m (4.5 – 9.1 cm/y)There appears to be an acceleration in rate of subsidence in recent years.

Lateral variation in magnitude of subsidence is not a function of underlying lithology.

Piezometric Level 1951 (NHRC, 1991)

270000 280000 290000 300000 310000 320000

270000 280000 290000 300000 310000 320000

1560

000

1570

000

1580

000

1590

000

1600

000

1610

000

1620

000

1630

000

1640

000

1650

000

1560

000.

0015

8000

0.00

1600

000.

0016

2000

0.00

1640

000.

00

L A GU NA L A K E

M A NIL A BA Y

262000

MALOLOS

BULACAN

GUIGUINTO

BALAGTAS

BOCAUE

MARILAOMEYCAUYAN

VALENZUELA

PLARIDEL PANDI

BUSTOSANGAT

STA. MARIA

CITY OF SAN JOSE DEL MONTE

CALOOCAN CITY

NORZAGARAY

RODRIGUEZ (MONTALBAN)

QUEZON CITY

NAVOTAS

CITY OF MANILA

SAN MATEO

CITY OF MARIKINA CITY OF ANTIPOLO

CAINTA

TAYTAY

ANGONO

PASIG

MANDALUYONG

SAN JUAN

MAKATIPATEROS

TAGUIG

TERESA

CITY OF PARANAQUE

CITY OF LAS PINAS

BACOOR

IM US

KAW IT

CAVITE CITY

NOVELETA

TANZA

GEN TRIAS

TRECE MARTIRESCITY

DASMARINAS SAN PEDRO

GEN. MARIANOALVAREZ

CARMONABINAN

STA. ROSA

SILANG

AMADEO

TAGAYTAY

330000

330000

OBANDO

1560

000

1570

000

1580

000

1590

000

1600

000

1610

000

1620

000

1630

000

1640

000

1650

000

C EST, Incorporated

NATIO NAL W ATER R ESO U RC ES BO AR D 2004 G R O UND W ATER SUR FACE M AP FIG U R E

5-7W A TE R R E SO U R C ES

A S S E S S M E N T FO R P R IO R IT IZE D C R IT IC A L AR E AS

PASAY CITY

CITY OF MALABON

CITY OF MUNTINLUPA

BINAGONAN

-40- 200

-40

- approx. aquifer's areal extent

N

LEGEND:

SCALE IN KILOMETERS

0 2 4 6 8 10

- Munic ipality

- Groundw ater Level Contour (mas l)

2 0

- L ake/sea

- Well

0 - Sea Level GW Level Contour

CALOO CAN CITY

- A rea w here GW Surfac e is below Sea Level

- A rea w here GW Surfac e is above Sea Level

NOTE: masl - meters above sea level

47

-120

Piezometric Surface

2004 (CEST, 2004)

(Sources: 1:50,000 topographic maps of Namria, 1990 and 1992)

M 6-7 earthquakes recur every 200 to 400 years (Nelson et al., 2000) and have an associated ~0.5 m vertical displacement (R. Rimando pers. comm.)

Trace of West Marikina Valley Fault

Subsidence along the Marikina Valley can be due to combined natural, earthquake and human induced compaction.

Other SE Asian sites experiencing subsidence due to over extraction of

groundwater SUBSIDENCE

LOCATION PERIOD Meters cm/year

Tokyo, 1918-87 4.5 6.5 Japan

Tokyo

Osaka, 1934-68 2.8 8.2 Japan

Osaka Shanghai, 1921-65 2.63 6 China

Shanghai

Yun-Lin, 1989-97 0.66 8.25 Taiwan (Fishpond area!)

Yun-Lin

Hanoi, 1988-93 0.1-0.3 2-6 Vietnam

Hanoi

CAMANAVA 1991-2002 0.3 - 1 2.7 – 9.1

Manila

Bangkok, 1980-90 0.5-1 5-10 Thailand

Bangkok

Jakarta, 1991-99 0.3-0.8 4-10 Indonesia Jakarta

121°30' E121°15' E121°00' E

121°30' E121°15' E121°00' E

14

°45

' N1

4°3

0' N

14

°15

' N

14

°45

' N1

4°3

0' N

14

°15

' N

N

121°30' E121°15' E121°00' E

121°30' E121°15' E121°00' E

14

°45

' N1

4°3

0' N

14

°15

' N

14

°45

' N1

4°3

0' N

14

°15

' N

Bathymetric data based on 1920 to 1939 hydrographic

surveys

Lake surface area922 km2

Total lake volume2.32 x 109 m3

Average waterdepth2.52 m

1

2

3

4

1 2

3

4

0 5 10 15 Km

4

contour interval 0.5m

Bathymetric data based on 1997 to 1998 hydrographic

surveys

Lake surface area869 km2

Total lake volume1.95 x 109 m3

Average waterdepth2.24 m

1 11

1

22

2

22

3

3

3

3 343

4

c o n to u r in te rv a l 0 .5 m0 5 1 0 1 5 K m

1

1

1

1

22

2

2

2

3

3

3

33

4

3

4

contour in te rva l 0 .5m0 5 10 15 Km

Change in Bathymetry (1939 to 1968)

Change in Bathymetry (1968 to 1998)

The Manggahan Floodway is a major source of sediment.

Immediate and long-term solutions to Laguna de Bay inundation …

Increase the number of channels draining the lake - widen Taguig River and revive other rivers in Taguig Delta Plain.

For the long-term, modification of Napindan structure might be required.

Increase the capacity of Pasig River through channel widening – remove major constrictions.

… a shallow but wide channel is more efficient than a deep but narrow channel because the gradient is almost flat.

… allow planned, episodic high discharges to flush accumulated sediment and other debris within the channel.

Control erosion in the watersheds and sedimentation in Laguna de Bay. We need a good forest cover.

The Ondoy tragedy is due to an extreme event …

But …..

Magnitude and extent could have been much less

Given wider and deeper channel ways

Greater capacities of natural retention ponds

For the future,

among others we should increase, widen and deepen our channel ways,

implement easement rules,

reforest, allocate retention ponds

FLOOD HEIGHT: 4-5m

Houses on stilt in Candaba

Photo by J. Ong

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000YEAR

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Sta

nd

ard

De

par

ture

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-1

0

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Sta

nd

ard

De

par

ture

Pacific Decadal Oscillation

Multivariate ENSO Index