Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 20112009 Typhoon Ondoy Flood Disasters in Metro Manila
Teruko SATO* and Tadashi NAKASU***

Visiting Researcher, National Research Institute for Earth Science and Disaster Prevention,*
Tokiwa University, Japan**
International Centre for Water Hazard and Risk Management under the auspices of UNESCO (ICHARM), Japan

Abstract
From September 25 – 26, 2009, Typhoon #16 (Ondoy) struck southwest Luzon in the Philippines. Flood disasters
caused by this heavy rainfall affected 872,097 people throughout the entire metropolitan area, causing 241
fatalities, 394 injuries, and damaging 65,521 buildings (of which 12,563 were completely destroyed). Infrastructuredamages (not including agricultural losses) amounted to 570,187,587 Philippine pesos (NDCC, 2009a).

We investigated the great urban flood disaster that occurred in the megacities of the developing country, which are
expected to grow to a population of 25 million by 2015. The conditions caused by runoff, flooding, and damages
as well as mitigation measures relating to the hydrological conditions, land environments, and social economic
conditions in the Philippines are reported based on field investigations and interviews with related parties.
Key words: 2009 Typhoon Ondoy, Urban flood, Metro Manila, Pasig-Marikina-Laguna Lake Complex

1. Introduction
From September 25 – 26, 2009, Typhoon #16 (Ondoy)
struck the southwest Luzon in the Philippines, causing
torrential rainfall. Within 24 hours, 455.0 mm of rain fell at
the Quezon City Science Garden, 258.5 mm fell at the Port
Area, and 331.8 mm fell in the municipality of Tanay inneighboring Rizal province. The amount of precipitation at
the Science Garden reached levels expected only once per
century or more (for rainfall in a 24-hour period) or once
every 150 years or more (for rainfall in a 12-hour period),
and the 92 mm of rain that fell between 11 a.m. and noon wasof a level expected only once every 5 – 10 years (PAGASA,2009).
This heavy rainfall affected 872,097 people throughout
the entire metropolitan area, causing 241 fatalities, 394
injuries, and damaging 65,521 buildings (of which 12,563
were completely destroyed). The infrastructure damages(not including agricultural losses) amounted to 570,187,587
Philippine pesos (NDCC, 2009a; NDCC, 2009b). Other
such losses were caused by traffic coming to a standstill
due to major city center thoroughfares such as Epifanio delos Santos Avenue being cut off by flood water and by thecancellation of domestic and international flights at Manila
airport (Manila Shimbun, 27 Sept.).

In this chapter, we discuss the flood disasters that occurredin the Manila Metropolitan Area (Metro Manila), which isa major region in the developing country and one of southeast Asia’s most prominent overpopulated centers with apopulation of 11.6 million according to the 2007 Census ofPopulation, of which population growth rate is 2.12.
2. Surveyed Area
As Fig. 1 shows, Metro Manila comprises 16 cities andthe municipality of Pateros, all of which lie within the PasigMarikina-Laguna Lake Complex (catchment area: 4,678 km2)
except for parts of the north and the southernmost tip which
lie along Manila Bay (Fig. 2). This chapter concerns the flood
disasters that took place in this river basin.
3. River systems and flood-prone areas
3.1 River Systems
As its name suggests, the Pasig-Marikina-Laguna Lake
Complex consists of two rivers and one lake. One of theseis the Marikina River, which has a catchment area of 516.50
km2 (at the Napindan junction) and flows out from the Sierra
Madre mountain range in the east part of the river basin.
The Marikina River meanders its way southwards along the
Marikina River flood plain, and floodwater is diverted into the* Miwa 1-430-1, Mito, Ibaraki, 310-8585, Japan** Minamihara 1-6, Tsukuba, Ibaraki, 305-8516, Japan－ 63 －

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Manggahan floodway from the Rosario weirin the left bank, where the Upper Marikina
River becomes the Lower Marikina River.
The Lower Marikina continues southwards,
and at Napindan junction it is joined by the
Pasig River that flows north from Laguna de
Bay (Laguna Lake).
The Pasig River is the only river thatflows out from Laguna Lake. The Napindan
channel flows north from the north coast of
Laguna Lake, and where it joins the Marikina
River, it starts to flow northwest across thecentral plateau and into the coastal lowland
alongside Manila Bay and then out into thebay near the old city district at the center ofthe lowland area. The Pasig River is joined by
the San Juan River as a right tributary, which
has the central plateau as its river basin.
With an area of 900 km2, Laguna Lake isthe largest lake in the Philippines, occupyinga large region extending from the central tosouthern parts of the river basin. The lakehas a catchment area of 3,820 km2, which isabout 80 % of the total catchment area. Thiswide and shallow lake temporarily storesthe water flowing from at least 20 tributary
river basins, and during floods it functions asa retarding reservoir for the Marikina River.
Water levels fluctuate from 10.5 m elevations in the summer
months to 12.5 m in the rainy seasons. The annual mean is an
11.32 m elevation (Edgardo C. Manda, 2008). When the sea
level in Manila Bay is higher than the water level in the lake,
the water flows backwards from the sea into the lake.
3.2 Flood-prone areas
The flood-prone areas in the Pasig-Marikina-Laguna Lake
Complex can be divided into the following four flood plainsas depicted in the flood hazard map in Fig. 3:
1) Coastal lowlands alongside Manila Bay: Land with analtitude of 3 meters or less next to Manila Bay and down the
Pasig River. This lies at the center of Metro Manila.
2) Marikina flood plain: Alluvial lowland with an altitudeof 5 – 30 m along the Marikina River, which is being
developed to the north and south at the western end of theriver basin. It is bounded to the west by the central plateau
that lies between the Manila Bay coastline and the coastal
lowland and to the east by the Sierra Madre mountain range
from where the Marikina River originates.
3) Laguna Lake Plain: The Marikina flood plain continues
on into the Laguna Lake Plain. This is a marshy plain with analtitude of just a few meters, where it is affected by the rise of
the water level of Laguna Lake.
4) Valley plains cutting through the central plateau: Narrow

Fig. 1 Map of Metro Manila (MMDA, 2009).

lowland areas alongside the Pasig and San Juan Rivers where
they cut across the central plateau.
In these flood plains, even floods with an estimatedfrequency of once every 2 – 10 years (shown in yellow) areliable to cover a substantial part of these areas, while floods
with an estimated frequency of once every 50 – 100 years(blue) are liable to cause flood damage over the entire flood
plain (Fig. 3).
4. Locality of flood disasters
The flooding of Metro Manila varies according to thehydrological conditions and land environments of the flood
plain and river basins. Table 1 shows the characteristics offlooding and flood damage in Metro Manila and how theflood inundation and damage varied between the four flood
plains. Inner water inundation may have also occurred in theriver basins where there was severe external overflow, but thisfigure charts the inundation phenomena that caused most of
the damage. Furthermore, administrative districts sometimes
cross over multiple topological zones and were therefore
divided into their main topological areas.
As a result, the flooding of Metro Manila can be divided－ 64 －

2009 Typhoon Ondoy Flood Disasters in Metro Manila － T. SATO and T. NAKASU

Fig. 2 Maps of the Pasig-Marikina-Laguna Lake Complex (NAMRIA Geographical Map 1:250,000)
R: Rosario weir, N: Napindan Janction.

into regions where increased damage was mainly causedby external flooding and into regions where it was mainly
caused by inner flooding. The Marikina flood plain and
San Juan valley plain can be placed in the former category
and the Laguna Lake Plain and coastal lowlands along theManila Bay coast can be placed in the latter, which can also
be subdivided into the coastal lowlands, which experienced ashort flooding duration, and the Laguna Lake Plain, where theflooding persisted for more than two weeks.
4.1 Marikina flood plain
In the Marikina flood plain, where damage was mainly
caused by external flooding, overflow well in excess of
twice the river channel discharge capacity occurred, andthe water level in the river rose rapidly by approximately 3

m in 3 h. The large depth of flood water combined with the
sharp increase in water level resulted in a severe inundationthat spread across the entire flood plain (Figs. 4 and 5).
Flood water depths of 7 m were recorded in some places
although the flooding was short-lived (JICA, 2009; ADB,
2009; P.B.GATAN, 2009). The flood caused damage on alarge scale (Photos 1, 2, 3, and 4), affecting many people
and causing 121 deaths (half the total for Metro Manila). The
flood plain lies mostly in Marikina City, but part of it extends
upstream into Quezon City. In Marikina City alone, there
were approximately 180,000 people affected by the flooding.
Other problems included a high incidence of infectious
disease and environmental damage caused by the runoff ofpollutants from small and medium scale factories in the river－ 65 －

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Fig. 3 Flood hazard map of Metro Manila (MGB, 2009).

basin.
4.2 Valley plain along the San Juan River
In the valley plain along the San Juan River (Photo 5),
where damage was caused mainly by external flooding, there
was external flooding from a flash flood from small andmedium-sized rivers descending from an altitude of 95 to 3
m. At the Quezon City Science Garden inside the river basin,
precipitation rates of 92 mm in 1 h and 455.0 mm in 24 h
were observed, showing that this river basin was inflicted bya torrential downpour. Since the catchment area is only about
one fifth the size of the Marikina River’s catchment area, it isexpected that flooding began earlier here than in the Marikina

River. Also, since the flooded region of the valley plain islimited, this area is generally prone to more severe floodingwith a greater depth of inundation (Fig. 6). Maps show thatthe inundation area expanded to the upper reaches of the plain.
This area suffered the second highest level of destruction
behind the Marikina flood plain, and there were 111 fatalities.
The number of people affected in this river basin (which
includes the cities of Quezon, San Juan, and Mandaluyong)reached 135,000.
4.3 Coastal lowland adjacent to Manila Bay
The coastal lowland adjacent to Manila Bay was affected
mainly by inner flooding. This is a low-lying and poorly－ 66 －

2009 Typhoon Ondoy Flood Disasters in Metro Manila － T. SATO and T. NAKASU
Table 1 Conditions of flood disasters caused by Typhoon Ondoy in Metro Manila in relation to landforms.
Flooding
Landforms

Related
Water
BodiesPredominant
PeriodType

Damage

Depth

CitiesPasig-Marikina-Laguna Basin

Southern Part of Metro Manila

Dead178,98573

113,420
2,234
19,660135,314
5,790
3,395
8,537
17,722
127,11032,320132,630
111,850
403,9109,851
19489,45099,4958,091
2,250
26,33028,580

48
121
57
3
3
63
9
7
0
16
23
0
0
3
26
1
0
3
4
8
2
1
3

872,097

241

Marikina Flood
Marikina R.
Plain

North Part

Farthest
South

Other Basins

within up to Marikina city
three the 2nd Quezon citydays
floor Sub total
Outer
Quezon city
Flooding
up toValley Plain
San Juan city
San Juan
withinthe䠄Central Plataeu)
Mandaluyong city
R.
1day
head
Sub total
Manila䚷city
Coastalup to
Passig R.,
Makati city
withinLowlandtheUrban
Pasay city
1week
(South Part)
chest
Draingage
Sub total
Innerpasig city
Lauguna
Flooding
up to Pateros
Lake, Passig
over 2
Laguna Lake R., Mangahan
Taguig city
the
weeks
Plain
Flood Way,
head Mantinlupa city
Taguig R.
Sub total
Malabon city
Nvotas city
Coastal Lowland
Caloocan city
(Sub total)
Valenzuela city
Central Plataeu
Paranaque city
Las Pinas city
Coastal Lowland(Sub total)
Unclassified Economic Loss
Total of Metro Manila

Affected
Population

Dead in the Quezon City is devided into 2 according to the landforms.
Flooding period refferred from JICA (2009) & Manila News Paper.
Damage reffered from NDCC㻌Report㻌No.42.

Flood Water Level (m)0.00 - 0.23
0.24 - 0.46
0.47 - 0.92
0.93 - 1.62
1.63 - 2.08
2.09 - 3.23
3.24 - 6.00

Fig. 4 Inundation depth by Typhoon
Ondoy in Marikina River flood
plain (NAMRIA, 2009).

(Interpotation Method:
Inverse Distance Weight (IDW))

Fig. 5 Maximum inundation
depth in Marikina flood
plain (Google, 2009).

－ 67 －

EconomicCompletely
Loss
Destroyed
House 䠄Infrastruncture)
1,083

39,639,300

140
0
1

58,285,016
24,720,000
6,999,370

00014,521,714
409,490
9,524,500

499
0
48
3,839
4,386
159
6,748
0

37,308,780
0
10,139,500
16,550,500
20,354,400
07,195,896

35
8
3

6,117,375
38,525,642
25,658,550

12,563

254,232,534
570,182,587

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Fig. 7 Geographical map of the low land along Manila Bay(JICA, 2004).

Fig. 6 Maximum inundation
depth by 2009’s
Typhoon Ondoy in San
Juan River flood plain(Google, 2009).

drained land environment with an elevation of 3 m or less(Fig. 7). Here, the Pasig River was partly overflowed, but it
was possible to continue operating the pumps that expel inner
water from lowland areas. However, in the lowland areas,
it was not possible for the heavy rainfall to drain away, andinner water inundation occurred (Fig. 8). The inundation
depth was deep enough to reach up to one’s head, but flooding
was fairly short-lived (from half a day to a few days). As aresult, the number of people affected in the coastal lowland
was only about 2 % of the total for Metro Manila as a whole,and there were only 19 fatalities in this area (Photos 6 and 7).
The Pasig River, flowing through the central areas ofFig. 8 Maximum inundation
depth by 2009’s
Typhoon Ondoy in the
Laguna Lake Plain(Google, 2009).

－ 68 －

2009 Typhoon Ondoy Flood Disasters in Metro Manila － T. SATO and T. NAKASU

Flood Water Level (m)Fig. 9 Inundation depth inLaguna Lake Plain(NAMRIA, 2009).

0.00 - 0.23
0.24 - 0.46
0.47 - 0.92
0.93 - 1.62
1.63 - 2.08
2.09 - 3.23
3.24 - 6.00

Fig. 10 Maximum inundation
depth in the Laguna Lake
Plain (Google, 2009).

(Interpotation Method:
Inverse Distance Weight (IDW))

Metro Manila, was spared from flooding due to the floodingof the Marikina River further upstream and due to the factthat the floodwater was diverted into Laguna Lake from theManggahan Floodway and Napindan channel so that theflood discharge of the Pasig River was kept down to 600 m3/
sec, which is just about within the river channel discharge
capacity (500 – 600 m3/sec) (MMDA, 2009; P. B. GATAN,
2009). In the city drainage channel, where drainage capacity
has decreased to the point where it can only cope with rainfall
levels estimated to occur once every 2 – 5 years, it was notpossible to protect the city from the inner flooding caused by
the heavy rainfall of Typhoon Ondoy.
4.4 The Laguna Lake Plain
The Laguna Lake Plain was affected mainly by inner
flooding and remained flooded for a long period of time (Figs.
9 and 10). It is a low-lying marshy area with an elevation ofjust a few meters that was affected by the increased waterlevel of Laguna Lake and was deeply flooded, with regions
close to the lake shoreline remaining submerged for morethan a month (Photos 8 and 9). Although the flood inundation
was not as severe as that in the Marikina flood plain, the flood
water rose to a considerable depth, and the prolonged floodinundation resulted in the greatest number of affected people

in the whole metropolitan area, reaching 400,000 people, or
45 % of the total. However, there were 26 fatalities in thisregion, which is about one fifth that of the Marikina flood
plain.
5. Society’s resilience to flood disasters
5.1 Reducing the flooding(1) Flood control facilities
The key component of Metro Manila’s flood control is
the Manggahan Floodway (Photos 10 and 11), which has
a drainage capacity of 2,400 m3/sec and is designed for aonce-per-century flood discharge. By diverting 70 % of the
Marikina River flood discharge into Laguna Lake from theRosario weir to reduce the flood discharge that continues
downstream to the Pasig River, it is possible to reduce theflood inundation of the Pasig River flowing through thecity center. When Typhoon Ondoy struck, flood water wasdiverted from the Marikina River into Laguna Lake at a rateof 3,000 m3/sec, and only a partial external overflow occurredin the Pasig River, so it was possible to continue operating
the inner water drainage pumps (MMDA, 2009; P.B.GATAN,
2009) .
The Pasig and Marikina Rivers are designed to withstand a－ 69 －

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Fig. 11 Illegal settlements in the city drainage channels (Jica, 2005).

once-in-30-years flood (Marikina River: 2,600 – 2,900 m3/sec; Pasig River: 500 – 600 m3/sec in the middle section and1200 m3/sec in the lower reaches), but the designed discharge
capacity is actually achieved only in the middle section of the
Pasig River. The drainage of the other areas is incomplete.
For example, the current discharge capacity of the Marikina
River is 1,500 – 1,800 m3/sec, which is smaller than thedesign scale.
To protect the regions that open out onto the Laguna Lake
Plain to the west of the Manggahan Floodway (the cities of
Taguig, Pateros, and Pasig) from becoming inundated due toa rise in the water level of Laguna Lake, work is under way

to construct a 9.5 km coastal bank along the lake, 8 weirs,
and 4 drainage pump stations (MMDA, 2009; P.B. GATAN,
2009). These inner water drainage facilities helped to reduce
the flooding duration of the inner water inundation caused by
Typhoon Ondoy (JICA, 2009).
(2) Maintenance of flood control systems
While flood control maintenance is continuing, various
problems have arisen such as the reducing functionalityof flood control facilities. Drainage performance is being
impaired due to the disposal of garbage (Photos 12 and 13)
and construction of shanty towns in drainage channels. Fig.11
shows that the ratio by area of illegal settlements in the city

－ 70 －

2009 Typhoon Ondoy Flood Disasters in Metro Manila － T. SATO and T. NAKASU

drainage channels is high (JICA, 2005). As a result, in thecity drainage channels, where the drainage capacity has
decreased to the point where it can only cope with rainfall
levels estimated to occur once every 2 – 5 years (JICA,
2005), it was not possible to protect the city from the heavy
rainfall caused by Typhoon Ondoy. In the same way, shanty
towns narrow the width of the Manggahan Floodway.
(3) Development of the river basin has increased flood
discharge
The changing patterns of land use associated withhaphazard development are changing the scale of floods.
For example, in the city center district that is developing in
the low-lying areas along the Manila bay, urban discharge
channels for discharging inner water were constructed every
ten years, having a coefficient of discharge of 0.4 – 0.5.
An increase of the coefficient of discharge up to 0.95 hasdecreased the degree of the safety of the drainage system(JICA, 2005). In the Marikina River Basin, a decreasein forests by slash-and-burn farming, illegal harvesting,disorderly cultivation, the bulldozing of livestock farms, andthe development of housing areas have been increasing flood
discharge (JICA, 1994).
To mitigate flood disaster risks, maintaining flood control
facilities and managing land usage are requisites.
5.2 Development of flood plain and damage potential(1) Development and an increase in damage potential
A common problem of rice-growing areas in the Asianmonsoon region is that urbanization driven by population
growth can lead to building development on low-lying flood
plains that are used for rice paddy fields and such, resulting
in a greater potential for loss in the event of a flood disaster.
Metro Manila is no exception.
For example, half a century ago (around 1966), theresidential areas in the low-lying Laguna Lake Plain wereconfined to the natural levee and a high coastal terrace(4 – 7 m above sea level), but gradually they have encroachedinto lower-lying areas while filling in the poorly-drained backmarshes, and development has now reached as far as the deltaon the shores of the lake. The change in landscape brought
about by filling in these marshes has also created an artificial
flood-prone basin and changed the spatial distribution offlooding, which has affected the hazard situation (Hara et al.,2002).
(2) Illegal settlements and an increase in damage potential
Another factor behind the increased damage potential is thegrowth of illegal settlements. For example, in the Manggahan
Floodway, buildings have been erected in places such as
floodwater channels that have an extremely high risk offlood damage, thus giving rise to a larger number of disastervictims. At the margin of Laguna Lake, which is vulnerable
to rising water levels, many people living there were injured.
(3) Infectious disease and an increase of death

Furthermore, there are many places in the flood plains
where flood water is not adequately drained away. This
results in water being retained for long periods of time,causing environmental contamination that has an adverse
effect on living conditions and can lead to major outbreaksof infectious disease after a flood disaster has struck. After
Typhoon Ondoy, an outbreak of Leptospirosis caused 178
fatalities in the Metro Manila area (NDCC, 2009a).
(4) Flood water contamination
The flood water accelerated water contamination by
washing out pollutants from small and medium-scale factories
in the river basin into the Marikina River and Laguna Lake
(UNEP/OCHA, 2009).
6. Conclusions
The Typhoon Ondoy flood disasters of 2009 occurred in the
Metro Manila region, which has a growing population of over
11.6 million in a developing country, that has the following
characteristics:
1) The flood control plan to protect the population of 11.6
million people from floods is to cope with a once-in-30- years
flood. The flood control facilities are still under construction,and these differences in the state of development were oneof factors behind the differences of flooding in the four flood
plains of Metro Manila, along with hydrological conditions
and land environments of the flood plain and river basins.
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. 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 theinundation was not as severe as in the flood plains where
external flooding was prominent. The Manggahan Floodway
especially played an important role in protecting the central
part of Metro Manila from severe external flooding by
reducing the flood discharge of the Pasig River.
2) After flooding, an outbreak of infectious diseases wascaused by the floodwater standing for long periods of time,largely affecting humans. To reduce human damage in Metro
Manila, it is important to take actions to steadily reduce thissort of damage.
3) In Metro Manila, flood risks continue to increase. As
the population grows, the river basin is further developed.
This brings about changes in the flood runoff and inundation
characteristics, increases the potential for damage, andreduces the functioning of flood control facilities due toillegal settlements and the dumping of refuse into channels.
Also, the illegal dwellings of poor inhabitants encroach
into river zones and lakeshores vulnerable to water related
hazards, thus increasing the number of people affected by－ 71 －

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011
Table 2 Flood Control Projects in Metro Manila by Foreign Assisted Projects (P.B. Gatan, 2009).
1 Mangahan Floodway Project (Yen Loan, completed in 1988)
2 Effective Flood Control Operation and Warning System Project (EFCOS: 10th Yen Loan, completed in 1992)
The Project for Rehabilitation of Flood Control Operation and Warning System (EFCOS) in Metro Manila (Japanese Grant, completed in
December 2001)
3 Metro Manila Flood Control Project – West of Mangahan Floodway (21st Yen Loan, completed in August 2007)
4 KAMANAVA Area Flood Control and Drainage System Improvement Project (Special Yen Loan, construction to be completed in 2009)
5 Pasig-Marikina River Channel Improvement Project (26th Yen STEP Loan, construction of Phase I started in September 2009)
6 Valenzuela-Obando-Meycauayan Area Drainage System Improvement and Related Works Project (Requested for Yen Loan)
7 Integrated Drainage Improvement Project in Ninoy Aquino International Airport and its Vicinity (Study was completed in March 2004: JETRO)
8 Drainage Improvement in the Core Area of Metropolitan Manila (Study was completed in March 2005: JICA)
East Mangahan Floodway Area Flood Mitigation Project (Study was completed in June 2007 and to be requested for implementation to JICA)
9 San Juan River Flood Control Project (Feasibility Study was completed in 2002: JICA)
10 Upper Marikina River Channel Improvement Project (Feasibility study was completed in 2002: JICA)
・1980~1983: Napindan Hydraulic Control Structure:・1974~1997: Manila Drainage System Improvement
・2000~2007: Drainage pumping stations (15), flood gates, drainage channel improvement
West of Mangahan Floodway
・2002~2009: Lake dike (9.4 km), drainage pumping stations (7), Napindan river channel dike/parapet wall (6.1 km), Floodgates (8), Drainage
channel improvement
11 KAMANAVA Area Flood Control and Drainage System Improvement project・1978, 1992, 2000~2002: Ring dike (8.6 km), Drainage pumping stations (5), EFCOS Project・2009~: Pasig-Marikina river improvement

flooding.
To reduce flood risk, it is necessary to make an effort tofind a solution to these complex issues with transdisciplinary
cooperation, involving a variety of social, economic, andgovernmental factors and researchers.
4) In interviews on the 2009 Ondoy Flood withgovernmental bodies and other such organizations, we weretold about the importance of working to improve the abilityof communities to mitigate disasters and about the activities
of disaster relief volunteers. We hope that these movements
become more active in introducing a more diverse and wider
range of human resources.
5) Improving 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 institutecomprehensive measures targeting whole river basins
and whole components of flood risk. For example, hazard
control measures in flood plains by local people, land use
management for reducing damage potential in flood plains,
and the decrease of flood runoff from flood plains, etc. In
addition, comprehensive measures need the cooperation ofvarious concerned bodies including social scientists.
Japan has contributed to the improvement of flood control
in Metro Manila (Table 2). Through many experiences,
Japan has accumulated a considerable amount of knowledge
on the 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 newperspective, we expect that Japan’s experiences will be
useful.

Photo 1 & 2 Provident village damaged by flooding (Courtesy of the PNRC-Rizal, 2009).
－ 72 －

2009 Typhoon Ondoy Flood Disasters in Metro Manila － T. SATO and T. NAKASU

Photo 3 & 4 Provident village damaged by flooding (Courtesy of the PNRC-Rizal, 2009).

Photo 5 Floodwall along San Juan River.

Photo 6 & 7 Inner flooding in Makati City (taken by Kazutami Shiga).

Photo 8 & 9 Flooding along Laguna Lake on Nov. 30, 2009 in Taguig City.
－ 73 －

Natural Disaster Research Report of the National Research Institute for Earth Science and Disaster Prevention, No. 45 ; February, 2011

Photo 10 Manggahan Floodway(Courtesy of the MMDA, 2009).

Photo 11 Rosario weir at the Manggahan Floodway(Courtesy of the MMDA, 2009).

Photo 12 & 13 Dredging urban drainage channels in Metro Manila (Courtesy of the MMDA, 2009).

References
111 ADB (2009) : Information obtained by the interview with
ADB staff in Dec. 2009.
222 Y. Hara, S. haruyama, S. Okubo, and K.takeuchi (2002):
Flood hazard response to the urbanized bank up areas of
Laguna Lacustrine Plain, Metro-Manila. Proceedings ofRural Planning, Vol.4, 19-24.
333 Edgardo C.Manda, Laguna Lake Development Authority(2008) The case of the Lauguna de Bay basin in thePhillippines, Water and Climete Change Adaption in
Asian River Basins, 1-5 Dec. 2008, Malaysia.
444 Google (2009) : Typhoon Ondoy Maximum Flood
Height. (http://maps.google.com/maps/ms?msa=0&msid=115956470311312588880.000474a230d17e01a3021&i
e=UT F8&z=13)555 JICA (1994): Developing plan of the Marikina watersourse forest in the Phillipine (Final Report), in Japanese.
666 JICA (2004): Earthquake Mitigation Planing Research in
Metro Manila, Phillipine (Final Report), Vol.7.
777 JICA (2005) : Urban drainage improving plan in thecenter of the Metro Manila. Phillipine (Final Report)
abridged edition, 97pp．
888 JICA (2009): Information obtained by the interview with

JICA staff in Dec. 2009.
999 MMDA (2009): Information obtained by the interview
with MMDA staff in Dec. 2009.
1111 MGB (2009): Flood Hazard Map in Metro Manila.
1111 Manila Shinbun (2009): Sept. 2009 ～ Nov. 2009.
1111 NDCC (2009a): National Disaster Coordinating Council
Situation Report No.1 ～ Final Report.
1111 NDCC (2009b): Information obtained by the interview
with NDCC staff in Dec. 2009.
1111 PAGASA (2009): Information obtained by the interview
with PAGASA staff in Dec. 2009 at NDCC.
1111 NAMRIA (2009): Flooded Area in eastern Metro Manila
ts “Ondoy” 26 September, 2009 (1:15,000).
1111 NAMRIA Geographical Maps (1:250,000).
1111 P. B. GATAN, Department of Public Works andHighways (2009): Presentation at at ADB Short Seminar“Water for all: Learning from the Ondoy flood: A
Dialogue with Experts” held on 14 Oct. 2009, AsianDevelopment Bank.
1111 UNEP/OCHA(2009): Environmental Assessment:
Philippines-Tropical Storm Ketsana 8-20 Octorber 2009,19pp.
（Accepted: November 25, 2010）－ 74 －