Technical paper on ulysses flooding

Analyzing Flood Events in Marikina, Rizal and Cagayan Valley related to
Typhoon Ulysses
November 30, 2020
On November 11, Typhoon Ulysses (international name: Typhoon Vamco) made landfall
in the Philippines and caused widespread damage to eight provinces in the island group of
Luzon. The most notable flooding events were in Marikina City in Metro Manila, adjacent
Rizal province, and in Region 2 or Cagayan Valley in northeastern Luzon. This study
analyzes the flooding events in these localities to identify key factors and how to mitigate
risk. Four main determinants stand out: (1) the degradation of natural watersheds (2) the
marginalization of the poor that render them vulnerable and exposed to disasters, (3)
stop-gap solutions that do not address the roots of our disaster vulnerability, and (4) that
the national government remains unprepared for disaster. Policy priorities among other
reforms are recommended based on this assessment.
Located along the Pacific typhoon belt, the Philippines has the distinction of experiencing the
most number of tropical cyclones in its territory than anywhere else in the world (PAGASA, n.d.).
This year, seven consecutive tropical cyclones – local names Ofel, Pepito, Quinta, Rolly, Siony,
Tonyo and Ulysses – entered the Philippines in the months of October and November alone.
While all seven left a trail of destruction, Typhoon Ulysses in particular struck wide swaths of
populations in its wake. As of writing, government figures report 73 dead, 24 injured, and 19 still
missing (NDRRMC, 2020). A total of 3.67 million Filipinos were also reported to be affected in
eight provinces on the island group of Luzon. 360 cities and municipalities experienced power
outages, while it is estimated that the storm cost more than 10 billion pesos in damages. These
figures, however, may paint a more conservative picture of Ulysses’ actual impact, as data from
remote areas are more difficult to gather.
This paper aims to analyze specific flooding events that seriously affected the most number of
Filipinos during and after Ulysses, namely those in Marikina, Rizal and Cagayan Valley.
Through this study, we hope to shed more light on the factors as well as actors that have led to
destructive flooding in these areas, to inform public calls and demands for accountability, and to
push for much-needed reforms in our disaster preparedness and risk reduction systems.
1. The Basic Science of Floods
Flooding occurs as a natural phenomenon as water overflows from a water body to dry land
(Ward, 1978). There are several types of floods (Newground, 2018). River flooding occurs when
the capacity of a river is exceeded. During the rainy season, excess water that cannot be
absorbed by the soil and water catchment structures flows to drainage canals down to creeks

and rivers. When the added water volume from rainfall exceeds the capacity of water channels,
these will overflow, causing flooding.
Surface water flooding happens when rainfall cannot be absorbed by land or drained away and
accumulates at the surface. Coastal flooding, on the other hand, occurs when coastal areas
become flooded by the sea, often due to storm surges. Groundwater flooding occurs when the
ground water table rises up to the surface during a prolonged wet period. Another type of
flooding, sewer flooding, happens when sewage systems overflow. Reservoir flooding occurs
when reservoirs like dams discharge water from their catchment areas. This can resemble river
and surface water flooding if water is discharged slowly, but can be disastrous when water is
discharged at large volumes. Based on reports, it appears that all six types of flooding occurred
during or in the aftermath of Typhoon Ulysses.
Figure 1. Different kinds of flooding (adapted from Newground CIC, 2018).
Geologically speaking, watersheds play an important role in flood dynamics. A watershed, also
called a river basin, is an area of land where rainfall collects and drains off into a common
outlet, such as into a river, bay, or other body of water. In nature, water from areas of higher
elevation flow downwards, driven by gravity, to lower lying areas and naturally form lakes or
rivers, which may drain into bays or oceans.
In urbanized areas, natural watersheds are deforested, paved, carved out, filled in, and
essentially altered. These modifications affect the way water from rainfall reaches the land; is
absorbed, pooled, and collected; travels; and is discharged onto larger water bodies. Some of
the major activities that affect natural watersheds include:
1. Deforestation. Forests play an important role in watersheds. Leaves in the tree canopy
intercept rainfall and slow the throughfall of water to the soil. Fallen leaf litter can also
intercept water and prevent them from reaching the soil. Tree roots absorb water in the
soil as well as protect it from erosion, thereby preventing siltation of water channels. The

interception of rainfall from tropical forest cover ranges from 10% - 60% (Raros, 1979)
depending on species, time of year, and precipitation rates (Cotrone, 2015).
2. Urban expansion. The encroachment of roads, houses, buildings, and structures onto
natural floodplains increases the area of impermeable surfaces and prevents the soil
from effectively absorbing water from rainfall. The same structures may block or divert
natural creeks and canals. These creeks, canals, and riverbeds often become silted due
to increasing human activity, reducing their carrying capacity of water. Both natural and
manmade waterways may also become obstructed due to inadequate solid waste
disposal practices and construction activities.
3. Dams and reservoirs. Dams and reservoirs are structures that impound river water and
prevent them from flowing naturally downstream. Large dams have hydrologic impact
with the diversion of rivers or creeks. A dam alters the hydraulic cycle of a river by
means of impounding sediments which, in effect, creates groundwater pressure
downstream.
4. Reclamation. Reclamation activities further alter the natural discharge of water in cities.
The reclamation of riverbeds and coasts reduces the flow gradient of water towards
rivers and bays since they are often at a higher elevation than mainland coastal plains
(Zoleta-Nantes, 2000b). These reclamation areas obstruct and retard the flow of water
from mainland streams towards the sea.
2. Ulysses-Related Floods in Marikina and Rizal
Marikina and Rizal sits in the Pasig-Marikina River Basin, a basin with a drainage area of
698.26 square kilometers (River Basin Control Office - DENR). It spans 197 barangays and 15
towns and cities in Bulacan, Rizal, and Metro Manila. Headwaters come from the highest
elevations or ridges of the basin found in the boundary of Rodriguez, Rizal and General Nakar,
Quezon that are part of the southern Sierra Madre mountains. From tributaries in the
north-eastern basin ridge, water converges in the Marikina River and leads to both the Pasig
River and the Laguna Lake through the Manggahan floodway. Water from the western, low-lying
part of the basin converges towards the Pasig river as well, which empties either onto Laguna
Lake or Manila Bay depending on the water levels of the two bodies.

Figure 2. Elevation map of the Marikina River Basin, from Santillan et. al, 2013
Almost half of the river basin and located in the eastern part of the basin is the Upper Marikina
Watershed Protected Landscape (UMWPL), a protected area 270 square kilometers in size that
spans Rodriguez, Antipolo City, Baras, and Tanay. Despite being declared a protected area,
three mining firms with Mineral Processing Sharing Agreements (MPSAs) operate within the
UMWPL with a combined tenement area of 1,344.7 hectares. These are Quarry Rock Group
Inc., Quimson Limestone Inc., and Rapid City Realty and Development Corp. (DENR, 2020 and
MGB-IV, 2020).
Outside the UMWPL, there are three MPSAs covering 417 hectares in Rodriguez, one 124.26
ha. MPSA in Baras, and 15 MPSAs covering 1,480 ha. in Antipolo. There are also 10 quarries
with a combined area of 50 hectares within the bounds of the watershed that were reported to
be operational in 2019 (MGB-IV, 2019).
Also located inside the Marikina River Basin is the Wawa dam, a gravity dam built in the 1900s
to service the water needs of Metro Manila. It is now being rehabilitated under the P20-billion
Wawa Bulk Water Supply Project of Enrique Razon. The dam impounds water from four major
tributaries in the mountainous areas of Rodriguez, namely Tayabasan River, Montalban River,
Boso Boso River, and the Wawa River which meets the Marikina River just upstream of the
dam. While there is a sharp slope between Wawa Dam and the Sierra Madre Mountains,
downstream the Marikina river slopes gently towards its floodplains in San Mateo, Marikina and
Pasig.

Figure 3. Mining tenements located in the Marikina watershed. From MGB-IVA, 2020
Marikina River itself spans 78 kilometers from its headwaters in Rizal to its confluence with
Pasig River, with a depth between 3 to 21 meters and width of between 70 to 12 meters. The
riverbank has an elevation of 8 meters above sea level (m.a.s.l.) at the boundary of San Mateo
and Marikina. The lowest elevation is along Brgy. Calumpang, Marikina City which is 2.0 m
above sea level. Historically, in the 1940s to 1950s, the lowest-lying areas of the riverbank were
marshland that were planted with rice and mangroves (ESSC, Inc., 2010). These areas are now
paved with residential and commercial structures. These areas coincide with having both the
lowest elevation and lowest slope, especially near the confluence of Marikina River and Pasig
River (Berkman International Inc., 2015). Out of approximately 11.23 square kilometers of
marshland from 1947 to 1955, only 8% was left by 1997 (ESSC, Inc. 2010). Flood hazard maps
from the DENR River Basin Control Office show that most of Marikina City and parts of San
Mateo and Rodriguez in Rizal near the Marikina river — area that used to be marshland — are
at risk of flooding (see Figure 4). Flood hazard maps from the DOST-UP DREAM and
Phil-LiDAR Program published in 2017 also delineate similar areas of hazardous high-risk flood
areas (DOST-UP DREAM and Phil-LiDAR Program, 2016).

Figure 4. Left: Marikina River Basin Flood Hazard Map (Berkman Int’l, 2015), and Right: Marshland Marikina of the
1940s-1950s (ESSC, 2015)
Kasiglahan Village is a socialized low-cost housing project conceptualized during the Ramos
administration as a relocation site for informal settlers living along the Pasig River. Construction
of 55,600 units and resettlement started during the Estrada administration. At present, families
residing in Kasiglahan include resettlers from Pasig river, survivors of the Payatas garbage
landslide in 2000, as well as resettlers from urban poor communities in Quiapo, Valenzuela,
Tatalon, San Roque in Quezon City (Delos Reyes et al., 2013). It is bounded by the Marikina
river in the South and the Puray river in the east.
Figure 5. Location map of Kasiglahan village with adjoining water bodies, taken from Google Earth.

In 2015, AGHAM published a report assessing the structural integrity and flood risk of
Kasiglahan Village. Based on simulations of flood heights during Typhoon Ondoy in 2009, we
found that most of the area is in high danger of being flooded. Some areas were also identified
to be in red zones, with > 5.0 meter flood depth, specifically the areas of Southville 8B and
along Sitio Bulak creek. The report’s recommendations include that:
1. An in-depth be conducted to determine why relocations sites were positioned in such a
high-risk area
2. A moratorium on resettlement at least in Rodriguez be done pending any investigation
3. Immediate interventions such as community-based disaster risk management be
instituted in the area
A quick look at existing quarrying permits with the Mines and Geosciences Bureau’s show that
there are six quarries operating in San Isidro, Rodriguez. These quarries have a total area of
nearly 30 hectares. A look at 2020 satellite images from Google Earth show that these quarries
are located upstream and at a higher elevation than Kasiglahan.
Figure 6. Location of quarry sites relative to Kasiglahan Village and tributaries that drain to the Marikina River, taken
from Google Earth.

Marikina and Rizal During Typhoon Ulysses
PAGASA issued its earliest flood advisory the afternoon of November 10, warning that the
Upper Marikina river was likely to be affected by the typhoon, and residents in low lying areas of
rivers and local DRRMCs were advised to be alert for possible flash floods and landslides
(DOST PAGASA, 2020x). The next day at 4AM, its regional weather forecast warned about
possible landslides and flooding in Rizal, and asked the public and local Disaster Risk
Reduction and Management Council Councils (DRRMCs) to continue monitoring advisories and
warnings from the agency (DOST PAGASA, 2020y). On November 11 at 3 PM, eight hours
before the Marikina River reached first alarm, the agency issued its lone flood advisory for the
Pasig-Marikina basin, predicting rainfall levels of 250 - 300mm to fall in the next fifteen hours. It
warned against localized flooding in some areas due to poor drainage systems and impounding
water (DOST PAGASA, 2020z). For comparison, the mean monthly rainfall for November in the
Marikina basin is at 237 mm (Berkman International Inc., 2015).
Actual data from PAGASA’s stations would later record a total of 374 mm of rainfall in just 15
hours at Mt. Oro (De Vera-Ruiz, 2020), which sits at the north-wastern ridge of the basin in
Rodriguez, Rizal. Two weeks prior, Typhoon Rolly already saturated the metropolis with rain,
while a week earlier Tropical Depression Tonyo also caused rains in the basin. This means that
the absorptive capacity of the soil was already reduced as Ulysses unleashed large volumes of
rainfall especially upstream.
Given the historical propensity of areas adjoining the Marikina River south of Wawa Dam to
flooding, it comes as no surprise that most of Marikina and western Rizal were inundated. In
less than four hours, the water level in the Marikina River rose from 15 meters to 18 meters,
prompting forced evacuation protocols in Marikina City (CNN Philippines, 2020). Nine hours
after the first alarm was raised, water levels in the river surpassed that of Typhoon Ondoy,
breaching 21.5 meters and topping at over 22 meters by noon of November 12.
Barangays Nangka, Barangka, Tumana, and Malanday in Marikina were reported to be severely
flooded, with nearly 50,000 houses in these areas reported to be completely submerged
(Servallos & Cabrera, 2020). 10 out of 15 barangays in San Mateo were flooded (GMA News,
2020), while families pleaded for rescue atop their rooftops in Rodriguez. Over 25,000 families
sought shelter in evacuation centers throughout Rizal (CNN Philippines, 2020). The worst hit
were Provident Village in Marikina and Kasiglahan Village, where flood waters were reported by
social media users to reach more than 3 meters (10 feet).
The Marikina and Rizal flooding events and their destructive aftermath is not entirely an act of
nature. Warnings given by PAGASA, especially its flood warning for the basin, already pointed
to a month’s worth of rain to pour in a span of fifteen hours. This should have already given both
the national and local DRRMCs, as well as concerned LGUs, enough pause to consider
appropriate measures. Flood models and hazard data have already shown the vulnerability of
low-lying communities to flooding, and yet not enough measures were taken to inform and
secure affected families.

In a 2011 study of Ondoy floods that inundated Marikina, AGHAM member and hydrologist
Catherine Abon observed that the sheer amount of rainfall in the watershed will result in the
expected floods in extreme rainfall events. Her study also found that enough lag time between
upstream and downstream floods is usually present, such that flood preparation is possible. The
events of Ulysses show that even with some flood warning systems in place in the aftermath of
Ondoy, it is still not enough.
Zoleta-Nantes (2000b) pointed out the urgency in reducing deforestation and mining activities in
the Marikina watershed and the Sierra Madre and to regularly clean drainage canals.
Fast-forward to twenty years later, and mining operations continue to deforest and denude the
basin. Continued quarrying operations in northeastern Rodriguez, in particular, pose an
additional hazard to housing projects downstream. The removal of forest cover reduces the
absorption of water while drainage canals become more and more silted, adding more water
runoff downstream.
Typhoon Ulysses also underscored that in Marikina and Rizal, as elsewhere, urban poor
communities are the most heavily impacted by flooding, and carry the heaviest burden of its
disastrous consequences. Many of the residents affected by flooding in Marikina and Rizal are
urban poor families who have been resettled to housing projects in flood prone-areas. This is
particularly the case in Malanday, Nangka, and Tumana in Marikina, Silangan in San Mateo,
and San Jose and San Isidro in Rodriguez when Ulysses struck. Despite knowledge that these
areas are flood-prone and even hazardously so, the National Housing Authority as well as local
government units knowingly placed these communities in danger.
3. Ulysses-Related Floods in Cagayan Valley
The Cagayan River Basin (CRB) is the largest river basin in the Philippines, with a drainage
area of 27,281 km2
and spanning 10 provinces throughout the Cagayan Valley and Cordillera
Administrative Region. Cagayan and Isabela are downstream of Benguet, Nueva Vizcaya,
Quirino, Ifugao, and Mountain Province, with the southeastern part of Apayao at the upper end
of the watershed. It is bordered by three mountain ranges: Sierra Madre, Cordillera Central, and
Caraballo-Maparang in the east, west, and south, respectively. Upper watershed areas from
these ranges are the source of water flowing into the Cagayan River. This river spans about 520
kilometers from its headwaters at the 5,000-feet Caraballo Mountains in central Luzon, flows
through the flat alluvial plains of the Cagayan Valley, and exits into the Babuyan Channel in
Aparri in the north.

Figure 7. Cagayan River Basin, major rivers and tributaries, provinces and weather stations. From Principe, 2012.
The Cagayan river also has bottlenecks or constricted sections. Notable among its constricted
sections is the Magapit Narrows, a 30-kilometer stretch of the Cagayan River that starts at
Tupang in Alcala and ends at Magapit in Lal-lo town. Along this stretch, Cagayan River merges
with the Chico River in Santo Nino town and with Dummun river from Gattaran, while right
upstream of it in Alcala, the Pared river from the Sierra Madre mountains merges with Cagayan
river. The Regional Development Council in 2006 identified three specific bottleneck sites in the
Magapit Narrows, specifically those in Tupang and Nassiping in Alcala, and Magapit in Lal-lo.
Because of these unique hydro-geological characteristics, water rises at the narrows at its
confluence points while it also has a tendency to flow back due at its bottlenecks, thereby
significantly retarding the flow of floodwaters to the Aparri Delta and finally to the Babuyan
Channel.

Figure 8. Left: Magapit Narrows and bottlenecks at Tupang, Nasiping and Magapit. Right: location of Magapit
Narrows relative to Tuguegarao. Images from Google Earth Pro.
In terms of climate, the area has a short dry period and relatively consistent rainfall year-round.
It is also relatively flat (approximately 50% of its land area), broken by low rising ridges and
hummocks in some places (BRS-DPWH in Principe and Blanco, 2013). The northern and
southern ridges of the basin have an average annual rainfall of 1000 mm and 3000 mm
respectively (Nippon Koei Co. Ltd and Nikken Consultants Inc., 2002). Based on the Shuttle
Radar Topography Mission Digital Elevation Model (SRTM-DEM with 90-m resolution), the
slope map showed that almost half of the Cagayan Valley is relatively a flat terrain while one
third has slopes between 17-42% (ranging from very strong to extreme slope) while the rest are
with steep slopes (>42%).
High rates of soil erosion and runoff in Cagayan Valley are exacerbated by degraded watershed
forests
Most soil falls away from the steep areas of the CRB due to gravity, leaving only a thin layer of
undifferentiated soil in the upper watershed areas, as seen in Figure 9 below. Thin soil cover is
more vulnerable to runoff owing to decreased pore volume reducing its ability to absorb water.
On the valley floor, the predominant soil cover is fine clay loam or clay (TCAGP, 2015), which
also cannot readily drain water. The soil composition allows the Cagayan River and tributaries
to flow in a steady stream. These conditions also render this area especially vulnerable to
flooding.

Figure 9. Map of the upper watershed areas of the Cagayan River Basin
Based on the study conducted by the UPLB College of Forestry and Natural Resources funded
by the River Basin Control Office-Department of Environment and Natural Resources on the
land capability zoning, more than half of the CRB has a soil erosion potential (SEP) that falls
within the range of 0-5 tons/hectare. Soil erosion potential pertains to the measurement of the
amount of soil per hectare of land lost to erosion per year (UPLB-CFNR, n.d.). Flood inundation
in the CRB has been a persistent problem affecting the agriculture and infrastructure in its
provinces.
The geological characteristic of the Cagayan River is described as having a less permeable
bedrock composition, which makes it vulnerable to flood risk. For example, Sierra Madre is
composed of metamorphic ophiolitic rocks, as opposed to more porous sandstone. Caraballo
and the Palali Mountain Range in Sierra Madre are composed of poorly-draining syenite. In the
Cordillera Mountain Range, there is a mixed geology of less porous (limestone, siltstone, diorite
intrusives) and more porous bedrock (conglomerates). The areas upstream and downstream of
the Magat Dam area are also mixed in composition, with parts being relatively porous
(conglomerates, sandstone) or less porous (mudstone, shale).
Since the soil and geology of upper watershed areas are not conducive for water infiltration,
adequate forest cover in the CRB is critical for reducing flooding risk. In 2002, only 41.7% of the
watershed and catchment basin areas of Cagayan were reported to be forested (Nippon Koei,
2002). The forest cover map of the CRB in 2015 also shows that large portions of watershed in
the Cordillera / Nueva Vizcaya side are grassland, bushland, or cultivated (lighter green), which

are not as effective as canopy forests (dark green) at reducing runoff. Canopy forests, like those
covering the Sierra Madre side, are larger with wider leaves and deeper roots to absorb water,
stabilize soil layers, and soften the impact of rainfall on the earth. We also find that the
vegetation cover upstream of Magat Dam (marked with a star) is thin and shallow, thus less
capable of reducing runoff. When heavy rains from the typhoon fell, it is no wonder that the dam
quickly went over capacity.
Figure 10. Landcover map of the Cagayan River Basin
Forestland comprises 69% of the CRB, while the remaining is alienable and disposable land.
Large portions of the forestland area in the CRB are protected forests according to NEDA-RDC
Cagayan Valley and DENR River Basin Control Office. Among these forests are the Northern
Sierra Madre Natural Park (NSMNP) in Isabela and Aurora, comprising 287,861 hectares of
terrestrial forest that overlaps the eastern ridges of CRIB. The park is home to 89 species of
trees, eight of these species endemic and ten species critically-endangered. The park is
tentatively listed as a UNESCO World Heritage Site. Activities such as upland migration,
charcoal making, timber poaching, unsustainable upland farming and kaingin have induced
forest cover loss in CRB (CFNR-UPLB and RBCO, 2017).
Deforestation has long been a problem in the upland watershed areas of CRB. Between 1965 to
1987, 27,000 km2
of forest in the area disappeared (Oosterberg, 1997). This can be traced to
heavy logging operations beginning in the 1960s, when timber license agreements (TLAs) were
granted to various companies owned by cronies of President Marcos. Notably in San Mariano,
Isabela, five such logging companies received concessions for a total of 110,625 hectares and
operated until 1992, when DENR issued a logging moratorium over widespread forestry

violations. Another effect of TLAs was the introduction of permits for other “forest-use
concessions.” In Cagayan Valley, at least 444,600 hectares of forest area are currently in legal
commercial, private, and community use under different grants issued by the DENR. Other than
commercial (legal or illegal) logging and forest use, another contributor to deforestation of CRB
watersheds are kaingin and small-scale illegal logging for livelihood. Landlessness and poverty
are also undeniable factors in the degradation of watersheds.
Open-pit mining also plays a major role in watershed denudation, as it entails the stripping away
of trees and vegetation to access mineral ores under the ground. MGB-Region 2 reports three
metallic mines spanning 18,350 hectares in Cagayan Valley. Two of them, Oceanagold in
Kasibu and FCF Minerals in Quezon town, are located in the Caraballo-Maparang mountains of
Nueva Vizcaya where the northernmost headwaters of the Cagayan River are found. The third,
in Dinapigue, Isabela, sits on the Sierra Madre range. There are also some 124 sand and gravel
operations in the region, with a total area of around 648.4 hectares (MGB-II, 2019).
The situation of Magat Dam
The Magat dam is a rock-fill dam that impounds water from the Magat watershed consisting of
Magat river and its tributaries. Dam capacity is affected by siltation, or the depositing of loose
sediments at the bottom of the reservoir. When the siltation rate is high, an increasing volume of
the dam becomes “dead storage” and lowers water storage capacity of the reservoir. The Magat
Dam was designed to accommodate 5.5 mcm/year siltation rate. However, National Irrigation
Administration (NIA) - Magat reports that the Magat Dam has been experiencing
higher-than-expected siltation rates for at least two decades, above 10 mcm/year.
Figure 11. Measured siltation for Magat Dam. Source: NIA-DRD
With such high siltation, we can expect Magat Dam to spill more easily, especially during a
heavy typhoon. On October 31, 2007, the Operation, Maintenance and Safety Manual for the

Magat Dam was issued by the NIA. The Manual has its references from the 1985 Manual
initiated by NIA and the 1992 Flood Operation Rule jointly prepared by NIA, the National Power
Corporation and the PAGASA in coordination with the technical people of the SN ABOITIZ Inc.
(SNAP). The need to update the manual was compelled by the drastic weather changes that
affect the dam operations. The dam operation and maintenance also considered that Magat
Dam has hydroelectric power generation owned by SNAP, a private power corporation. On
December 13, 2006, NIA and SNAP entered into an Operation and Maintenance Agreement
that defines the terms and obligations of all both parties.
In the Action Plan for Emergency Release of Water, the responsibilities of various entities are
defined. The PAGASA shall provide forecasting of rainfall in the watershed and the expected
volume and rate of flood flows and shall advise the Magat River Integrated Irrigation System
Operations Manager (MARIIS-OM) and the Dam and Reservoir Division (DRD) Manager on the
decision in the pre-release of water. Upon receiving the advisory of PAGASA, the DRD
Manager shall inform the Operations Manager for the detailed information on the pre-release
particularly, the volume to be released and the time of pre-release.
The DRD Manager shall, likewise inform the Office of the Civil Defense and the Department of
Waterworks and Highways (DPWH) information about the prelease. The Operations Manager
shall advise the Governors of Nueva Vizcaya, Isabela and Cagayan and the Mayors in the
identified affected municipalities. The Officer-In-Charge of the Municipal’s Office shall issue the
order at least three hours before the actual release of water. All forms of communication shall
be used for the timely delivery of information to the affected communities. A log book shall be
maintained at the office of the Instrumentation and Flood Forecasting Warning Section of the
DRD for the recording of date and time the information was sent and received. The Disaster
Coordinating Councils of every municipality and barangay shall be responsible for the disaster
preparedness.
On the obligation of SNAP based on its signed agreement with NIA, the power company will be
providing needed vehicles of the staff of MARIIS Field Personnel, as this has been identified as
the limitations of the staff of the dam to perform accordingly (Magat River Integrated Irrigation
System, 2007).
Historical Flooding in the Cagayan River Basin
The historical flooding in the Cagayan River in 1973, 1980, 1998 have resulted in flooded areas
covering 1,806 km2
, and 1,740 km2
and 620 km2
, respectively, as seen in Figure 12. These
major flood events have placed the communities residing within the river into frequent flood
risks. The 1973 flood has been recorded to be equivalent to about 25 year probable flood. The
flooding that took about two to three days to subside in most of the floodplains can be attributed
to the significantly low discharge capacity of the river (2,000 m3
/s from Tuguegarao to the river
mouth) when compared to the two-year probable flood discharge of 6,400 m3
/s and the
100-year probable discharge of 21,400 m3
/s respectively. The slow downward flow of the
floodwater is due to its surface retention over the extensive flood plain, the extremely gentle

slope of the Cagayan River and the retardation of floodwater due to the Magapit Narrows and
the meandering river (Nippon Koei Co. Ltd and Nikken Consultants Inc., 2002).
This explains why the CRB has been frequently experiencing severe floods that exacerbate its
current condition. Based on the flood hazard map from MGB, about 388,494 hectares are
susceptible to flooding and 60% of these areas have high to very high susceptibility. Moreover,
these areas contain residential areas and key establishments. Any massive flooding would
therefore incur a high cost in damages to both agriculture and infrastructure in the river basin.
Figure 12. Historical flooding in Cagayan (from Nippon Koei Co. Ltd and Nikken Consultants Inc., 2002)
In December 2019, massive flooding of a scale of 100-year flood also occurred in the CRB after
heavy rains. Flooding was reported in 113 locations inCagayan, Isabela, Quirino, Apayao and
Kalinga, displacing 75,000. In Alcala town alone, six barangays were totally inundated and more
than 5,000 homes were submerged (Floodlist, 2019 and Antonio, 2020). This led the mayor of
Alcala to commission a study with UP scientists, who reiterated that a combination of
geomorphological characteristics and forest denudation leads to massive flooding. They also
recommended widening the river at the Magapit commons, relocating communities vulnerable to
riverbank erosion, and the replanting of trees and other vegetation to mitigate floods. The first
suggestion, part of recommendations by JICA made back in 1987, remains undone (Antonio,
2020).
It is acknowledged by various studies conducted that more intense rainfall brought by climate
change may cause more damage in the future. Based on a vulnerability assessment conducted
by UPLB, inundated areas will increase in 2020 and 2050 scenarios except for the 2-year flood
event in 2050. Prolonged and extensive flooding has been a long-term problem in CRB. As a
result, floods occur not just during typhoons but also during monsoon rains.

Flooding Events Related to Typhoon Ulysses
PAGASA’s Cagayan River Basin Flood and Forecasting & Warning Center (CRB-FFWC) issued
its first flood advisory for the CRB on November 8th, warning of possible river flooding and flash
floods due to rainwater accumulation from tropical depression Tonyo and the northeast
monsoon. On November 9th at 3pm, PAGASA issued its first dam advisory for the Magat
sub-basin, advising residents and local DRRMCs to take appropriate actions as one gate was
already opened at 1 meter for Magat dam, and by 5pm 2 gates were already open at 4 meters.
CRB-FFWC’s 5PM flood bulletin warned of threatening floods in low-lying areas around
Tuguegarao and Tumauini, Isabela, and possible flooding in areas around Echague, Ramon,
Gamu, and Tuao.
By 5AM of November 10th, with typhoon Ulysses 580 km east of Virac, the CRB-FFWC was
already warning of threatening floods in all of Cagayan River and its tributaries, and advised
people near low-lying areas and particularly adjacent to and along rivers and tributaries against
possible landslides and flash floods. It also advised concerned DRRMCs to take appropriate
measures. The 6AM dam bulletin reported Magat dam reservoir levels already at 191.09 meters.
Ave. CRB
rainfall (mm)
Magat Dam
Water Level (m)
Opened Gate status
Nov.8 4AM to Nov.9 4AM 68.13 Nov.8 6AM: 189.05 No open gates
Nov.9 4AM to Nov.10 4AM 29.00 Nov.9 6AM: 189.34
4PM: 191.03
6AM: none
4PM: 2 gates, 4 meters
Nov.10 4AM to Nov.11 4AM 21.10 Nov.1
0
6AM: 191.09 6AM: 2 gates, 4 meters
Nov.11 4AM to Nov.12 4AM 58.81
Nov.1
1
6AM: 190.14 6AM: 2 gates, 4 metersNov.11 8AM to Nov.12 8AM 72.13
Nov.12 2AM to Nov.13 2AM 86.35
Nov.1
2
6AM: 190.1
8AM: 190.7
1PM: 192.4
3PM: 192.82
6AM: 2 gates, 4 meters
1PM: 7 gates, 14 meters,
3007 cms outflow
3PM: 7 gates, 22 meters,
4522 cms outflow
3
6AM: 192.7
8AM: 192.64
11AM: 192.56
7PM: 192.46
6AM: 7 gates, 24 meters,
5037 cms outflow
11AM: 7 gates, 14 meters,
3447 cms outflow
7PM: 5 gates 10 meters,
2535 cms outflow
4
6AM: 192.16 6AM: 3 gates, 5 meters
Nov.15 4AM to Nov.16 4AM 3.6 Nov.1 6AM: 192.15 6AM: 1 gate, 2 meters

Figure 13. Measured rainfall levels versus reported Magat dam levels and gate situation, Nov.8 to Nov.15. Data
culled from PAGASA flood bulletins, dam bulletins, general flood advisories, and Magat dam situationers posted on
Twitter, and Cagayan PIO announcements on its Facebook page.
In its 5AM advisory on November 11th, the CRB-FFWC reported that water levels were already
above alarm levels for lower and middle Cagayan River and its tributaries, and that flood is still
threatening throughout the CRB particularly near low-lying areas and in areas adjacent and
around rivers and tributaries in the basin. News reports cited 1,000 families pre-emptively
evacuated throughout Cagayan Valley by the Municipal DRRM Office due to flash floods
triggered by continuous rains (Cerrudo, 2020). 3PM reports cited more than 1,300 families were
also reported to be affected by floods and landslides in northern parts of Cagayan, with four-feet
high floods reported in Aparri, Pamplona, Sta. Praxedes, Claveria, Sanchez Mira, Ballesteros,
Lal-lo, Camalaniugan, Lasam, and Tuguegarao City, and bridges submerged in Baculod and
Cabiseria 8 in Ilagan; Alicaocao, Sipat and Villa Concepcion in Cauayan; Cansan in Cabagan
and Santa Maria towns (PNA, 2020).
The FFWC’s 5PM advisory warned of a new rise in water levels throughout the Cagayan River.
The recorded average rainfall for the CRB also more than doubled on the 11th of November,
from 21.1mm to 72.13mm between 8am of November 11th to 8am of November 12th.
On 3AM of November 12th, Typhoon Ulysses was reported to be in the vicinity of Bulacan. 3
gates and 5 meters of Magat dam was already opened by 8AM. By 11AM, the CRB-FFWC
reported flooding already occurring throughout the river basin, with a forecast of moderate to
heavy rains. Concerned DRRMCs were advised to take appropriate actions. 4 hours later at
3PM, a total of 7 gates and 22 meters were opened at Magat dam, with the dam level at 192.82
meters and very near spilling level. News reports cited PAGASA hydrologists warning of
widespread flooding in Isabela and Cagayan by 8PM (De Vera-Ruiz, 2020b). The Magat dam
opened its gates 2 meters more by 6AM of November 13, despite a slow decrease in dam water
levels.
Despite light rains throughout the day, social media and news reports started widely covering
extensive flooding in the Cagayan throughout November 13, with families spending the night on
their rooftops in pitch black darkness as the waters continue to rise, especially in Tuguegarao.
Rescuers were reported to have difficulties in their rescue boats because of the strong currents
of the floodwaters, and had to turn back. Mayor Cristina Antonio of Alcala reported 24 out of its
25 barangays as flooded, with seven that were ‘’totally submerged.” (Paciente, 2020)
The 12th flood bulletin of PAGASA’s CRB-FFWC on November 14th at 5AM reported that
despite only 2.67mm of average rainfall measured over the past day, there was still persistent
flooding throughout along the Cagayan river and its tributaries, with water levels either still
above critical (in Tumauni and Buntun) and above alarm levels (Upper Cagayan, Gamu, Tuau).
5 9AM: 192.22 9AM: 1 gate, 2 meters
6
6AM: 192.28 6AM: 1 gate, 2 meters

It warned that low-lying areas will continue to be affected. By 5PM the water was reported to be
above critical at Gamu as well.
On November 15, the 4th day of flooding, flood waters continue to persist in Middle Cagayan
(Gamu, Tuaini) and in Tuguegarao despite a gradual recession in water levels. On November
16th, only PAGASA’s Buntun station in Tuguegarao continued reporting persistent floods and
waters still above alarm levels. It was only on November 17, almost a week into flooding, that no
more floods were reported by the CRB-FFWC. The Magat dam, however, continues to release
water as its levels are still beyond 190 meters even as of this writing.
Typhoon Ulysses-related flooding in the Cagayan River Basin appears to be caused by a
confluence of several factors, chief among them:
1. Extensive watershed degradation in the Sierra Madre and Cordillera mountains due to
rapid deforestation from logging, mining, and agriculture
2. Release of very large volumes of water from Magat dam, which triggered the floods in
the middle and upper Cagayan river. This was compounded by the high siltation at the
reservoir, which greatly reduced its holding capacity and also led to riverbank
sedimentation and erosion downstream.
3. Accumulation and backflow of floodwaters at the Magapit Narrows, which prolonged
flooding in the areas around Lower Cagayan River
4. Insufficient mechanisms for flood information dissemination, preparedness, evacuation
and mitigation.
Despite extensive studies since the 1980s pointing to the vulnerability of the Cagayan River
floodplains to extensive flooding, it appears that no sufficient mechanisms have been put in
place to (1) mitigate flooding impacts, (2) sufficiently inform communities of imminent flooding,
and (3) secure residents, their houses, and farms from flooding.
According to Cagayan Gov. Manuel Mamba, they did not know the extent of the effect of the
flooding itself. Even if they were told to expect 6,000 cubic meters of water would be released
per second, it remained unclear what this would mean. The extent of the damage and
devastation was completely unexpected. This belies the lack of information and situational
awareness at the local levels, which could have been facilitated and mediated by national
disaster agencies.
4. Typhoon Ulysses Floods in Marikina, Rizal, and Cagayan Valley: Conclusions and
Recommendations
As put by disaster risk reduction and developmental studies expert Terry Cannon in 1994,
hazards are natural but disasters are not (Cannon, 1994); disasters are preventable and can be
mitigated. According to the Routledge Handbook of Disaster Risk Reduction (DasGupta &
Shaw, 2017), disaster risk is a function compounded by hazards, exposure, and vulnerability,
and inversely proportional to coping capacity:

1. Watershed degradation enhances flooding hazards in river basins
Watershed degradation is a focal point in both flooding events in the Pasig-Marikina River and
Cagayan River basins. Most notable is the widespread deforestation caused by logging,
quarrying, mining, and land conversion activities that greatly diminish the ability of the
watershed to retain water and cause massive siltation in drainage canals and rivers. Unplanned
and mismanaged urban expansion notably in Marikina and Rizal has also led to river siltation
and the obstruction of canals and rivers due to construction activities and solid waste
accumulation. Extreme rainfall events therefore trigger faster and more expansive flooding
events.
2. Vulnerability as a function of inequitable “growth” and systemic poverty
In the Philippines, not only are hazards high, but with one in five Filipinos considered to be in
extreme poverty (Intellasia, 2019) wide swaths of the population are rendered vulnerable and
exposed as a function of their poverty. As succinctly put by Zolantes-Nantes in 2015, “economic
power is a decisive factor in the level of vulnerability that impinges on any group or household.”
The lack of affordable, decent and safe housing options leave the urban poor at the mercy of
the elements. They live in shanties in the riversides or are resettled in housing projects with
substandard construction and in hazard-prone areas. Rural poor who are mostly farmers are left
without income for several months when extreme weather events topple coconut trees and
inundate rice and corn fields. These are painfully highlighted by the experiences of residents of
housing projects in Marikina and Kasiglahan, and by corn and rice farmers in Cagayan Valley.
The vulnerability of the urban and rural poor to disaster is compounded by their political
marginalization in government planning and priorities. Housing projects are haphazardly done in
flood-prone areas. Government planning and priorities favor big businesses and the pockets of
corrupt politicians. This is evidenced by the proliferation of mining and logging businesses in
forested areas despite their deleterious impacts to watershed hydro-geography and biodiversity.
Real estate and construction booms are not properly managed and regulated by city and local
officials, thereby taxing the carrying capacity of the capital’s drainage systems and encroaching
on watershed areas.
3. Stop-gap solutions further disadvantage the urban and rural poor
To address disasters, big-ticket infrastructure projects are being brandished as miracle fixes
without due consideration of their impacts to affected ecosystems and displaced communities.
Government agencies like the DENR and DPWH put an emphasis on flood control projects such
as the Pasig-Marikina River Basin Flood Management Project and the Cagayan River Basin
Project that rely heavily on structural controls like dams and dikes to mitigate flooding. These

measures, however, do not address the root causes of flooding and its disastrous impacts. As
Bankoff pointed out in 2003, the actions of governments that heavily rely on technological
solutions have limited outcomes and may even aggravate conditions often to the disadvantage
of the urban and rural poor. This is not even to mention the massive corruption that goes with
multi-billion infrastructure projects like these (Mercado, 2020).
4. Government unprepared for disaster preparedness and slow to quick response
The United Nations Office for Disaster Risk Reduction also identifies lack of public information
and awareness as well as limited official recognition of risks and preparedness measures as
important factors worsening disaster vulnerability (UNISDR, 2015). Given the limitations of
weather forecasting, PAGASA-DOST was not remiss in issuing dam advisories and flood
bulletins during typhoon Ulysses. The concerned local DRRMCs and LGUs, however, failed to
act sufficiently and proactively in terms of pre-emptive evacuations and massive information
dissemination campaigns at the community level. In the case of Cagayan Valley, it appears that
local leaders were not completely aware of the implications of flood warnings and dam gate
opening advisories. This is illustrative of current gaps that exist between scientific advice and
policy.
At the national level, a glaring example of government neglect for disaster preparedness is in
the limited budget appropriated for the Calamity and Quick Response Funds. The Calamity
Fund (CF), also called the National Disaster Risk Reduction and Management Fund is a lump
sum, annual fund for aid, relief, and rehabilitation services done by the national government to
areas affected by calamities. The Quick Response Fund (QRF), on the other hand, are standby
funds for immediate use by agencies to quickly respond to areas stricken by catastrophes and
crises. These funds would have augmented the capability of calamity-stricken communities,
especially the poor, to cope with disaster.
For the 2020 fiscal year, the only P16 billion was allocated for the CF and P6.3 billion for the
QRF. P8.5B of the P16-B CF was already earmarked for the rehabilitation of Marawi (P5 billion)
and areas in Davao and Soccskargen affected by the 2019 earthquake. This leaves only P7.5
billion for relief, rehabilitation, and recovery (DBM, 2020). As of October 31, the CF had a
negative balance of more than 195,000 pesos (DBM, 2020-2). As stated earlier, Typhoon
Ulysses alone incurred 10 billion pesos in damages to agriculture and infrastructure (NDRRMC,
2020). Despite its glaring inadequacy, the calamity fund budget remained unchanged for 2021.
Weather forecasting plays a crucial role in disaster preparedness. PAGASA’s budget for 2020,
however, was cut by 12.5%. Its Flood Forecasting and Warning Program received a budget cut
of 1.7 million pesos, while its Weather and Climate Forecasting and Warning Program budget
was cut by 50.1% (CPBRD, 2019). This diminishes its ability to efficiently carry out its mandate
to provide accurate and robust science-based weather-related information and services. This
situation reduces, instead of enhances, the country’s safety and resilience to disaster risks.

Grossly insufficient government funding for and prioritization of DRR explains the visibly wanting
government rescue and relief operations for Typhoon Ulysses. Residents of flood-ravaged
Marikina and Tuguegarao had to spend their night shivering and hungry atop their rooftops
waiting to be rescued, while the President spent valuable resources doing photo-ops of aerial
surveys. Residents interviewed during AGHAM’s relief operations in Marikina City, Antipolo City,
Kasiglahan Village in Rizal, and Baseco in Tondo all lament the lack of much needed aid which
mostly came from non-government organizations and the private sector. Appeals keep pouring
for assistance to affected communities even two weeks after Ulysses.
To sum, the negligence of the national government as well as local government units and
DRRMCs, coupled with the profit-oriented interests of logging, mining, quarrying, and real estate
businesses led to the disastrous impacts of Typhoon Ulysses.
5. What should be done?
Thousands of families affected by the series of typhoons these past months urgently need
support. Existing economic difficulties have been double-whammied by both the COVID-10
pandemic and typhoon-related disasters. Aside from citizen relief initiatives, the national
government should be pressed to rechannel unimportant and non-essential funds to relief,
rehabilitation, and recovery.
Government allocation for calamity and quick response funds should be increased, and
stringent measures put in place so that these are not used to minimize corruption as well as its
use for self-aggrandizement of politicians. The country’s ability to reliably predict natural
hazards should be boosted with sufficient funding for climate, weather, and flood forecasting
including forecasting-related research and development activities.
Flood control infrastructure programs should be scrutinized closely if they do more harm than
good to the ecosystem and communities, and are free from malfeasance. Efficient early warning
systems, proactive evacuation procedures, calamity-proof evacuation shelters, sufficient
prepositioned relief and disaster response resources should be ensured at the local levels.
Land use zoning and land use development protocols should be properly implemented. Mining,
quarrying, and logging be banned in flood- and landslide-prone watershed areas. Companies
implicated in disasters should be held accountable along with colluding local politicians.
We should also address, of course, the root of why millions Filipinos are always vulnerable and
exposed to disasters.
Zolantes-Nantes in 2015 emphasized the need for a more spatially and socially equitable
resource allocation and regional development to truly address flooding events and its impacts
on communities. To do this, cities need to be decongested by ensuring sufficient opportunities
for the rural poor. A significant step would be to free millions of landless farmer-tenants from the
yoke of serfdom that render them chronically poor through a genuine agrarian reform program.

Local manufacturing and productive processes should be encouraged and supported over our
standing economic dependence on imported machineries and consumer goods and slide into a
service-dominated economy to ensure sufficient employment and economic stability. This will
also stimulate the development of our local science and technology.
Pending a complete overhaul of the country’s elite-dominated and graft-ridden bureaucracy,
people’s movements are important change agents to push for much-needed reforms in our DRR
systems and to demand accountability for government negligence that lead to disasters.
Democratic freedoms and spaces for people’s movements to maneuver, extend support to
communities in need, and demand redress should be protected and respected at all cost.
The flooding events related to Typhoon Ulysses has shown that more than any government
official or agency, it is the unity and will of a people moved to action that can translate to real
change. From social media appeals for rescue and relief, to a clamor for more resolute and
logical action from the country’s Commander in Chief, citizenry-led and people-driven actions
yield tangible results. Amid a backdrop of government disinterest and neglect, it becomes a
necessity to collectively push for meaningful change in the country’s leadership and economic
systems in order to break away from our socially entrenched disaster vulnerability.##

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