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CAGAYAN RIVER BASIN
Location:
The Cagayan River basin, of which the catchment area is 27,281km2, is
located in the northeastern part of the Luzon Island. The basin lies between
15°52 and 18°25 north latitude and between 120°51 and 122°18 east longitude.
It is bounded in the east, west and south by the Sierra Madre, Cordillera
Central and Caraballo-Maparang mountain ranges.
Socio-economy:
In the Cagayan River basin, a population was estimated at 2.55 million
in the 1995 census year, distributing 2.13 million or 84% of the basin
population in Region 2, 0.50 million or 16% in CAR, and 9 thousand or
0% in Region 4. Thus, Region 2 would represent a basin socio-economic
character. GRDP of Region 2 in 1998 was 55.2 billion pesos, accounting
for 2.0% of the national GDP. GRDP per capita of Region 2 was 20,200 pesos
in the same year, accounting for 56% of the national one due to low agricultural
productivity caused by habitual flood inundation. At present, thus, the
regional economy is backward in economic condition in the country. In
the region, agricultural production attained the largest share (43%) among
the major economic sectors. It accounted for 5.3% of the national agricultural
production. In order to accelerate economic growth, the governments have
to intensify their effort to increase production factors such as capital
and labor, to increase productivity by improving technology level.
Topography and Geology:
The Cagayan River basin is mostly hilly to mountainous. Land with a slope
of less than 8% is around 9,500km2, which has been rather well developed
as the agricultural land. Hilly land with slopes between 8% and 18% covers
about 3,800km2. The substantial parts of the hilly land are left to be
grass land. The remaining 14,000km2 are mountainous. Rocks of the
Cagayan River basin is represented by a thick sequence of pre-Tertiary
metamorphic and plutonic rocks. An Oligocene to Pliocene Marine section
occupies the main basin area. Although many earthquakes were experienced
in northern Luzon, relatively fewer earthquakes occurred within the Cagayan
valley. Intense earthquakes are assumed to be tectonic origin and rarely
of volcanic nature. The magnitude of the earthquake occurred in July 1990
about 70km south from Santa Fe was recorded at 7.8 in Richter scale.
Hydrology:
The climate in the Cagayan River basin consists of monsoons, i.e. the
southwest monsoon and northeast monsoon. Typhoons normally strike during
July to December with about 8 times a year on an average. A primal portion
of annual rainfall of 2,600mm is, however, ascribed to the southwest monsoon.
The record indicates that the basin is affected by El Nino almost every
three years. Average annual runoff is estimated to be 1,343m3/s
at the mouth of the Cagayan River. The 100 year probable flood is estimated
to be 21,400m3/s at the mouth under the present river condition.
River System:
The total basin area and river length of the Cagayan are 27,281km2 and
520km, respectively. The major tributaries of the Cagayan River are Chico
River (basin area of 4,550km2), Siffu-Mallig River (2,015km2), Magat River
(5,110km2) on the left bank, and Pared River (970km2), Tuguegarao River
(660km2), Tumauini River (960km2) and Ilagan River (3,130km2) on the right
bank.
Major Dimensions: Major dimensions of the main Cagayan River
are as follows:
Riverbed Slope
- River mouth to Magapit Bridge: 1/13,000
- Magapit Bridge to Alcala: 1/8,500
- Alcala to confluence with the Tuguegarao River: 1/9,000
- Tuguegarao River confluence to Cabagan: 1/7,000
Channel
Width
- River mouth to Magapit Bridge: 1,000 to 2,000 m
- Magapit Bridge to Alcala: 300 to 1,000 m
- Alcala to Tuguegarao: 500 m - Upstream of Tuguegarao: 600 m
Carrying Capacity
- River mouth to Magapit Bridge: 10,000 to 18,000 m3/sec
- Magapit Bridge to Alcala: 5,000 to 15,000 m3/sec
- Alcala to Cabagan: 3,000 to 6,000 m3/sec
The carrying capacities below the riverbank elevation of both the rivers
Chico and Tuguegarao are summarized below.
Carrying Capacity of the Lower Chico River
- Confluence to 10 km upstream: 5,000 to 10,000 m3/sec
- 10 km to 14 km upstream: 2,000 to 4,000 m3/sec
Carrying Capacity of the Lower Tuguegarao River
- Confluence to 3 km upstream: 3,000 m3/sec
- 3 km to 9 km upstream: 6,000 m3/sec
- 9 km to 14 km upstream: 2,000 m3/sec
River Geomorphology:
Compound actions of repeated upheaval and lowering ground movements in
the prehistoric time formed a Cagayan Valley with bottlenecks of Magapit
Narrows, in the zone between tectonic lines of north-south and east-west
directions. Afterwards, alluvial plain in the Cagayan River was gradually
developed in combination with the repeated both the actions of sedimentation
by rivers and fluctuation of seawater level. The present alluvial plain
extending over the upstream at Alcala was thus formed largely by backwater
phenomena due to the bottlenecks in the Magapit Narrows. Similarly, river
meandering naturally and violently proceeded in the alluvial plain because
of gentle slope gradient.
Variation of River Channel:
River course shifting in the reach from Alcala to upstream of Tuguegarao
is so significant. Active shifting is caused by fairly gentle water surface
slope due to backwater from the bottlenecks in the Magapit Narrows. Just
upstream at Iguig, the extent of shifting reaches 5 km in an interval
for only the past 50 years. Such shifting generally occurs not gradually
through years but suddenly or accidentally in the flood time. The tendency
of the riverbed variation is
1) no significant change in the reaches from the river mouth to Magapit
bridge and from confluence with the Tuguegarao River to Cabagan, and
2) slightly raised in the reaches from Magapit bridge to confluence with
the Tuguegarao River.
There is no remarkable increase of the sandbars near the Cagayan River
mouth, although its local shifting has been observed. In the Cagayan River,
river channel meanders especially in the reach from Alcala to upstream
of Tuguegarao. There is a tendency of the said reach changing to a straight
river course.
Bank Erosion and Sedimentation:
Bank erosion is observed in various places of the main Cagayan River and
its tributaries, and is one of the flood control problems. Average annual
bank erosion rate in the downstream of the Magapit Narrows reaches 10m,
while that in the upstream of Alcala reaches 24m. The existing bank protection
works consist of spur dike and revetment. The sedimentation in the Magat
reservoir is serious, of which the accumulated sediment volume was recorded
at 188 million m3 in 1999. In the lower Cagayan River, it can be said
that sedimentation is not serious in view of the actual variation of riverbed
and sandbars, although local sedimentation is observed at the inlet of
Amulung pumping station and the confluence with a small tributary of the
Appagonan River at Aparri.
Inundation Area:
The Cagayan River has about 1,860km2 flood prone areas, which are presently
used as production areas of rice, corn, legumes and vegetables. The area
of 1,860km2 was estimated from that brought by the 1973 flood, which was
the biggest one in the past. The inundation areas are within the limited
areas of lower alluvial plain except for some natural levees with higher
elevations. Afterwards, alluvial plain in the Cagayan River was gradually
developed in combination with the repeated both the actions of sedimentation
by rivers and fluctuation of seawater level. The present alluvial plain
extending over the upstream at Alcala was thus formed largely by backwater
phenomena due to the bottlenecks in the Magapit Narrows. Similarly, river
meandering naturally and violently proceeded in the alluvial plain because
of gentle slope gradient.
Present Prevention System:
Disaster Coordinating Council (DCC) prepares damage reports upon occurrence
of disasters. According to the damage reports, the damages were estimated
in Region 2 to be 1.8 billion pesos for Typhoon Iliang in 1998, 0.5 billion
pesos for Typhoon Loleng in 1998 and 0.3 billion pesos for Typhoon Pepang
in 1999. In Region 2, RDCC2 prepared the general action plan for typhoons/floods
OPLAN BAGYO/LAYOS in May 1998. Cordillera RDCC also prepared Cordillera
Regional Disaster Management Plan in 1994. The purposes of the disaster
action plans are to implement effective disaster preparedness, mitigation
and prevention activities to minimize damage to property and human suffering.
In the Cagayan River basin, some joint operation on the disaster management
is conducted between RDCC2 and Cordillera RDCC so that an assistance of
the RDCC2 is given on the occasion of emergency in the Chico or other
river basins. There are two existing flood forecasting and warning systems,
one is the Cagayan Flood Forecasting and Warning System operated by PAGASA
and the another is Magat Dam Flood Forecasting and Warning System under
NIA. Both systems have problems of malfunction of equipment and insufficient
operation and maintenance of the system. The existing evacuation system
is operated and maintained by RDCC, PDCC, CDCC/MDCC and BDCC. There are
464 designated evacuation centers in Region 2. Major problems are insufficient
supply of drinking water and food, and lack of cooking facilities and
comfort rooms in the evacuation centers.
Present Watershed Condition:
The forest cover of the Cagayan River basin has been decreased and the
SAFDZ data shows the present forest cover of 37% of the basin. The erosion
map of BSWM indicates moderate to severe erosion areas in the upper Magat,
upper Cagayan and upper Chico watersheds. In the upper Magat River basin,
issues on land collapse and sediment deposit caused by the earthquake
occurred in 1990 are remarkable, which affect the reservoir sedimentation
of the Magat Dam.
Present Watershed Management:
DENR Region 2 has several forest plantation and other programs/projects
focused on the rehabilitation, development and protection of the watershed
in the Cagayan River basin. DENR CAR has also implemented some projects
such as check dam construction and stone masonry. Other government agencies
such as NIA and NPC and LGUs also worked hand in hand with DENR in the
watershed management projects including Magat River basin and Casecnan
Project. Some foreign assisted watershed management projects were implemented
or ongoing, which include forestry sector project of JBIC, DENR-ITTO project
and OISCA project. DENR Region 2 and CAR have their respective regional
master plan for forestry development.
Present Land Use:
Out of 27,281 km2 of the Cagayan River basin,
about a half of the area is more than 400 m in elevation and area of land
slope over 18% covers more than 50%. Forest occupies 37%, grassland 34%,
agricultural area 27% and others such as settlement, water area, etc.
2% in the basin. The agricultural area of 741,000 ha consists of fruit
tree area (44,000 ha) and crop field (697,000 ha). The crop field comprises
paddy field (474,000 ha), corn field (151,000 ha) and other upland crop
field (72,000 ha). Most of the potentially cultivable area is already
used as the agricultural land.
Present Agricultural Condition:
The Philippine is currently insufficient in staple food supply. Averaged
imported rice (1995-99) is estimated at 12% of national consumption, although
rice production has an increasing trend. Corn production in the Philippines
has been slightly decreasing mainly due to decreasing of white corn production.
Department of Agriculture (DA) is the leading agency to extend agricultural
support services. The progress of CARP in Region 2 and CAR is 87% and
84%, respectively. About 70% of the primary cooperatives in the area are
multipurpose agricultural cooperatives followed by multipurpose non-agricultural
cooperatives.
Problems on Agriculture:
The problems on marketing and post-harvest in the area are,
1) deficit of working capital,
2) poor condition of farm to market roads,
3) shortage of labor for harvesting,
4) lack of drying floors and facilities, and
5) low price of product.
The existing constraints/challenges for the development in the basin are;
a) environmental degradation in agriculture,
b) inadequacy of economic opportunities, limited investment to the sector
and weak global competitiveness,
c) inadequacy of rural infrastructure, and d) high poverty incidence in
the rural areas.
Needs of Agriculture:
Further growth of agricultural sector will need to be attained through
expansion of areas under irrigated agriculture with effective water use,
higher crop yields, improved cropping patterns, and increased productivity
of livestock and coastal fisheries activities. At the same time, particular
attention is required to be paid to increasing small farm productivity.
Present Irrigation Condition:
Out of total potential irrigable area of about 3.1 million ha in the Philippines,
43% or some 1.3 million ha is counted as the service area by NIA. Increase
rate of irrigation service area became dull in 1990s from various reasons.
Potential irrigation development area in the Cagayan River basin is estimated
around 511,000 ha. Existing irrigation service area is obtained to be
222,000 ha or 43% of total irrigable area. Irrigated cropping intensity
(ICI) in NIS and CIS is 132% in average in the basin. Constraints in irrigation
development and in existing system include technical and financial insufficiency,
natural calamities including flood by typhoon, land slide by earthquake,
drought, etc., and social problems.
Terrestrial Flora:
The number of family and species recorded is 79 and 298, respectively.
Of all the species recorded, there are 7 species that are considered endangered
being pressured by human activities and/or due to its habitat loss. The
results of on-site survey shows that tree species still dominate the lower
Cagayan River area in terms of number of species (88 species). They are
followed by the shrub (24 species) and then the grass species (10 species).
Terrestrial Fauna:
A total of 75 families and 182 species of terrestrial fauna were recorded
in the Cagayan Valley based on secondary data. Among those recorded, the
number of species listed in IUCN Red List and CITES List is 19 and 29,
respectively. The results of on-site survey show that a total of 54 species
were recorded on sampling areas, including 42 species of birds, 6 of mammals,
4 of reptiles and 2 of amphibians.
Protected Area:
DENR, Region 2, designated eighteen protected areas in the whole Cagayan
basin, eleven of which are located in Region 2, six are in CAR, and one
straddles over the 2 regions. None of those are located within riverbed
of the Lower Cagayan River although Peņablanca Protected Landscape lies
over Pinacanauan de Tuguegarao River, a tributary of the Cagayan River.
Aquatic Ecology:
There are some fifty nekton species, or Class Pisces, Class Crustacea
and Class Mollusca, found in the river system. The results of on-site
survey shows that a total of 141 species were noted for the entire Cagayan
River System, which is composed of 44 phytoplankton, 18 zooplankton, 15
benthos, 47 fishes, 7 macro crustaceans and 10 molluscs. There are 16
migratory species in the river and all are catadromous.
Water Quality:
Results of water quality sampling shows that Cagayan River and its tributaries
are of good water quality under Class C Category especially in terms of
high DO and low BOD, EC, nitrogen, and phosphate. However, microbial quality
as Coliform Bacteia of surface water generally exceeded the standards
set. This implies that sewage from residences and buildings including
domestic waste is inflowing to the Cagayan River system. As a whole, however,
the water quality of the Cagayan river is usable for agricultural irrigation.
Groundwater is of good quality, except those that exhibit acidic water
pH with increased conductivity, turbidity, and total solids. Microbial
quality indicates Coliform contamination, rendering these wells unsuitable
for drinking without treatment such as by boiling or chlorination.
Air Quality and Noise:
Results of the ambient air quality sampling indicate that the values
of all air quality parameters are much lower than the corresponding air
quality standards as defined in DAO 14 suggesting ambient air quality
is possibly not of major concern within the study area at the present.
Noise levels in residential areas were less than any class of Ambient
Noise level Criteria provided by DENR. In town centers, noise levels were
within 57 to 76 except that of Town Market in Ilagan with noise level
of 90.9 dBA.
Fisheries:
The fishing industry in Region 2 is one of the most productive in the
Philippines. A considerable portion of the population in the region relies
on the industry for food and for income generation. The total number of
fishing households is 31,301 in 1996, occupying 5.7% of total households.
Cagayan River and Magat Dam are listed as one of the major fishing grounds
in the Region. At least 30 species of edible fishes and shellfishes are
recognized in the lower Cagayan River.
Navigation:
17 routes for navigation currently exist along the river. The navigation
routes are important for economic activities in this area in terms of
trip, transportation and commute under such conditions that insufficient
road network or lack of bridges. Of the 17 navigation routes, six are
located in the lowest reach between river mouth and Gattaran. Five are
located between Alcala and Tuguegarao, and the rest are over the upstream
reach of Tuguegarao.
Water Rights:
The total number of the grantees is 1,584 as of 1999, including private
person, company and Government, i.e. NIA, FSDC, NPC, and so on. Sources
of water intake are surface water and groundwater. The main use of water
is irrigation with the number of 1,427, counting for 90.1% of all the
water intakes. The rest is as domestic (111), power (26), industrial (7),
livestock (6), fisheries (5) and recreational (2).
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