Agno River
Encyclopedia
Agno River is a river
in the Philippine
island of Luzon
, in the province of Pangasinan
. It is the fifth largest river system in the country with drainage area of 5,952 km². It originates in the Cordillera Mountains
and empties into the South China Sea
via the Cordillera Mountains
. The river is 206 km long.
of 5,952 square kilometers. It is the third largest river in Luzon (next to Cagayan River
and Pampanga River
) and the fifth largest river in the Philippines.
The Agno is the largest Philippine river in terms of water discharge, draining around 6.6 cubic kilometers of fresh water into Lingayen Gulf
, or almost 70% of the total fresh water input into the gulf.
The headwaters of Agno River are at the slopes of Mount Data in the Cordillera Mountains at an elevation of 2,090 m, where it drains Cretaceous to Paleocene igneous basement rocks, and marine siliciclastic and carbonate rocks. Of its total length, about 90 kilometers runs through mountainous terrain and canyons.
As the river descends following a southerly course, it exhibits a braided channel pattern. It then transforms into a southwest-directed meandering river as it crosses the Central Luzon Plain. From its confluence with the Tarlac River
emanating from the south, the Agno River then veers northward while draining the eastern flanks of the Zambales Mountains
.
The Agno's principal tributaries include the Pila, Camiling, Tarlac and Ambayoan Rivers. The main branch of the Agno River is Tarlac River which originates from Mount Pinatubo
(elevation 1,745 m) in Tarlac
and joins the Agno River at Poponto Swamp near Bayambang
. The swamp has an area of about 25 square kilometers and temporarily retains flood waters from Tarlac River
.
After passing through mountains at an average elevation of some 2,000 feet (600 m) ASL, the Agno River forms a vast alluvial fan and delta called the Pangasinan Plain, a historically vital ecoonomic hub on Luzon Island.
A number of faults of local and regional significance cut across the river. Joint systems are also found in the area. These faults and joints reduce the rock strength and rock coherence through which water could pass or slippage could occur.
The Philippine Fault System
, including the Digdig Fault, which has been assessed as the causative fault of the 16 July 1990 Luzon earthquake
, and the San Manuel Fault, Bulangit Fault and the San Roque Fault are some of the major fault lines crossing the river.
and nipa palm trees which served as habitat to many marshland wildlife species.
But the catchment area is now severely deforested. Primary forest has almost completely disappeared apart from a few areas above 800 m ASL. The forests have been replaced by grassland and riceland.
The Pangasinan Plain suffers from recurrent and destructive floods. The catastrophic floods of July-August 1972 and May 1976 inundated the entire Pangasinan Plain, including the flood plains of the Tarlac River.
The Philippine Atmospheric, Geophysical and Astronomical Services Administration, the national weather bureau, has established a flood monitoring and warning center in Pangasinan.
, Kankanaey and Kalanguya people live. The Ibaloi people of Benguet regard the river as sacred because it gives life.
Barangay
Dalupirip, Itogon in Benguet province is held sacred by its people. Portions of the land serve as the burial grounds of their ancestors. The place holds great historical value and is considered one of the remaining seats of Ibaloi culture.
Archaeological sites were discovered at Sitio Camanggaan, Barangay San Roque in San Manuel, Pangasinan and in surrounding areas. Yields consisted of tradeware and earthenware shards and Palaeolithic and Neolithic stone tools.
There are several mining concessions in the upper reaches of the river.
The government has also established the Agno River irrigation system to provide irrigation water to some 60 to 100 square kilometers of ricelands in Pangasinan.
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
in the Philippine
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
island of Luzon
Luzon
Luzon is the largest island in the Philippines. It is located in the northernmost region of the archipelago, and is also the name for one of the three primary island groups in the country centered on the Island of Luzon...
, in the province of Pangasinan
Pangasinan
Pangasinan is a province of the Republic of the Philippines. The provincial capital is Lingayen. Pangasinan is located on the west central and peripheral area of the island of Luzon along the Lingayen Gulf, with the total land area being 5,368.82 square kilometers . According to the latest census,...
. It is the fifth largest river system in the country with drainage area of 5,952 km². It originates in the Cordillera Mountains
Cordillera Mountains
*Andes in South-America *Cordillera Central in the Philippines...
and empties into the South China Sea
South China Sea
The South China Sea is a marginal sea that is part of the Pacific Ocean, encompassing an area from the Singapore and Malacca Straits to the Strait of Taiwan of around...
via the Cordillera Mountains
Cordillera Mountains
*Andes in South-America *Cordillera Central in the Philippines...
. The river is 206 km long.
Topography
The Agno River is the main drainage system of the area and has a catchment areaDrainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
of 5,952 square kilometers. It is the third largest river in Luzon (next to Cagayan River
Cagayan River
The Cagayan River is the longest and largest river in the Philippine Archipelago. It is located in the Cagayan Valley region in northeastern part of Luzon island and traverses the provinces of Nueva Vizcaya, Quirino, Isabela and Cagayan.-Topography:...
and Pampanga River
Pampanga River
Pampanga River is the second largest river in the island of Luzon, next to Cagayan River and the third largest river in the Philippines...
) and the fifth largest river in the Philippines.
The Agno is the largest Philippine river in terms of water discharge, draining around 6.6 cubic kilometers of fresh water into Lingayen Gulf
Lingayen Gulf
The Lingayen Gulf is an extension of the South China Sea on Luzon in the Philippines stretching . It is framed by the provinces of Pangasinan and La Union and sits between the Zambales Mountains and the Cordillera Central...
, or almost 70% of the total fresh water input into the gulf.
The headwaters of Agno River are at the slopes of Mount Data in the Cordillera Mountains at an elevation of 2,090 m, where it drains Cretaceous to Paleocene igneous basement rocks, and marine siliciclastic and carbonate rocks. Of its total length, about 90 kilometers runs through mountainous terrain and canyons.
As the river descends following a southerly course, it exhibits a braided channel pattern. It then transforms into a southwest-directed meandering river as it crosses the Central Luzon Plain. From its confluence with the Tarlac River
Tarlac River
The Tarlac River is a river in the Philippines, located in the province of Tarlac.It is visible from the dike near the Tarlac City Wet Market. It was formerly the site of traditional balsa or bamboo raft riding, until the river was heavily silted by sticky lahar or mud flow brought by Mt. Pinatubo...
emanating from the south, the Agno River then veers northward while draining the eastern flanks of the Zambales Mountains
Zambales Mountains
The Zambales Mountains is a mountain range located on western Luzon island in the Philippines. The mountains separate Luzon's central plain from the South China Sea. Its most prominent section is known as the Tri-Cabusilan Mountain Range composed of Mt. Pinatubo, Mount Negron and Mount Cuadrado...
.
The Agno's principal tributaries include the Pila, Camiling, Tarlac and Ambayoan Rivers. The main branch of the Agno River is Tarlac River which originates from Mount Pinatubo
Mount Pinatubo
Mount Pinatubo is an active stratovolcano located on the island of Luzon, near the tripoint of the Philippine provinces of Zambales, Tarlac, and Pampanga. It is located in the Tri-Cabusilan Mountain range separating the west coast of Luzon from the central plains, and is west of the dormant and...
(elevation 1,745 m) in Tarlac
Tarlac
Tarlac is a landlocked province of the Philippines located in the Luzon Island. Its capital is Tarlac City. Tarlac borders Pampanga to the south, Nueva Ecija to the east, Pangasinan to the north, and Zambales to the west...
and joins the Agno River at Poponto Swamp near Bayambang
Bayambang, Pangasinan
Bayambang is a 1st class municipality in the province of Pangasinan, Philippines. According to the latest census, it has a population of 103,145 people in 17,897 households.-Etymology:...
. The swamp has an area of about 25 square kilometers and temporarily retains flood waters from Tarlac River
Tarlac River
The Tarlac River is a river in the Philippines, located in the province of Tarlac.It is visible from the dike near the Tarlac City Wet Market. It was formerly the site of traditional balsa or bamboo raft riding, until the river was heavily silted by sticky lahar or mud flow brought by Mt. Pinatubo...
.
After passing through mountains at an average elevation of some 2,000 feet (600 m) ASL, the Agno River forms a vast alluvial fan and delta called the Pangasinan Plain, a historically vital ecoonomic hub on Luzon Island.
A number of faults of local and regional significance cut across the river. Joint systems are also found in the area. These faults and joints reduce the rock strength and rock coherence through which water could pass or slippage could occur.
The Philippine Fault System
Philippine Fault System
The Philippine Fault System is an inter-related system of faults throughout the whole of the Philippine Archipelago, primarily caused by tectonic forces compressing the Philippines into what tectonic geophysicists call the Philippine Mobile Belt....
, including the Digdig Fault, which has been assessed as the causative fault of the 16 July 1990 Luzon earthquake
1990 Luzon earthquake
The Luzon earthquake occurred on Monday, July 16, 1990, at 4:26 PM local time in the Philippines. The densely populated island of Luzon was struck by an earthquake with a 7.8 Ms...
, and the San Manuel Fault, Bulangit Fault and the San Roque Fault are some of the major fault lines crossing the river.
Flora and fauna
Spanish explorers who documented the catchment area of the river in the 16th century say the mouth of the Agno was an extensive marshland with rich alluvial soil. It was thickly covered with mangroveMangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
and nipa palm trees which served as habitat to many marshland wildlife species.
But the catchment area is now severely deforested. Primary forest has almost completely disappeared apart from a few areas above 800 m ASL. The forests have been replaced by grassland and riceland.
Flooding
Since the Agno River basin is characterized by mountainous topography, the Ambuklao water reservoir was built to keep it from gushing down and causing devastating effects on the lower levels of the river, the flood runoff estimated annually at about 6,654 million cubic meters reaches the plain in several hours in the river mouth in about a day. Average annual rainfall varies from 2,000 mm in the neighborhood of Tarlac to 4,000 mm in the upper reaches of the Agno River.The Pangasinan Plain suffers from recurrent and destructive floods. The catastrophic floods of July-August 1972 and May 1976 inundated the entire Pangasinan Plain, including the flood plains of the Tarlac River.
The Philippine Atmospheric, Geophysical and Astronomical Services Administration, the national weather bureau, has established a flood monitoring and warning center in Pangasinan.
People
The Agno traverses several towns in Benguet province where some 35,000 indigenous IbaloiIbaloi
The Ibaloi or Nabaloi is an indigenous ethnic group found in the northern Philippines. The Ibaloi are one of the indigenous peoples collectively known as Igorot, who live in the mountains of the Cordillera Central on the island of Luzon...
, Kankanaey and Kalanguya people live. The Ibaloi people of Benguet regard the river as sacred because it gives life.
Barangay
Barangay
A barangay is the smallest administrative division in the Philippines and is the native Filipino term for a village, district or ward...
Dalupirip, Itogon in Benguet province is held sacred by its people. Portions of the land serve as the burial grounds of their ancestors. The place holds great historical value and is considered one of the remaining seats of Ibaloi culture.
Archaeological sites were discovered at Sitio Camanggaan, Barangay San Roque in San Manuel, Pangasinan and in surrounding areas. Yields consisted of tradeware and earthenware shards and Palaeolithic and Neolithic stone tools.
Economic importance
The river has three hydroelectric plants: Binga Dam in Itogon, Benguet (29 km upstream); Ambuklao Dam in Bokod, Benguet (37 km upstream) and the San Roque Dam in San Manuel, Pangasinan. Binga has been operational since 1960 and Ambuklao since 1956.There are several mining concessions in the upper reaches of the river.
The government has also established the Agno River irrigation system to provide irrigation water to some 60 to 100 square kilometers of ricelands in Pangasinan.
Further reading
- Siringan, Fernando P. and Mateo, Zenon Richard P. Sediment load partitioning of the Agno River and changes in the shoreline position, National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City
- Torres, Ronnie C.; Paladio, Ma. Lynn O.; Punongbayan, Raymundo S.; and Alonso, Rosalito A. Mapping of Areas Affected by Liquefaction during the 16 July 1990 Earthquake Philippine Institute of Volcanology and Seismology and University of the Philippines National Institute of Geological Sciences