Río Grande de Cagayán
|Native name||Bannag (Ibanag)|
|• location||Dupax del Sur, Nueva Vizcaya|
|• elevation||1,524 m (5,000 ft)|
|0 m (0 ft)|
|Length||505 km (314 mi)|
|Basin size||27,753 km2 (10,715 sq mi)|
The Cagayan River, also known as the Río Grande de Cagayán, is the longest river and the largest river by discharge volume of water in the Philippines. It has a total length of approximately 505 kilometres (314 mi) and a drainage basin covering 27,753 square kilometres (10,715 sq mi). 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.
The river's headwaters are at the Caraballo Mountains of the Central Luzon at an elevation of approximately 1,524 metres (5,000 ft). The river flows north for some 505 kilometres (314 mi) to its mouth at the Babuyan Channel near the town of Aparri, Cagayan. The river drops rapidly to 91 metres (299 ft) above sea level some 227 kilometres (141 mi) from the river mouth. Its principal tributaries are the Pinacanauan, Chico, Siffu, Mallig, Magat and Ilagan Rivers.
Magat River, is the largest tributary with an estimated annual discharge of 9,808 million cubic meters. It lies in the southwestern portion of the basin, stretching approximately 150 kilometres (93 mi) from Nueva Vizcaya down to its confluence with Cagayan River about 55 kilometres (34 mi) from the river mouth.
Both Magat and Chico Rivers have extensive drainage areas which comprise about 1/3 of the whole basin.
The Ilagan River originates from the western slopes of the Sierra Madre and drains the eastern central portion of the Cagayan River basin with an estimated yearly discharge of 9,455 million cubic meters. It flows westward and joins the Cagayan River at Ilagan, Isabela, 200 kilometres (120 mi) from the mouth.
The Siffu-Mallig system lies on the slope of the Central Cordillera ranges flowing almost parallel to the Magat River. Marshes and swamps are found in some parts of its lower reaches.
Cagayan River and its tributaries have deposited sediments of Tertiary and Quaternary origin, mostly limestone sands and clays, throughout the relatively flat Cagayan Valley which is surrounded by the Cordillera Mountains in the west, Sierra Madre in the east and the Caraballo Mountains in the south.
The estimated annual discharge is 53,943 million cubic meters with a groundwater reserve of 47,895 million cubic meters.
The average annual rainfall in 1,000 millimetres (39 in) in the northern part and 3,000 millimetres (120 in) in the southern mountains where the river's headwaters lie. Water from the mountains flow down very slowly because of surface retention over the extensive flood plain, the gorges in the gently-sloping mountains and the meandering course of the river.
Inundations of the Cagayan River and its tributaries have caused great loss of life and property and substantial losses to the local and national economies. The Philippine government has established several flood warning stations along the river. Experts are specifically monitoring the lower reaches from Tuguegarao to Aparri and the alluvial plain from Ilagan to Tumauini, Isabela.
In November 2020, after the onslaught of Typhoon Vamco (Ulysses), the river reached its peak level and caused floods along its vicinity due to the rainfall accumulated from the typhoon. This flooding was one of the worst floods in the river's history. The Magat Dam also contributed to the floods along the river when its floodgates opened due to a potential overflow.
Flora and fauna
The Cagayan River passes through one of the few remaining primary forests in the Philippines.
It supports the lives of numerous endemic and endangered species, like the Luzon bleeding-heart pigeon (Gallicolumba luzonica), Philippine eagle (Pithecophaga jefferyi) and a rare riverine fish, locally called ludong (Cestreaus plicatilis).
The ludong spawns in Cagayan River's upper reaches in Jones, Isabela. In late October until mid-November, the fish travel down the river to release their eggs at the river mouth near Aparri.
In February, ludong fry by the millions are again caught in fine nets as these travel upstream.
Due to the dwindling number of ludong caught yearly, local governments have imposed a ban on catching the fish and its fry, but the ban has failed.
The river drains a fertile valley that produces a variety of crops, including rice, corn, bananas, coconut, mangoes, citrus and tobacco.
Fish were a plentiful source of nutrition for centuries, but in recent decades issues such as fertilizer runoff, destructive fishing methods and a burgeoning human population have led to a great decline in the river's fish stocks. With worsening weather patterns and regular severe storms, even traditional agricultural means are insufficient to feed families although they were bountiful in the past century, leading to the more aggressive use of destructive techniques. This has been part of a vicious cycle of environmental degradation.
Families still go to the banks of the river and its tributaries to wash clothes or have picnics.
Until recently, boatmen would provide ferry service. For example, the towns of Lasam and Gattaran are directly across the river from each other. A crossing by boat was the most convenient, but emergencies could be dangerous, such as having to fetch the doctor in Gattaran during a storm at night. Now the best way is by vehicle over the Magapit bridge.
There are dams in two of the river's tributaries, the Magat and Chico Rivers, and there are also several mining concessions in the mineral-rich Cordillera Mountains near the headwaters of the two tributary rivers.
The provincial governments along the river have also developed tourism programs that offer activities on the river, particularly whitewater rafting.
From mouth to source:
- Magapit Suspension Bridge ( AH 26 (N1) (Pan-Philippine Highway), Lal-lo, Cagayan)
- Buntun Bridge ( N51 (Santiago–Tuguegarao Road), Tuguegarao City and Solana, Cagayan)
- Santa Maria Overflow Bridge (Cabagan–Santa Maria Road, Santa Maria and Cabagan, Isabela)
- Cansan-Bagutari Overflow Bridge (Cabagan-Santo Tomas Road, Cabagan and Santo Tomas, Isabela)
- Delfin Albano Bridge (Ilagan–Delfin Albano–Mallig Road, Delfin Albano and Tumauini, Isabela)
- Lullutan Bridge (Ilagan–Delfin Albano–Mallig Road, Ilagan, Isabela)
- Gamu Bridge (Gamu–Roxas Road, Gamu, Isabela)
- Naguilian Bridge ( AH 26 (N1) (Pan-Philippine Highway), Naguilian, Isabela)
- Alicaocao Overflow Bridge (Cauayan, Isabela)
- New Pigalo Bridge (Angadanan–Alicia Road, Angadanan, Isabela)
- Anafunan Overflow Bridge (Echague, Isabela)
- Gucab Overflow Bridge (Echague, Isabela)
- Dalibubon Bridge (Santiago–San Agustin Road and Echague–Jones–Maddela Road, Echague and Jones, Isabela)
- Jones II Bridge (Santiago–San Agustin Road, Jones, Isabela)
- San Pedro Bridge (Maddela, Quirino)
- Dumabato Bridge (Maddela, Quirino)
- Abbag Bridge (Cordon–Diffun–Maddela–Aurora Road, Nagtipunan, Quirino)
The Pan-Philippine Highway generally follows the course of the river from Echague until the Magapit Suspension Bridge where it continues west.
- Kenneth Kimutai too (July 24, 2018). "Longest Rivers In The Philippines". worldatlas.com. WorldAtlas. Retrieved September 9, 2019.
- Vicente B. Tuddao Jr. (September 21, 2011). "Water Quality Management in the Context of Basin Management: Water Quality, River Basin Management and Governance Dynamics in the Philippines" (PDF). www.wepa-db.net. Department of Environment and Natural Resources. Retrieved April 5, 2017.
- "Taming the Cagayan River, Inquirer.net". Retrieved May 20, 2017.
- "Principal River Basins of the Philippines", Published by the National Water Resources Board, October 1976 (p. 12)
- "Flood Forecasting and Warning System for River Basins; The Cagayan River Basin". Philippine Atmospheric, Geophysical and Astronomical Services Administration. Archived from the original on March 12, 2016. Retrieved March 12, 2016.
- San Juan, Alexandria Dennise (November 13, 2020). "Residents near Ipo, Ambuklao, Binga, and Magat dams warned of flooding as reservoirs continue to release water". Manila Bulletin. Retrieved December 22, 2020.
Magat Dam in Isabela province has also released water at 5,073 cms as seven gates have been opened 24 meters.
- De Vera-Ruiz, Ellalyn (November 12, 2020). "Widespread flooding in Isabela, Cagayan feared as Magat Dam releases more water". Manila Bulletin. Retrieved December 22, 2020.
- Wernstedt, F. L.; J. E. Spencer (1967). The Philippine Island World. Berkeley and Los Angeles: University of California Press.