Editing Cagayan River (section)

==Topography==
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The river's [[headwaters]] are at the [[Caraballo Mountains]] of the [[Central Luzon]] at an elevation of approximately {{convert|1524|m}}. The river flows north for some {{convert|505|km}}<ref>"Principal River Basins of the Philippines", Published by the National Water Resources Board, October 1976 (p. 12)</ref> to its mouth at the [[Babuyan Channel]] near the town of [[Aparri]], [[Cagayan]]. The river drops rapidly to {{convert|91|m}} above sea level some {{convert|227|km}} from the river mouth. Its principal [[tributaries]] are the [[Pinacanauan River|Pinacanauan]], [[Chico River (Philippines)|Chico]], [[Siffu River|Siffu]], [[Mallig River|Mallig]], [[Magat River|Magat]] and [[Ilagan River]]s.

[[Magat River]], is the largest tributary with an estimated annual [[discharge (hydrology)|discharge]] of 9,808 million cubic meters. It lies in the southwestern portion of the [[drainage basin|basin]], stretching approximately {{convert|150|km}} from [[Nueva Vizcaya]] down to its [[confluence]] with Cagayan River about {{convert|55|km}} 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 (Philippines)|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]], {{convert|200|km}} from the mouth.

The Siffu-Mallig system lies on the slope of the Central [[Cordillera Central (Luzon)|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 Central (Luzon)|Cordillera Mountains]] in the west, [[Sierra Madre (Philippines)|Sierra Madre]] in the east and the [[Caraballo Mountains]] in the south.

The river has a drainage area of about {{convert|27300|km2}}. in the provinces of [[Apayao Province|Apayao]], [[Aurora Province|Aurora]], Cagayan, [[Ifugao Province|Ifugao]], Isabela, [[Kalinga Province|Kalinga]], [[Mountain Province]], Nueva Vizcaya, and Quirino.

The estimated annual discharge is 53,943 million cubic meters<ref name="PAGASA">{{cite web|title=Flood Forecasting and Warning System for River Basins; The Cagayan River Basin|url=https://web.pagasa.dost.gov.ph/index.php/flood-forecasting-and-warning-system-for-river-basins#cagayan-river-basin|website=Philippine Atmospheric, Geophysical and Astronomical Services Administration|access-date=March 12, 2016|archive-url=https://web.archive.org/web/20160312125930/https://web.pagasa.dost.gov.ph/index.php/flood-forecasting-and-warning-system-for-river-basins#cagayan-river-basin|archive-date=March 12, 2016|url-status=dead}}</ref> with a groundwater reserve of 47,895 million cubic meters.