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The Cagayan River, also known as the Rio Grande de Cagayan, 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== The river's headwaters are at the Caraballo Mountains of the Central Luzon at an elevation of approximately 1,524 meters. The river flows north for some 505 kilometers〔"Principal River Basins of the Philippines", Published by the National Water Resources Board, October 1976 (p. 12)〕 to its mouth at the Babuyan Channel near the town of Aparri, Cagayan. The river drops rapidly to 91 meters above sea level some 227 kilometers 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 kilometers from Nueva Vizcaya down to its confluence with Cagayan River about 55 kilometers 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 kilometers 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 river has a drainage area of about 27,300 km². in the provinces of Apayao, Aurora, Cagayan, Ifugao, Isabela, Kalinga, Mountain Province, Nueva Vizcaya, and Quirino. The estimated annual discharge is 53,943 million cubic meters with a groundwater reserve of 47,895 million cubic meters. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cagayan River」の詳細全文を読む スポンサード リンク
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