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Agno River

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Through Drainage system (geomorphology), Drainage basin and Hydroelectricity

Lab · Class 6–12Himalayan GeographyLab · Class 8–12Hydroelectric Power

The river originates in the Cordillera Mountains and empties into the South China Sea via Lingayen Gulf. The river is 248 kilometres (154 mi) long, making it the sixth longest river in the country. Roughly two million people live in the Agno River Valley, making it one of Philippines' larger population clusters.

The river is dammed by three hydroelectric power plants: the Ambuklao Dam in Bokod, the Binga Dam in Itogon, and the San Roque Dam in San Manuel.

Geography

The Agno River is the main drainage system of the area and has a catchment area of 5,952 square kilometres (2,298 sq mi). 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 metres (6,860 ft), where it drains Cretaceous to Paleocene igneous basement rocks, and marine siliciclastic and carbonate rocks. Of its total length, about 90 kilometres (56 mi) 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 metres (5,725 ft)) in Tarlac and joins the Agno River at Poponto Swamp near Bayambang. The swamp has an area of about 25 square kilometres (9.7 sq mi) and temporarily retains flood waters from Tarlac River.

After passing through mountains at an average elevation of some 2,000 feet (610 m) ASL, the Agno River forms a vast alluvial fan and delta called the Pangasinan Plain, a historically vital economic 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 July 16, 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.

The river's headwaters and upstream basin in the Cordillera Central range are designated conservation areas that lie within the Mount Data National Park, the Upper Agno River Basin Resource Reserve and the Lower Agno Watershed Forest Reserve.

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