Kapuas River

Kapuas
The Kapuas River as it flows through Pontianak
Country	Indonesia
Basin features
Main source	Müller Mountain Range 0 m (0 ft)
River mouth	South China Sea
Basin size	98,749 km2 (38,127 sq mi)
Physical characteristics
Length	1,143 km (710 mi)

The Kapuas River (or Kapoeas River) is a river in the Indonesian part of Borneo island, at the geographic center of Maritime Southeast Asia. At 1,143 kilometers (710 mi) in length, it is the longest river of Indonesia and one of the world's longest island rivers. It originates in the Müller mountain range at the center of the island and flows west into the South China Sea creating an extended marshy delta. The delta is located west-southwest of Pontianak, the capital of West Kalimantan province. This Kapuas River should be distinguished from another Kapuas River, which starts on the other side of the same mountain range in central Borneo, but flows to the south, merging with the Barito River and discharging into the Java Sea.

The river is 1,143 km (710 mi) long and up to 700 m (2,300 ft) wide at its delta; with a total area of 98,749 km², the river basin covers more than 67% of West Kalimantan. The discharge rate varies through the year, averaging around 6,000–7,000 m³/s at the delta and 2,000 m³/s upstream, at the confluence of the Tawang River. The discharge peaks during the rainy seasons in April and November, during which the water level may rise by 10–12 m overnight, overflowing river banks and flooding the nearby areas.

The river originates near the center of Borneo, south from the Indonesian-Malaysian border, in the joint between the western slope of the Müller Mountain Range, which runs through the island center, and the southern slope of the Upper Kapuas Range (Indonesian: Kapuas Hulu), which is located more to the west. For about 165 km it flows through a mountainous terrain and then descends to a marshy plain. There, the elevation decreases by only 50 meters (160 ft) over 900 km (560 mi) from Putussibau to the river delta. About 350 km from the source, near the northern shore of the river, lies a system of Kapuas Lakes which are connected to the river by numerous channels. These lakes are Bekuan (area 1,268 hectares), Belida (600 ha), Genali (2,000 ha), Keleka Tangai (756 ha), Luar (5,208 ha), Pengembung (1,548 ha), Sambor (673 ha), Sekawi (672 ha), Sentarum (2,324 ha), Sependan (604 ha), Seriang (1,412) Sumbai (800 ha), Sumpa (664) and Tekenang (1,564 ha). When the monthly precipitation exceeds about 300 mm, the river overflows its banks, diverting much of its waters to the lakes at a rate of up to 1,000 m³/s, and forming a single volume of water with them. This outflow prevents massive flooding of the lower reaches of the river; it also promotes fish migration from the river to the lakes for spawning, but drives birds away from the lakes.