The Kafue River is the longest river lying wholly within Zambia at about 1,576 kilometres (979 mi) long. Its water is used for irrigation and for hydroelectric power. It is the largest tributary of the Zambezi, and of Zambia's principal rivers, it is the most central and the most urban. More than 50% of Zambia's population live in the Kafue River Basin and of these around 65% are urban. It has a mean flow rate of 320 m³/s through its lower half, with high seasonal variations. The river discharges 10 km³ per year into the Zambezi River.