Viliui

a river in the Yakut ASSR and Krasnoiarsk Krai; the largest left tributary of the Lena River. The Viliui is 2,650 km long and has a basin of 454,000 sq km. It flows through the Central Siberian Plateau and in its lower course, through the Central Yakut Lowlands. In its upper reaches it cuts across a swampy lacustrine plain and further down, flows through areas of traprock. Here the valley is of a mountainous type with canyon-like narrowings (to 160 m) and is extremely winding. The slopes are precipitous and are covered by forests; the river has rapids at this point. From the urban-type settlement of Chernyshevskii to the mouth of the Chirkuo River, the Viliui is part of the reservoir of the Viliui Hydroelectric Power Plant (that began producing electricity in 1967). Below the village of Suntar the valley broadens. From the town of Viliuisk to the mouth, the Viliui flows through a broad valley with a floodplain terrace; here the river has a forked channel and islands. (Khochentakh Island is up to 15 km long.)

The chief tributaries are the Ulakhan-Vava, Chirkuo, Chona, Ulakhan-Botuobuia, and Ochchugui-Botuobuia on the right and the Akhtaranda, Markha, and Tiung on the left. The Viliui is fed predominantly by snow. The average annual discharge at Chernyshevskii (the Viliui Hydroelectric Power Plant) is about 600 cu m per sec; at Suntar it is about 800 cu m per sec; and at the mouth, about 1,700 cu m per sec. The maximum spring discharge in the middle course is 10,000-15,000 cu m per sec, and the minimal winter discharge is 2-5 cu m per sec. The rise in the level during the spring is up to 10-15 m. The period of stable ice begins in the middle of October, and the ice breaks up in the middle of May. In the spring there are ice jams in the lower course.

The Viliui is navigable from the mouth upstream for a distance of 1,170 km, and when water is released from the reservoir, it is navigable as far as the settlement of Chernyshevskii. The main ports are Viliuisk, Niurba, and Chernyshevskii. The Viliui abounds in fish (sturgeon, taimen, Braehymystax lenok, Stenodus leucichthys, nelma, and others). In the basin of the Viliui there are deposits of diamonds (Mirnyi, Aikhal, and others), coal, natural gas, and common salt.