the name of several rivers in the mountainous region of the Dagestan ASSR, of which the main ones are the Andiiskoe Koisu and the Avarskoe Koisu; they form the Sulak River.
The Andiiskoe Koisu rises from two sources in the eastern part of the Greater Caucasus (Georgian SSR). It is 144 km long, 192 km from the largest component, and has a basin area of 4,810 sq km. It is a typical mountain river, with numerous rapids. It is fed by various means, but predominately by thawing snow. Floods occur from May through August. The average rate of flow at a distance of 9 km from the mouth is 69.6 eu m per sec.
The Avarskoe Koisu (in the upper reaches the Dzhurmut) begins on the slopes of Mount Guton and flows around the Nukatl’ Range in a narrow valley that has partly the form of a canyon. The river is 178 km long, with a basin area of 7,660 sq km. The river is fed by various means, but predominately by snow. The average rate of flow is 95 eu m per sec. The water is very muddy. A tributary on the right is the Karakoisu (93 km), with its right-hand tributary the Kazikumukhskoe Koisu (81 km). Timber is floated on the river, and its water is used for irrigation. On the Karakoisu River is the Gergebil’ Hydroelectric Power Plant (with a capacity of 1.2 megawatts).