The Sulak drains most of the mountainous interior of Dagestan northeast into the Caspian Sea. It and most of its branches flow in canyons. Its main tributaries are, from north to southeast:The Andi Koysu flows north-northeast and joins the Avar Koysu to become the Sulak. A few of its upper tributaries are in Georgia. Near the junction of the two rivers w…The Sulak drains most of the mountainous interior of Dagestan northeast into the Caspian Sea. It and most of its branches flow in canyons. Its main tributaries are, from north to southeast:The Andi Koysu flows north-northeast and joins the Avar Koysu to become the Sulak. A few of its upper tributaries are in Georgia. Near the junction of the two rivers were the Siege of Akhoulgo and the Battle of Gimry.