The Little Zab or Lower Zab (, al-Zāb al-Asfal; or ; , Zâb-e Kuchak; , Zāba Taḥtāya) is a river that originates in Iran and joins the Tigris just south of Al Zab in the Kurdistan region of Iraq. It is approximately long and drains an area of about . The river is fed by rainfall and snowmelt, resulting in a peak discharge in spring and low water in summer and early fall. Two dams have been built on the Little Zab, regulating the river flow, providing water for irrigation and generating hydroelectricity. The Zagros Mountains have been occupied since at least the Lower Palaeolithic, but the earliest archaeological site in the Little Zab basin, Barda Balka, dates to the Middle Palaeolithic. Human occupation of the Little Zab basin has been attested for every period since then. Course The Little Zab rises in the Zagros Mountains in Iran at an elevation of circa amsl. In its upper reaches, the course of the Little Zab is determined by the alignment of the major mountain chains that make up the Zagros. Thus, the river flows through valleys that are predominantly aligned along a northwest–southeast axis, parallel to the major mountain chains of the Zagros, only to change its direction abruptly where it cuts through these chains in narrow gorges. Along the way, it collects the waters coming down from the eastern face of the Qandil Mountains, which now form the border between Iran and Iraq. The Little Zab enters the Mesopotamian plain south of Dukan, where it first assumes a roughly westward course before turning to the southwest upstream from the town of Altun Kopru and uniting with the Tigris near the town of Al Zab. Most tributaries join the Little Zab upstream from Dukan, with the largest being the Baneh River and the Qala Chulan. A number of smaller streams joined the Little Zab in the Ranya Plain, which is now partly inundated by Lake Dukan. Different estimates have been given for the length of the Little Zab: , and . For a short distance, the Little Zab forms the border between Iran and Iraq, and along its lower course it also constitutes the border between Erbil Governorate and Sulaymaniyah Governorate, and Erbil and Kirkuk Governorates. The river is fed by snowmelt and rainfall, resulting in a peak discharge in the period February–May. Low water levels are recorded for the period