The Arghandab is a river in Afghanistan, about 400Â km (250Â mi) in length. It rises in Ghazni Province, west of the city of Ghazni, and flows southwest, passing near the city of Kandahar, before joining the Helmand River 30Â km (19Â mi) below the town of Grishk. In its lower course, it is much used for irrigation, under the control of the Helmand and Arghandab Valley Authority, and the valley is cultivated and populous; yet the water is said to be somewhat brackish. It is doubtful whether the ancient Arachotus is to be identified with the Arghandab or its chief confluent the Tarnak, which joins it on the left 50Â km (31Â mi) southwest of Kandahar. The Tarnak, which flows south of Kandahar, is much shorter (length about 320Â km or 200 miles) and less copious.