Direction of water courses, in general, is from west to south i.e. from the watersheds of Sulaiman Mountains to the Indus. There are two principal rivers in the Agency, Gomal of Luni and Tank Zam. Some important rivulets are Khaisora, Shaktu, Siplatoi, Toi Khwla, Shuza, Shinkai and Shahur. The rest are mountain streams which can become dangerous and impassable during heavy rains which frequently occur during the months of July and August. The Gomal River rises in two branches in the eastern slopes of the western Sulaiman range in the Barmal District of Afghanistan not far from the source of the Tochi River. The Tank Zam is formed by the junction of the Tauda China and the Baddar Toi, at Dwa Toi, south of Razmak.