The Tarnak River is a river of Ghazni

Ghazni Province

Ghazni is one of the thirty-four provinces of Afghanistan. Babur records in his Babur-Nama that Ghazni is also known as Zabulistan It is in the east of the country. Its capital is Ghazni City...

, Zabul

Zabul Province

Zabul is a historic province of Afghanistan. Zabul became an independent province from neighbouring Kandahar in 1963, with Qalat being named the provincial capital. It should not be confused with the city Zabol, on the Iranian side of the border with Afghanistan.- Political and security situation...

 and Kandahar

Kandahar Province

Kandahar or Qandahar is one of the largest of the thirty-four provinces of Afghanistan. It is located in southern Afghanistan, between Helmand, Oruzgan and Zabul provinces. Its capital is the city of Kandahar, which is located on the Arghandab River. The province has a population of nearly...

 provinces of Afghanistan

Afghanistan

Afghanistan , officially the Islamic Republic of Afghanistan, is a landlocked country located in the centre of Asia, forming South Asia, Central Asia and the Middle East. With a population of about 29 million, it has an area of , making it the 42nd most populous and 41st largest nation in the world...

. It rises in Hazarajat

Hazarajat

The Hazarajat is the original homeland of the Hazara people, and lies in the central highlands of Afghanistan, among the Koh-i-Baba mountains and the western extremities of the Hindu Kush. Its physical boundaries, however, are roughly marked by the Bamiyan Basin to the north, the headwaters of...

, near 33°7′N 67°56′E, south of the Lomar Pass. It flows towards the south-west for some 350 km before it joins the Dori River

Dori River

The Dori, also called Lora and Kadanai is a river of Afghanistan and Pakistan. It is a tributary of the Arghandab River and sub tributary of the Helmand River and runs for 320 kilometres through Kandahar Province in Afghanistan and Balochistan in Pakistan.The Dori begins north of the city of...

 some 30 km downstream of the Dori-Arghastan confluence, and some 30 km upstream of the Dori-Arghandab

Arghandab River

Arghandab is a river in Afghanistan, about in length. It rises in the Hazarajat country north-west of Ghazni, and flows south-west falls into the Helmand below Girishk. In its lower course it is much used for irrigation, and the valley is cultivated and populous; yet the water is said to be...

 confluence, at 31°24′N 65°33′E. The combined waters of these rivers join the Helmand

Helmand River

The Helmand River is the longest river in Afghanistan and the primarily watershed for the endorheic Sistan Basin....

 at 31°27′N 64°23′E, near Qal'eh ye-Bost.